显示样式:     当前期刊: Solar Energy    加入关注       排序: 导出
我的关注
我的收藏
您暂时未登录!
登录
  • Performance analysis of a solar-driven liquid desiccant cooling system with solution storage under adjustable recirculation ratio
    Sol. Energy (IF 4.374) Pub Date : 2018-04-03
    Fan Zhang, Yonggao Yin, Xiaosong Zhang

    Solar cooling is one of the most promising solutions to the worsening energy and climate issues. A solar-driven liquid desiccant evaporative cooling air-conditioning system with solution storage tanks was proposed. The daily performance of the proposed system under the variable solution recirculation ratio (Rs) adjusting method in a typical hot-humid summer day of Nanjing was investigated using a quasi-dynamic mathematical model. The solution storage effect and the coupled characteristics of the solar collecting subsystem and the liquid desiccant cycle were taken into account. The effects of water tank volume (Vwt), the initial solution mass in the solution storage tank (Ms,storage,tank) and the area of solar collector (Asc) on the overall system performance were also evaluated. The results show that with the help of the stored solution, the proposed system can effectively handle the space cooling load during the whole period of operation. The average values of thermal coefficient of performance (TCOP) and solar coefficient of performance (SCOP) are 0.66 and 0.31, respectively. The variable Rs adjusting method can guarantee the required solution concentration and adapt well to the varying solar radiation. When Asc is limited, a smaller Vwt and a larger Ms,storage,tank are recommended to achieve a higher SCOP when covering the required space cooling load.

    更新日期:2018-07-14
  • Comparison of absorption refrigeration cycles for efficient air-cooled solar cooling
    Sol. Energy (IF 4.374) Pub Date : 2018-04-07
    Z.Y. Xu, R.Z. Wang

    Absorption chiller is a widely used technology owing to its capability to utilize low grade thermal energy including solar thermal energy and waste heat. Yet, most solar absorption cooling systems need cooling tower to dissipate heat rejection into ambient. The use of cooling tower increases both the initial investment and water consumption, which can be improved by air-cooled solar absorption cooling system. In this paper, to give the best absorption cycle options under different conditions, five absorption refrigeration cycles suitable for air-cooled solar cooling including three double lift absorption cycles and two semi-GAX (Generator-Absorber heat eXchange) absorption cycles were compared. Steady-state simulation is carried out. Efficiencies of these cycles were calculated with LiBr-water and water-ammonia working pairs in the scenario of air-cooled solar cooling. Heat source temperatures of 75–100 °C from non-concentrating solar collector and air temperatures of 20–40 °C were considered. Both air-conditioning condition with evaporation temperature of 5 °C and sub-zero condition with −10 °C were discussed. It is found that mass-coupled semi-GAX absorption cycle with ammonia-water is suitable for air-conditioning with higher heat source temperatures, mass-coupled double lift absorption cycle with water-LiBr is suitable for air-conditioning with lower heat source temperature and mass-coupled double lift absorption cycle with ammonia-water is suitable for sub-zero conditions.

    更新日期:2018-07-14
  • Latent and sensible energy storage enhancement of nano-nitrate molten salt
    Sol. Energy (IF 4.374) Pub Date : 2018-04-09
    Afrah Awad, Alan Burns, Muayad Waleed, Mortatha Al-Yasiri, Dongsheng Wen

    Molten salts have limited thermo-physical properties (such as specific heat capacity) which discourage their wide applications. Therefore, nanoparticles are dispersed in molten salt to improve the storage energy density. Thermophysical properties of CuO-nanosalt are compared with the nitrate binary solar salt. The effect of two different preparation methods of nanosalt samples have been studied and compared for the first time in one paper. Same weight concentration of nanoparticles in both methods of (1 wt.%) is conducted. The maximum increment in specific heat capacity was observed using the one step method by 21.24% in solid phase and 3.7% in liquid phase, respectively. Additionally, the sensible storage energy is improved in the case of nanosalt in comparison to nitrate salt by 9.27% in one step method. Moreover, the latent heat of 1 wt.% CuO-nanosalt (in one step method) increased by 67% in comparison to the nitrate binary salt without any additives while (in two step method) was 14.5%. This indicated the large effect of preparation methods of the nanosalt samples on different enhancements either in sensible heat or in latent heat. Samples are analysed using TEM which it showed an agglomerations of CuO nanoparticles prepared by the novel one step method.

    更新日期:2018-07-14
  • 10 key principles for successful solar air conditioning design – A compendium of IEA SHC Task 48 experiences
    Sol. Energy (IF 4.374) Pub Date : 2018-04-10
    Daniel Neyer, Manuel Ostheimer, Daniel Mugnier, Stephen White

    The results of past and ongoing activities, in successive IEA SHC (solar heating and cooling) Tasks, suggest enormous potential for solar cooling technologies to reduce greenhouse gas emissions. However, solar thermal cooling still faces barriers to emerge as an economically competitive solution. IEA SHC Task 48 was introduced to gather learnings from existing installations, and to find technological and market solutions, which could enable industry to deliver solar thermal driven heating and cooling systems that are efficient, reliable and cost competitive.The selected experiences of these research activities were clustered into 10 qualitative key principles for successful design and operation of SHC systems. Three existing systems are fully discussed in a solar cooling design guide (Mugnier et al., 2017). This paper aims to introduce these key principles in its general format. The background to the qualitative statements is explained, supplemented with examples from the context of Task 48 and compared with recent literature. Furthermore, a survey was conducted among SHC experts, who provide an assessment of the importance of the principles.The result shows that all principles have their eligibility. However, it turns out that there are three main categories of principles: (i) essential, (ii) important and (iii) controversial. Following the key principles is not a guarantee, but they can support researchers, designers and contractors to implement solar heating and cooling systems successfully.

    更新日期:2018-07-14
  • Technical and economic assessment of solar heating and cooling – Methodology and examples of IEA SHC Task 53
    Sol. Energy (IF 4.374) Pub Date : 2018-04-23
    Daniel Neyer, Manuel Ostheimer, Chiara Dipasquale, Rebekka Köll

    Assessing the performance of solar heating and cooling systems, especially cooling systems using solar thermal or photovoltaic driving energy, in a common comparable format, is complicated by the numerous, alternative energy sources and design possibilities. A generalized technical and economic assessment methodology was developed and tested in the course of IEA SHC Task 53. This paper is summarizing the key facts for the assessment and showing the evaluation on the basis of two simulated cases including sensitivity analysis of main boundary conditions.One case is comparing an air/water heat pump with photovoltaic and solar thermal support for a small multifamily house located in Madrid. The second case is comparing a solar thermal driven absorption chiller with a photovoltaic supported heat pump system for a hotel with dominant domestic hot water demand in Innsbruck.The sensitivity analysis shows that photovoltaic and solar thermal systems are cutting across with the same trends. Lower costs have to be derived first, followed by the efficiency of the system. Cost competitiveness is achievable for both technologies with appropriate system design and control strategies.

    更新日期:2018-07-14
  • Cu2ZnSn(S,Se)4 from annealing of compound co-sputtered precursors – Recent results and open questions
    Sol. Energy (IF 4.374) Pub Date : 2018-04-23
    Sven Englund, Nishant Saini, Charlotte Platzer-Björkman

    Cu2ZnSn(S,Se)4 (CZTS) thin film solar cells have reached efficiencies of up to 12.6% and current research is focused on understanding reasons for device limitations. At Uppsala University, a CZTS synthesis route based on compound sputtering and annealing in elemental vapors is used. Variation of chemical composition and annealing conditions is used as a tool to try to understand defect-related material- and device properties. Front and back contacts are also studied with focus on energy band matching at the hetero-interface using atomic layer deposition buffer layers and chemical stability of the back contact. In this review, we discuss recent work from our group, with reference to related work in the literature and with regards to areas for future work.

    更新日期:2018-07-14
  • High-field magnetotransport in Cu2ZnGeS4 single crystals
    Sol. Energy (IF 4.374) Pub Date : 2018-04-26
    Elena Hajdeu-Chicarosh, Erkki Lähderanta, Maxim Guc, Konstantin Lisunov, Mikhail Shakhov, Ivan Zakharchuk, Serghei Levcenko, Ernest Arushanov

    The quaternary chalcogenides, attracting much attention in recent time as promising solar energy materials, permit an effective optimization of their composition by the Ge incorporation. In particular, this implies an interest to the Cu2ZnGeS4 compound, which utilization requires, however, a deeper understanding of its electronic properties in general. Here, we investigate magnetotransport of the p-type Cu2ZnGeS4 single crystals, including resistivity, ρ (T), magnetoresistance (MR) and Hall effect, in pulsed magnetic fields up to B = 20 T. The Mott variable-range hopping charge transfer has been established within a broad temperature interval of T between ∼100 and 200 K by investigations of ρ (T) in zero field. The positive and negative contributions to MR have been observed, attributing them to shrinkage of the impurity wave functions by the magnetic field and to the destructive interference of the hopping charge carriers, respectively. Observation of the negative Hall coefficient, RH (T), exhibiting the dependence close to that of ρ (T), gives a strong support to the Mott conduction mechanism in our p-type Cu2ZnGeS4 material. In addition, the conductivity, connected with thermal activation of holes on the mobility edge, Ec, has been identified both below and above the Mott conduction interval. Finally, the joint analysis of the ρ (T) and MR data has yielded a series of important microscopic parameters. These include such details of the hole spectrum in the acceptor band, as its semi-width, W, the density of localized states, g (μ), at the Fermi level, μ, the positions of μ and Ec, as well as values of the localization radius of holes, a, and of the acceptor concentration, NA.

    更新日期:2018-07-14
  • Life cycle costing as a bottom line for the life cycle sustainability assessment in the solar energy sector: A review
    Sol. Energy (IF 4.374) Pub Date : 2018-04-27
    Alex Ximenes Naves, Camila Barreneche, A. Inés Fernández, Luisa F. Cabeza, Assed N. Haddad, Dieter Boer

    This review focus on LCC Assessment (LCCA) and the adoption of this methodology for the economic pillar evaluation of the Sustainability Life Cycle in the Solar Energy sector. Research showed the effectiveness of this methodology as the main component for assessing sustainability in the economic domain, and the relationship with the primary methods of environmental and social areas. The energy industry has been responsible for a significant number of publications, and the use of LCCA for different scale solar energy solutions as vehicles, houses, buildings, highways, rural properties and power plants indicates the usefulness of this methodology. In the large-scale solar energy solutions, for Solar Photo Voltaic (SPV) and Concentrated Solar Power (CSP), the use of LCCA can upraise the advantages for choosing or integrating both solutions. Also clarifying the feasibility of their critical ancillary solutions, named Electrical Energy Storages (EES) and the Thermal Energy Storages (TES). In minor scale solar energy solutions where the crescent technological evolution of SPV Cells has resulted in higher energy efficiency rates, the use of the LCCA can demonstrate the sensitive reduction on the Levelled Cost of Energy (LCOE), reflecting on the feasibility of solutions as the Zero Energy Buildings (ZEB). These facts allied to the crescent number of studies and publications shows that LCCA is a promising field of studies and a powerful tool to achieve a most complete and reliable Life Cycle Sustainability Assessment of solar energy technologies and also the solar energy implementation projects, mainly in the design phase.

    更新日期:2018-07-14
  • A design of selective solar absorber for high temperature applications
    Sol. Energy (IF 4.374) Pub Date : 2018-04-30
    A. AL-Rjoub, L. Rebouta, P. Costa, N.P. Barradas, E. Alves, P.J. Ferreira, K. Abderrafi, A. Matilainen, K. Pischow

    This study presents a design of multilayer solar selective absorber for high temperature applications. The optical stack is composed of four layers deposited by magnetron sputtering on stainless steel substrates. The first is a back-reflector tungsten layer, which is followed by two absorption layers based on CrAlSiNx/CrAlSiOyNx structure for phase interference. The final layer is an antireflection layer of SiAlOx. The design was theoretically modelled with SCOUT software using transmittance and reflectance curves of individual thin layers, which were deposited on glass substrates. The final design shows simultaneously high solar absorbance α = 95.2% and low emissivity ε = 9.8% (calculated for 400 °C) together with high thermal stability at 400 °C, in air, and 600 °C in vacuum for 650 h.

    更新日期:2018-07-14
  • Latent thermal energy storage for solar process heat applications at medium-high temperatures – A review
    Sol. Energy (IF 4.374) Pub Date : 2018-07-10
    Alicia Crespo, Camila Barreneche, Mercedes Ibarra, Werner Platzer

    Solar thermal energy has the potential to cover the heat demands of industrial processes. However, there may be a time mismatch between energy supplied by the solar field and the process demand. In this case, a thermal energy storage (TES) allows the use of heat at hours without solar irradiation available. Thermal energy storage for solar hot water or heating systems using low temperatures have been optimized since many decades and are in a mature stage. Developments at high temperatures (above 200 °C) for CSP applications have also been deeply studied. However, until this present paper, limited attention has been paid to TES for solar thermal industrial applications at medium-high temperatures (120–400 °C), where there is a potentially huge demand. When talking about TES several aspects have to be discussed: the heat demand that TES is going to be designed to supply, the material where the energy will be stored and the performance of the TES system which includes not only the material but also tanks, piping and connections. In this review, food, brewery and chemical industries were identified as the industries with higher potential in which TES and solar energy could be integrated. Heat integration methodologies have been reviewed to optimize the use of the solar energy in the industrial processes. Regarding the material, latent heat storage or phase change materials (PCM) were selected for this study because they are a very promising type of storage to be integrated in thermal industrial processes, although the state of the art of latent heat thermal energy storage (LHTES) systems is still far from broad commercialization. Until now, no reviews of latent heat storage for industrial applications at medium-high temperatures (120–400 °C) have been published. Therefore, literature related to PCM and latent heat storage (LHS) systems to be used in industrial thermal processes is here reviewed in order to have a general overview of the available technologies for their integration together with solar thermal energy in industrial processes at both experimental and numerical level. More than 100 potential PCMs for heat storage applications in the range of temperatures 120–400 °C have been found. Inorganic eutectic compositions are the group with more potentially available PCM for these applications, with values of heat of fusion between 74 and 535 kJ/kg. Finally, the works related to the performance of the system from the experimental and modelling point of view were presented. The review of experimental TES systems which include PCM in the studied range of temperatures 120–400 °C showed that most of the experimental set-ups were developed for direct steam generation for CSP applications. Regarding numerical modelling, the type of configuration more simulated is the shell and tube configuration.

    更新日期:2018-07-12
  • Valorization of solar drying process in the production of dried Moroccan sweet cherries
    Sol. Energy (IF 4.374) Pub Date : 2018-07-07
    Rachida Ouaabou, Bouchra Nabil, Nadia Hidar, Lamyae Lahnine, Ali Idlimam, Abdelkader Lamharrar, Hafida Hanine, Mostafa Mahrouz

    This study presents the convectional drying process of two types of Moroccan sweet cherry, namely, Burlat and Van. 40 g of cherries were taken, pitted, cut in two halves, and were dried using a partially indirect solar convective dryer, which has an area of 2.5 m2. The thin-layer drying of sweet cherry were carried out in July 2017 at three air temperatures of 60, 70 and 80 °C and for two drying air flow rate 150 and 300 m3/h. Moreover, the cherry fruits are sufficiently dried in the ranges between 34 and 40 °C of ambient air temperature, 17–27% of relative humidity, and 200–900 W/m2 of solar radiation. The evolution of the moisture dry content and the drying rate as a function of drying time for different temperatures are shown graphically. Experience shows that as the air drying temperature increases the drying time decreases. During the experiments, pitted cherries were dried and the moisture content was decreased from 82.12 for Burlat and 85.45 for Van to 23 ± 3% (w.b). The drying temperature of 80 °C and air velocity of 300 m3/h were the optimum values for cherry fruit drying in a minimum time of 240 min. The characteristic drying curve (CDC) applicable to both types of cherry has been established as a polynomial of order 3 in reduced moisture content.

    更新日期:2018-07-08
  • Recent advancements in sorption technology for solar thermal energy storage applications
    Sol. Energy (IF 4.374) Pub Date : 2018-06-30
    Valeria Palomba, Andrea Frazzica

    Sorption thermal energy storage (STES) technology, belonging to the wider class of thermochemical TES, represents a promising alternative to common sensible and latent TESs, especially for applications at low-medium temperature (i.e. below 130 °C). The interest towards this technology is confirmed by the huge amount of research and development activities ongoing, represented by scientific publications as well as funded projects and international working groups.In such a context, the present paper reports about the most recent activities in the STES field. Particularly, it focuses on the analysis of innovative sorbent materials currently under development, comprising liquid absorption, physical adsorption, chemical reactions in pure salts and composite sorbents. Analysis of critical issues like achievable storage density, stability and corrosiveness were reported for each sorbent material.Furthermore, prototypes recently developed for each of the sorbent classes above reported were presented, highlighting the achievable performance, with particular attention towards the TES density attained under typical working conditions for heat and cold storage applications, both with open and closed TES systems.Finally, the most recent international activities focusing on the further development of STES, to help achieving higher Technology Readiness Level (TRL) were reported. These mainly comprise funded R&D projects and international working groups supported by intergovernmental organizations and research and innovations alliances.

    更新日期:2018-07-01
  • Smart integration of photovoltaic production, heat pump and thermal energy storage in residential applications
    Sol. Energy (IF 4.374) Pub Date : 2018-06-18
    Andrea L. Facci, Vesselin K. Krastev, Giacomo Falcucci, Stefano Ubertini

    The optimal design of distributed generation systems is of foremost importance to reduce fossil fuel consumption and mitigate the environmental impact of human activities in urban areas. Moreover, an efficient and integrated control strategy is needed for each of the components of a distributed generation plant, in order to reach the expected economic and environmental performances. In this paper, the transition from natural gas to electricity-based heating is evaluated for residential applications, considering the interplay between photovoltaic electricity produced on site and the thermal energy storage, to grant the optimal management of heating devices. The energy demand of an apartment building, under different climatic conditions, is taken as a reference and four power plant solutions are assessed in terms of energy cost and pollution reduction potential, compared to a baseline plant configuration. The performance of each power plant is analyzed assuming an optimized control strategy, which is determined through a graph-based methodology that was previously developed and validated by the authors. Outcomes from our study show that, if heat pumps are used instead of natural gas boilers, energy costs are reduced up to 41%, while CO2 CO 2 emissions are reduced up to 73%, depending on the climatic conditions. Our results provide a sound basis for considering the larger penetration of photovoltaic plants as an effective solution towards cleaner and more efficient heating technologies for civil applications. The simultaneous utilization of heat pumps (as substitutes of boilers) and photovoltaic panels yields a positive synergy that nullifies the local pollution, drastically cuts the CO2 CO 2 emission, and guarantees the economical sustainability of the investment in renewable energy sources without subsidiary mechanisms.

    更新日期:2018-06-19
  • Water consumption analysis of Moroccan concentrating solar power station
    Sol. Energy (IF 4.374) Pub Date : 2018-06-11
    Mohamed Soufiane Ben Fares, Souad Abderafi

    The development of solar power plants for electrical production is made through the new strategy of the Moroccan Kingdom, to limit its energy dependency. 2016 marks the start of the electricity production of the first plant Noor 1 in Ouarzazate city. This plant use the CSP technology, with parabolic through collector. To ensure its operation and guarantee its power supply, a large amount of water is needed. In this study analyze of the water consumption per hours during the twelve months of the year indispensable for electricity production of Noor 1 plant was carried out, by using System Advisor Model (SAM). Simulation results compared to industrial data allowed us to propose optimal recommendations concerning mainly the reduction of water consumption and increase electricity production. By exceeding the required amount of water by 2%, to produce about 487 GWh instead of an anticipated quantity equal to 500 GW, the operator have to minimize its consumption to gain 32 m3 of water which can be exploited in the new stations and at the same time increase its production by 13 GWh.

    更新日期:2018-06-12
  • Effect of carbon nanotubes on the global aging behavior of β-nucleated polypropylene random copolymers for absorbers of solar-thermal collectors
    Sol. Energy (IF 4.374) Pub Date : 2018-06-08
    Gernot M. Wallner, Michael K. Grabmann, Clemens Klocker, Wolfgang Buchberger, David Nitsche

    This paper deals with the effect of carbon nanotubes (CNT) on the basic characteristics and the global aging behaviour of β-nucleated polypropylene random copolymer absorber material for overheating protected solar thermal collectors. Hot air aging experiments at an elevated temperature of 135 °C were carried out using micro-sized specimens with a thickness of 100 µm. The unaged specimens were characterized as to the antioxidant content and the mechanical and thermal properties. The CNT pigment affected the semi-crystalline morphology (less β-content) and increased the stiffness significantly. The aging indicators strain-at-break, average molar mass, primary antioxidant content and oxidation temperature were monitored for up to 4000 h. A more pronounced degradation was deduced for the compounds with CNT. Compared to carbon black modified grades a higher deterioration rate was ascertained for the CNT compounds. The amount of CNT should be kept at low levels (<0.1 wt%) just needed to achieve sufficient solar absorbance (>90%) of the absorber sheet.

    更新日期:2018-06-08
  • Improved satellite-derived PV power nowcasting using real-time power data from reference PV systems
    Sol. Energy (IF 4.374) Pub Date : 2017-11-22
    Jamie M. Bright, Sven Killinger, David Lingfors, Nicholas A. Engerer

    Rapid growth in the global penetration of solar photovoltaic (PV) systems means electricity network operators and electricity generators alike are increasingly concerned with the short-term solar forecasting (nowcasting) of solar irradiance. This paper proposes a methodology that considers a varying number of available reference PV systems for supporting satellite-derived PV power real-time nowcasting. We evaluate conventional satellite-only and upscaling-only PV fleet estimate methodologies and compare them to two newly developed correction and hybrid cases. When using only a single reference PV system to estimate the aggregated power of 48 independent target PV systems for the location of Canberra, Australia; we show that the newly proposed correction or hybrid cases improve the performance of the satellite-derived PV power estimate medians in terms of MBE, rMBE, RMSE and rRMSE from 0.031  W / W p , 7.46 % , 0.079  W / W p and 23.4 % , down to 0.006  W / W p , - 0.711 % , 0.068  W / W p and 20.0 % , representing relative improvements of 80.6%, 90.5%, 13.9% and 14.5%, respectively. Similarly, when using 30 reference PV systems, we report median improvements from 0.036  W / W p , 8.25 % , 0.083  W / W p and 24.8 % , down to 0.01  W / W p , 1.41 % , 0.049  W / W p and 11.4 % , representing relative improvements of 72.2%, 82.9%, 41.0% and 54.0%, respectively. We discuss the fundamental challenges facing the use of reference PV systems, satellite-derived power estimates, combining the two data sources, and the knowledge required to address these issues. We ultimately conclude that combining satellite-based PV power estimates with data from reference PV systems is always more beneficial than either on their own.

    更新日期:2018-06-03
  • Short-term solar irradiance forecasting via satellite/model coupling
    Sol. Energy (IF 4.374) Pub Date : 2017-12-01
    Steven D. Miller, Matthew A. Rogers, John M. Haynes, Manajit Sengupta, Andrew K. Heidinger

    The short-term (0–3 h) prediction of solar insolation for renewable energy production is a problem well-suited to satellite-based techniques. The spatial, spectral, temporal and radiometric resolution of instrumentation hosted on the geostationary platform allows these satellites to describe the current cloud spatial distribution and optical properties. These properties relate directly to the transient properties of the downwelling solar irradiance at the surface, which come in the form of ‘ramps’ that pose a central challenge to energy load balancing in a spatially distributed network of solar farms. The short-term evolution of the cloud field may be approximated to first order simply as translational, but care must be taken in how the advection is handled and where the impacts are assigned. In this research, we describe how geostationary satellite observations are used with operational cloud masking and retrieval algorithms, wind field data from Numerical Weather Prediction (NWP), and radiative transfer calculations to produce short-term forecasts of solar insolation for applications in solar power generation. The scheme utilizes retrieved cloud properties to group pixels into contiguous cloud objects whose future positions are predicted using four-dimensional (space + time) model wind fields, selecting steering levels corresponding to the cloud height properties of each cloud group. The shadows associated with these clouds are adjusted for sensor viewing parallax displacement and combined with solar geometry and terrain height to determine the actual location of cloud shadows. For mid/high-level clouds at mid-latitudes and high solar zenith angles, the combined displacements from these geometric considerations are non-negligible. The cloud information is used to initialize a radiative transfer model that computes the direct and diffuse-sky solar insolation at both shadow locations and intervening clear-sky regions. Here, we describe the formulation of the algorithm and validate its performance against Surface Radiation (SURFRAD; Augustine et al., 2000, 2005) network observations. Typical errors range from 8.5% to 17.2% depending on the complexity of cloud regimes, and an operational demonstration outperformed persistence-based forecasting of Global Horizontal Irradiance (GHI) under all conditions by ∼10 W/m2.

    更新日期:2018-06-03
  • Production of polycrystalline silicon from silane pyrolysis: A review of fines formation
    Sol. Energy (IF 4.374) Pub Date : 2017-12-26
    Pan Zhang, Jihai Duan, Guanghui Chen, Jianlong Li, Weiwen Wang

    Silane is a major silicon source gas for production of polycrystalline silicon. Production of polysilicon from silane has several benefits: lower energy consumption, much easily obtaining electronical polysilicon and less impact on the environment. There is, however, a major challenge that silane homogenous decomposition may result in amorphous silicon powders (fines) formation. In this review we focus on the fines formation with silane as feed gas. Firstly, this paper reports the situation of the production of silane source gas, the mechanism of the silane decomposition and fines formation. The reactor design, operation parameters and carrier gas, all of these would affect fines formation. This study also reviews on emerging trends in these aspects in outcome studies.

    更新日期:2018-06-03
  • Past, present, future of solar cooling: Technical and economical considerations
    Sol. Energy (IF 4.374) Pub Date : 2018-01-08
    R.M. Lazzarin, M. Noro

    A large fraction of cooling demand depends on solar radiation intensity, therefore a strong attention was directed toward solar cooling immediately after the 1973 energy crisis. Whereas pilot solar cooling plants were built up and experimented, this technology never really took off. A recent survey reported something more than 1000 plants operating, a very modest number with respect the great potential of solar cooling. A review of technologies as they developed in the past, operate in the present with a forecasting for the future is here proposed to follow how the technology evolved during almost half a century regarding the solar section and the relative refrigeration equipment. The analysis allows to take stock of the situation selecting solar sections, cooling machines and their coupling which seem nowadays more suitable for wide application in the near future. A study is proposed at the end to put together some energy evaluations in different climates and much more difficult economical evaluations to investigate whether a possible fossil fuel parity cost can be attained, if not today, in a near future.

    更新日期:2018-06-03
  • Low-temperature processes for passivation and metallization of high-efficiency crystalline silicon solar cells
    Sol. Energy (IF 4.374) Pub Date : 2018-01-31
    A. Descoeudres, C. Allebé, N. Badel, L. Barraud, J. Champliaud, G. Christmann, F. Debrot, A. Faes, J. Geissbühler, J. Horzel, A. Lachowicz, J. Levrat, S. Martin de Nicolas, S. Nicolay, B. Paviet-Salomon, L.-L. Senaud, C. Ballif, M. Despeisse

    This paper reviews recent progress made at CSEM on the development of low-temperature processes for the fabrication of amorphous silicon-based passivated contacts and for the metallization of high-efficiency silicon heterojunction (SHJ) solar cells. Intrinsic a-Si:H passivation layers were optimized by trying to minimize the drop in lifetime usually observed after the deposition of the p-doped a-Si:H layer on top. State-of-the-art passivation levels are obtained, demonstrated by minority carrier lifetimes above 50 ms on lowly doped wafers, and close to 18 ms on actual SHJ cell precursors with buffer layers as thin as 4 nm. Regarding cell metallization, the screen-printing process of low-temperature Ag pastes has been optimized, resulting in finger width as low as 16 µm. Alternatively, a photolithography-free copper electroplating process has been developed. Using inkjet printing of hotmelt for patterning, 25-µm-wide and highly conductive fingers can be deposited. This process was tested in SHJ cell pilot production conditions, showing high cell performance (22.3% median efficiency) and good reproducibility. Finally, using the developed passivated contacts and screen-printing process, SHJ solar cells fabricated with industry-compatible processes showed efficiencies up to 23.1% on large-area devices and up to 23.9% on 4 cm2 devices.

    更新日期:2018-06-03
  • Past, present and future of the thin film CdTe/CdS solar cells
    Sol. Energy (IF 4.374) Pub Date : 2018-01-31
    A. Bosio, G. Rosa, N. Romeo

    Recently, the CdTe solar cell technology reached a high-tech level able to realize devices showing efficiencies close to 22%. Nowadays, this technology acquires more and more market share, becoming the most promising among the thin film technologies. These important achievements are the result of more than 40 years of studies and researches that have synergically group together the photovoltaic module manufacturing technology with semiconductor and interfaces physics, modeling, characterization and measurements on electronic devices. This paper shows the main steps of the production process of the thin film CdTe/CdS-based solar cells both from a technological and from a physical point of view. In particular, the main differences between cells fabricated in superstrate and in substrate configuration will be highlighted. For each of these two structures the fundamental layers, their main alternatives, chemical and thermal treatments, interfaces, the won challenges and the still open-problems will be presented and discussed.

    更新日期:2018-06-03
  • Cu(In,Ga)Se2 solar cells on low cost mild steel substrates
    Sol. Energy (IF 4.374) Pub Date : 2018-01-31
    Lucas Zortea, Shiro Nishiwaki, Thomas Paul Weiss, Stefan Haass, Julian Perrenoud, Lukas Greuter, Thomas Feurer, Ganesan Palaniswamy, Stephan Buecheler, Ayodhya N. Tiwari

    Thin film Cu(In,Ga)Se2 (CIGS) solar modules can be grown on flexible and lightweight substrates allowing their direct integration into building elements. Such multifunctional building elements would significantly reduce the installation cost of photovoltaic systems provided that CIGS solar cells with high conversion efficiency can be obtained. Also, there is a need for low cost substrate foil. Mild steel is a promising low cost substrate material due to its excellent mechanical stability and already wide acceptance as component in building envelopes and in numerous other applications. During the growth of the CIGS absorber layer certain elements, e.g. iron, can diffuse from the metallic substrate into the semiconductor deteriorating the device performance. Here we present an effective diffusion barrier and device architecture for processing of highly efficient CIGS solar cells on mild steel substrates. The CIGS absorber layers were grown on mild steel foils by a multistage co-evaporation process at different substrate temperatures. The mild steel substrates were plated with an industrially scalable electrodeposited Ni/Cr bi-layer. The diffusion barrier layer properties of this Ni/Cr coating were investigated directly by measuring the metallic impurities within the absorber by secondary ion mass spectrometry and indirectly by admittance spectroscopy. The Ni/Cr bi-layer was found to be effective up to a nominal CIGS growth temperature of 500 °C. A certified cell efficiency of 18.0% was achieved on a Ni/Cr coated mild steel substrate using a low temperature CIGS deposition process and a NaF and RbF post deposition treatment method.

    更新日期:2018-06-03
  • Interdigitated back contact silicon heterojunction solar cells featuring an interband tunnel junction enabling simplified processing
    Sol. Energy (IF 4.374) Pub Date : 2018-02-03
    B. Paviet-Salomon, A. Tomasi, D. Lachenal, N. Badel, G. Christmann, L. Barraud, A. Descœudres, J. Geissbühler, A. Faes, Q. Jeangros, J.P. Seif, S. Nicolay, B. Strahm, S. De Wolf, C. Ballif, M. Despeisse

    This paper reports on the development of an innovative back-contacted crystalline silicon solar cell with passivating contacts featuring an interband tunnel junction at its electron-collecting contacts. In this novel architecture, named “tunnel-IBC”, both the hole collector patterning and its alignment to the electron collector are eliminated, thus drastically simplifying the process flow. However, two prerequisites have to be fulfilled for such devices to work efficiently, namely (i) lossless carrier transport through the tunnel junction and (ii) low lateral conductance within the hole collector in order to avoid shunts with the neighboring electron-collecting regions. We meet these two contrasting requirements by exploiting the anisotropic and substrate-dependent growth mechanism of n- and p-type hydrogenated nano-crystalline silicon layers. We investigate the influence of the deposition temperature and the doping gas concentration on the structural and the selectivity properties of these layers. Eventually, tunnel-IBC devices integrating hydrogenated nano-crystalline silicon layers demonstrate a conversion efficiency up to 23.9%.

    更新日期:2018-06-03
  • History and trends in solar irradiance and PV power forecasting: A preliminary assessment and review using text mining
    Sol. Energy (IF 4.374) Pub Date : 2018-02-03
    Dazhi Yang, Jan Kleissl, Christian A. Gueymard, Hugo T.C. Pedro, Carlos F.M. Coimbra

    Text mining is an emerging topic that advances the review of academic literature. This paper presents a preliminary study on how to review solar irradiance and photovoltaic (PV) power forecasting (both topics combined as “solar forecasting” for short) using text mining, which serves as the first part of a forthcoming series of text mining applications in solar forecasting. This study contains three main contributions: (1) establishing the technological infrastructure (authors, journals & conferences, publications, and organizations) of solar forecasting via the top 1000 papers returned by a Google Scholar search; (2) consolidating the frequently-used abbreviations in solar forecasting by mining the full texts of 249 ScienceDirect publications; and (3) identifying key innovations in recent advances in solar forecasting (e.g., shadow camera, forecast reconciliation). As most of the steps involved in the above analysis are automated via an application programming interface, the presented method can be transferred to other solar engineering topics, or any other scientific domain, by means of changing the search word. The authors acknowledge that text mining, at its present stage, serves as a complement to, but not a replacement of, conventional review papers.

    更新日期:2018-06-03
  • Progress in and potential of liquid phase crystallized silicon solar cells
    Sol. Energy (IF 4.374) Pub Date : 2018-02-09
    Cham Thi Trinh, Rutger Schlatmann, B. Rech, Daniel Amkreutz

    Liquid phase crystallization of silicon (LPC-Si) offers great potential for high-quality Si films and a cost effective fabrication technique for thin crystalline silicon solar cells on glass. In this work, we report on the progress on LPC-silicon at HZB in the past years. Beginning with a brief description of the fabrication process, we summarize the work on the different contact systems developed for these absorbers before focusing on the interdigitated back contact architecture on which the highest efficiencies were reported. State-of-the art cells form the basis for a detailed discussion of the status of this technology. We investigate the current loss mechanisms and explore the potential for further improvement. Finally, based on this comprehensive quality assessment, we develop a roadmap to increase the cell efficiencies to wafer-equivalent values.

    更新日期:2018-06-03
  • High-performance p-type multicrystalline silicon (mc-Si): Its characterization and projected performance in PERC solar cells
    Sol. Energy (IF 4.374) Pub Date : 2018-02-14
    Pietro P. Altermatt, Zhen Xiong, QiuXiang He, WeiWei Deng, Feng Ye, Yang Yang, Yifeng Chen, ZhiQiang Feng, Pierre J. Verlinden, Anyao Liu, Daniel H. Macdonald, Tabea Luka, Dominik Lausch, Marko Turek, Christian Hagendorf, Hannes Wagner-Mohnsen, Jonas Schön, Wolfram Kwapil, Thorsten Trupke

    Recent progress in the electronic quality of high-performance (HP) multicrystalline silicon material is reported with measurements and modeling performed at various institutions and research groups. It is shown that recent progress has been made in the fabrication at Trina Solar mainly by improving the high excess carrier lifetimes τ due to a considerable reduction of mid-gap states. However, the high lifetimes in the wafers are still reduced by interstitial iron by a factor of about 10 at maximum power point (mpp) conditions compared to mono-crystalline Cz wafers of equivalent resistivity. The low lifetime areas of the wafers seem to be limited by precipitates, most likely Cu. Through simulations, it appears that dislocations reduce cell efficiency by about 0.25% absolute. The best predictors for PERC cell efficiency from ingot metrology are a combination of mean lifetime and dislocation density because dislocations cannot be improved considerably by gettering during cell processing, while lifetime-limiting impurities are gettered well. In future, the material may limit cell efficiency above about 22.5% if the concentrations of Fe and Cu remain above 1010 and 1013 cm−3, respectively, and if dislocations are not reduced further.

    更新日期:2018-06-03
  • CIGS thin films grown by hybrid sputtering-evaporation method: Properties and PV performance
    Sol. Energy (IF 4.374) Pub Date : 2018-02-19
    Maurizio Acciarri, Alessia Le Donne, Stefano Marchionna, Maurilio Meschia, Jacopo Parravicini, Andrea Gasparotto, Simona Binetti

    We present a comprehensive overview on a new hybrid sputtering-evaporation (HSE) system for the deposition of Cu(In,Ga) Se2 (CIGS) thin-films aimed at photovoltaic applications. Such a technique employs the sputtering process to deposit the metal precursors on suitable rotating transfer cylinders, from which they are subsequently evaporated, in Se atmosphere, on the substrate. This procedure allows to combine the features of both the sputtering and evaporation techniques, enabling a fine tuning of the stoichiometry and an easy transfer to industrial processes. The key elements of this growth method are here explained in detail. The HSE CIGS layers have been investigated through secondary ion mass spectrometry, Raman and photoluminescence spectroscopies, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy. Moreover, the solar cell performance of the grown films has been investigated, through external quantum efficiency and J-V curves under 1 Sun illumination measurements. The obtained experimental results are exhaustively shown and discussed, indicating advantages and open issues of the presented deposition technique.

    更新日期:2018-06-03
  • Solar driven two-step CH4 reforming and H2O splitting using Al2O3 for Co-production of Al, syngas, and H2
    Sol. Energy (IF 4.374) Pub Date : 2018-03-02
    Rahul R. Bhosale

    The thermodynamic equilibrium and efficiency analysis of the solar-driven Al2O3-based CH4 reforming and H2O splitting process is performed in two sections: (1) Al and syngas producing open process (AS), and (2) Al, syngas, and H2 producing semi-open process (ASH). The equilibrium analysis indicate that with the rise in the CH4/Al2O3 molar ratio, formation of Al and syngas (via methanothermal reduction of Al2O3) improves and reaches its maximum value at 2530 K (in case of CH4/Al2O3 molar ratio = 3). The efficiency analysis (for both cycles) is carried out at a steady thermal reduction temperature (TH) equal to 2530 K. In case of the ASH process, the water-splitting reactor is employed for the production of H2 and the effect of water splitting temperature (TL) on the process efficiency values is explored. Obtained results shows that the solar-to-fuel energy conversion efficiency in case of the ASH process is higher as compared to the AS process. Furthermore, this efficiency (in case of the ASH process) can be increased up to 50.7% via heat recuperation.

    更新日期:2018-06-03
  • Conceptual design and feasibility assessment of photoreactors for solar energy storage
    Sol. Energy (IF 4.374) Pub Date : 2018-03-02
    Ilenia Rossetti, Elnaz Bahadori, Antonio Tripodi, Alberto Villa, Laura Prati, Gianguido Ramis

    The experimental results of testing with different irradiation power are compared and used as a basis for the feasibility assessment and conceptual design of a photoreforming reactor. The highest H2 productivity (0.276 mol H2/h kgcat) was achieved with 1 g/L of 1 wt% Au/TiO2 P25 catalyst by using a 113 W/m2 UVA irradiation. Insufficient hydrogen productivity for practical deployment was achieved, following reactor design. However, the comparison with the state of the art evidenced that also the energy storage potential of the literature photocatalysts do not allow a short term feasibility of the proposed technology. The potential productivity of hydrogen, as well as solar energy storage efficiency are discussed both for the present experimental values and for the best results in the literature. On the other hand, solar energy can be used to artificially fix CO2, e.g. captured and stored from combustion processes that can be converted back to chemicals or regenerated fuels. The production of H2, HCOOH, HCHO and CH3OH by photoreduction of CO2 has been evaluated as for daily production potential. CO2 photoconversion to formaldehyde can be envisaged as solar energy storage mean with 13.3% efficiency, whereas for the other products the solar energy storage efficiency was below 1%.

    更新日期:2018-06-03
  • Part II: Thermal analysis of naturally ventilated BIPV system: Modeling and Simulation
    Sol. Energy (IF 4.374) Pub Date : 2018-03-02
    Rafaela A. Agathokleous, Soteris A. Kalogirou

    This is the second part of a two-part study based on the thermal behaviour of a naturally ventilated BIPV systems. In the first part an experimental analysis of the thermal behaviour of a naturally ventilated BIPV system is presented and two new correlations for the estimation of the convective heat transfer coefficients in the air gap between the PV panel and a second skin are given, for windy and non-windy conditions. The present study (second part) presents a simulation based thermal analysis of a naturally ventilated vertical BIPV system. The simulation model is created using the developed equations for the estimation of the convective heat transfer coefficients presented in the first part of the present study, and the model is validated with the use of experimental data shown in the first part as well. The experimental based correlations are imported in the mathematical model, in order to be able to investigate the effect of other parameters on the thermal behaviour of the system such as the height of the system, the size of the air gap and the air velocity in the duct. These parameters are not easy to be investigated experimentally and their investigation would be very time consuming. The simulation model has a good agreement with the experimental results. The results shown that an air gap of 0.1 m can create adequate air flow on naturally ventilated systems and can ensure low PV temperatures to avoid efficiency decrease. This can be done when the air gap has bottom and top openings to allow air circulation. In taller systems, the temperatures are higher and there is a drop of the efficiency of the system.

    更新日期:2018-06-03
  • Low substrate temperature CdTe solar cells: A review
    Sol. Energy (IF 4.374) Pub Date : 2018-03-02
    Alessandro Romeo, Elisa Artegiani, Daniele Menossi

    CdTe photovoltaic technology is one of the first being brought into production together with amorphous silicon (already in the mid 90s Solar Cells Inc. in USA, Antec Solar and BP Solar in Europe were producing 60 × 120cm modules) and it is now the largest in production among thin film solar cells (Photovoltaics Report, 2014). CdTe has high chemical stability and a large variety of successful preparation methods available, which makes this technology one of the most suitable for large area module production. Historically there are two large categories of CdTe photovoltaic devices depending on the substrate deposition temperature, typically low temperature processes are considered when substrate temperature is below 450 °C. In this paper we will describe the last progress of CdTe based thin film solar cells, fabricated with low substrate temperature process, and their pros and cons.

    更新日期:2018-06-03
  • Part I: Thermal analysis of naturally ventilated BIPV system: Experimental investigation and convective heat transfer coefficients estimation
    Sol. Energy (IF 4.374) Pub Date : 2018-03-02
    Rafaela A. Agathokleous, Soteris A. Kalogirou

    The purpose of this two-part study is to present the experimental analysis carried out on a naturally ventilated Building Integrated Photovoltaic (BIPV) system and the new correlations developed for the estimation of the convective heat transfer coefficients (CHTC) in the air gap, and use the developed correlations to construct a simulation model which is validated with the experimental data. In BIPV systems the air gap is responsible to cool the PVs and remove excess heat to avoid building overheating. The ventilation of the air gap can be natural or mechanical. However, naturally ventilated systems are less studied although they have important advantages over the mechanically ventilated ones, such as the avoidance of extra energy of the fans, maintenance and noise. The present Part I of this study presents an experimental based thermal analysis of a naturally ventilated vertical BIPV system. A series of experiments on a custom made BIPV system were carried in real outdoor conditions as well as indoors with the use of a large scale solar simulator to measure the thermal characteristics of the system and its thermal behaviour. Indoor experiments were performed to avoid external disturbances from wind that may occur outside. The results show that an open-ended air gap of 0.1 m can create adequate air flow on naturally ventilated systems and can ensure low PV temperatures to avoid PV efficiency decrease. The experimental data are then used to estimate the convective heat transfer coefficients to fit the real conditions of the BIPV systems. Then two correlations are proposed for the estimation of the Nusselt number that fits best the thermal characteristics of a naturally ventilated BIPV system.

    更新日期:2018-06-03
  • A review of the application of carbon materials in solar thermal energy storage
    Sol. Energy (IF 4.374) Pub Date : 2018-03-03
    Heinrich Badenhorst

    Graphitic materials can potentially mitigate the issue of low thermal conductivity in phase change materials (PCM) when used in solar thermal energy storage. However, carbon can form an exceedingly wide variety of allotropes which are difficult to distinguish. This study has examined an extensive range of energy storage carbon composites including: synthetic and natural graphite, graphitic fibres, graphitic foams, expanded graphite, graphite nano-platelets, graphene, carbon nanotubes and amorphous carbons. The thermal energy storage media covered include conventional low temperature materials such as paraffins, alcohols, fatty acids and numerous others, as well as high temperature salts. In addition, a wide range of both steady and unsteady state thermal conductivity measurement techniques are represented. Based on the collated results it is evident that particulate additives are limited, potentially due to contact resistance, to improving PCM thermal conductivities by a factor of less than ten. On the other hand, matrix materials like compressed expanded graphite and graphitic foams are capable of achieving enhancements in excess of 10,000%. Compressed expanded graphite composites appear to be the most economically favourable option. Nanomaterials do not perform as anticipated and indications are that costs must drop by more than three orders of magnitude before they become attractive. It has been demonstrated that it may be possible to predict composite thermal conductivity for all carbon materials using a single model, if an additional structural parameter could be measured.

    更新日期:2018-06-03
  • An overview on electrodeposited Cu(In,Ga)(Se,S)2 thin films for photovoltaic devices
    Sol. Energy (IF 4.374) Pub Date : 2018-03-08
    V. Bermudez

    Industrial implementation of Cu(In,Ga)(Se,S)2 (CIGS) solar cells based technologies is usually based on two vacuum deposition techniques: thermal evaporation and sputtering. Despite the ability to produce high purity and high efficiency solar cells with reasonable reproducibility, they exhibit some limitations with respect to their suitability for high-throughput and large area manufacturing and a better materials using rate that would in turn reduce production costs. The sophisticated vacuum equipment requires high capital investment, decreases the flexibility to implement changes and thus it is more vulnerable to predict the desired results. The compositional control that is required in CIGS solar cells in particular is difficult to maintain during up-scaling to large area modules by means of vacuum methods. Implementation of a roll-to-roll process with the use of large, flexible substrates to decrease processing time and increase throughput would further raise the desire of cost effective and fast non-vacuum processes that omit pumping times and are inherently easy to up-scale. The historical developments and main advantages of CIGS thin film photovoltaic devicesis revised and costs considerations are argued to support the interesting approach of electrodeposition as a preferred technique for industrial CIGS substituting sputtered precursors.

    更新日期:2018-06-03
  • Benchmarking three low-cost, low-maintenance cloud height measurement systems and ECMWF cloud heights against a ceilometer
    Sol. Energy (IF 4.374) Pub Date : 2018-03-08
    P. Kuhn, M. Wirtz, N. Killius, S. Wilbert, J.L. Bosch, N. Hanrieder, B. Nouri, J. Kleissl, L. Ramirez, M. Schroedter-Homscheidt, D. Heinemann, A. Kazantzidis, P. Blanc, R. Pitz-Paal

    Cloud height information is crucial for various applications. This includes solar nowcasting systems. Multiple methods to obtain the altitudes of clouds are available. In this paper, cloud base heights derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) and three low-cost and low-maintenance ground based systems are presented and compared against ceilometer measurements on 59 days with variable cloud conditions in southern Spain. All three ground based systems derive cloud speeds in absolute units of [m/s] from which cloud heights are determined using angular cloud speeds derived from an all-sky imager. The cloud speed in [m/s] is obtained from (1) a cloud shadow speed sensor (CSS), (2) a shadow camera (SC) or (3) derived from two all-sky imagers. Compared to 10-min median ceilometer measurements for cloud heights below 5000 m, the CSS-based system shows root-mean squared deviations (RMSD) of 996 m (45%), mean absolute deviations (MAD) of 626 m (29%) and a bias of −142 m (−6%). The SC-based system has an RMSD of 1193 m (54%), a MAD of 593 m (27%) and a bias of 238 m (11%). The two all-sky imagers based system show deviations of RMSD 826 m (38%), MAD of 432 m (20%) and a bias of 202 m (9%). The ECMWF derived cloud heights deviate from the ceilometer measurements with an RMSD 1206 m (55%), MAD of 814 m (37%) and a bias of −533 m (−24%). Due to the multi-layer nature of clouds and systematic differences between the considered approaches, benchmarking cloud heights is an extremely difficult task. The limitations of such comparisons are discussed. This study aims at determining the best approach to derive cloud heights for camera based solar nowcasting systems. The approach based on two all-sky imagers is found to be the most promising, having the overall best accuracy and the most obtained measurements.

    更新日期:2018-06-03
  • Aluminum-doped ZnO thin films deposited on flat and nanostructured glass substrates: Quality and performance for applications in organic solar cells
    Sol. Energy (IF 4.374) Pub Date : 2018-03-09
    Pontsho Mbule, Dong Wang, Rolf Grieseler, Peter Schaaf, Burhan Muhsin, Harald Hoppe, Bakang Mothudi, Mokhotjwa Dhlamini

    Transparent conductive aluminum-doped zinc oxide (AZO) thin films were deposited on a flat and nanostructured borosilicate glass substrates by using DC-magnetron sputtering. The aluminum doping concentration was kept at 3.3 wt% and the film thickness (100–400 nm) was varied. The thin films were then annealed at 250 °C for 1 h in nitrogen and/or argon atmosphere, respectively. AZO thin films exhibited hexagonal wurtzite structure of ZnO with an intense (0 0 2) diffraction peak, indicating that they have c-axis preferred orientation. Optical transmittance was observed to be greater than 80% in the visible range for films deposited on both flat and nanostructured glass substrates. The lowest resistivity of 9.7 × 10−4 Ω cm was observed for AZO film of 400 nm thickness on flat glass substrate, annealed in Nitrogen atmosphere. The power conversion efficiency (PCE) of 0.27% and 2.24% were recorded for organic solar cell devices based on AZO deposited on nanostructured and flat borosilicate glass, respectively. In comparison with the latter, the PCE of ITO based device was recorded to be 3.17%. Due to their good optical and electrical properties, AZO thin films are promising candidates as transparent electrodes in organic solar cells.

    更新日期:2018-06-03
  • The off-grid PV-battery powered home revisited; the effects of high efficiency air-conditioning and load shifting
    Sol. Energy (IF 4.374) Pub Date : 2018-03-12
    M.J. Goldsworthy, S. Sethuvenkatraman

    The potential for residential households to go ‘off-grid’ with a photovoltaic-battery storage system in a location where a conventional connection to the electricity network is available has received recent attention. Several studies have reported that at present, in Australia the economics are not justified. These studies have used unmodified electricity consumption profiles from grid-connected households as input to their off-grid system analyses. However, households looking to go off-grid may be motivated to make basic modifications to their consumption pattern so as to minimise the size of the PV-battery system. Here the effects of (i) shifting the booster time of electric storage hot water system to coincide with peak irradiance, (ii) improving the efficiency of air-conditioning appliances, and (iii) shifting pool pump operation and improving pump efficiency are compared and assessed. The analysis uses sub-circuit measurements of electricity consumption from 28 households for up to 2 years. Results show that the hot water and air-conditioning adjustments in particular can improve the economics considerably, even accounting for the fact that the appliance efficiency improvements also lower the grid connected electricity costs. For households seeking to go off-grid, any changes to electricity load profiles that provide a more uniform match of consumption to generation in particular, improve off-grid system economics in comparison to grid electricity, since the true cost of delivering electricity from the grid at peak times is typically spread across all consumers.

    更新日期:2018-06-03
  • Worldwide inter-comparison of clear-sky solar radiation models: Consensus-based review of direct and global irradiance components simulated at the earth surface
    Sol. Energy (IF 4.374) Pub Date : 2018-03-16
    José A. Ruiz-Arias, Christian A. Gueymard

    Clear-sky irradiance (CSI) modeling constitutes an essential component of the evaluation of the solar resource at any location, and is involved in a large number of applications. In solar applications, most common CSI models provide broadband irradiance predictions based on a number of simplifications and/or empirical components compared to the rigorous radiative transfer models used in atmospheric sciences. Thus, these common CSI models have to undergo continuous quality assurance evaluations to delineate the range of validity of such simplifications. Traditionally, these evaluations have consisted in direct comparisons against high-quality ground observations. A review of 36 such validation studies of the literature is provided here, highlighting which CSI models were recommended over different climatic areas. This review underlines the difficulty of generalizing these results due to a number of methodological difficulties. In particular, the availability of ground observations is limited and does not cover the full extent of the atmospheric conditions over which the CSI models are regularly operated. In this review study, fifteen of the most highly cited CSI models of the literature are compared to each other using a global synthetic input database built from atmospheric reanalyses. It guarantees that most of the operating conditions of CSI models are potentially covered. The study focuses on the global horizontal (GHI) and direct normal (DNI) irradiance predictions of the CSI models. Overall, a better agreement for GHI than for DNI is found. The largest inter-model discrepancies span throughout Asia, the Middle East and central and northern Africa, precisely coinciding with some of the regions with the highest interest for solar energy applications. The most important sources of discrepancies are traced down to high loads of aerosols, high site elevations, and low solar altitudes. Usage of the Linke turbidity factor as input to a popular type of simplified CSI model is found to be a significant source of uncertainty, preventing accurate simultaneous predictions of GHI and DNI. Other models, which tend to mispredict GHI or DNI over, e.g., hazy areas, are identified.

    更新日期:2018-06-03
  • Transition metal doped ceria for solar thermochemical fuel production
    Sol. Energy (IF 4.374) Pub Date : 2018-03-17
    G.D. Takalkar, R.R. Bhosale, A. Kumar, F. AlMomani, M. Khraisheh, R.A. Shakoor, R.B. Gupta

    In this paper, the effect of doping of transition metal cations on thermal reduction and CO2 splitting ability of Ce0.9M0.1O2−δ materials (where, M = Ni, Zn, Mn, Fe, Cu, Cr, Co, Zr) is investigated by performing multiple thermochemical cycles using a thermogravimetric analyzer. The Ce0.9M0.1O2−δ materials are successfully derived via co-precipitation method and analyzed via powder X-ray diffraction (PXRD), scanning electron microscope (SEM), and BET surface area analyzer (BET). The Ce0.9M0.1O2−δ materials derived are further tested towards their O2 releasing and CO production capacity by performing ten thermochemical CO2 splitting cycles. The obtained TGA results indicate that CeZn and CeFe are capable of releasing higher amounts of O2 as compared to other Ce0.9M0.1O2−δ materials at 1400 °C. Likewise, these two oxides are again observed to be better than other Ce0.9M0.1O2−δ materials in terms of their CO production capacity at 1000 °C. For instance, CeZn and CeFe releases an average of 50.5 and 50.0 μmol of O2/g·cycle during ten thermochemical cycles in which the thermal reduction step is performed at at 1400 °C. Also, the CO production capacity of CeZn and CeFe material is observed to be equal to 103.3 and 96.3 μmol of CO/g·cycle for ten thermochemical cycles in which the CO2 splitting is carried out at 1000 °C. The compositional and thermal stability of all Ce0.9M0.1O2−δ materials is also analyzed after performing ten thermochemical cycles. The phase composition of all the Ce0.9M0.1O2−δ materials remain unchanged after performing ten thermochemical cycles. However, the crystallite size of all the Ce0.9M0.1O2−δ materials increases after performing the ten thermochemical cycles due to the high temperature processing.

    更新日期:2018-06-03
  • Pump Speed Optimisation for Solar Thermal System
    Sol. Energy (IF 4.374) Pub Date : 2018-03-22
    Liviu Hrisca, Wim J.C. Melis

    Photovoltaic as well as solar thermal systems have been particularly useful for harvesting the inexhaustible energy from the sun and to reduce the carbon emissions normally produced by burning fossil fuels. In either of these cases, reaching a higher efficiency obviously brings substantial benefits, and while much research has been performed on PV efficiency, most research has focused on the solar thermal collectors themselves, while our approach considers the system’s perspective by optimizing the pump speed based on the performance of the various heat exchangers within the full system. In order to test the theory, a prototype solar thermal system was built, in which the pump speed was adjusted by considering: the water demand, the input and output temperatures of the solar panel and the output temperature of the produced hot water. By combining the solar thermal system with an existing gas boiler and continuously adjusting the pump speed, a reduction of between 10% and 30% in gas consumption and 5–10% in electricity consumption was observed.

    更新日期:2018-06-03
  • Corrosion of stainless steel 316 in eutectic molten salts for thermal energy storage
    Sol. Energy (IF 4.374) Pub Date : 2018-03-24
    Madjid Sarvghad, Theodore A. Steinberg, Geoffrey Will

    Stainless steel 316 was examined for compatibility with the eutectic mixtures of NaCl + Na2CO3 and NaCl + Na2SO4 at 700 °C and Li2CO3 + K2CO3 + Na2CO3 at 450 °C in air for thermal energy storage. Electrochemical measurements combined with advanced microscopy and microanalysis techniques were employed. NaCl + Na2CO3 was found as the most aggressive salt at 700 °C. The attack morphology on the surface was uniform corrosion with no localized degradation at 450 °C. Microscopy observations showed grain boundary oxidative attack as the primary corrosion mechanism at 700 °C with depletion of alloying elements from grain boundaries.

    更新日期:2018-06-03
  • Study on operation strategy of a silica gel-water adsorption chiller in solar cooling application
    Sol. Energy (IF 4.374) Pub Date : 2018-03-28
    Q.W. Pan, R.Z. Wang

    Conventional operation strategy of silica gel-water adsorption chiller in solar cooling application uses fixed cycle time, but it deviates from real optimal cycle time because of varied solar hot water temperature. Mathematical model and simulation of a solar silica gel-water adsorption chiller was done and performance comparison in two operating strategies (fixed and varied cycle time) was made according to experiment data of a real solar system. An estimating equation for the optimal cycle time was developed by the simulation results, considering both COP and SCP by a weighting factor. Correlation of optimal cycle time and hot water temperature was fitted in a linear equation. Optimal half cycle time decreased with increasing hot water temperature and weighting factor. COPs of varied cycle time were much larger than those of fixed cycle time whereas SCPs of varied cycle time and fixed cycle time were nearly the same. So operation strategy of silica gel-water adsorption chiller with varied cycle time can significantly improve the whole utilization efficiency of solar cooling system without any decrease in cooling capacity.

    更新日期:2018-06-03
  • Decoupling of optoelectronic properties from morphological changes in sodium treated kesterite thin film solar cells
    Sol. Energy (IF 4.374) Pub Date : 2018-03-29
    C. Andres, T. Schwarz, S.G. Haass, T.P. Weiss, R. Carron, R. Caballero, R. Figi, C. Schreiner, M. Bürki, A.N. Tiwari, Y.E. Romanyuk

    Sodium is typically used during the synthesis of kesterite thin films to enhance the performance of solar cells. As sodium tends to affect grain growth and morphology, it is difficult to analyse solely the electronic effects of sodium as dopant. To decouple the structural and electronic effects from each other, two processes were designed in this work to successfully incorporate sodium into a vacuum-processed Cu2ZnSnSe4 absorber without changing the morphology. A thin layer of NaF is deposited before precursor deposition (Pre-NaF) or after absorber synthesis to undergo a post deposition treatment (NaF-PDT). While composition and distribution of matrix elements remain unchanged, the sodium concentration is increased upon sodium treatment up to 140 ppm as measured by inductively coupled plasma mass spectrometry. X-ray photoelectron spectroscopy showed that the surface composition was not altered. Within its detection limit, sodium was not present at the absorber surface. For a Pre-NaF sample measured with atom probe tomography a sodium concentration of 30 ppm was measured in a grain, suggesting that sodium might segregate at grain boundaries. The additional sodium content in the film leads to an increased acceptor concentration, which results in improved open-circuit voltage and fill factor.

    更新日期:2018-06-03
  • Influence of OLA and FA ligands on the optical and electronic properties of Cu2ZnSn(S, Se)4 thin films and solar cells prepared from nanoparticle inks
    Sol. Energy (IF 4.374) Pub Date : 2018-03-29
    S. Campbell, Y. Qu, L. Bowen, P. Chapon, V. Barrioz, N.S. Beattie, G. Zoppi
    更新日期:2018-06-03
  • Hydrothermal assisted chemical bath deposition of (Cd:Zn)S thin film with high photosensitivity and low dark current
    Sol. Energy (IF 4.374) Pub Date : 2018-06-01
    Joissy Mathew, E.I. Anila

    In this work we observed high-quality nanocrystalline ternary films obtained by hydrothermal assisted chemical bath deposition on glass substrates. Deposition has been carried out at 200 °C for one hour. The alloying effect and the photoelectric properties of the material is enumerated in this paper along with the structural, Optical, morphological and photoluminescence properties. The structural properties analysed by X-ray diffraction (XRD) reveals the hexagonal phase of CdZnS film with preferred orientation along the (1 0 0) plane and the average grain size was observed to be 28 nm. Scanning electron microscopy (SEM) images showed clusters of nanofibers grown on the film. The optical bandgap obtained from the optical absorption studies using UV–Vis-NIR spectroscopy was 2.98 eV. Broad and asymmetric emission from intrinsic point defects was observed in the PL spectrum recorded using Fluromax-4Spectrofluorometer. The photoconductivity of the film was investigated by using Keithley SMU2450 four probe source measure unit under illumination by light from 300 W/82 V halogen lamp. In the dark condition, the I–V Curve showed non-linear behaviour, whereas the film showed ohmic behaviour under illumination. The photoresponse of the film was recorded at intervals of 100 s. The photocurrent increased under illumination and the current recovered to the original dark level when light was switched off. Under 100 s of illumination the photocurrent increased and became almost constant. This work presents a simple way to obtain photodetectors and will benefit in the manufacture of optoelectronic devices.

    更新日期:2018-06-01
  • A review of solar thermal energy storage in beds of particles: Packed and fluidized beds
    Sol. Energy (IF 4.374) Pub Date : 2018-05-21
    J.A. Almendros-Ibáñez, M. Fernández-Torrijos, M. Díaz-Heras, J.F. Belmonte, C. Sobrino

    This review summarizes different solar thermal energy storage techniques from a particle technology perspective, including sensible, latent and thermochemical techniques for low- and high-temperature applications that use particles as the storage medium in the thermal energy storage system. The focus is on applications, experimental results, modeling and future trends. This review describes two different particle technologies used to store thermal energy: packed and fluidized beds. The advantages and disadvantages of both technologies are reviewed throughout different studies found in the literature for various thermal energy storage systems. Packed beds have the main advantage of thermal stratification, which increases the efficiency of solar collectors in low-temperature sensible energy storage systems and augments the exergy content in the bed. Moreover, they have been proven to be suitable as dual-media thermocline storage systems for CSP plants. In contrast, the high mixing rates of fluidized beds makes them suitable for the rapid distribution of concentrated solar energy in particle receiver CSP systems. In addition, their high heat and mass transfer rates, compared with those of packed beds, make them the preferred particle technology for thermochemical energy storage applications. This review also notes that it is important to find new materials with an appropriate size and density that can be properly used in a fluidized bed. Additionally, more specific research efforts are necessary to improve the understanding of the behavior of these materials during the fluidization process and over a high number of charging/discharging cycles.

    更新日期:2018-05-22
  • Efficient energy storage technologies for photovoltaic systems
    Sol. Energy (IF 4.374) Pub Date : 2018-05-16
    Hoda Akbari, Maria C. Browne, Anita Ortega, Ming Jun Huang, Neil J. Hewitt, Brian Norton, Sarah J. McCormack

    For photovoltaic (PV) systems to become fully integrated into networks, efficient and cost-effective energy storage systems must be utilized together with intelligent demand side management. As the global solar photovoltaic market grows beyond 76 GW, increasing onsite consumption of power generated by PV technology will become important to maintain electricity grid stability. This review paper provides the first detailed breakdown of all types of energy storage systems that can be integrated with PV encompassing electrical and thermal energy storage systems. The integration of PV-energy storage in smart buildings is discussed together with the role of energy storage for PV in the context of future energy storage developments.

    更新日期:2018-05-17
  • A study of granular flow through horizontal wire mesh screens for concentrated solar power particle heating receiver applications – Part II: Parametric model predictions
    Sol. Energy (IF 4.374) Pub Date : 2018-05-16
    Matthew Sandlin, S.I. Abdel-Khalik

    Numerical methods are increasingly being used to study granular flow phenomena, given the difficulty in extracting data from physical studies. Two common methods are the discrete element method (DEM), and a two fluid computational fluid dynamics (CFD) method. A companion paper (Sandlin and Abdel-Khalik, 2018) compared a DEM model and a CFD model of a granular flow through horizontal wire mesh screens, with experimental data. The aim of this study is to assess the sensitivity of both models to various input parameters. The results of this investigation will guide future modelers of particle heating receivers and other flowing particulate systems in selecting the appropriate modeling options and parameters to enhance the models ability to predict the actual particulate flow characteristics. For the DEM model, it was found that the granular material properties, especially the values for normal and rolling friction, had the largest impact on simulation results. For the CFD model, it was found that the constitutive relationships for frictional pressure, viscosity, and the treatment of physical boundary conditions had the largest impact on simulation outcomes. In addition, both numerical models exhibit a non-monotonic relationship between mass flux and the granular coefficient of restitution, and show reduced mass flux when using a simulation domain with offset wire meshes. The influence of other material properties and sub-modeling options is less pronounced. Methods of obtaining appropriate material properties and sub-modeling options are discussed.

    更新日期:2018-05-16
  • Numerical coupling model to compute the microclimate parameters inside a street canyon: Part I: Methodology and experimental validation of surface temperature
    Sol. Energy (IF 4.374) Pub Date : 2018-05-13
    Khaled Athamena, Jean-François Sini, Jean-Michel Rosant, Julien Guilhot

    This decade has been marked by a fast development of software and hardware systems. The numerical simulation models of microclimate provide much better information and analysis capabilities about thermodynamic behaviors for many ranges of urban configurations. The street canyon forms a basic geometric unit of the built environment. The morphology and materials that make up the canyons of a city greatly influence the urban climate. In the first step, this paper presents a methodology for a numerical approach based on the coupling between the CFD Model, Code_Saturne (software developed by EDF1) and the thermo-radiative model, Solene (software developed by CRENAU2 laboratory). In the second step, the surface temperatures output results of coupled simulations are compared with the in situ data obtained during the EM2PAU3 campaign. The experimental configuration was conducted using two lines of steel containers buildings composing one street canyon. The simulated surface temperatures are compared with the measurements for a full week period representative of relatively warm period with varied weather conditions. The simulation results show a good coherence with measurements during daytime for all surfaces as well as disagreements during nighttime for the street due partly to inappropriate choice of physical properties of street canyon materials.

    更新日期:2018-05-14
  • A universal method for performance evaluation of solar photovoltaic air-conditioner
    Sol. Energy (IF 4.374) Pub Date : 2018-05-12
    B.Y. Zhao, Y. Li, R.Z. Wang, Z.G. Zhao, R.A Taylor

    Photovoltaic air-conditioner (PVAC) exhibits the advantages of high energy efficiency and convenient building integration, among solar cooling and heating technologies. The objective of this study is to propose a universal and straightforward method for performance evaluation of PVAC. Sixteen scenarios are simulated by TRNSYS to compare the performance of PVAC in different climates and building types defined by the Chinese national standards. Indicators such as solar fraction (SF), self-consumption ratio (SCR), solar COP, and return of investment (ROI) are used for evaluating energy and economic performances. The results demonstrate that the performance of PVAC is significantly affected by climatic conditions and building types, and thus, the feasibility of PVAC can be conveniently estimated based on the data provided by the Chinese national standards. A PVAC exhibits higher SF and SCR in areas subjected to high temperatures during summer and in office buildings, business malls, and hospital buildings, which mainly operate in the daytime. The building types in the order of decreasing ROI are business mall, hospital buildings, hotel, and office buildings. A comprehensive evaluation indicator is proposed to optimize the PV capacity and is useful to evaluate both the energy and economic performances of PVAC.

    更新日期:2018-05-12
  • High-field magnetotransport in Cu2ZnGeS4 single crystals
    Sol. Energy (IF 4.374) Pub Date : 2018-04-26
    Elena Hajdeu-Chicarosh, Erkki Lähderanta, Maxim Guc, Konstantin Lisunov, Mikhail Shakhov, Ivan Zakharchuk, Serghei Levcenko, Ernest Arushanov

    The quaternary chalcogenides, attracting much attention in recent time as promising solar energy materials, permit an effective optimization of their composition by the Ge incorporation. In particular, this implies an interest to the Cu2ZnGeS4 compound, which utilization requires, however, a deeper understanding of its electronic properties in general. Here, we investigate magnetotransport of the p-type Cu2ZnGeS4 single crystals, including resistivity, ρ (T), magnetoresistance (MR) and Hall effect, in pulsed magnetic fields up to B = 20 T. The Mott variable-range hopping charge transfer has been established within a broad temperature interval of T between ∼100 and 200 K by investigations of ρ (T) in zero field. The positive and negative contributions to MR have been observed, attributing them to shrinkage of the impurity wave functions by the magnetic field and to the destructive interference of the hopping charge carriers, respectively. Observation of the negative Hall coefficient, RH (T), exhibiting the dependence close to that of ρ (T), gives a strong support to the Mott conduction mechanism in our p-type Cu2ZnGeS4 material. In addition, the conductivity, connected with thermal activation of holes on the mobility edge, Ec, has been identified both below and above the Mott conduction interval. Finally, the joint analysis of the ρ (T) and MR data has yielded a series of important microscopic parameters. These include such details of the hole spectrum in the acceptor band, as its semi-width, W, the density of localized states, g (μ), at the Fermi level, μ, the positions of μ and Ec, as well as values of the localization radius of holes, a, and of the acceptor concentration, NA.

    更新日期:2018-04-27
  • Cu2ZnSn(S,Se)4 from annealing of compound co-sputtered precursors – Recent results and open questions
    Sol. Energy (IF 4.374) Pub Date : 2018-04-23
    Sven Englund, Nishant Saini, Charlotte Platzer-Björkman

    Cu2ZnSn(S,Se)4 (CZTS) thin film solar cells have reached efficiencies of up to 12.6% and current research is focused on understanding reasons for device limitations. At Uppsala University, a CZTS synthesis route based on compound sputtering and annealing in elemental vapors is used. Variation of chemical composition and annealing conditions is used as a tool to try to understand defect-related material- and device properties. Front and back contacts are also studied with focus on energy band matching at the hetero-interface using atomic layer deposition buffer layers and chemical stability of the back contact. In this review, we discuss recent work from our group, with reference to related work in the literature and with regards to areas for future work.

    更新日期:2018-04-25
  • Technical and economic assessment of solar heating and cooling – Methodology and examples of IEA SHC Task 53
    Sol. Energy (IF 4.374) Pub Date : 2018-04-23
    Daniel Neyer, Manuel Ostheimer, Chiara Dipasquale, Rebekka Köll

    Assessing the performance of solar heating and cooling systems, especially cooling systems using solar thermal or photovoltaic driving energy, in a common comparable format, is complicated by the numerous, alternative energy sources and design possibilities. A generalized technical and economic assessment methodology was developed and tested in the course of IEA SHC Task 53. This paper is summarizing the key facts for the assessment and showing the evaluation on the basis of two simulated cases including sensitivity analysis of main boundary conditions. One case is comparing an air/water heat pump with photovoltaic and solar thermal support for a small multifamily house located in Madrid. The second case is comparing a solar thermal driven absorption chiller with a photovoltaic supported heat pump system for a hotel with dominant domestic hot water demand in Innsbruck. The sensitivity analysis shows that photovoltaic and solar thermal systems are cutting across with the same trends. Lower costs have to be derived first, followed by the efficiency of the system. Cost competitiveness is achievable for both technologies with appropriate system design and control strategies.

    更新日期:2018-04-25
  • Assessment of the impact of meteorological conditions on pyrheliometer calibration
    Sol. Energy (IF 4.374) Pub Date : 2018-04-13
    F. Ferrera Cobos, R.X. Valenzuela, L. Ramírez, L.F. Zarzalejo, B. Nouri, S. Wilbert, G. García

    Pyrheliometer calibration must be done following strict procedures in order to ensure the required robustness and accuracy. These procedures are described in the ISO 9059:1990 and ASTM E 816 – 15 international standards. However, their application requires information that may not always be available or may be subjective, inaccurate or incomplete, as for example, the determination of “percent of cloud coverage” or “the existence of clouds 15° around the Sun”. The irradiance measurements made by the reference and test instruments involved should also be collected over wide periods after, close to and before solar noon, which might not always be the case depending on the weather conditions during calibration. When those data are not available, the standard cannot be applied properly, and the experts have to decide which data can be used for the calibration. In this study, the abovementioned two main standards for pyrheliometer calibration were thoroughly reviewed, and a harmonized protocol is proposed that uses only the main data recorded. Nineteen field pyrheliometers were calibrated to verify the proposed procedure, and the results show its robustness. After calibration, we analyzed the variability in the calibration constant and the influence of some experimental conditions on the calibration results. As in previous references, the results show that variations in solar elevation and wind speed during the day still influenced the calibration constants of most of the test devices. On the contrary, neither the angle between the wind direction and the solar azimuth nor Linke turbidity seemed to influence the calibration constants calculated. The influence of the Linke turbidity is low as the viewing geometry of all involved pyrheliometers is very similar to each other and as low turbidity prevailed. The correlation between the solar elevation and the wind speed was analyzed and calibration constants were found to vary linearly with solar elevation and wind speed, respectively. Pyrheliometer calibration measurement testing was carried out in Summer 2014 at the Plataforma Solar de Almeria (PSA) in the context of the Solar Facilities for the European Research Area 2 Project (SFERA2).

    更新日期:2018-04-25
  • Proposal and evaluation of subordinate standard solar irradiance spectra for applications in solar energy systems
    Sol. Energy (IF 4.374) Pub Date : 2018-04-10
    Wilko Jessen, Stefan Wilbert, Christian A. Gueymard, Jesús Polo, Zeqiang Bian, Anton Driesse, Aron Habte, Aitor Marzo, Peter R. Armstrong, Frank Vignola, Lourdes Ramírez

    Reference solar irradiance spectra are needed to specify key parameters of solar technologies such as photovoltaic cell efficiency, in a comparable way. The IEC 60904-3 and ASTM G173 standards present such spectra for Direct Normal Irradiance (DNI) and Global Tilted Irradiance (GTI) on a 37° tilted sun-facing surface for one set of clear-sky conditions with an air mass of 1.5 and low aerosol content. The IEC/G173 standard spectra are the widely accepted references for these purposes. Hence, the authors support the future replacement of the outdated ISO 9845 spectra with the IEC spectra within the ongoing update of this ISO standard. The use of a single reference spectrum per component of irradiance is important for clarity when comparing and rating solar devices such as PV cells. However, at some locations the average spectra can differ strongly from those defined in the IEC/G173 standards due to widely different atmospheric conditions and collector tilt angles. Therefore, additional subordinate standard spectra for other atmospheric conditions and tilt angles are of interest for a rough comparison of product performance under representative field conditions, in addition to using the main standard spectrum for product certification under standard test conditions. This simplifies the product selection for solar power systems when a fully-detailed performance analysis is not feasible (e.g. small installations). Also, the effort for a detailed yield analyses can be reduced by decreasing the number of initial product options. After appropriate testing, this contribution suggests a number of additional spectra related to eight sets of atmospheric conditions and tilt angles that are currently considered within ASTM and ISO working groups. The additional spectra, called subordinate standard spectra, are motivated by significant spectral mismatches compared to the IEC/G173 spectra (up to 6.5%, for PV at 37° tilt and 10–15% for CPV). These mismatches correspond to potential accuracy improvements for a quick estimation of the average efficiency by applying the appropriate subordinate standard spectrum instead of the IEC/G173 spectra. The applicability of these spectra for PV performance analyses is confirmed at five test sites, for which subordinate spectra could be intuitively selected based on the average atmospheric aerosol optical depth (AOD) and precipitable water vapor at those locations. The development of subordinate standard spectra for DNI and concentrating solar power (CSP) and concentrating PV (CPV) is also considered. However, it is found that many more sets of atmospheric conditions would be required to allow the intuitive selection of DNI spectra for the five test sites, due in particular to the stronger effect of AOD on DNI compared to GTI. The matrix of subordinate GTI spectra described in this paper are recommended to appear as an option in the annex of future standards, in addition to the obligatory use of the main spectrum from the ASTM G173 and IEC 60904 standards.

    更新日期:2018-04-11
  • 10 key principles for successful solar air conditioning design – A compendium of IEA SHC Task 48 experiences
    Sol. Energy (IF 4.374) Pub Date : 2018-04-10
    Daniel Neyer, Manuel Ostheimer, Daniel Mugnier, Stephen White

    The results of past and ongoing activities, in successive IEA SHC (solar heating and cooling) Tasks, suggest enormous potential for solar cooling technologies to reduce greenhouse gas emissions. However, solar thermal cooling still faces barriers to emerge as an economically competitive solution. IEA SHC Task 48 was introduced to gather learnings from existing installations, and to find technological and market solutions, which could enable industry to deliver solar thermal driven heating and cooling systems that are efficient, reliable and cost competitive. The selected experiences of these research activities were clustered into 10 qualitative key principles for successful design and operation of SHC systems. Three existing systems are fully discussed in a solar cooling design guide (Mugnier et al., 2017). This paper aims to introduce these key principles in its general format. The background to the qualitative statements is explained, supplemented with examples from the context of Task 48 and compared with recent literature. Furthermore, a survey was conducted among SHC experts, who provide an assessment of the importance of the principles. The result shows that all principles have their eligibility. However, it turns out that there are three main categories of principles: (i) essential, (ii) important and (iii) controversial. Following the key principles is not a guarantee, but they can support researchers, designers and contractors to implement solar heating and cooling systems successfully.

    更新日期:2018-04-10
  • Latent and sensible energy storage enhancement of nano-nitrate molten salt
    Sol. Energy (IF 4.374) Pub Date : 2018-04-09
    Afrah Awad, Alan Burns, Muayad Waleed, Mortatha Al-Yasiri, Dongsheng Wen

    Molten salts have limited thermo-physical properties (such as specific heat capacity) which discourage their wide applications. Therefore, nanoparticles are dispersed in molten salt to improve the storage energy density. Thermophysical properties of CuO-nanosalt are compared with the nitrate binary solar salt. The effect of two different preparation methods of nanosalt samples have been studied and compared for the first time in one paper. Same weight concentration of nanoparticles in both methods of (1 wt.%) is conducted. The maximum increment in specific heat capacity was observed using the one step method by 21.24% in solid phase and 3.7% in liquid phase, respectively. Additionally, the sensible storage energy is improved in the case of nanosalt in comparison to nitrate salt by 9.27% in one step method. Moreover, the latent heat of 1 wt.% CuO-nanosalt (in one step method) increased by 67% in comparison to the nitrate binary salt without any additives while (in two step method) was 14.5%. This indicated the large effect of preparation methods of the nanosalt samples on different enhancements either in sensible heat or in latent heat. Samples are analysed using TEM which it showed an agglomerations of CuO nanoparticles prepared by the novel one step method.

    更新日期:2018-04-09
  • Comparison of absorption refrigeration cycles for efficient air-cooled solar cooling
    Sol. Energy (IF 4.374) Pub Date : 2018-04-07
    Z.Y. Xu, R.Z. Wang

    Absorption chiller is a widely used technology owing to its capability to utilize low grade thermal energy including solar thermal energy and waste heat. Yet, most solar absorption cooling systems need cooling tower to dissipate heat rejection into ambient. The use of cooling tower increases both the initial investment and water consumption, which can be improved by air-cooled solar absorption cooling system. In this paper, to give the best absorption cycle options under different conditions, five absorption refrigeration cycles suitable for air-cooled solar cooling including three double lift absorption cycles and two semi-GAX (Generator-Absorber heat eXchange) absorption cycles were compared. Steady-state simulation is carried out. Efficiencies of these cycles were calculated with LiBr-water and water-ammonia working pairs in the scenario of air-cooled solar cooling. Heat source temperatures of 75–100 °C from non-concentrating solar collector and air temperatures of 20–40 °C were considered. Both air-conditioning condition with evaporation temperature of 5 °C and sub-zero condition with −10 °C were discussed. It is found that mass-coupled semi-GAX absorption cycle with ammonia-water is suitable for air-conditioning with higher heat source temperatures, mass-coupled double lift absorption cycle with water-LiBr is suitable for air-conditioning with lower heat source temperature and mass-coupled double lift absorption cycle with ammonia-water is suitable for sub-zero conditions.

    更新日期:2018-04-08
  • A reevaluation of the solar constant based on a 42-year total solar irradiance time series and a reconciliation of spaceborne observations
    Sol. Energy (IF 4.374) Pub Date : 2018-04-06
    Christian A. Gueymard

    A reevaluation of the solar constant is undertaken here to take into account the progress in space radiometry that has occurred since the early 2000s. Various sources of spaceborne total solar irradiance (TSI) observations are investigated here, including the long-term ACRIM and PMOD composites, as well as recent observations from the SORCE-TIM, TCTE-TIM, and PICARD-PREMOS instruments. A proxy model is constructed using daily data of sunspot number, radio flux at 10.7 cm, and MgII index, as predictors for TSI over the 42-year period 1976–2017. These daily estimates are used to fill in 9.7% of missing TSI observations during that period. By comparison with these proxy estimates, the PMOD composite appears generally more reliable than the ACRIM composite before 2003, and particularly before 1981. The 42-year time span is separated into nine periods, each defining the revised TSI daily values from one or more sources that are selected based on the trend of their resemblance with the proxy model. A final correction is added to emulate the highly accurate absolute calibration of PREMOS. Based on the resulting TSI reconstruction, a revised solar constant value of 1361.1 W/m2 is obtained, with a standard uncertainty of 0.5 W/m2. The revised solar constant is ≈5 W/m2 less than the previous values promulgated in ASTM and ISO standards. A revision of these standards is thus highly recommended.

    更新日期:2018-04-06
  • Application of a single wire-mesh sensor in a parabolic trough facility with direct steam generation
    Sol. Energy (IF 4.374) Pub Date : 2017-10-03
    A. Hoffmann, E. Schleicher, L. Keller, J. León Alonso, R. Pitz-Paal

    The direct steam generation process can contribute to increase the cost-effectiveness of line-focused solar thermal power plants. The current research focuses on the once-through mode as very promising option for large-scale commercial plants. However, the existing pool of knowledge about the steam–water flow in the horizontal receiver pipes reveals knowledge gaps. The present contribution aims to experimentally investigate the two-phase flow in the receiver pipes of the DISS test facility at the Plataforma Solar de Almería, Spain, by an invasive measurement device for the first time. Therefore, a conductance wire-mesh sensor is employed in the low-quality evaporation section of the DISS test facility. This measurement device measures the local instantaneous void fraction that is used to describe the prevailing flow pattern under different pressures and mass flow rates. The results show slug flow, roll waves, wavy flow, and stratified-wavy flow in the horizontal receiver pipes within pressures of 30–80 bar. The probability of slug flow or large-amplitude waves decreases with higher pressures. The findings provide a valuable knowledge about the flow structure within the receiver pipes and confirm the proof of function of the wire-mesh sensor under conditions of the direct steam generation process.

    更新日期:2017-12-14
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
化学 • 材料 期刊列表