Enhancement of solar energy use by an integrated system for five useful outputs: System assessment

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Abstract

In this paper, we present a newly developed integrated solar energy based system with a supercritical geothermal, a Brayton cycle gas turbine power plant with heat recovery system, and a thermochemical copper chlorine (Cu-Cl) hydrogen production cycle. The integrated system is capable of producing multiple useful outputs. Solar and geothermal energy sources are utilized with a Brayton cycle with heat recovery system to produce hydrogen, heat, domestic hot water, electricity, and fresh water. Hydrogen is considered to be produced at industrial scale for commercial purposes. Other useful commodities are considered to be utilized for applications in the community which is located in Larderello, Italy. A supercritical geothermal system, a Braytoncycle gas turbine power plant with heat recovery, a parabolic trough concentrated solar power (CSP) plant, a multi-effect desalination (MED) unit, a residential heat pump, and a thermochemical Cu-Cl hydrogen production plant are designed, developed, and investigated. Subsystems and the overall system are simulated for the selected location with various software packages. Energy and exergy approaches are applied to thermodynamically analyze the components, subsystems, and the overall system. The parametric studies are carried out to understand the effects of various parameters on the overall system and its subsystem performances. The overall system is evaluated to operate at 52.6% energy and 47.1% exergy efficiencies for the average ambient conditions for Larderello in Italy.

Introduction

The anthropogenic climate change is one of the most challenging issues for the human society. Current energy infrastructure is based on the fossil fuel combustion. More than 80% of global energy is produced via fossil fuel combustion [1]. With deforestation, fossil fuel combustion is the major contributor to the anthropogenic climate change, regarding the carbon dioxide generation. Alternative energy infrastructure research and development suggests that renewable energy systems are the potential alternative energy systems to replace the conventional fossil fuel-based systems. However, the transition of the energy infrastructure needs long periods and large investments, in contrast to information technology or biotechnology infrastructure transitions. Instead of complete transformation, integration of renewable systems to the existing infrastructure is an alternate solution for the transitional period [2].

Solar-based power generation has attracted plenty of attention in the recent years. More than 100GWp solar power plants have been built annually since 2018 [3]. Alongside solar photovoltaic (PV) technology, CSP plants have also gained interests both for commercial and research purposes. Parabolic trough collectors (PTC) and solar power towers (SPT) are the major CSP plant types. The main principle is to concentrate the solar irradiation via mirrors, and collect the heat from the concentrated irradiation via heat transfer fluid. Thereafter, heat can be used via various applications, to turn it into useful output. In contrast to 592TWh electricity generation of Solar PV plants in 2018, CSP plants produced 12TWh electricity [4]. Heat transfer fluids, heat transfer methods, collector types, concentration ratios, and derivation processes were discussed with current and future PTC CSP projects by Fuqiang et al. [5].

In order to improve the performances of solar thermal systems, different methods are available. Rashidi et al. [6] investigated different thermal systems regarding their entropy generation. They discussed various models and optimization methods. Bozorg et al. [7] investigated a novel PTC with synthetic oil-Al2O3 nanofluid. They conducted parametric studies to investigate the effects of different parameters on heat transfer, pressure drop, and thermal efficiency. Their modifications resulted in an increase in thermal efficiency between 8% and 15%, an increase in overall energetic effciency between 5% and 14%, and an increase in exergetic efficiency between 7% and 15%. Saffarian et al. [8] changed the flow directions in a flat plate solar collectors with Al2O3-water and CuO-water nanofluis, where up to 78.3% heat transfer increase was obtained. In another study, Moravej et al. [9] performed an experimental study to investigate the effect of replacing water with TiO2-water nanofluids for flat plate solar collector applications. Different nanoparticle concentrations were tested in their study. 17.4%, 27.1%, and 33.5% the maximum efficiency gains were obtained with 1 wt%, 3 wt%, and 5 wt% nanoparticle concentration, respectively. Rashidi et al. [10] studied nanofluid turbulent flow inside a solar heater with ribbed absorber plate. Nanofluids were employed with rough surfaces in order to decrease entropy generation. 21.05% thermal entropy decrease was found by increasing the rib height between 0.025 and 0.033 for Re = 3200. Rahbar et al. [11] performed an exergetic and economic analyses for a double slope solar still. In order to improve the performance, thermoelectric modules were employed. The maximum exergy efficiency was found to be 25%. Between 0.15 and 0.25 $/L/m2 distilled water production costs were found.

Solar energy possesses intermittent availability because of day-night cycles and weather conditions. Therefore, storage techniques or energy distribution methods should be applied in order to use solar energy when it is needed. Thermal energy storage (TES) applications are a potential solution for the intermittency problem. Combination of CSP plants with TES system is a common practice. Commercial TES systems were reviewed by Gonzalez - Roubaud et al. [12] with focus on steam accumulators, molten salts, and application types with levelized cost of electricity (LCOE) comparisons. Power cycles are the important parts of CSP plants. Different type of cycles can be considered due to the commodity requirement. Stein and Buck [13] comparatively reviewed different types of power cycles. Advanced power cycles were focused in their study. Combined power cycles with gas turbines were emphasized due to its high energy efficiency. Different types of power cycles such as helium Brayton cycle, regenerated carbon dioxide Brayton cycle, carbon dioxide recompression Brayton cycle, steam Rankine cycle, and combined carbon dioxide organic Rankine cycle were reviewed by Dunham and Iverson [14]. Steam Rankine cycles and carbon dioxide recompression Rankine cycles were emphasized due to their high efficiencies. A development of small scale 10 kW CSP plant with organic Rankine cycle were studied by Pikra et al. [15]. Stand-alone application for remote areas was targeted as the main application area of their proposed system.

Earth’s major plate borders are the potential geothermal spots, especially for deep drilling applications. Geothermal energy systems are not widely in-use in contrast to solar energy systems. In 2018, annual geothermal electricity production was 90TWh [1]. Asmundsson et al. [16] showed their efforts in the high temperature geothermal project by the High Temperature Instruments (HiTI). Their study included up to 400 °C geothermal well project investigation. Stimac et al. [17] discussed supercritical geothermal resources in California, United States. They explained challenges and costs of potential systems for the fields. For the sustainable development of remote communities, Mahbaz et al. [18] introduced enhanced and integrated geothermal systems for the northern communities of Canada. Al-Ali and Dincer [19] studied a multigenerational system with geothermal source. Five useful outputs, namely, electricity, space heating, cooling, domestic hot water, and industrial heating were considered. 78% energy and 36.6% exergy efficiencies were calculated for their overall system. Calise et al. [20] studied solar and geothermal based multigenerational system. Their system included PTC CSP plant and geothermal system. 50% overall exergy efficiency was calculated for their overall system in the heat recovery mode.

Combined cycle gas and steam turbines are expected to achieve higher efficiency than simple single cycles. In order to prevent waste production, steam turbine exploits excess heat and turns it into useful electricity [21]. Siddiqui and Dincer [22] presented solid oxide fuel cell-gas turbine combined cycle integration with a multigenerational system. Their proposed system were included SPT type CSP plant, ammonia alkaline fuel cell, proton exchange membrane (PEM) electrolyzer, and Rankine cycle. Hydrogen, cooling, space heating, domestic hot water, and electricity were considered as useful outputs. Their analyses showed that combined cycle was capable to work at 68.5% and 55.9% energy and exergy efficiencies, respectively. Boretti and Al-Zubaidy [23] investigated the integration of combined power cycle with PTC based CSP plant without thermal energy storage for Trinidad and Tobago. Around 57% conversion efficiency were presented in their study.

Hydrogen is a promising environmentally benign energy carrier medium with various application areas. Hydrogen production with green methods provides a zero or low carbon emission fuel alternative. Acar and Dincer [24] investigated the environmental impacts of hydrogen production systems. Social, economic, and environmental impacts were assessed comparatively for natural gas steam reforming, coal gasification, solar and wind-based electrolysis, biomass, thermochemical methods, and high-temperature electrolysis were discussed comprehensively and comparatively. Ratlamwala and Dincer [25] compared two different solar based Cu-Cl thermochemical hydrogen production systems. Photocatalytic reactor absence were changed between the systems when the Cu-Cl cycle, Kalina cycle, and SPT type CSP plant were stayed. Their system with photocatalytic reactor were performed the best results among their other proposed systems. 56.4% exergy efficiency were calculated.

Temiz and Dincer [26] studied solar and geothermal based integrated system. Freshwater, electricity, hydrogen, and space heating were considered as the useful outputs. Their system was able to operate at energy and exergy efficiencies of 16.3% and 14.9% respectively. Different components were used in this study with different irradiation amount and different underground water charactheristic. Additionally, a natural gas based combined power generation unit with heat recovery for power and hydrogen generation, a domestic hot water production unit, and a thermochemical Cu-Cl hydrogen production cycle is considered to be integrated. Overall multigenerational system is designed, developed, and investigated in the current study. Cu-Cl cycle is considered to be powered by concentrated solar with TES, heat recovery system from Brayton cycle, and geothermal system. The specific objectives of this study include: (i) to develop a utility scale integrated system for multigeneration, (ii) to analyze the proposed system and components with energy and exergy approaches of thermodynamics, (iii) to perform sensitivity analysis for various parameters to study their effects on the overall system performance.

Section snippets

System description

The proposed multigenerational system produces utility scale hydrogen, electricity, space heating, domestic hot water, and freshwater commodities for commercial and consumption purposes. Both hydrogen and domestic hot water are available for commercial market, where hydrogen can be transported in Europe and domestic hot water can be used for touristic thermal spa applications. In addition, electricity, space heating, and freshwater can be used for auxiliary systems and consumption in the

Analysis

The comprehensive analyses performed in this study includes thermodynamic analyses with energetic and exergetic approaches along with various simulations.

The following assumptions and considerations are made accordingly for this study: (i) air is an ideal gas, (ii) isentropic efficiencies vary between components from 70% to 90%, (iii) processes are adiabatic for compressors, expansion valves, pumps, and turbines, (iv) thermal energy storage system have three processes as charging, discharging,

Results and discussion

Utility-scale multigenerational system is proposed for Larderello in Italy. NREL’s SAM is employed for the analysis of PTC based CSP plant with hot molten salt TES system. Cu-Cl cycle is analyzed with Aspen plus software. Other components and units are analyzed via engineering equation software (EES) with its built-in thermophysical properties. Different ambient conditions and input parameters are used to carry out the parametric study. Thermophysical properties of all state points can be seen

Conclusions

In this paper, an integrated solar and geothermal based system for multigeneration is considered for possible implementation in Larderello, Italy. A supercritical geothermal field is employed and its geothermal source is enhanced via heat recovery system. PTC type CSP plant with molten salt TES is considered in the overall system. Exhaust gases from the gas turbine are exploited via heat capturing system. Heat capturing system is allowed to increase efficiency, to operate the processes reliably

CRediT authorship contribution statement

Mert Temiz: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Data curation, Writing - original draft. Ibrahim Dincer: Conceptualization, Resources, Writing - review & editing, Supervision, Project administration, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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