Sustainable microgrids with energy storage as a means to increase power resilience in critical facilities: An application to a hospital

https://doi.org/10.1016/j.ijepes.2020.105865Get rights and content

Highlights

  • An optimal microgrid considering power resilience for a hospital was designed.

  • Economical profit and minimum resilience were considered for components sizing.

  • Up to 12 scenarios have been analyzed in REopt® observing a significant impact.

  • Positive net savings and more than 1 day of minimum survival time can be achieved.

Abstract

This manuscript proposes to study different cases that require the use of renewable energies in addition to diesel generators and energy storage systems with the aim of increasing the resilience of a microgrid feeding critical facilities. The aim of the work here presented is to quantify the benefits provided by an improvement of the energy resilience that could be achieved by installing a microgrid in a hospital fed by renewable energy sources. The microgrid will use a scheme based on solar PV in addition to diesel generators and an energy storage system based on electrochemical batteries. First, it has been evaluated how the implant of the microgrid increases the resilience of the power supply when a power failure occurs, considering that the main application in a hospital, even in the event of breakdowns, is to ensure the continuity of the surgical procedures and safely store drug stocks. Thus, these have been defined as the critical loads of the system. The components sizes have been optimized by considering both economic profitability but also the resilience capacity, observing that, by installing solar photovoltaic modules, Li-ion batteries and diesel generators, according to simulations performed in REopt® software, the microgrid could save approximately $ 440,191 on average over a 20-year life cycle of the facility (both considering the mitigation of energy provide by the power grid and the avoided losses during probable power services interruptions), while increasing the minimum resilience of the installation more than 34 h.

Introduction

Microgrids can be defined as small grids with the ability to operate autonomously, independently of the conventional power grid [1]. Because of its autonomy, it can be found in a number of end-uses such as military bases, hospitals or university campuses. Microgrids have the ability to isolate themselves from the power grid when a power outage occurs. Then, they continue to supply their critical loads without interruption, which is of great importance for critical facilities. This paper concerns in particular with the implantation of microgrids in hospitals, which are considered critical facilities that must guarantee electrical energy services for certain critical processes, such as surgery procedures or drugs storage.

Energy resilience has become vital in recent years as a result of many successive natural disasters. In the US, it has been found that power cuts due to the absence of an effective energy resilience policy have caused substantial economic losses in the last times. In particular, since 1980, on average, six disasters have exceeded $1 billion dollars per year [2]. The consequences are much more dramatic and add to this heavy toll: loss of production in industries and safety in critical facilities. One solution to this problem might be to set up a REHS (Renewable Energy Hybrid System) microgrid comprising photovoltaic panels, batteries and diesel generators. It has been shown that, in some cases, the use of diesel generators might not be appropriate because they have not worked during periods of major disasters (when test phases showed the opposite). This was the case, for example, during Hurricane Sandy at Coney Island Hospital, where patients had to be evacuated due to the lack of functioning diesel generators [3]. But the failure of diesel generators has another cause: refills of fossil fuels add an uncertainty to the facility [2].

In other countries, such Kuwait or Egypt, the installation of photovoltaic panels has been proved as a means to reduce the pressure on power plants and meet the growing demand for electricity [4], [5]. The solution would avoid, on the one hand, the increase in the use of fossil fuels and, on the other hand, crises in electricity production. The consequences are also catastrophic for the country's industrial, social and economic sectors. As a result, the main international challenge will be to design green electrical systems that will not harm the environment [6]. However, there are a number of barriers that hamper the installation of microgrids [5]. In this case, energy support policies to reduce the investment costs and promote a faster implementation has been proved to be successful in some regions, such as in Sicily (Italy) [7].

Nowadays, in the US, hospitals’ energy consumption represents nearly 5.5% of the total consumption of the country [1]. A potential hospital microgrid could assess electricity prices from the grid, and possibly “buy” electricity when its cost is low [1], and conversely, re-sell electricity when its cost would be high. In this case, intraday “electrical hours” have a great deal of influence on electricity. In the scientific literature, it has been shown that the establishment of microgrids has been promoted by favorable aid policies [8], [9], [10], [11]. Other analyses also reveal the physical aspect to be considered because of the existing weaknesses in the system: the presence of a transitional regime of the generators might, in some circumstances, lead to the complete collapse of the microgrid [12]. In addition, the various strategies that can be implemented to increase and boost resilience were investigated. According to [13], [14], [15], [16], it will be necessary to set up self-sufficient microgrids by implementing the appropriate number of renewable energy sources (this design is a result of an “electrical point of view” of electrical systems adapted to extreme disasters). Many successful efforts have been done in order to optimize the economic dispatch of energy storage systems in microgrids with high penetration of renewable energy sources, demonstrating that installing energy storage systems (ESS) in microgrids reduce operating costs and that it is necessary to have an efficient operation strategy to allow the maximization use of the ESS [17]. However, very few works nowadays consider both the economic approach and the resilience capacity. Lastly, the fight against cyber-attacks should neither be overlooked [18], [19]. Main opportunities and challenges of microgrids focusing on applications in enhancing grid performance can be found summarized in the review conducted in [20]. The islanded operation of the microgrids is one of the main challenges these facilities may face in the near future.

The majority of designs considering energy storage systems for resilience enhancement are focused mainly on the maximization of the survival probability to an outage, which usually conducts to not optimal economic sizing of generators and energy storage systems. This approach is mandatory for those facilities connected to not trustable or weak power grids, typical from undeveloped countries. However, the deployment of microgrids, especially those which account with renewable energy generators, in developed power grids in order to help the transition to a decarbonized power grid, forces new approaches. Under this new scenario, although the need to satisfy a critical load is still present, it must be considered with more relevance the normal operation conditions. Thus, in this paper, the sizing of power supply for critical loads has been approached mainly from the economical point of view, trying to minimize costs (or even maximize benefits for surplus energy selling to the grid), while valuating the resilience capacity considering both the outage probability and duration in a modern power grid from a developed country, which results much more realistic to real life scenarios. Moreover, this approach also differs from the business as usual sizing which depreciates the resilience capacity, which is highly valuated in critical facilities such as hospitals or military bases, among others.

This manuscript consists of three other sections. The following section brings together all the elements for analyzing the economic benefits and advantages of resilience with renewable energies. In this section the parameters to be entered during the simulation will be presented. The third section will be based on a series of simulations on a real case study. Finally, the last section will summarize the obtained results and the main authors’ conclusions.

Section snippets

Materials and methods

This section explains the approaches addressed by REopt® [21] and the comparison between other software tools that can conduct a number of simulations related to the topic here addressed. The last part details the different families of inputs offered by the aforementioned software.

Results

The work which follows takes up a series of simulations carried out with the REopt® software. The objective is to evaluate the performance of the microgrid through twelve scenarios (two extreme daylight duration times, two starting times and three outage durations for each case), presented in the Materials and Methods section, with the aim to study the share from PV to feed the loads, the energy used to charge the batteries and the energy exported to the power grid. For the readers’ help, Table

Conclusions

The research here presented estimates the savings that could be achieved over the lifecycle of a critical microgrid, in this case, considering a hospital as case study. Evaluations conducted in this research paper presented a breakdown among the different end-uses of the electricity produced by solar PV, i.e., battery charging, energy supplied to the microgrid loads, and energy resold to the electricity grid. For the proposed scheme, it was noted that most of the energy used by the loads of the

Credit authorship contribution statement

Alexis Lagrange: Data curation, Writing - original draft. Miguel de Simón-Martín: Writing - review & editing, Methodology. Alberto González-Martínez: Visualization, Investigation. Stefano Bracco: Supervision. Enrique Rosales-Asensio: Conceptualization, Methodology, Supervision.

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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