Definition, analysis and experimental investigation of operation modes in hydrogen-renewable-based power plants incorporating hybrid energy storage L. Valverde ⇑ , F.J. Pino, J. Guerra, F. Rosa Departamento de Ingeniería Energética, Escuela Técnica Superior de Ingeniería, Universidad de Sevilla, 41092 Seville, Spain article info Article history: Received 2 August 2015 Accepted 16 January 2016 Available online 10 February 2016 Keywords: Operating modes Hydrogen Hybrid energy storage Renewable Fuel cell Electrolyzer abstract This paper is concerned with Operating Modes in hybrid renewable energy-based power plants with hydrogen as the intermediate energy storage medium. Six operation modes are defined according to plant topology and the possibility of operating electrolyzer and fuel cell at steady-power or partial load. A methodology for the evaluation of plant performance is presented throughout this paper. The approach includes a set of simulations over a fully validated model, which are run in order to compare the proposed operation modes in various weather conditions. Conclusions are drawn from the simulation stage using a set of Key Performance Indicators defined in this paper. This analysis yields the conclusion that certain modes are more appropriate from technical and practical standpoints when they are implemented in a real plant. From the results of the simulation assessment, selected operating modes are applied to an experimental hydrogen-based pilot plant to illustrate and validate the performance of the proposed oper- ation modes. Experimental results confirmed the simulation study, pointing out the advantages and dis- advantages of each operation mode in terms of performance and equipment durability. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Due to increasing pressures to reduce CO 2 emissions and the depletion of traditional fossil fuels, renewable energies have received great interest and development. However, due to the unpredictability, non-dispatchability and high variability of renew- able energy sources, such as wind or solar, new challenges have arisen for including them into the current electrical system. Major concerns are related to problems of stability and reliability of elec- trical supply caused by the natural fluctuations of this type of energy. The use of energy storage systems to store surplus power in off-peak hours and to supply peak demand could provide a fea- sible solution to the aforementioned issues and contribute to a more secure and reliable grid infrastructure. Among the possible energy storage systems, those based on hydrogen production by electrolysis and subsequent utilization in fuel cells offer an attractive alternative to conventional systems (water pumping, compressed air, batteries, etc.), in terms of flexi- bility, energy density, long-term efficiency and added value as a marketable chemical for industry [1]. However, a major effort in applied research and demonstration projects must be made in order to make this technology more reliable, competitive and effi- cient. Therefore, to further the development of such applications, it is necessary to have a validation of the technology in real condi- tions, study of system design and investigation of operation strate- gies, among other issues. A renewable power plant based on hydrogen energy storage consists of a renewable source (typically wind or solar), an elec- trolyzer (a machine that produces hydrogen using electricity), hydrogen storage (compressed, liquefied metal hydride) and an energy conversion system, typically a fuel cell, as shown in Fig. 1. The design and operation of hydrogen-based power plants is a highly complex problem as it requires the characterization of hydrogen production/consumption, control of the renewable power and the stability of the power supplied by the fuel cell. In these plants, hybridization has positive impacts on system effi- ciency and flexibility. Energy-intensive and power-intensive stor- age devices can be combined to add flexibility and more potential sources of revenue for grid balancing and renewable-energy shift- ing in a configuration such as the one shown in Fig. 2 [3]. However, the inherent complexity of hybridization brings with it technical and economic questions which have not yet been fully answered. Many concerns are related to how to manage the energy in the system in an effective manner which leads to increased performance and economic benefit for the plant. Thus, one of the http://dx.doi.org/10.1016/j.enconman.2016.01.036 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: lvalverde@etsi.us.es (L. Valverde). Energy Conversion and Management 113 (2016) 290–311 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman