Hybrid systems are presented as a viable, safe and effective solution to minimize the associated problems of the dependence on renewable energies with the environmental resources. In this way different renewable systems such as photovoltaic, wind, hydrogen and so on, can work together to configure hybrid renewable systems. However, to make them work properly in a holistic way by creating synergies among them is not an easy task. Recently hydrogen technology has appeared as a promising technology to hybridize renewable energy systems, since it allows the generation (by electrolyzers) and storage of hydrogen when there is a surplus of energy in the system, and at a later time (e.g. when there are insufficient renewable resources available) using the stored hydrogen to generate electrical energy by fuel cells. The choice of a correct energy management strategy should guarantee an optimum performance of the whole hybrid renewable system; therefore, it is necessary to know the most important criteria in order to define a management strategy that ensures the best solution from a technical and economic point of view. This paper presents a critical review and analysis of different energy management strategies for hybrid renewable systems based on hydrogen backup. In the same way, a review is also presented of the most important technical and economic optimization criteria, as well as problems and solutions studied in the scientific literature.

In the field of energy, hydrogen as an energetic vector is becoming increasingly important. Specifically, fuel cells powered by hydrogen are becoming an alternative in automotive and other fields because of their ability to produce electricity without any pollution. Therefore, at this time there is a very active research field. A fuel cell can be described as a scale down industrial plant that consists of different subsystems whose purpose is to make the stack works properly. Air Cooled Polymer Electrolyte Fuel Cells (AC-PEFC) are receiving special attention due to their potential to integrate the oxidant and cooling subsystems into one, which in term gives the fuel cells their capability to reduce its weight, volume, cost and control complexity. In these fuel cells, the Oxidant/Cooling subsystem is of crucial importance and along with three others (Fuel, Electrical and Control subsystems) make up the Balance of Plant (BoP), which together with the stack comprise the full fuel cell system. The aim of this paper is to present a comprehensive experimental study of an AC-PEFC paying particular attention to the Oxidant/Cooling subsystem configuration. According to the scientific literature, this subsystem has not received the same attention as other subsystems like the Fuel and Control subsystems. However, a suitable design and size is critical for the proper functioning of the stack. The analysis carried out in this paper tries to solve some problems that can appear if the design of the Oxidant/Cooling subsystem has not been optimized. These problems are related to important aspects such as the performance and the efficiency of the whole system and temperature distribution over the stack.

This paper presents a new simulator for Hydrogen hybridization with Renewable Energy based Systems. The aim of this simulator is to provide a new solution for testing different energy management strategies of hydrogen hybridization based on renewable systems, in order to optimize them for implementation. The simulator uses the open architecture philosophy and has been developed in MATLAB ® -SIMULINK environment. Its main feature is calculating technical and economical parameters for a deepened analysis of influences on energy management strategies. It considers each element of the hybrid system and the whole system function. A simulation case shows the proper functioning of the simulator.

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Air Cooled Polymer Electrolyte fuel cells (AC-PEFC) are recently receiving especial attention because they offer the possibility to integrate the oxidant and cooling subsystems in just one. This feature reduces not only the fuel cell weight, volume and cost but also the control complexity. In these fuel cells, the Oxidant/Cooling subsystem along with three others (Fuel, Electrical and Control) make up the Balance of Plant (BoP), which together with the stack comprise the full fuel cell. It is common to find works focused on analysing the influence of the Oxidant/Cooling subsystem on the fuel cell. Nevertheless, studies in which the Fuel subsystem (it is responsible for providing the hydrogen for its reductioneoxidation reaction with oxygen to form water) is investigated are hard to find on the scientific literature. It seems like the Fuel subsystem configuration would not have influence over the whole system performance. Contrary to what one might think, and in basis on experimental results, this paper shows how the fuel cell performance is conditioned by the Fuel subsystem configuration. The aim of this paper is to present a comprehensive experimental study of an AC-PEFC paying particular attention, so unexplored so far, to Fuel subsystem configuration, giving the keys for the most suitable BoP configuration which guarantees the best performance, with the easiest BoP design and the lowest complexity.

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