ElectrolyzersOff-grid systems a b s t r a c tThe aim of this paper is to present and evaluate a proposal for designing an off-grid offshore electrolysis plant powered by wave energy. This plant includes PEM electrolyzers, a Reverse Osmosis system to produce water with adequate conductivity, a compression unit to store the hydrogen for transport, and batteries for temporary storage of electricity for short-time balances. First, the systems that compose the proposed plant are justified and described. Then a proposal for sizing these subsystems is given, based on using buoy-measured data at the expected location and simple mathematical models of the different sections of the plant. Finally the performance of the plant in a specific location is tested in detailed by using measured data, studying the influence of sizing on the expected performance.Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. IntroductionThis paper refers to a renewable energy offshore plant to produce hydrogen currently under development. It is well known that hydrogen is a clean energy carrier independent of energy sources [1]. The full benefits of hydrogen will be obtained when is produced from renewable energy sources. Different renewable energy sources have already been studied for electrolyzation, such as wind [2,3] and solar energy [4,5]; the feasibility of these sources to produce hydrogen has been demonstrated, with the main drawback the variability of these sources (see, for example [5], for a detailed feasibility and economical study), and the significant cost of solar hydrogen [6]. There are some published works on using reverse osmosis to obtain hydrogen from seawater, involving wave energy for generating the energy for the process [7,8]. There are even patents available that take into account this idea [9,10]. This paper concentrates on offshore systems: the source considered in this work is wave energy as wave converters provide lower variability in the energy production in comparison with other sources [11]. Offshore power links are known to be significantly expensive [12], so the system is here assumed to be fully isolated from the grid: it is parallel to the grid independent wind-hydrogen generation presented in [6]. Thus, power consumption adapts to power production by connecting or disconnecting sections of the electrolyzation plant (following a Smart Grid approach for the microgrid in the plant), and using a temporary storage of electricity for shorttime balances and increase of autonomy (that is a relevant issue in offshore installations). Automatic cleanings and maintenance operations are scheduled in the sections that are temporarily disconnected, to improve overall efficiency. Compared with previous proposals [8e10], this paper concentrates on using commercially available components that are already tested in the marine environment. Special * Corresponding author. Tel.: þ34 983184859.E-mail addresses: alvaro.serna@autom.uva.es, alvarosercan@hotmail.com (Á . Serna).Availab...
Predictive control Wave energyWind energy a b s t r a c t An Energy Management System (EMS), based on Model Predictive Control (MPC) ideas, isproposed here to balance the consumption of power by a set of electrolysis units in an offshore platform. In order to produce renewable hydrogen, the power is locally generated by wind turbines and wave energy converters and fully used by the electrolyzers. The energy generated at the platform by wind and wave is balanced by regulating the operating point of each electrolysis unit and its connections or disconnections, using an MPC based on a Mixed-Integer-Quadratic-Programming algorithm. This Predictive Control algorithm makes it possible to take into account predictions of available power and power consumption, to improve the balance and reduce the number of connections and disconnections of the devices. Two case studies are carried out on different installations composed of wave and wind energies feeding a set of alkaline electrolyzers. Validation using measured data at the target location of the platforms shows the adequate operation of the proposed EMS.
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