Seite - 136 - in Clean Water Using Solar and Wind - Outside the Power Grid

136 Clean Water Using Solar and Wind: Outside the Power Grid This is a highly unstable configuration, and therefore immediately reacts with another hydrogen atom to produce H2, molecular hydrogen gas. At the other electrode (the anode), oxidation occurs. The OH− ions are attracted to the positive electrode, where they are oxidised to form oxygen gas (O2) and hydrogen ions (H+). The anode reaction is 2OH− → 4e− + O2 + 2H+ Combining the cathode and anode reactions, we get the overall reaction: 2H2O → 2H2 (gas) + O2 (gas) Producing hydrogen from solar PV is probably the cheapest method available today. However, it must be recognised that electrolysis, plus the associated equipment to compress and store hydrogen, is capital- intensive. The cost of equipment will probably come down, but the cost is currently still an obstacle. Hydrogen does not need to be stored as a gas in pressure tanks. A new technology makes it possible to store the hydrogen in liquid form, a technology called Liquid Organic Hydrogen Carrier (LOHC). The technology is based on two separate processes: the loading (hydrogenation) and the unloading (dehydrogenation) of a liquid energy carrier. This liquid is composed of an organic molecule having similar physico-chemical properties to diesel. The LOHC-module consists of a hydration and dehydration unit and two tanks. One of the tanks contains the LOHC liquid carrier in its initial state. The hydration unit inserts hydrogen into the fluid in a chemical reaction. The loaded LOHC is then stored inside the second tank. Hydrogen can be discharged from the dehydration unit by an endothermic reaction (a chemical reaction that absorbs energy from its surroundings). The fluid returns to the initial tank. A big advantage of hydrogen being chemically bonded to the liquid carrier is that it can be stored under ambient conditions (normal pressure and temperature) without suffering any self-discharge or the loss of hydrogen. One litre of the energy carrier can store an equivalent of 2 kWh thermal energy or, after reconversion, 1 kWh electrical energy. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user