Solar energy in progress and future research trends
Hydrogen storage and transport
Any discrepancy between the energy supply and demand can be offset by hydrogen storage, and its use at the time of need as a source of energy. Hydrogen can be stored at large scale in the aquifers as underground storages, in depleted petroleum or natural gas reservoirs, and artificial caverns as a result of mining activities. The latter method is the most commonly used alternative in some countries. Hydrogen can be transported to consumption places from the production plants through underground pipelines in gaseous form and by supertankers in liquid form. Hydrogen can be stored in stationary or mobile storage systems at the consumer site depending on the end use. It can be stored either as a pressurized gas or as a liquid, or using some of its unique physical and chemical properties in metal hydrides and in activated carbon. Hydrogen can be used instead of fossil fuels virtually for all purposes. As a fuel for surface and air transportation heat production and production of electricity directly (in fuel cells) or indirectly (through gas and steam turbine driven generators) [140].
Hydrogen can be converted to electricity electrochemically in fuel cells with high efficiencies. It is not subject to Carnot cycle limitation, which is the case with the present day thermal power plants whether they burn fossil or nuclear fuels. It has been stated by Veziroglu [140] that Tokyo Electric Utility started experimenting with a 4.5 MW United Technologies fuel cell years ago. Now, they have another 11 MW fuel cell on line.
Another unique property of hydrogen is that it will combine with certain metals and alloys easily in large amounts forming hydrides in exothermic chemical reactions. Hydrogen is released when hydrides are heated. The temperature and pressure characteristics vary for different metals and alloys. Many household appliances working with hydrogen do not need chlorofluorocarbons and hence, they will not damage the ozone layer.
On the other hand, hydrogen has further property that it is flameless or the catalytic combustion in the presence of small amounts of catalysts, such as platinum or palladium. Catalytic combustion appliances are safer and have higher second thermodynamic law efficiencies and environmental compatibility.
