Hydrogen Storage and Transport

It is an unfortunate characteristic of solar energy that it arrives in a quite random manner depending on the meteorological conditions and it does not arrive at all time to suit our needs. Since the time of usage does not always match with the time of availability, it is necessary to store the solar energy at times of availability so as to use it at times of need.

The need for new and renewable energy alternatives due to the depletion of con­servative energy sources also brought about studies on the efficient usage and trans­mission of available energies. As is well known, the major criticism against these energy alternatives is the problem of energy storage (Tsur and Zemel 1992). Uneven solar energy potential in the world causes an imbalance in its production among var­ious regions, some of which are relatively richer in solar energy than others. Such imbalances can be avoided only through an efficient energy transportation system.

If the storage and transmission of solar energy can be achieved then the coal, fuel oil, and natural gas requirements of any country will be reduced significantly. Such solar energy transmission system will provide benefits for great trade centers,

Fig. 7.12 Fuel cell principle factories, and, especially, its application to illuminate green plants will lead to reduc­tion in the fossil energy use to a minimum, and provide continuity in the renewable energy alternatives.

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 on a large scale underground in the aquifers, in depleted petroleum or natural gas reservoirs, and in 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 the places of consumption from the production plants in gaseous form through underground pipelines 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 electricity directly (in fuel cells) or indirectly (through gas and steam turbine driven generators) (Veziroglu 1995).

Hydrogen can be converted to electricity electrochemically in fuel cells with high efficiency. It is not subject to Carnot cycle limitations, which is the case with the present day thermal power plants whether they burn fossil or nuclear fuels. It has been stated by Veziroglu (1995) 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 the hydrides are heated. The temperature and pressure characteristics vary for different metals and alloys. Many household appli­ances working with hydrogen do not need CFCs and, hence, they will not damage the ozone layer.

Hydrogen has the further property that it is flameless when it burns or the cat­alytic combustion is in the presence of small amounts of catalysts, such as platinum or palladium. Catalytic combustion appliances are safer, have higher second ther­modynamic law efficiencies, and are environmentally compatible.

The “technology readiness” of hydrogen energy systems needs to be acceler­ated, particularly in addressing the lack of efficient, affordable production processes; lightweight, small volume, and affordable storage devices; and cost-competitive fuel cells. The hydrogen energy system has the potential to solve two major energy chal­lenges that confront the world today: reducing dependence on petroleum imports and reducing pollution and greenhouse gas emissions.