A reversible solid oxide fuel cell energy storage system

Renewable energy provides the best means of combating CO2 emissions, which contribute to global warming. However most renewable forms of energy are intermittent, such as wind or offshore wave, or diurnal, such as solar or tidal. As the electricity is not necessarily generated when required, there needs to be some form of storage or load levelling. This can be the grid, but most networks can typically only tolerate 10-20% of a intermittent supply and for non-grid connected locations there needs some form of local storage. A fuel cell coupled with an electrolyser can act as an energy storage device. The use of high temperature fuel cells also allows the waste heat to be exploited if required, raising the efficiency of the system. Typically the hydrogen is produced in an electrolyser from excess electric production, and compressed into storage tanks. The stored hydrogen can then be fed into a fuel cell when more energy is needed than is being generated. The clean water supply for the electrolyser, compressors, regulators, sensors and valves add considerably to the balance of plant and so to the cost. These active components use power and so lower the efficiency, and also add complexity to the system which will reduce the time before failure of the system. A prototype reversible solid oxide fuel cell system, consisting of both electrolyser and fuel cell, with greatly reduced balance of plant will be described and discussed. This system will be cheaper and more robust and will be ideal for connecting to the slowly changing output of diurnal power sources.