3.4.1 Fuel cell CHP
Fuel cells can produce electricity and heat without combustion. They can be thought of as large batteries which only work when supplied with a stream of hydrogen gas as fuel, which ends up being oxidised to water. CHP units using fuel cells are now becoming commercially available and are widely used in the USA and Japan.
In 2001 a 200 kWe phosphoric acid fuel cell (PAFC) was installed at a leisure centre in Woking as part of a scheme incorporating a further 1 MWe of gas engine CHP and 9 kW of photovoltaic panels. The hydrogen to run the fuel cell was produced by reacting natural gas with steam, also producing carbon dioxide. The individual fuel cell elements are stacked together to produce approximately 400 volts DC, which is connected to the grid via an AC inverter. Hot water from the fuel cell is used to provide heating and to run an absorption chiller unit for cooling the leisure centre. Performance monitoring showed that the fuel cell operated with approximately the same electrical generation efficiency, 37%, as a comparable gas engine CHP unit (DTI, 2005).
At present, capital costs and maintenance costs are higher than for gas engines, but these could fall. Fuel cell CHP has two main advantages over engine-driven CHP: the units are almost silent, with no moving parts, and they have high electrical efficiencies, which in the longer term could reach 50%, i.e. competitive with large combined cycle gas turbine (CCGT) power stations (IEA, 2005).
In the longer term, towards 2040, it is possible that natural gas could be replaced by hydrogen as a common heating fuel distributed through the existing pipe network.