Page 36 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

Introduction to SQFCs 17

been attempted. An objective of current research is to formulate a fuel which can
operate in an SOFC and a vehicle engine simultaneously [39,40].

1.11 Competition and Combination with Heat Engines
If the SOFC is to be successful commercially, then it must compete with existing
heat engines that are currently used to produce electricity from hydrocarbon
combustion. Such engines operate by burning fuel to heat a volume of gas,
followed by expansion of the hot gas in a piston or turbine device driving a
dynamo. These are inefficient and polluting when compared with fuel cells but
can be surprisingly economic as a result of a century’s development,
optimisation and mass production. Ostwald got it famously wrong in 1892 when
he said that ‘the next century will be one of electrochemical combustion’. Fuel
cells are still significantly more costly than conventional engines which can be
manufactured for less than $50 per kWe. The SOFC advantages of efficiency,
modularity, siting and low emissions count for little if they cost $10,000 per
kWe. These arguments are considered more fully in Chapter 13.
In the 1980s, it was envisaged that SOFCs could compete commercially
with other power generation systems, including large centralised power
stations and smaller cogeneration units [41]. This has not yet happened
because costs have remained high despite large injections of government
funding for SOFCs development in the USA, Japan and Europe. It has been
estimated that costs of $400 per kWe could be achieved with mass production
using powder methods [42]. Such costs would be competitive with present large
power station costs.
One of the most promising applications of SOFCs for the future is in
combination with a gas turbine as indicated in Chapter 3. The flow scheme is
shown in Figure 1.10. The SOFC stack forms the combustor unit in a gas turbine
system. Compressed air is fed into the SOFC stack where fuel is injected and
electrical power drawn off. Operating near 50% conversion of fuel to electrical
power, this SOFC then provides pressurised hot gas to a turbine operating at 35%
efficiency. The overall electrical conversion efficiency of this system can approach
75%, and this could be further improved by adding a steam turbine [43].

Fuel

Power converter

Figure 1.20 CombinationofSOFC withagns turbinegenerator.