Fuel Cells

Fuel cells promise to deliver electrical conversion efficiencies in the range of 40 to 60%. Even higher total energy conversion efficiencies (approaching 80 to 90%) are possible when used in co-generation applications, where both electricity and the heat of reaction are utilized. Another promising feature of fuel cells is low emissions. Since they produce electricity without combustion, the usual products of combustion are not present. Fuel cells also operate quietly and reliably.

Fuel cells are being developed in the size range of a few kilowatts up to a few megawatts. However, larger units (up to 20 MW, and smaller micro-fuel cells (for portable electronic devices) are also being investigated. The driving force behind fuel cell development is not just the electric power industry but also the automotive/transportation industry. This cross-industry interest has helped to accelerate progress towards commercially available fuel cells.

PAFC

The electrical conversion efficiencies of phosphoric acid fuel cell units have been demonstrated in the range of 35-40%. Reliability has been good for many of the units in service.

MCFC

Deployments of pre-commercial field units have demonstrated electrical efficiency (LHV) near 50%.

SOFC

Vendor assessments have placed SOFC electrical efficiency (LHV) at around 50%. With SOFC/gas turbine hybrids, when the fuel cell is used as a topping cycle, the overall electrical efficiency can exceed 60%.

PEMFC

It is estimated that the most likely near term, cost-optimized efficiency of PEMFC technology will be in the 30 - 33% range. Efficiencies could increase to the 40% level in a 2005 timeframe if the following technical accomplishments are realized:

• Stack costs are reduced so as to allow for cost-effective operation at 0.8 V/cell or higher
• Fuel cell hydrogen utilization with reformate fuels is increased to 80% or higher
• Fuel cell cathode excess air requirements are reduced to 50% or less

Additionally, the development of high temperature fuel cell membranes could dramatically increase the potential for fuel cell technology by both increasing the system efficiency and simplifying the design of PEMFC systems.