The phosphoric acid fuel cell (PAFC) is the only type of fuel cell which is already commercially available today. The US-based company UTC (formerly ONSI) has already launched several hundred of such PAFC cogeneration units. Its product called PC25 has been available since 1991. United Technologies Corporation (UTC), another US company, also played a considerable role in developing phosphoric fuel cells. Its product called PC25 has been available since 1991. Some years ago, UTC switched from PAFC production to the development of another type of fuel cell because additional cost reductions required for PAFC development did not seem realistic. However, plans to continue the old PAFC development activities have emerged in the meantime.