Improved Rating for Residential Fuel Cells

A new performance rating system for residential fuel cells developed at the National Institute of Standards and Technology (NIST) can help prospective buyers assess the economic value of alternative fuel-cell technologies.

Residential fuel cells now being developed combine hydrogen from natural gas or propane with oxygen from the air to produce electricity. Homeowners might be able to meet all of their energy needs with a residential fuel cell and, in some cases, even sell excess energy to a utility. Currently, PTC 50, an ASME standard, is used to measure fuel cell system performance, but it does not take into account either seasonal changes in heating and cooling requirements, or a residence's quickly changing demands for electricity.

To bridge the gap between the PTC 50 standard and the information that consumers will need to make economic decisions on installing a fuel cell, NIST researchers have published proposed test and rating methods that will help consumers assess the economic feasibility of four different types of residential fuel cells under different climate conditions in six different geographic locations. The rating will provide the annual electrical energy produced, fuel consumed, thermal energy for domestic water heating and space heating delivered, and water used by the residential fuel cell system.

The four fuel cell types studied include systems that operate independent of the power grid with all generated power used by the residence itself; systems connected to the grid, in which electrical power output remains constant and excess electricity is sold to the utility; systems for thermal space and domestic water heating similarly connected to the grid to supplement the fuel cell power when needed; and similar but smaller systems used primarily for water heating.

The NIST test methodology and performance rating procedure uses building energy simulation results for three days, one each for winter, spring/fall, and summer for a prototypical house located in a representative city within six Department of Energy (DOE) designated climate zones, including Jacksonville, Fla.; Charleston, S.C.; Memphis, Tenn.; Pittsburgh, Pa.; Minneapolis, Minn.; and Astoria, Ore.

The NIST researchers expect to present their test methodology and performance rating procedures to standards organizations this summer. Several manufacturers have provided input on the rating methodology.

M.W. Davis, M.W. Ellis and B.P. Dougherty. Proposed test methodology and performance rating standard for residential fuel cell systems, NISTIR 7131, June, 2006. Go to http://www.nist.gov/manuscript-publication-search.cfm?pub_id=822194.