Fuel cells that can run on the biogas produced by the anaerobic digestion of dairy manure are not economically feasible at present; however, as fuel cell costs decline, they are projected to become affordable by approximately 2010. Fuel cells are more efficient than diesel engine generators at converting biogas to electricity (40-50% vs. 10- 30%). They also generate more heat. If the heat is recovered for use on the farm, fuel cell efficiencies could be as high as 80-90%, making them potentially more profitable than diesel engine generators. Finally, fuel cells are quieter and emit far fewer greenhouse gases. Biogas must be scrubbed of hydrogen sulfide (H2S) before it can be used by fuel cells.