Wikipedia has some reasonable figures about Cogeneration fuel cells (Ene-Farm is one of those "MicroCHP" fuel cell systems for home usage[1]: > Co-generation s

Wikipedia has some reasonable figures about Cogeneration fuel cells (Ene-Farm is one of those "MicroCHP" fuel cell systems for home usage[1]: > Co-generation systems can reach 85% efficiency (40–60% electric and the remainder as thermal).[5] Phosphoric-acid fuel cells (PAFC) comprise the largest segment of existing CHP products worldwide and can provide combined efficiencies close to 90% For the "95% […] efficiency", I guess they take the hydrogen heat input for calculation of efficiency. What I miss are the losses from conversion of natural gas to hydrogen. This has to be considered when comparing efficienies eg. with gas fired power plants. So when it comes to large-scale Combined Heat and Power plants [2], it depends. There are not only different types of power plants (coal fired, gas fired, etc.) but also the heating part varies (process steam, district heating, etc.). If you go thermodynamically strict, you would also have to consider the quality of heat (at which pressure & temperature level is the heat extracted). This is normally not considered in the standard efficiency formula. [1] https://en.wikipedia.org/wiki/Fuel_cell#Efficiency_of_leading_fuel_cell_types https://en.wikipedia.org/wiki/Fuel_cell#Efficiency_of_leadin... [2] https://en.wikipedia.org/wiki/Cogeneration https://en.wikipedia.org/wiki/Cogeneration