Fuel cell technology has an inherent advantage of other types of distributed energy such as solar and wind - it does not require an additional energy storage system for times when the sun is not shining or the wind is not blowing. This avoids the cost of the additional storage system. It also means there is no need to worry that your supply will match your demand.
All fuel cells operate by combining hydrogen and oxygen to form water. The process of combining them in a fuel cell generates both electricity and heat. If the source of hydrogen is a hydrocarbon fuel - natural gas, propane, diesel - then there will be additional output besides water but these byproducts are more than 50% lower than the emissions produced by burning the same fuels.
There are many designs for fuel cells. Two of the most common are PEM - Proton Exchange Membrane - and SO - Solid Oxide. Solid Oxide fuel cells run very efficiently, can provide useful heat, have a good life span and perform best if operated continuously. LTPEM - Low Temperature PEM - fuel cells run very efficiently, do not provide much useful heat, have a good life span and can be turned on and off easily to follow demand.
A fuel cell that runs very efficiently, provides useful heat, has an exceptional life and can be turned on and off easily to follow demand would be the best of both worlds.