Since 75% of the universe is hydrogen, would it be sustainable to use fuel cell electricity generators? Fossil fuel generators won't last forever, because there is not an endless supply of fossil fuels, and solar power is only best when the sun is out. Fuel cell generators can be used any time of the day. So, are fuel cell generators sustainable?
A residential hydrogen-fuel-cell is a solid-oxide-fuel-cell which makes a lot of heat when it produces electricity.
The waste heat has obvious uses for the house or building but also the most likely source of hydrogen is to steam propane or natural-gas. So there is plenty of heat for that process once the fuel-cell is running. The only thing needed is the natural-gas feedstock but of course that's the fossil fuel use.
Here are two links to hydrogen-fuel-cells designed for RV's but that can also be used in multiple units for a house:
Now a hydrogen fueling station for vehicles can produce hydrogen by electrolysis of water using electricity. And then the only issue is the source of electricity.
It's possible that the source of electricity could be wind power, solar power, or hydro power.
Or hydrogen in general could be produced from ethanol with the ethanol produced from sorghum and that is near carbon neutral. Note that sorghum can be grown without irrigation only requires about 12" of rainfall during a growing season. Also, sorghum needs less fertilizer than corn.
No. There is no readily available supply of net-positive-energy hydrogen on Earth, where most human power usage takes place. Hydrogen fuel cells may be a useful component of a total energy system but they are not a source of generation capacity. Hydrogen is more like a battery than a supply of energy. Hydrogen can be liberated from water by using energy. Some of this energy can be recovered by using the resulting hydrogen in a fuel cell. This may be useful but the original energy to liberate the hydrogen must come from another source.
The focus on electricity is probably secondary: Any energy source can be converted into electric energy.
The focus on fuel cells is probably secondary, too: Hydrogen can simply drive combustion engines as well; if the hydrogen and oxygen sources are sustainable, then the combustion engine will be as sustainable as the fuel cell (minus potential efficiency considerations).
Having these out of the way, the question is simply whether hydrogen can be produced in a sustainable way. Since there is almost no free hydrogen on earth, it must be produced from water in an endothermic reaction — that is, a reaction which needs an injection of energy.
This means that the focus on hydrogen is probably secondary. Your question boils down to whether there is a sustainable energy source. And the answer is:
The only virtually (for the next couple billion years) sustainable energy source on earth is solar radiation.
Hydrogen may be useful to store and transport solar energy, and a fuel cell may be an efficient method to convert it into electric energy at convenient locations in space and time.
Another potentially virtually sustainable energy source would be fusion, if it can be made to work on an industrial scale, including a self-sustaining Tritium production.
Solar radiation provides not only just energy — energy as such is plentiful; it provides low-entropy energy which can be put to use.
So, are fuel cell generators sustainable?
Yes. The hydrogen will be generated using spare electricity when wind and/or sunshine are plentiful. It will be stored, and used later to create electricity when there is no wind and sunshine.
The key here is that the hydrogen is generated in a sustainable manner: using renewables, not from steam reforming of natural gas.