Mission critical data centres uses battery backup and generator. If natural gas is available that is the fuel of choice. Propane or diesel is next and gasoline are for smaller applications.
Storing gas for generators (leaving in tank or external gas cans) - make sure you add gas stabilizer to the stored gas.

20kW is almost full 200A service at 110V. If everybody is only using minimal it can power a few neighbour's house as well.