In principle hydrogen should not be on this list, because hydrogen is not a source of energy, nevertheless I have included it since many people believe that hydrogen can be created very cheaply. It must be understood that hydrogen does not exist in any directly usable form, H2, anywhere on Earth. Hydrogen has to be made in a process which demands energy. Two processes are either
The former process is economically cheaper, but it depends on natural gas, and emits CO2. In addition the fuel cell energy output of hydrogen made from methane is lower than the energy output of burning the methane gas directly. Therefore burning hydrogen emits even more CO2 albeit from a power plant where it could possible be sequestered - the energy efficiency is worse though.
In any case the required energy has to come from a primary source. Nuclear seems to be a likely source. To keep up with the diminishing supply roughly 150GW has to be installed each year for the next 30 years. These nuclear plants should be very large and designed specifically for the purpose of providing the electricity for the hydrogen production, since using the largest base load generators of today would require far too many.