The power system must be fully off-grid and completely decoupled from outside weather events. With this in mind, geothermal power stands out as a renewable, reliable and continuous energy source.
By combining a deep geothermal power source with a more shallow (cold) aquifer for cooling, the power installation will not connect to atmosphere in any way.
This allows the human capsule to be constructed undergrond and to be run completely independent from the outside world.