Energy prices (in USD per kWh) may decrease in the future (solar? fusion?)
Solar costs do fall exponentially if the last decades are any indication. If you are fine with not getting 365/7/24 energy because energy is your biggest cost they will give you cheap power.
There might also be a time where you want to fly your solar cells nearer to the sun to pick up more sun. Computers in space could be powered that way.