The idea was to have dual use so that they're not obsoleted when we get around to installing sufficient power storage for renewables and also a less heat intensive way to do it too.
The power is coming from energy that's otherwise going to heat the planet regardless (solar rays).
If you really wanted to be clever, your best bet would probably be to turn it into a laser beam and send it back to space. Would mimic that energy getting reflected instead of absorbed, albeit through a pretty inefficient and convoluted process.
Might make more sense to run carbon capture devices at that point, but again - in either of these cases we're back into the "it's getting pretty expensive to waste this energy" spot.
