[ovi256]

They'll recharge batteries that they'll then return to earth on a cheap BFR-like reusable launcher. /joke

Internet points to anyone who computes:

- how expensive that makes the marginal kWh returned to earth likes this.

- how low launch and return-to-earth costs must go for this to become competitive with current kWh costs.

[adrianN]

First you build a space elevator to geosynchronous orbit, then you can use full batteries as counterweight for lifting empty batteries. That way you only have to overcome friction losses.

[ovi256]

Even better! Now it's less of a joke idea. You still have a small shuttle transfer from geosync orbit to wherever the solar farm is (heliosync or a lagrange point to avoid earth shadow), but the delta-v for that is tiny.

However space elevators are still soft SF (still missing a material with enough tensile strength), whereas BFR cheap reusable launchers are hard SF, achievable with current known tech.