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.
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.
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.