$2000 per kwh
I think it would be economic to buy power on Earth at $2000 per kwh, guaranteed for 20 years.
That's around 10 c per KW at today's money. Solar power units cost around $10 for 1 Wh, or $10,000 per kwh...
Either NASA is massively underwiting space electricity and completely absorbing the launch costs, or I've slipped a decimal point or three!