Alan Boyle has a good rundown on the current state of play. I wonder, though about the assumptions underlying this comment:

To be competitive with other power sources, Maness figures that the powersat system’s launch costs would have to be around $100 per pound – which is roughly one-hundredth of the current asking price. Launch costs may be heading downward, thanks in part to the rise of SpaceX’s Falcon rockets, but Maness can’t yet predict when the charts tracing cost and benefit will cross into the profitable zone.

Launch costs to where? They’re that high to GEO, but not to LEO, and it doesn’t say where the satellite constellation will live. It’s going to be a long time before it’s a hundred bucks a pound to GEO, though though a robust market for LEO propellant depots will be a help in that regard. But we’re not far from having a thousand bucks a pound to LEO. Anyway, it would be nice to see more details on these things.

The bottom line, though, and the reason that I’m not that sanguine on the business prospects for SBSP, at least for base load, is this:

In addition to potential environmental concerns, large-scale solar farms can’t generate a steady flow of electricity at night, or during cloudy weather. But if engineers ever figure out a way to store up the intermittent energy generated by solar cells or wind turbines, at levels high enough to keep utilities flush with power, Maness thinks that would deal a heavy blow to his powersat dreams.

“At that point, I take my marbles and go home,” he said.

Yup. It’s not the technical risk of the space hardware and launch costs, but the risk of terrestrial competition as technology evolves, that is the biggest risk of all.