I'm not sure where you get your numbers from.<br /><br />The "losses" of terrestrial solar power, since it's in shadow at least 50% of the day, and might require cleaning, and might be in shadow sometimes, are close to 60% even in the best locations.<br /><br />The "losses" of space based PV, assuming photocells of similar efficiency (which is cheating, since a space system is going to lag behind a terrestrial system by a few percent, since it's tougher to upgrade; but bear with me) are far less.<br /><br />First though, I have to clear up the myth about the microwaves: they aren't as hazardous as people fear. The system should be tuned so that they are 1/4 the power of raw sunlight, and they cover a rather small area, and their energy is absored by the rectenna so that the space under is less hazardous yet.<br /><br />Sulfur emissions from coal power is a much larger concern. Nuclear waste is a much larger concern. Greenhouse gasses are a much larger concern.<br /><br />Anyway, the rectenna operates at better than 80% efficiency with 25% less energy, 24 hours of the day, as oposed to terrestrial solar cells, operating at 20% to maybe 30% efficiency from 100% sunlight, less than 12 hours each day. So energy delivered into the grid is roughly double with the space-based system.<br /><br />And that'll stay true, no matter how much PV improves. You'll always get more electricity delivered if you bring the energy down from space.<br /><br />PS I'd like super-conducting tethers, too. Solar cells at the space end, power grid at the bottom. But we don't have to wait for that.