Taylor Dinerman calls for space solar power in this week's The Space Review. He trots out hydrogen as an alternative energy source. No--it's an alternative energy delivery method. Last time I checked, to get hydrogen, we had to use another fuel source and lose energy to crack the hydrogen. To make space solar power viable, we need an advance that will advantage space solar power to terrestrial solar power. Does this meet the objective:

One technology that might radically reduce the weight requirements for these systems is the technique pioneered at the University of Notre Dame where single-walled carbon nanotubes are added to a film made of titanium-dioxide nanoparticles, doubling the efficiency of converting ultraviolet light into electrons. Any solar cell technology that could reach conversion factors of over 50% or even higher would reduce the size and weight of an SPS and thus make it easier and cheaper to build and launch.

It also makes terrestrial solar power potentially reach conversion factors of over 50% too. To make space solar better than terrestrial solar, we need launch costs to be no more than 3x manufacturing costs per kg if space solar is 4x as efficient. With manufacturing costs $350/kg, we need launch costs $1000/kg to make space solar viable.

Even ignoring manufacturing costs and assuming $250/kg to GEO launch costs, you couldn't make SPS economic against mass produced nuclear power.

In a high radiation environment the panels and electronics would barely last 20 years before requiring replacement, structure might be lucky to last twice as long.

Or of course arrange that the materials don't have to be launched out of Earth's gravity well at all. Moon materials can be delivered at very low cost; energy isn't the problem, reaction mass for manouvering is, and that can be supplied from the slag created while you're refining the ore.

Do it right, and the whole thing can be done by robots with very little human intervention.

Hell, Gerard O'Niell said all this in the early 70s!

SPS is virtually inevitable if New Space succeeds, so the real question is when.

The "When?" question is very interesting to potential investors. If it's 100 years from now, they will pass.

Using mass drivers from the Moon would add more than a decade to development time and make the business case less likely to pass the laugh test.

We as a country and a world may have a strong preference for space solar over nuclear power. But that still leaves carbon, wind, water and terrestrial solar to outperform/outprefer.