None of the 4 new design concepts now offer as credible a price tag as the SERT designs, simply because sufficient funding has not yet been available to evaluate the uncertainties and develop sharp cost estimates. But in at least 3 of the 4 cases, there is excellent reason to expect that costs will be much less than 17 cents / kWh when we get there. There are important risks – but with all 4 options together, the objective risk of not being able to beat coal or fission on cost is probably less here than with any other technology large enough to meet all the world’s energy needs.

Why are we wasting time and money on ethanol again? Another company thinks 2500MW of space based solar power plants for $4b is doable. A similar nuclear reactor would come to ~$18b.
2021-09-01: With starship, this now seems feasible and perhaps inevitable.

Assuming a 70% transmission loss from orbit (beaming power by microwave to antenna farms on Earth is inherently lossy) we would need 60TW of PV panels in space. Which is 60k GW of panels, at 1 km^2 per GW. With maximum optimism that looks like somewhere in the range of 3k-60k Starship launches, at $2M/flight is $6b to $120b … which, over a period of years to decades, is chicken feed compared to the profit to be made by disrupting the 95% of the fossil fuel industry that just burns the stuff for energy. The cost of manufacturing the PV cells is another matter, but again: ground-based solar is already cheaper to install than shoveling coal into existing power stations, and in orbit it produces 4x as much electricity per unit area. Even if Musk doesn’t go there, someone is going to get SBPS working by 2030-2040, and in 2060 people will be scratching their heads and wondering why we ever bothered burning all that oil. But most likely Musk has noticed that this is a scheme that would make him unearthly shitpiles of money (the global energy sector in 2014 had revenue of $8t) and demand the 1000s of Starship flights it will take to turn reusable orbital heavy lift into the sort of industry in its own right that it needs to be before you can start talking about building a city on Mars.

2023-06-09: Prototype confirmation

A satellite has steered power in a microwave beam onto targets in space, and even sent some of that power to a detector on Earth. “No one has done this before. They’re bringing credibility to the topic by demonstrating this capability.” The transmitted power was small, just 200 milliwatts, less than that of a cellphone camera light. But the team was still able to steer the beam toward Earth and detect it with a receiver at Caltech.

2024-01-22: NASA study goes into great detail, and concludes

The following combination of revised assumptions yields SBSP solutions that are cost competitive with terrestrial alternatives, with lower GHG emissions:

• launch cost: $50M per launch, or $500/kg; $425/kg with 15% block discount
• electric propulsion orbital transfer from LEO to GEO
• extended hardware lifetimes: 15 years
• cheaper servicer and debris removal vehicles: $100M and $50M, respectively
• efficient manufacturing at scale: learning curves of 85% and below