Why NASA thinks you should forget about space-based solar power – Physics World

Carbon, Energy, Environment, Solar

Why NASA thinks you should forget about space-based solar power – Physics World

Space-based solar power sounds a cool idea but with a new NASA report suggesting it will never make economic sense, James McKenzie thinks we should just crack on building solar plants here on Earth

Extraterrestrial solar cells — **Dream on** NASA has cast doubt on the economics of using sunlight captured by solar cells in space to power the electrical grid. (Courtesy: Shutterstock/naratrip)

The other day I was watching the hugely entertaining Amazon Prime documentary series Clarkson’s Farm, which depicts the broadcaster Jeremy Clarkson’s attempts to run a farm in Oxfordshire. In one episode, Clarkson is named the National Farming Union’s “farming champion for 2021” for highlighting the challenges farmers face in making a living from the land. Particularly difficult for him are the rules that let local planning officials stop him from doing stuff that he feels ought to be allowed.

Clarkson appealed against some of the decisions and eventually won his case. But his experience inspired me to look into the UK’s planning system to see how objections have slowed the progress of wind farms and solar farms to a snail’s pace. Despite it being government policy to deploy more of these renewable forms of energy, I soon discovered that the country’s thorough but overly bureaucratic planning process is being hijacked by the “not in my back yard” (NIMBY) brigade.

Space-based solar power is not a new idea of course, first being mooted in a 1941 science-fiction short story by Isaac Asimov

These are people who want all the benefits and upsides of renewable energy systems – so long as they’re installed somewhere else, well out of eyeshot. One comment I read even suggested that the best place for solar power farms would be in space. Having written about the favourable economics of photovoltaic panels and the unfavourable economics of “solar concentrators”, I immediately wondered if “space-based solar power” could stack up financially let alone technically, especially in such an extreme and unforgiving environment.

Space-based solar power is not a new idea of course, first being mooted in a 1941 science-fiction short story by Isaac Asimov called Reason. It sounds simple in principle: all you have to do is place a solar array at a location in space where the Sun always shines. You then convert the electrical energy from the solar cells into microwaves and beam them to a ground station down on Earth, where they can be collected and turned into electricity for the grid.

Because the Sun’s always shining on the array, the electricity’s permanently on tap and there’s no need for storage. The upshot is that such an array – if it were ever built – would count as baseload generation like a coal, gas or nuclear plant. The UK government is certainly taking the idea seriously, having commissioned an independent report from Frazer-Nash Consultancy into space-based solar power back in 2021.

As Physics World discussed at the time in a news story and feature, the report examined two main concepts – the US-led SPS Alpha and the UK-led CASSIOPeiA. The report called for a thorough cost and economic analysis of both options, which surely is the whole point. The best way of doing this would be by using the “levelized cost of energy” (LCOE), which compares different energy-generation technologies talking all the various costs into account.

Given how many cool and fantastic technical ideas can be dashed on the rocks of reality by economics, I was intrigued to find that the UK government’s feasibility report had already crunched through the numbers. It said that space-based solar power has a 2050 projected LCOE of £50/MWh compared to £33/MWh for Earth-based solar farms (as of 2023 this sat at £41/MWh) and £96/MWh for large nuclear reactors.

Technical challenges

As far as the CASSIOPeiA project is concerned, it would consist of a 2000 tonne satellite roughly 1.7 km in diameter flying in a geosynchronous orbit about 35,800 km about the Earth. It would generate 3 GW of electricity that would be converted into microwaves with a frequency of 2.45 GHz, which can passed largely unhindered through the atmosphere and any clouds.

Getting 2000 tonnes of payload up into space wouldn’t be easy or cheap. The report estimates we’d need about 68 SpaceX Starship launches – an ambitious goal given that, at the time of writing, the company has never launched one of these rockets, let alone reused them. Although I am confident that SpaceX will succeed and that launch costs will fall, building a huge satellite of that kind isn’t the main hurdle.

CASSIOPeiA would also need a ground antenna receiver and grid interface in the form of an elliptical microwave receiver about 6.7 km by 13 km in size. Delivering 2 GW of power into the grid day and night, each receiver would be roughly equivalent to a single large nuclear power station. Overall, development costs are estimated to be an eye-watering £16.3bn and it would take 18 years to deploy. Still, assuming CASSIOPeiA is funded, and that all goes to plan, it could be powering your toaster and TV by 2042.

Space-based solar power: could beaming sunlight back to Earth meet our energy needs?

It should come as no surprise, though, that there are plenty of big technical challenges, with the UK report ranking 10 of the 13 crucial subsystems for the satellite of “high” or “very high” technical difficulty. As a high-level report, it naturally glosses over the practical details, but a more in-depth study has been carried out by Henri Barde, a retired engineer who used to work for the European Space Agency (ESA) in Noordwijk, the Netherlands.

Published by the IEEE in its proceedings of the European Space Power Conference 2023, Barde’s report looks at issues, such as how to cool solar cells and microwave systems that have gigawatts of power coursing through them. It also examines how to deal with temperature swings of about 300 ^oC a couple dozen times a year as the satellite passes suddenly across the Earth’s shadow (so, no, they’re not actually “on all the time”). Barde gives an overview of the huge, if not insurmountable, technical challenges in the June 2024 issue of IEEE Spectrum.

Further cold water was poured on space-based solar power by NASA, which earlier this year published a detailed report from its Office of Technology, Policy and Strategy

As for the ground-based microwave receiver, it would have a power density of about 29 W/m² for the 2 GW produced and require about a third of the area of a conventional Earth-based solar-power plant. Given that the UK, where I am based, has an average solar power density of 10 W/m², we could get the same output with only about three solar plants. What’s more, the solar cells in such plants could (unlike in a microwave antenna) be sensibly spread out over a large area. That sounds very appealing, especially as there is zero technical risk and we could have them now (or nearly now), planning permitting.

NASA weighs in

Further cold water was poured on space-based solar power by NASA, which earlier this year published a detailed 91-page report from its Office of Technology, Policy and Strategy. In worrying news for the technology’s supporters, it concludes that a 2 GW solar-space facility would, by 2050, be “more expensive than terrestrial alternatives and may have lifecycle costs per unit of electricity that are 12–80 times higher”. Even the cheapest system, NASA says, would cost hundreds of billions of dollars.

The NASA report also assesses the overall emissions, in terms of equivalent carbon-dioxide emissions per kilowatt-hour, and reckons that space-based solar power would be higher than terrestrial alternatives. Although NASA admits the costs could be improved with investment, it diplomatically concludes “cost competitiveness may be achieved through a favourable combination of cost and performance improvements related to launch and manufacturing beyond the advancements assumed in the baseline assessment”.

Which, to me, sounds like a polite way of saying “we’re right, but if you think you can do better, go knock yourself out!”.

Solar energy does, however, have lots of potential, with 87% of the world’s nations able to power themselves using less than 5% of their land. The UK is not one of those lucky countries: one-eighth of the whole nation would have to be blanketed with solar panels to power itself. That’s a huge area, given that 6% of the country is already built on, although efficiency improvements are on the way with perovskite solar cells, which will help a bit.

But the economics contained in the NASA report are surely the end of the debate for space-based solar power. If I were spending my own money, I would much rather invest it in lots of terrestrial solar farms. After all, there’s no risk involved and it’s much cheaper. And you don’t need to take my word for it: the benefits of solar power were fully laid out last year in Tesla Corporation’s influential Master Plan 3.

The only snag seems to be is getting planning permission to build those solar plants right now from local planning officials. In fact, wouldn’t it be great if Clarkson had a go at deploying a couple of fields full of photovoltaic solar panels at his farm in future episodes. That would test the reality of the situation – and make entertaining TV too.