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‘This helps to solve energy security and net zero’: Q&A with Space Solar co-CEO Martin Soltau

Joseph Flaig

An artist's impression of Space Solar's Cassiopeia satellite beaming power to Earth
An artist's impression of Space Solar's Cassiopeia satellite beaming power to Earth

We need new sources of energy, and we need them quickly. As net zero targets draw ever closer, increasing energy consumption makes them harder to achieve – and all the more important.

In the search for a solution, some eyes are turning to space. Government-backed research is exploring space-based solar power, which would use huge satellites to constantly harvest sunlight, convert it to microwaves, and beam it to receivers on Earth.

That work is picking up pace at Space Solar, based in the thriving UK space hotspot of Harwell in Oxfordshire. Recent achievements at the company include demonstrating 360º energy beaming technology, which could transmit power to Earth without the need for moving parts – a hugely valuable feature when reliability and performance are key.

We spoke to co-CEO Martin Soltau about the company’s plans to turn a sci-fi vision into reality.

With renewables improving and capacity expanding, why do we need space-based solar power?

Despite the claims that wind and solar are cheap and expanding and getting cheaper, looking at our future energy system as a complete system we've obviously got to have the ability to address intermittency and maintain the reliability and the affordability of the energy system. And the real challenge is that the back-up, the baseload and storage, don't exist yet at commercial scale. It’s really important that we try and develop carbon capture and storage, battery storage, and other storage technologies, but they're a very long way away from being commercialised.

As a system, wind and solar are not so cheap, because we need to have duplicated energy sources for when the wind isn't blowing and the sun isn't shining.

We're working quite closely with Professor Goran Strbac at Imperial College. He does a lot of the modelling for the government on net zero pathways and he's a strong proponent of space-based solar power precisely because of this huge challenge, and recognises that we need to have these new options.

It's about a system that will provide affordable, reliable energy. The independent studies done for the government and for the European Space Agency showed that when it's developed, space-based solar power could in its own right be very affordable indeed. And it also provides good integration with wind, solar and others.

Then it can provide some really unique things, like the ability to act as a transmission system as well as a generation system, delivering energy closer to the point of demand, and this is key for the future grid. At the moment part of the huge cost, which is not included in the headline ‘Cheap, affordable wind and solar’, is the massive cost of building up the grid infrastructure to connect up the very low-density renewables.

The final reason why we need to look at energy from space is that these low-density renewables consume huge amounts of materials and minerals, which need to be mined and refined.  Globally, to reach net zero largely with wind, solar and batteries, we will need between 20- and 70-times the amount of mining, depending on the mineral we're looking at, for an industry where a 10% increase is huge. Mining is itself not an environmentally friendly activity, and the materials are mined in countries that are geopolitically challenging, and refined in other countries which are also geopolitically challenging.

Of course, [space-based solar power] doesn't exist yet. It's low TRL. But what it does do is provide another option for governments. There's massive uncertainty about how to get to net zero, this provides a very credible and capable option.

What does your design look like?

The solar power satellite harvests solar energy in space at gigawatt scale, using space-rated solar panels, not dissimilar to solar on Earth. The electricity is converted to microwaves in the one to 10 gigahertz range, and at that frequency the RF (radio frequency) transmits through the atmosphere almost without loss. And with the right design, you can harvest and beam power to Earth, day and night, 24/7, through all seasons and weather, so you've got this nirvana of continuous, reliable and dispatchable energy.

As the satellite is going around the Earth, it needs to have the solar collector always pointing at the Sun, and the transmitter always pointing at the rectenna on Earth. The angle between the Earth and Sun is constantly changing and thus we need to steer the beam, which is an important function of the design. 

They are very large. The reason for that is that they’re in a high Earth orbit, tens of thousands of kilometres above the Earth so that the satellites can see the Sun the whole time, out of Earth’s shadow. The diffraction physics of power beaming mean that you need a large transmitting aperture to form a tight collimated beam and a reasonable size of ground-based rectenna.

That defines the size of it, and it's probably the one reason why space-based solar power isn't really a thing yet, because your first commercial system has to be really quite large and therefore quite expensive. It’s difficult to make small-scale commercially viable products. 

Space Solar co-CEO Martin Soltau

Space Solar co-CEO Martin Soltau

We’re pursuing a design called Cassiopeia. It is about 1.7km in diameter, and about 4km end-to-end. So very, very large, many, many-times larger than anything that's ever been put into space, but it's just five-times the mass of the International Space Station.

It's made of hundreds of thousands of modules. Each of the modules has the ability to collect, convert and transmit the energy, and there's no functional connection between them, so you've got no single points of failure. Space is a harsh environment so we will have failures, and this modularity provides resilience with a very graceful degradation in performance over time.

The modularity also means that the unit production cost comes right down with the production learning curves, which is critical to the economics. It also provides a pathway to scale up the systems, and we can have a material impact on net zero because we will build and commission tens of gigawatts per year in full production.

What would the individual modules look like?

They’re about the size of a coffee table. We're working at the moment on a government-funded programme to define the optimum design and sizing, but essentially the modules are wafer thin elements comprising the concentrating lenses, the high concentration photovoltaics and a graphene heat-spreader that provides thermal management, together with the RF power amplifier circuitry and the transmitting antennas. The structural rigidity is provided by a lightweight carbon composite structure exoskeleton, which is also modular.

How will the modules be assembled into a complete satellite?

We're looking at robotic assembly systems design at the moment, but essentially they're going to be akin to Amazon warehouse-type robotics, which could run along guide rails or crawl over the structure, collecting the modules from the delivery hub, then clipping them into place to build the satellite. So the robotics are relatively simple compared to the Perseverance rover on Mars. These are not free-flying robots, they're not manoeuvring in space, they're operating in a very structured environment, assembling a small number of module types which are all designed for assembly.

I don't diminish the challenge of this, but it is as much to do with the economics as the engineering. Making the robots light, simple and reliable, these are the engineering challenges that we are going to need to address.

Northrop Grumman have done a very successful programme which has been servicing a satellite up in geostationary orbit which wasn't ever designed to be serviced. So we are already operationalising the sorts of technologies that we need.

Do you have any partnerships working on the robotic assembly?

One of our technical advisors is Professor Mini Rai, formerly from Lincoln University. She's one of the leading space robotics experts in the UK. We've also got a partnership forming with the world's leading space robotics company.

Have you calculated the efficiency of the system?

You've got this efficiency chain through the energy stream, from the Sun right through to the plug. The overall efficiency from the Sun to the AC you get out of the inverter on the ground is about 18%.

Efficiency matters only because it dictates the size and cost of the system. When the energy is free, it's much more about the economics. If we compare the efficiency of terrestrial solar in the same way, i.e. from the Sun to the plug, terrestrial solar is about 1% efficient, because actually, most of the time you're not generating anything – at night, dawn and dusk periods, weather and seasons and so forth. Looking at this another way, the utilisation of space-based solar power is almost 100%, compared to around 11% for terrestrial solar. 

Have you looked at the associated greenhouse gas emissions of the system, including rocket launches?

This was looked at by the University of Strathclyde a couple of years ago. They did a study, which was a lifecycle analysis on space-based solar power using a Cassiopeia architecture, and it concluded that the carbon footprint is about 24g of CO2 (carbon dioxide) per kilowatt hour. That's roughly half of terrestrial solar, even with all those rocket launches, and the reason for that is partly that it's got a very high yield.

The report identified some really helpful ways that we can further reduce the carbon footprint. The rectenna is a big part of that. We think we can get it right down, well below 24g CO2 per kilowatt hour, with much more modern materials.

Critical minerals is another important environmental issue.  One of the reasons why we're able to use a lot less minerals and help address that critical minerals challenge is that it's inherently much higher density as an energy generator than other renewables. And part of that is because we're using high concentration photovoltaics, concentrating anywhere between 10- and several hundred times, with very small PV (photovoltaic) devices.

What timeframes are you working to?

We've got a six-year development programme to retire most of the technical risks. At the end of that, we'll have a megawatt-scale demonstrator in space, beaming power to Earth. On the journey there will be multiple demonstrators to show that we're meeting the increasing TRL.

The six-year point is a tipping point for multiple reasons – it’s when the government has said they’re going to come in with Contracts for Difference and when the big energy companies are likely to be engaging strongly with space-based solar power in their near-term roadmaps. By year nine, we’ll have a 180MW-scale, first-of-a-kind commercial product.

And then three years later, at year 12, we'll have our gigawatt-scale system in space. Thereafter we'll be ramping up production. The latter six years is all about maturing the production, industrialisation, supply chains and manufacturing processes to get the cost down. We'll be in a position then to scale up very rapidly indeed, and it's all to do with this modularisation. In this respect it’s quite unlike nuclear fission where it takes a decade to get the planning, another decade to get the power station built, and at the end of that time you've got two gigawatts. We're going to be building 10 gigawatts per year, it's really going to have a big difference globally.

How much will it cost?

The CapEx (capital expenditure) costs are about $2.5bn per gigawatt, it's less than a quarter of the cost of nuclear. And the levelised cost of electricity, which is the CapEx and OpEx (operating expenditure) divided by the yield, is about £26 per megawatt-hour. So that's again very competitive with, if not cheaper, than wind and solar, and yet it's much more capable, being able to dispatch and provide baseload and export.

How does it feel to be working on a system that could provide a cheap and efficient new way of generating electricity?

Excited is an understatement. It is incredibly exciting. And it's largely because it really does feel as though it will have a huge impact. It helps to solve energy security and net zero in a really serious and sustainable way.

We haven't started recruiting yet, and we've had well over 400 applicants. And a lot of support from around the world, people really wanting to help us succeed, because net zero is so challenging, and so urgent and important. It blends real societal need with some pretty cool tech, so you can't get much better than that. It's really sparked huge excitement, because it's fantastically interesting and could have a real game-changing, transformational effect.

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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.


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