by Lars Schellhas
The idea of space-based solar power has been around since the 1960s, but has recently gained new momentum. While we already use solar power today on Earth, there are a few drawbacks to putting solar panels on our rooftops or fields. The most important is the intermittent nature of Earth-based solar power, as its power generation fluctuates during the day – and goes down to zero at night. In addition, to compensate for this intermittency and the low load factor (appx. 11 % yearly average), large areas of land have to be covered with solar power to produce enough energy, and storage or backup capacities are needed for the nights and winter months.
Space-based solar power offers a solution to these problems. Instead of putting solar cells on the ground, the concept suggests placing the solar power plants directly high in Earth’s orbit. These solar power satellites (SPS) could receive sunlight throughout day and night, each moment of the year. With a load factor of close to 100 %, the same area of solar PV cells could generate much more energy than on Earth’s surface.
In 2021 alone, the world invested $1.9 trillion into energy infrastructure – because there is a business case for it.
This energy would then be transferred back to Earth using wireless energy transfer. This transfer can utilise two technologies: lasers or microwaves. The SPS would have a laser or microwave emitter which converts the electric energy from the solar cells. The laser or microwave beam would then be directed at a receiver station on Earth, which transforms the beam back to electric power.
Currently, the cost of space-based solar power is still prohibitive to its development. But this is rapidly changing as the cost of rocket launches is dropping at unprecedented speed nowadays. There even have been a series of international programs and a series of startups that are actively targeting the development and deployment of space-based solar power by the end of this decade.
Energy is not free
Up until today, everyone who launched anything into space, whether it was a satellite, a shuttle, or a space station, had to design their energy system. And in space there are only two sources of energy available: the one you bring with you or solar power. Due to this, most satellites, the international space station, and parts of a future lunar base will be powered by solar power.
But taking your own solar PV cells with you every time is heavy, too, and is just another thing you need to do instead of focusing on your core business (e.g., running a communication system or operating a lunar base). On Earth, we do not build our own energy system either every time we build a house or start a business. We rely on our power providers to deliver reliable (and sustainable) power. Over the last century, competition and technological advancements have driven down the cost of energy more and more.
What if we could utilise this highly efficient energy industry to drive down the cost of space exploration, whether in orbit, on the Moon, or beyond? New Space has enabled us to bring much more equipment (and people) into space by bringing down launch costs. But we will need to bring down upfront investments and operational costs of space missions, too, starting with energy.
The cost of energy for satellites
The key to lowering the cost of anything is investing in reusable infrastructure, which might require upfront investments, but generates continuous value, by providing a good at a lower cost than before. There are many examples of that, including railroads, airports, reusable rockets, and giant towers with chopstick robot arms to catch landing rockets. But one thing that comes to mind more quickly should be power lines, distribution grids, and power stations. The availability of a power grid in front of your house allows you to cook on an electric stove without building a power plant first.
However, in space there is no readily available infrastructure to provide these low-cost services to us. Instead, we have to bring our own energy system, including backups, some margin for degradation of solar panels, and batteries.
For example, one exemplary solar panel for satellites delivers 88 W. Over the guaranteed lifetime of the cells, 5 years, it will spend half of its time in Earth’s shadow (if in LEO) or in the Moon’s night if used for a Moon base. It will therefore produce appx. 220 Wy or 2 MWh throughout its lifetime.
The same panel has a mass of appx. 1.5 kg. Just launching it into space currently costs between $2000 and $2500 using the most cost-efficient available launch vehicle (Falcon Heavy). And that does not even include the cost of the panel itself.
On Earth, producing 2 MWh with solar PV costs between $10 to $20 (not thousands).
Energy in space is currently roughly 100 times more expensive than on Earth – but it doesn’t have to stay this way. To bring down the cost of energy supply in space, we need to be able to produce power centrally where it is cheapest and transport to it where it is needed.
Reusable space infrastructure
The lifetime of solar cells on Earth can easily reach 20 years and beyond. In space, conditions are a bit harsher due to stronger radiation, but if designed right, you can still get 20+ years of operation out of current cell designs. Up to 40 years, if we are looking at launching durable infrastructure in the future.
However, most satellites launched today have much shorter life spans than that. Especially in low earth orbit, where most of the satellites are today, satellites have to constantly work against the drag of the atmosphere. When they run out of fuel, they have to deorbit and burn up in the atmosphere. For example, Starlink satellites are expected to be replaced every 5 years. This is partially because the satellites have a low orbit to provide low-latency connections, but it’s also used to continuously improve the technology used in the satellites.
However, the solar cells used by those satellites are nowhere near the end of their lifespan when they are deorbiting, driving up the cost of electricity used.
Energy in space is currently roughly 100 times more expensive than on Earth – but it doesn’t have to stay this way.
An alternative would be to build long-lasting power satellites in higher orbits designed for longer lifetimes. Their single purpose would be to produce electricity and to beam it to other satellites, either by microwave or laser. Over their lifespan, they would be able to support a series of satellite generations with electricity, which would only require a receiver, instead of larger solar arrays and batteries, thus reducing the mass needed for the satellite to operate. In return, this lower mass could provide additional space for fuel and prolong the lifetime of an otherwise short-lived satellite. The company Space Power is currently building such a system, where a single power satellite provides auxiliary power to satellites in LEO. This reduces the need for batteries to cover going through Earth’s shadow and, therefore, the weight and cost of the satellites.
Some companies are already planning a global network of power-relaying satellites, which could provide energy to satellites in orbit, as well as power users on Earth. This system could be provided electricity from a space-based solar power satellite, but it could also utilise power from Earth beamed up as long as it is cheaper to do so.
Energy for the Moon
We are going back to the Moon in this decade. And this time we are coming to stay. This means that the infrastructure we will be building for and on the lunar surface will be used longer than anything we have ever built in human exploration. It also means, our perspective will have to switch from a short-term “get this mission done” to a long-term “let’s make the most out of our resources”. To enable others to follow in the footsteps of early missions and pave the way for sustained human (and economic) activity on the Moon and other planets, space agencies around the world should start to build long-lasting infrastructure.
Power on the Moon is far more expensive than on Earth or even in LEO. While space-based solar power is not competitive, yet, on Earth. It might well be competitive on the lunar surface. Constructing such heavy infrastructure is capital-heavy, especially in space. And space agencies alone won’t be able to finance the development – nor should they. Earth’s energy industry is one of the strongest economical forces out there. In 2021 alone, the world invested $1.9 trillion into energy infrastructure – because there is a business case for it.
There is a business case building up in space and around the Moon right now. As part of the Solaris project, ESA is engaging with many major players in the energy sector to bring them on the journey, too. However, most of Earth’s energy companies are still not even aware of space-based solar power or the new building market they could expand to beyond our horizons. Luckily, a few startups targeting SBSP and others who see the Moon as a stepping stone for it. It’s time that we create incentives and open a new energy market.
It’s time that space agencies flip that switch and start procuring energy for their space operations to foster the build-up of a sustainable space infrastructure. Earth, LEO, GEO, the Moon. and beyond: Wherever we are, we will profit from it.
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Lars Schellhas is a founder, consultant and writer who is passionate about climate innovation and entrepreneurship. He has a background in mechanical and energy engineering from RWTH Aachen University and has worked in various cleantech startups and for several energy companies. He founded his own sustainability data startup SimplyLCA and is currently a consultant for the energy sector at AFRY. Lars became aware of the climate crisis after watching Al Gore’s “An Inconvenient Truth” in 2006. He decided to dedicate his life to finding and supporting solutions for the biggest challenge of our time. He joined the green party in Germany, started a newspaper about renewable energy and climate innovation, and since 2022 writes his newsletter The Climate Innovator. As a founder and CEO of Schellhas Engineering, Lars helps investors and founders to strengthen the best climate innovations. He connects the dots between different domains, problems, solutions and communities that are driving change for a better future. Furthermore, he provides services around business analysis & financial modelling, market research & technology analysis, and engineering & system design services. He also shares his insights and deep dives into the latest climate innovations on his newsletter The Climate Innovator.