Next generation: could space-based solar farms solve our energy woes?

Space-based solar power, a concept once confined to the world of science-fiction, may be closer to reality than we think. This year, various organisations within the global space sector are exploring its feasibility with hopes that, ahead of 2050, it could become a viable, constant source of clean energy.

Whilst research into space-based solar power is picking up pace, the concept isn’t new, researchers having explored it since the 1970s. Continued interest in its potential has sparked intermittent activity from the likes of NASA and the European Space Agency (ESA) over the years, but until recently, it was deemed economically unviable.

Now, with the cost of launches coming down and decarbonisation becoming more urgent, researchers are excited about the prospect of a reliable renewable energy source which, for the first time, could be within reach.

A space-based solar power system would see solar energy harvested in space through a constellation of kilometre-scale Solar Power Satellites (SPS) in geostationary orbit, each equipped with solar panels and mirrors, which reflect the sunlight onto the panels. The energy would then be converted into radio frequency waves which would be beamed wirelessly to a receiving ‘rectenna’ on Earth, converted to DC electricity, and  then put through an inverter to deliver AC power into the grid.

Sanjay Vijendran - ESA

Sanjay Vijendran, leader of ESA’s SOLARIS initiative, believes that space-based solar power is something the energy sector should be paying attention to and investing in at similar levels to other advanced technologies. The goal of SOLARIS is to pave the way for a final decision on whether to power ahead with the development of space-based solar in 2025, through further research, technical activities and international collaboration.

“It is solar power as you know it, with solar panels converting sunlight into electricity, but in a way that is not possible to get on the surface of the Earth because of weather, the day and night cycle and the seasons,” Vijendran told The Engineer.

“You’re essentially putting your solar farm in full visibility of the sun, 24 hours a day. That changes the nature of the power that you can provide … you’re now having a source of green energy that is constant, and terrestrially, it’s not possible to attain that. Whether it’s wind, solar or hydro power, they’re still at some level environment-dependent.”

While an attractive idea, there are numerous challenges involved in beaming solar energy from space to Earth. Many critics believe the concept just won’t be financially viable, and for many years, cost has been a huge barrier.

Vijendran pointed out that while being able to launch large amounts of hardware into space has traditionally been very expensive, we’re now moving toward reusable launchers which allow a frequency of flight that will mean cost drops ‘dramatically’. For this reason, he believes we could soon be able to launch fleets of SPS at a price that allows the electricity to be competitive with terrestrial systems.

“Our cost benefit study that we did [last year] confirmed that with some reasonable assumptions on improved performances of equipment, as well as lowering launch costs in the next 10-15 years, it is foreseeable that we can build these kind of structures that can produce GW of power at a similar price to what nuclear stations are today,” he said.

The satellites would be able to generate a similar amount of energy per year as a nuclear power station, therefore sell electricity for a similar cost – around €200-300/MWh, he said.

“This is of course more expensive than terrestrial solar or wind, but because the electricity is a constant source, its value is higher than the intermittent sources,” said Vijendran.

“Obviously if we were in the thousands of euros per MWh, that’s going to be in a different ballpark and difficult to compete, particularly with nuclear and fossil fuels. But we are trying to get rid of the fossil fuels and we do need a source of baseload, 24/7 power.”

Another challenge is how large the structures need to be, both in space and on Earth. To build structures that are around 2km in size in orbit will require advanced autonomous technologies for in-orbit robotic manufacturing. While these technologies have advanced in recent years for other applications, space based solar power will take it ‘to the extreme’, Vijendran said.

“On the ground, the receiving side is relatively simple … it’s just finding the space that is large enough to put these receivers in the countryside and near cities where energy is needed.”

There’s also a challenge in getting the power from the satellite to the ground through RF waves, similar to how satellites currently communicate for TV and internet connectivity.

“Unlike with communications where you’re trying to put a wide beam of signals across a region like Europe or the UK, to cover many individual receivers like a mobile phone or a television dish, here you’re trying to collect all that power because you want to convert it to electricity on the ground and sell it to people,” Vijendran said.

“You don’t want to lose any of that energy along the way, so that means your beam cannot be a very wide beam, you want it to be as direct as possible, and direct it at a receiver large enough to fully capture the entire beam.”

Meanwhile, the beam can’t be such a high intensity that it becomes dangerous. The requirement will be for frequencies and power levels to be designed to ensure safe regions of operation compatible with satellites and planes passing through the beam, and from the ground, he explained.

During Engineering Futures’ virtual Aerospace and Defence event in November 2022, Dr Alice Bunn OBE, chief executive of the Institution of Mechanical Engineers and former UK Space Agency director, touched on this and the need to address public safety concerns.

“The thing most people worry about is it being a ‘death ray’, and its not a death ray. In fact, the maximum intensity of theat beam is about a quarter of your typical mid-day sun, so not such a challenge,” she said.

“The engineering itself may be a challenge, but some of the wider challenges will come from outside engineering.

“Much like the wider energy debate, much of this will come down to political support as well as thinking about the technologies.”

Whilst other countries such as the US, China and Japan are already making strides on the concept and technologies involved, there has been a flurry of activity on space-based solar power here in the UK over the past few years.

After a study conducted by Frazer-Nash Consultancy concluded space-based solar was viable, BEIS provided £3m in funding to projects that are developing relevant technologies. A government-backed organisation, Space Energy Initiative (SEI) has been established, with 46 members including Thales Alenia Space, Airbus, National Grid and International Electric Company (IECL).

In fact, SEI member IECL’s patented ‘CASSIOPeiA’ (Constant Aperture, Solid-State, Integrated, Orbital Phased Array) satellite has been hailed as a breakthrough for the potential of space-based solar. Presented by IECL chief engineer Ian Cash, the CASSIOPeiA design features a high-gain antenna with omnidirectional coverage and 100 per cent array utilisation.

SEI believes that the satellite can provide the solution we need to make space-based solar power achievable in the coming years. SEI’s aim is to establish an orbital SPS demonstrator by 2030, with a constellation operational by the mid-2040s.

“The overall efficiency from the DC you generate on the satellite to the AC that goes into the grid is about 50 per cent, and each satellite is providing 2GW into the grid,” said Space Energy Initiative co-chair Martin Soltau, during an Engineers Australia UK Chapter ‘Spring Forward’ panel discussion on space-based solar last February.

“For Britain, in 2050, we might have 15 of these providing 30GW or 260TWh, so that’s about 30 per cent of our forecast electricity demand in 2050 which is going to be over three times what it is today.”

Across the pond, a demonstrator has already been launched by scientists at the California Institute of Technology (Caltech). Its 50kg Space Solar Power Demonstrator (SSPD) prototype spacecraft was launched aboard a SpaceX rocket on the Transporter-6 mission on  January 3rd, consisting of three experiments tasked with testing different technologies for space-based solar power.

The ‘DOLCE’ (Deployable on-Orbit ultralight Composite Experiment) demonstrates the architecture and deployment of the modular spacecraft which would eventually make up a kilometre-scale constellation, while ‘ALBA’ comprises 32 types of PV cells to test their effectiveness in space conditions, a process which could take up to six months. Finally, ‘MAPLE’ (Microwave Array for Power-transfer Low-orbit Experiment) aims to test and demonstrate wireless power transmission in space.

“Ultimately, the recent launch of the Space Solar Power Demonstrator (SSPD) … will tell us if space-based power is viable,” said Paul Kostek, IEEE senior member and commercial space expert.

“The satellites and arrays will need to be designed to address debris issues, such as changes to the orbit, whilst also being capable of operating if any damage does occur, for example damage to the modular systems. Additional costs will include the development of the base stations to receive the power; the way in which the power will be stored and distributed will be another significant cost item.”

Whilst it’s early days and many are yet to be convinced, those working to bring space-based solar power to the UK are optimistic that supported by the right investment, our engineering capabilities can launch this green energy source into the net zero mix.

“It is an ambitious concept, there are many challenges, but the underlying physics is very well understood. We don’t need any breakthroughs in materials or component performance – it’s not in the same league as nuclear fusion,” said SEI co-chair Martin Soltau during the Spring Forward panel.

“In the face of…uncertainty, governments need options. What space solar power offers is a new option to help us get to net zero with much greater chance of success.”