In late November, a top-level meeting of European science ministers will convene in Paris. Their job is to decide the next priorities for the European Space Agency (Esa), of which the UK is still a member, and one of the items on their list to consider is a proposal for testing the feasibility of building commercial power stations in orbit. These huge satellites would bask in the sunlight, converting it to power and beaming it down to Earth to be fed into the power grid. The proposed project, known as Solaris, would determine whether the idea can contribute to Europe’s future energy security – or if it is all still pie in the sky. If the study gets the go-ahead, it will be like coming home for the space industry, which has always been at the forefront of solar power development. A year after the Russians launched the battery-powered Sputnik 1 in 1957, the Americans launched Vanguard 1. This was the fourth satellite in orbit and the first to generate its power using solar energy. Since that time, solar panels have become the primary way of powering spacecraft, which has helped to drive research. Vanguard 1’s solar cells converted just 9% of the captured sunlight into electricity. Today, the efficiency has more than doubled, and continues to increase, while the cost of fabrication has been falling. It’s a winning formula. “The cost of solar has been decreasing rapidly over the past 20 years, and faster than most players in the industry expected,” says Jochen Latz, a partner at management consultant McKinsey & Company. So much so, that in the Middle East and Australia, solar power is now the cheapest way to generate electricity. According to Latz, as the technology continues to develop, this will become true in the mid-latitude countries too. “In 2050, we expect more than 40% of the energy in the EU to come from solar power – if the countries achieve their committed targets,” says Latz. That would make solar power the single largest contributing energy source to the EU. However, there are obvious problems that need solutions if we are to fully utilise solar panels on Earth. For one thing, what do we do at night? In May, Ned Ekins-Daukes, associate professor at the school of photovoltaic and renewable energy engineering at the University of New South Wales, Australia, and his team of researchers demonstrated a solar cell that could generate electricity from the emission of infrared rather than from the absorption of sunlight. This works perfectly at night because the Earth stores energy from the sun in the form of heat, which it then radiates back into space as infrared radiation. The prototype device is based on the same kind of technology used in night-vision goggles and at present it can only generate a few milliwatts of power, but Ekins-Daukes sees the potential. “This is the beginning – it’s the world’s first demonstration of thermal radiative power,” he says, indicating that the team is aiming for a finished product that is “10,000 times more powerful”. At those levels, it is possible that a rooftop installation of such devices, probably fabricated in some way as an additional layer to conventional solar panels, would capture enough energy to power the house overnight – that is, keeping the fridge, wifi router and so on running. While that is a modest saving for each household, multiplied across a country’s population, it becomes significant. Another obvious issue with solar power is that some days will be cloudy. To alleviate this, excess electricity generated on sunny days needs to be stored in batteries but storage capacity is currently woeful. “The EU will need about 200 gigawatts [GW] of battery storage by 2030, but as of 2021 there was only 2.4GW of storage in place, so a massive increase will be needed,” says Aidan McClean, chief executive of UFODrive, an all-electric car rental company. To help with this shortfall, McClean champions a scheme called vehicle-to-grid – V2G – which uses the battery in an electric vehicle (EV) to store excess energy generated by a home’s rooftop solar panels and then transfer it back into the house when needed in the evening, or even sell it on to National Grid at other periods of high demand. “If V2G becomes widely adopted, the expected storage capacity of all the EVs will vastly exceed any expected storage requirements the grid will require going into the future,” says McClean. A recent V2G trial in Milton Keynes, Buckinghamshire, showed that participants saved money and cut their carbon footprint by using an “intelligent” charging system that topped up the batteries when renewables were generating electricity. Another approach is to use solar power not to generate electricity but to produce sustainable vehicle fuels. Virgil Andrei of the department of chemistry at Cambridge University and his colleagues have developed a thin “artificial leaf” that draws its inspiration from photosynthesis. In plants, photosynthesis takes in sunlight, water and carbon dioxide (CO2) and converts them into oxygen and sugars. In the artificial leaves, the output is syngas, or synthetic gas. This mixture of hydrogen and carbon monoxide can be used to produce a number of fuels via various industrial processes. It is even possible to produce petrol and kerosene. “We envisioned using CO2 from the atmosphere or other industrial processes and pouring that into these types of systems to create green fuel. Instead of releasing more CO2 into the atmosphere, we just have a circular carbon economy,” says Andrei. In effect they would piggyback off carbon-capture plants, which are currently being deployed to harness CO2 from industrial processes, and “recycle” it into sustainable fuels. The team first made an artificial leaf in 2019 but it was a bulky construction of glass and metal that sat on a bench top. This year, however, the team announced the results of a smaller, actual leaf-like structure that the researchers floated on the River Cam. The leaf was sealed inside a transparent plastic bag with the precursor gas and water and then left on the river for a number of days. The team then opened the bag and tested what gases had been produced by photosynthesis. The artificial leaves themselves are composed of materials called perovskites. The archetypal perovskite is a naturally occurring mineral of calcium titanium oxide – also known as calcium titanate – which was discovered in 1839 in the Ural mountains of Russia by German mineralogist Gustav Rose and named after his Russian counterpart Lev Perovski. Modern perovskites can have different chemical constituents and some have shown that they can function as solar cells. “These materials are very new and very exciting,” says Andrei. Laboratory tests show that they can be more efficient than the silicon used in conventional solar panels. Perovskites could even replace silicon in the solar panels of the future as they can be fabricated more easily and in thin, flexible layers. Another bonus is that these materials produce higher currents and voltages than their silicon counterparts, which allows more energetic processes such as the reactions that were used in the artificial leaves study. As promising as all this sounds, though, there is one insurmountable problem when generating solar power from the surface of the Earth: the atmosphere. The molecules in our atmosphere scatter about half the sunlight out of the direct beam. This scattered light bouncing around is what creates the blue sky we are so familiar with. In space, there is no atmosphere, so the sun’s light is undiluted. And as the aerospace engineers at the beginning of the space race found, put a solar panel in orbit and it will automatically generate about twice as much power as the equivalent panel on Earth. Unsurprisingly then, engineers and visionaries have been dreaming of putting solar power-producing satellites into orbit for decades. The basic principle is simple. A fleet of spacecraft with giant solar panels collects sunlight, before converting it into power and then beaming that energy back to Earth. How do you wirelessly beam energy across space? It turns out we’ve been doing it for decades. Every telecommunications satellite since the 1960s has used a solar panel to generate electricity, which is then converted into a microwave signal and sent to Earth. On the ground, antennas convert the microwaves back into electrical energy and read the signals. “The physics involved in that whole chain is exactly the same for space-based solar power, but the scale of it is completely different,” says Sanjay Vijendran of Esa, who is coordinating the proposed Solaris programme to study the feasibility of space-based solar power. Every few decades since the beginning of the space race, the idea of space solar power has been investigated. On every occasion, the story has been the same: the cost of launching such large satellites is prohibitive. But now, things are different. “In 2015, a miracle happens. The Falcon 9 reusable rocket flies for the first time,” says John Mankins, a former Nasa physicist who is now president of Artemis Innovation Management Solutions. Mankins is an expert on solar-power satellites, having worked on many of the feasibility studies over the decades. With the advent of a truly reusable rocket, the cost of sending equipment into orbit is tumbling. Instead of costing about $1,000 to launch every kilogram into space, Mankins now expects the price to come down to closer to $300 a kilogram. “That’s the holy grail for space solar power. It is not just possible some day – it’s inevitable in the next five or seven years,” he says. Others are similarly optimistic. In September 2021, the Frazer-Nash Consultancy published a report for the UK government that concluded: “Space solar power is technically feasible, affordable, and could both bring substantial economic benefits for the UK, and could support net zero pathways.” In late August, Esa released its own studies on space-based solar energy, which arrived at a similar conclusion for the whole of Europe. As a result, the agency will request in November that its member states fund a three-year feasibility study into solar-power satellites to examine in detail whether such a system might become commercially viable. “Solaris is a bridge to check that this is really doable and that it would really help before we ask for billions of euros,” says Vijendran. Whether or not such satellites go into orbit, there can be no doubt that solar power is set to dominate the energy landscape of the future. And as the current Ukraine crisis shows, that could lead to better energy security as well as reducing our carbon output.