If you happened to look up at the sky in Europe on a cold night on February 5, 1993, there’s a chance you saw a faint flash of light. That flash came from a Russian space mirror experiment called Znamya-2.
Znamya-2 was a 20-meter-long reflective structure, similar to aluminum foil (Znamya means “banner” in Russian), deployed from a spacecraft that had just undocked from Russia’s Mir space station. The goal was to demonstrate that solar energy can be reflected from space to Earth.
This was the first and only time a mirror was ever launched into space for that purpose. But thirty years later, colleagues and I believe it is time to rethink this technology.
Unlike proposals to build solar power plants in space and transport energy to Earth, all of the generation would still take place here. Crucially, these reflectors can help solar farms generate electricity even when direct sunlight is not available, especially during the evening and early morning hours when demand for clean energy is greatest. Colleagues and I call this concept “orbiting solar reflectors.”
Pioneering rocket scientist Hermann Oberth recognized the potential as early as 1929, when he envisioned reflectors in space that transmitted sunlight to illuminate major cities and shipping lanes. He predicted that these reflectors would be very large, thin and ultra-light, and would be built in space by astronauts wearing diving suits.
Colleagues and I recently published a paper exploring the possibility of putting solar reflectors into orbit in the short term. We believe Oberth’s vision may now be feasible thanks to emerging technologies such as robotic spacecraft that can fabricate and assemble structures in space. The reflectors and other materials needed to build such large structures could be launched by modern rockets like SpaceX’s colossal Starship.
Every time a reflector passes over a solar farm, it can position itself at an angle to illuminate the solar farm and its immediate surroundings. Each ‘pass’ extends the ‘day’ of the solar park and therefore the number of hours of electricity generation.
When the reflector can no longer illuminate the solar park, it can be turned so that its side faces the sun and no light is reflected to the ground. For this reason, we expect that the potential disruption to ground-based astronomical observations will be minimal.
Illuminate an area of 10 km
Because the reflectors orbit 900 km above us – about twice the height of the International Space Station – we estimate that the illuminated area on Earth would be about 10 km wide at its brightest. Therefore, a system like this would not be aimed at individual solar panels on roofs, but at large solar energy farms, which are usually located far from inhabited areas.
Each pass would extend power generation around sunrise or sunset by about 15 to 20 minutes. This is important because during those hours the demand for electricity is highest and often exceeds the amount generated by wind and solar energy, meaning that coal and gas-fired power stations are used to compensate. Reflectors can therefore help reduce the use of fossil fuels without having to store energy during the day.
These reflectors would be high enough to serve multiple solar farms in the same orbit. Their orbits can even be used to determine where to build new solar farms in particularly sunny regions.
Our proposal uses hexagonal reflectors with sides of 250 meters long. They weigh about 3 tons each. It would currently cost a few thousand dollars per kilogram to launch something like that into space, although costs are trending downward. If costs are reduced to a few hundred dollars per kilo, we expect revolving reflectors to be viable within a few years.
We expect these reflectors to continue to function for 20 to 30 years, although the carbon footprint of a system like this is difficult to estimate because spacecraft generally take a long time to design, build and operate. Further research will be needed to provide a full life cycle assessment, but in the long term we expect the reflectors will help generate enough clean energy to exceed their carbon footprint.
No more night?
Three days after news of the Znamya-2 experiment was published in the New York Times, a reader wrote to the editor asking if we would give up our nights. The short answer is no.
Even at the brightest, we estimate that illumination levels would last only a few minutes per reflector and would not exceed cloudy day levels. This means that unless you are very close to the solar farm, most of the time the lighting is not even noticeable, especially at dawn and dusk when the sky is already quite clear compared to nighttime.
We also estimate that the reflector itself would not be visible to the naked eye unless you are close to the solar farm. These estimates suggest that the impact of these reflectors on the natural environment surrounding the solar farm may also be minimal, although more research is needed.
When the reflectors are old or no longer needed, they can “sail” on sunlight to less crowded higher orbits or to a lower orbit to burn safely.
Circling solar reflectors are still a long way off. But they represent a way to connect the space and energy sectors to help accelerate the clean energy transition and tackle climate change.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Onur Çelik and his colleagues receive funding from the European Research Council. He worked with Dr. Andrea Viale, Dr. Temitayo Oderinwale, Dr. Litesh Sulbhewar and Prof. Colin R. McInnes in preparation of the article and on the SOLSPACE project. The SOLSPACE project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No. 883730)