by If you happened to be looking at the sky in Europe on the cold night of February 5, 1993, chances are 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 reflective structure resembling aluminum foil (Znamya means “rust” in Russian), untethered from a spacecraft that had just lifted off from Russia’s Mir space station. His goal was to demonstrate that solar energy could be reflected from space to Earth.
This was the first and only time a mirror had ever been sent into space for this purpose. But, three decades later, my colleagues and I believe that it is time to revisit this technology.
Unlike proposals to build solar power stations in space and transmit energy down to earth, all the generation would still happen here. Crucially, these reflectors could help solar farms generate electricity even when direct sunlight is not available, especially during evening and early morning hours when demand for clean energy is greatest. My colleagues and I call this concept “sun reflectors”.
Pioneering rocket scientist Hermann Oberth recognized the potential all the way back in 1929, when he envisioned reflectors in space re-reflecting sunlight to illuminate major cities and ship routes. He predicted that these reflectors would be very large, thin and ultralightweight, and that astronauts would be taken into space wearing diving suits.
Colleagues and I recently published a paper in which we explored the possibility of orbiting solar reflectors in the near term. We think Oberth’s vision could now be realized thanks to emerging technologies such as robotic spacecraft that can manufacture and assemble structures in space. The reflectors and other materials necessary to build such large structures could be launched with modern rockets such as SpaceX’s giant Starship.
Every time a reflector passes over a solar power farm, it may make an angle to illuminate the solar farm and its immediate surroundings. Each “pass” would extend the solar farm’s “day” and therefore its electricity generation hours.
When the reflector can no longer illuminate the solar farm, it can be rotated so that it is on the edge of the sun and no light is reflected on the ground. For this reason, we expect that the disturbance to ground-based astronomical observations will be minimal.
Lighting distance 10km
With the reflectors orbiting 900km above us – about twice the height of the International Space Station – we estimate that the illuminated area on Earth would be about 10km across at its brightest. Therefore, a system like this would not focus on individual solar panels on the roof but on large solar power farms, which are usually located away from residential areas.
Each pass of energy generation would extend about 15 to 20 minutes around dawn or night. This is important because these are the times when electricity demand is highest and often exceeds what is being generated by wind and solar, which means that coal and gas power plants are used as compensation. So reflectors could help reduce fossil fuel use without the need to store energy during the day.
These reflectors would be tall enough to service multiple solar farms in the same orbit. Their orbit could even be used to inform where to build new solar farms in particularly sunny regions.
Our proposal uses hexagonal reflectors with sides 250 meters long. Each one weighs about 3 tons. Currently it would cost a few thousand US dollars per kilogram to send something like this into space, although the costs are coming down. If costs are reduced to a few hundred US dollars per kilogram, we would expect orbital reflectors to be viable within a few years.
We expect these reflectors to operate for 20 to 30 years, although the carbon footprint of a system like this is difficult to estimate since it takes a long time to design, build and operate spacecraft. More research will be needed to do a full life cycle assessment, but in the long run, we expect the reflectors to help generate enough clean energy to offset their carbon footprint.
No more night?
Three days after the news of the Znamya-2 experiment was published in the New York Times, a reader wrote to the editor wanting to know if we would get through our nights. The short answer is no.
Even at its brightest, we estimate that the illumination levels would only last a few minutes per reflector and would not exceed the level of a cloudy day. This means that unless you are very close to the solar power farm, the lighting may not be noticeable most of the time, especially at dawn and dusk when the sky is relatively clear. already bright compared to the night.
We also consider that the reflector itself would not be visible to the naked eye unless you are close to the solar farm. These estimates suggest that these reflectors may have very little impact on the natural environment around the solar farm, although further research is needed.
When the reflectors are old or no longer needed, they could “sail” the sunlight into a higher, less crowded orbit or into a lower orbit to burn it off safely.
Solar reflectors are still orbiting far away. But they are a way to connect the space and energy sectors to help accelerate the transition to clean energy and tackle climate change.
This article from The Conversation is republished 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, with Dr. Temitayo Oderinwale, by Dr. Litesh Sulbhewar and with Professor Colin R. McInnes in the 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 Vision 2020 research and innovation program (grant agreement No. 883730).
