Reflectors in space could make solar farms on Earth run longer every day

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Andrea Viale (University of Glasgow)

If you were looking 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 reflective structure much like aluminum foil (Znamya means “flag” in Russian), deployed from a spacecraft that had just undocked from the Russian Mir space station. Their goal was to demonstrate that solar energy could be reflected from space to Earth.

This was the first and only time a mirror was launched into space for that purpose. But three decades later, my colleagues and I believe it’s time to revisit this technology.

Unlike proposals to build solar power stations in space and transmit power to Earth, all generation would occur down here. Crucially, these reflectors could 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 highest. My colleagues and I call this concept “solar reflectors in orbit.”

Satellite with reflective material

Satellite with reflective material

Pioneering space scientist Hermann Oberth recognized the potential as early as 1929, when he imagined searchlights in space that transmitted sunlight to illuminate large cities and ship routes. He predicted that these reflectors would be very large, thin and ultralight, and would be built in space by astronauts wearing diving suits.

My colleagues and I recently published a paper in which we explored the possibility of launching solar reflectors into orbit in the near term. We believe Oberth’s vision may now be achievable 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 spotlight passes over a solar farm, it could be tilted to illuminate the solar farm and its immediate surroundings. Each “pass” would extend the “day” of the solar park and therefore its hours of electricity generation.

Reflectors in space that bounce sunlight back to Earth.Reflectors in space that bounce sunlight back to Earth.

Reflectors in space that bounce sunlight back to Earth.

When the reflector can no longer illuminate the solar park, it can be turned so that it faces the Sun and does not reflect light towards the ground. For this reason, we expect that the potential disruption to ground-based astronomical observations will be minimal.

Illuminates an area of ​​10 km.

With the reflectors orbiting 900 km above us (about twice the altitude of the International Space Station), we estimate that the illuminated area of ​​Earth would be about 10 km wide at its brightest point. Therefore, a system like this would not be aimed at individual solar panels on rooftops, but at large solar energy parks, usually located far from inhabited areas.

Satellite image of the solar park in the desertSatellite image of the solar park in the desert

Satellite image of the solar park in the desert

Each step would extend power generation by 15 to 20 minutes around dawn or dusk. This is important because those hours are when demand for electricity is highest and often exceeds the amount generated by wind and solar power, meaning coal and gas power plants are used to compensate. Therefore, reflectors can help reduce the use of fossil fuels without needing to store energy during the day.

These reflectors would be tall enough to serve multiple solar farms in the same orbit. Their orbits could even be used to inform where to build new solar parks in especially sunny regions.

Our proposal uses hexagonal reflectors with sides 250 meters long. Each one weighs about 3 tons. Currently, launching something like this into space would cost a few thousand dollars per kilogram, although costs are trending downward. If costs are reduced to a few hundred dollars per kilo, then we would expect orbiting 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 spacecraft typically take a long time to design, build and operate. More research will be needed to produce a full life cycle assessment, but in the long term, we hope the reflectors will help generate enough clean energy to offset 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 wondering if we would give up our nights. The short answer is no.

Even at its brightest, we estimate that illumination levels would last only 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 energy park, the lighting may not even be noticeable most of the time, especially at dawn or dusk when the sky is already quite bright compared to night. .

Diagram of terrestrial and solar reflectors.Diagram of terrestrial and solar reflectors.

Diagram of terrestrial and solar reflectors.

We also estimate that the reflector itself would not be visible to the naked eye unless it is close to the solar farm. These estimates suggest that the impact of these reflectors on the natural environment around the solar energy park may also be minimal, although more research is needed.

When the reflectors are old or no longer needed, they could “sail” with sunlight to less congested higher orbits or to a lower orbit to burn safely.

Solar reflectors in orbit are still far away. But they represent a way to connect the space and energy sectors to help accelerate the clean energy transition and address climate change.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The conversationThe conversation

The conversation

Onur Çelik and colleagues receive funding from the European Research Council. He collaborated with Dr. Andrea Viale, Dr. Temitayo Oderinwale, Dr. Litesh Sulbhewar and Prof. Colin R. McInnes in the preparation of the article and 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)

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