Energy from space: China is two years ahead of a program followed by NASA without success for 20 years

This screenshot, taken at the Beijing Aerospace Control Center on July 4, 2021, shows a view of the Earth from the perspective of the Tianhe Space Station.

This screenshot, taken at the Beijing Aerospace Control Center on July 4, 2021, shows a view of the Earth from the perspective of the Tianhe Space Station.

3Jin Liwang / Xinhua / AFP

Innovation

China is working to launch a solar power plant into space. This ambitious project will make it possible to redirect energy to Earth

Atlantico: China has launched a program to launch a solar power plant into space that will bring energy back to Earth within two years. What would be the point of such a project? How will this work theoretically?

Giles Flamingo: This project has different interests. Outside the atmosphere, solar intensity is about 40% higher, because the atmosphere absorbs part of the solar radiation. This makes it possible to get more energy per unit of surface exposed to the sun. The intensity that comes with each element is even more important.

The first launch of the Chinese project will use a test satellite in orbit to test the technology used to transmit power from the power plant.

The satellite will convert solar energy into microwaves or lasers, then point energy beams at targets, which include specific locations on Earth and moving satellites.

Geostationary satellites can see the sun permanently without changing between day and night. This is another plus. This is one of the advantages of this process.

It works thanks to photovoltaic cells. These cells will be replaced with what is in the soil. The solar spectrum is not one outside the atmosphere. We need to change the composition and spectral response, the way the cell converts solar energy into electricity. We need to change the structure of photovoltaic cells.

These cells will be exposed to much more intense ultraviolet radiation than soil. There will be questions of resistance and sustainability.

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Satellites are equipped with cells to ensure that part of the solar radiation is converted into electricity.

On the other hand, the important point and the most difficult concern to solve is the way in which electrical energy will be transferred to the earth. Questions are being raised about the method to be used with lasers and waves. Electromagnetic wave rays will require a large amount of energy to be transmitted. The technology is currently limited to transferring large amounts of wireless power.

If we assume that the satellite is geostationary, then the question of eclipse with the rotation cycle of the earth and the sun will arise.

The three main themes of this project are capture, transportation and reception. This is a conversion string. Each step raises scientific and technical questions.

The simplest step is to convert solar energy into electricity. The most delicate point of transport. For reception, the energy beam has to be converted back into electricity. A receiver will perform this function. It must be mobile or be located in a specific reception area around the world. If the satellite does not move in relation to the sun, it will raise questions about its ability to track its movements.

This kind of transformation, which is very promising, raises many questions about its implementation. The Chinese want to transport energy and test this beam.

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By converting a laser, converting electrical energy into laser radiation, it is not possible to achieve a conversion that is 100% efficient.

Performance is not optimal when converting. It stands at a few percent. There are losses at every stage.

The first conversion step is related to the conversion efficiency of solar radiation into electricity. If you convert this electrical energy into a beam of electromagnetic waves (either a laser or a microwave), you still have a conversion skill. You have a performance to capture electromagnetic waves on the ground. So there is a cascade of conversions which means there will be losses at every level. This element is also important to consider.

What are the current limitations, especially the technical ones, to implement it?

One of the major limitations of the need for photovoltaic cells to withstand these heights, with a strong component of ultraviolet radiation from the sun and gamma radiation. These questions have already been studied for a long time because satellites are powered by photovoltaic cells.

It is therefore important for cells to adapt to this extreme condition in terms of resistance and spectral response over time.

Another constraint concerns the problem of energy beam transport. You need to ask yourself about the actual performance.

So the whole question is how do we transport it and how do we receive it on earth.

A similar power project was proposed by NASA more than 20 years ago but never developed, when the UK government conducted independent research to support a UK version in orbit at a cost of 16 16 billion by 2035. This promising ground?

At each stage of transformation, transportation and reception, the technical lock has not yet been lifted. This project is still promising.

In order for a technology to be attractive, at each stage, a certain type of performance must be achieved. If you want to send 50% of the energy stored at the station level in orbit to the ground, it is possible to know the exact skills required for each intermediate step. But deep down, we never have that. This project may benefit from technological advances in other fields.

This project involves many technical challenges. This mission is a fairly old concept and one that comes up regularly. A technological leap has been observed in one area. Now all this needs to be put into action and chained. The energy, which must be transmitted by a microwave or laser beam, makes it possible to wonder about the most suitable way to get it on Earth before proceeding to the critical stage of conversion to electricity. Each step raises new technical challenges to solve. It needs to produce kilowatt hours to be economically profitable.

So the idea is to collect this huge amount of solar energy in orbit and send it to a certain point on Earth.

Unlike terrestrial renewable energy sources, orbital solar power plants will be able to supply energy to the earth day and night at any time of the year and whatever the weather.

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