Energy from space: China is advancing by two years a program pursued by NASA without success for 20 years

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

©Jin Liwang / Xinhua / AFP

Innovation

China is working on launching a solar energy plant in space. This ambitious project should make it possible to redirect energy to Earth

Atlantico: China has advanced its program to launch a solar power plant in space that will bring energy back to Earth by two years. What would be the purpose of such a project? How would this work theoretically?

Gilles Flamingo: This project has several interests. Outside the atmosphere, the solar intensity is higher, by about 40%, because the atmosphere absorbs some of the solar radiation. This makes it possible to have more power per. surface unit exposed to the sun. The intensity that arrives at each element is more important.

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

This satellite will convert solar energy into microwaves or lasers and then direct the energy rays to targets, including fixed locations on Earth and moving satellites.

The geostationary satellite can see the sun permanently without switching between day and night. This is another plus. This is one of the benefits of this process.

It works thanks to solar cells. These cells will be modified according to what is on earth. The solar spectrum is not the same outside the atmosphere. We need to change the composition and the spectral response, the way the cell converts solar energy into electricity. We will have to change the composition of the solar cells.

These cells will be exposed to much more intense ultraviolet radiation than on Earth. There will be issues of resistance and durability.

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The satellites are equipped with cells to ensure the conversion of part of the solar radiation into electricity.

On the other hand, the crucial and most difficult point is to solve the way in which the electrical energy will be transferred to the Earth. Questions arise about the method that will be used, via lasers and waves. It will be necessary to transport large amounts of energy on rays of electromagnetic waves. The technology is currently still quite limited to the transmission of very large amounts of wireless energy.

If we imagine that the satellite is geostationary, the question of reception will arise with the rotation cycle of the Earth and the Sun.

The three key issues in this project are capture, transport and reception. This is a conversion string. Each step raises scientific and technical questions.

The simplest step is to convert solar energy into electricity. Transportation is the most delicate point. For reception, the beam carrying the energy must be converted back into electricity. A receiver will perform this function. It must also be mobile or located in a well-defined reception area around the Earth. If the satellite does not move relative to the Sun, this will raise a question about its ability to track movements.

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

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By performing a laser conversion, the conversion of electrical energy into laser radiation, this does not make it possible to obtain a conversion which has 100% efficiency.

Performance is not optimal when converting. It is at a few tens of percent. There are losses at all stages.

The first conversion step concerns the conversion efficiency of solar radiation to electricity. If you convert this electrical energy into a beam of electromagnetic waves (either a laser or microwaves), you still have a conversion efficiency. You also have an achievement of capturing electromagnetic waves on Earth. There is therefore a cascade of transformations, which means that at every level there will be losses. This element is also important to take into account.

What are the current constraints, especially technical ones, for the implementation?

Among the main limitations is the need for the solar cells to be able to withstand this height with a strong component of ultraviolet radiation and gamma radiation coming from the Sun. These issues have already been studied for quite some time thanks to the fact that satellites are powered by photovoltaic cells.

It is therefore important to adapt the cells to these extreme conditions in terms of resistance over time and spectral response.

Another limitation concerns the problem of transporting the energy beam. You also need to ask yourself about the actual achievement.

The whole question, therefore, is to know how we transport it and how we receive it on Earth.

A similar energy project was proposed by NASA over twenty years ago, but was never developed, while the UK government has commissioned independent research to support a UK version in orbit by 2035, costing £ 16 billion. Is this a promising place?

At every stage of rebuilding, transport and reception, technological locks have not yet been lifted. This project is nonetheless promising.

For a technology to be attractive, a certain type of performance must be achieved at each stage. If it is desired to transmit to the ground 50% of the energy that has been captured at the level of the station in orbit, it is possible to know the exact efficiency required for each intermediate stage. But deep down, we never have it. This project can benefit from technological advances in other areas.

This project involves many technical challenges. This mission is a pretty old idea, and one that pops up regularly. A technological leap has been observed in one of the areas. It is now necessary to put all this into action and into a chain. The energy that must be transported by a microwave or laser beam makes it possible to wonder about the most appropriate way to receive it on Earth before moving on to the crucial stage of conversion to electricity. Each step raises new technological challenges to solve. It will also be necessary to produce kilowatt hours in order for this to be economically viable.

The idea is therefore to collect this abundant solar energy in orbit and transfer it to a fixed point on Earth.

Unlike terrestrial renewable energy sources, solar-powered circuits would be able to supply energy day and night on Earth, at any time of the year and regardless of the weather.

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