Energy from space: China presents for two years a program that NASA has pursued without success for 20 years

©Jin Liuang / Xinhua / Agence France-Presse

Atlantic: China has advanced its two-year program to launch a solar power station into space Which will return the energy to the earth. What would be the aim of such a project? How would this work in theory?

Gil flamingo: This project has many interests. Outside the atmosphere, the intensity of the sun is about 40% higher, because the atmosphere absorbs part of the solar radiation. This makes it possible to obtain more energy per unit surface exposed to sunlight. The intensity that each component reaches is more important.

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

This satellite would convert solar energy into microwaves or lasers, then direct the energy beams to targets, including fixed locations on the ground and moving satellites.

A geostationary satellite can see the sun permanently without alternating between day and night. This is another advantage. This is one of the advantages of this process.

It works thanks to photovoltaic cells. These cells will be modified in relation to what is on Earth. The solar spectrum is not the same outside the atmosphere. We will have to modify the composition and the spectral response, the way the cell converts solar energy into electricity. We will have to modify the composition of the photovoltaic cells.

These cells will be exposed to more intense ultraviolet rays than those on Earth. There will be questions about resistance and durability.

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

On the other hand, the crucial and most difficult point to solve relates to the manner in which electrical energy will be transmitted to the Earth. Questions are asked about the method that will be used with lasers and waves. It would be necessary to transmit large amounts of energy on beams of electromagnetic waves. The technology is currently still very limited to transmit very large amounts of wireless power.

If we imagine that the satellite is fixed relative to the Earth, then the issue of reception arises with the rotation cycle of the Earth and the Sun.

The three main issues 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. Transportation is the most sensitive point. For reception, the beam carrying the energy must be turned back into electricity. The receiver will perform this function. It must also be mobile or be located in a well-defined receiving area around the ground. If the satellite is not moving relative to the Sun, this raises the question of its ability to track motion.

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

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By performing laser conversion, converting electrical energy into laser radiation, this does not make it possible to achieve conversion with 100% efficiency.

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

The first conversion step relates to the efficiency of converting solar radiation into electricity. If you convert this electrical energy into a beam of electromagnetic waves (either laser or microwave), you still have a conversion efficiency. You also have a performance for capturing electromagnetic waves on Earth. So there is a series of transformations which means that there will be losses in each level. This element is also important to take into account.

What are the current obstacles to its implementation, especially the technical ones?

Among the main limitations is the need for photovoltaic cells to withstand this rise with a strong component of ultraviolet radiation and gamma radiation that comes from the sun. These questions have already been studied for a long time thanks to the fact that the satellites are powered by photovoltaic cells.

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

Another limitation is related to the power packet transfer issue. You also have to ask yourself about actual performance.

So the whole question is how do we transmit it and how do we receive it on Earth.

NASA proposed a similar power project more than twenty years ago but was never developed, while the UK government commissioned independent research to support a British version in orbit by 2035, at a cost of £16 billion. Is this promising ground?

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

For a technology to be attractive, a certain type of performance must be achieved at each stage. If 50% of the energy captured at the station level is to be sent in orbit to Earth, it is possible to know the exact efficiency needed for each intermediate stage. But deep down, we never had that. This project may benefit from technological advances in other areas.

This project includes several technical challenges. This task is a somewhat old idea that appears regularly. A technological leap has been observed in one area. Now it is necessary to put all this into practice and into the chain. The energy, which must be transmitted by microwave or laser beam, makes it possible to question the most appropriate way to receive it on Earth before proceeding to the crucial stage of reconversion into electricity. Each step raises new technological challenges to solve. It would also be necessary to produce kilowatt-hours in order for this to be economically profitable.

So the idea is to collect this abundant solar energy in orbit and transmit it to a fixed point on Earth.

Unlike terrestrial renewable energy sources, solar power plants located in orbit will be able to provide power day and night on Earth, at any time of the year and whatever the weather.