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Devangshu Datta: Going solar: Fact and fiction

How a space solar power system and wireless transmission could become a reality

Devangshu Datta 

Devangshu Datta

One of the recurrent ideas of science fiction (SF) is that of meeting primary energy needs from solar power. This is intuitively appealing. Stars are practically inexhaustible energy sources, and solar is a fairly clean form of energy. It's estimated that all the energy stores in reserves of coal, oil, natural gas are exceeded by the energy received in just 20-odd days from sunlight. Many SF writers, have played with ambitious ideas like transforming the solar system into a Dyson sphere (a sphere of material orbiting a central star and thus utilising all its energy).

The details can be glossed over in fiction. But translating concepts into working design has hit formidable barriers. Solar is intermittent, difficult to store, panels are expensive to make and require water to clean. Conversion ratios of solar energy to electricity are low. Wheeling solar onto commercial grids is tricky. Birds are often flash fried in mid-air with solar concentration designs.

However, researchers in different parts of the world have explored multiple approaches to try and get past those issues. Some engineering problems could be solved if solar power was captured in space. Intermittency and vagaries of weather would be eliminated if panels are placed on satellites orbiting well above the atmosphere. In fact, every space vessel uses solar power and has done so for decades. It may be an immense logistical problem getting really large solar generation capacity up into space. But this is a challenge that may be solved using current knowledge.

The other big issue with space solar energy is transmission. How does a space solar power system (SSPS) sitting 36,000 km above the Earth send down the power it collects to users on the ground? Cables are ridiculous - 36,000 km of anything would weigh a monstrous amount.

The holy grail of power transmission, therefore, is wireless. Transmitting large quantities of energy across major distances without using wires is formidably difficult. Japan has led the research in this area, looking for solutions because it desperately needs to find alternate energy sources after Fukushima. China is also energy-deficient and looking at large-scale solar power development in space.

There have been two encouraging demonstrations recently. The Japan Aerospace Exploration Agency recently beamed 1.8 kilowatts of electricity across a distance of 52 metres with pinpoint accuracy. Meanwhile, Mitsubishi Heavy Industries (MHI) successfully transmitted 10 kilowatts of electricity to a receiver located 500 metres away.

These are relatively small quantities of energy and not very large distances. But both energy and distances are orders of magnitude better than any earlier demonstration. There is hope that the technologies can be scaled to transmit much larger quantum of power across far greater distances, with total accuracy, ultimately making the SSPS concept feasible.

The SSPS concept has been outlined in papers with a timeline by MHI's team of researchers. The system would consist of millions of panels in geostationary orbit. The power collected would be beamed at microwave frequencies to a rectifying antenna (rectenna) on the ground.

The rectenna would convert microwave radiation to direct current and wheel it onto the grid. By roughly 2020, MHI hopes to have a 10 megawatt (Mw) SSPS up in space (this will weigh 100 tonnes). By 2030, commercial SSPS with capacity equivalent to a 400-Mw thermal station would be up. By then, weight should have scaled down to 400 tonnes (1 tonne per Mw). MHI hopes that the costs will be compatible with commercial power from other sources.

Very precise phase control would be required to ensure safety. MHI has to develop transmission control technology that allows such precision. The SSPS will have to be constructed from lightweight inflatable materials, which can be collapsed for launches and expanded once in orbit.

In order to run such systems, a formidable array of technical problems must be solved. Those solutions would find applications elsewhere. Wireless power transmission on a large scale would suddenly improve the viability of electric cars, which could be remotely recharged. In fact, wireless energy transmission could, on its own, revolutionise the concept of grid and off-grid and also be massively useful in managing disaster management since power could be quickly restored to a disaster zone.

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First Published: Thu, April 02 2015. 21:48 IST
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