Solar energy

The Sun is an immense source of energy. This energy reaches the Earth under the shape of solar radiation, radiation which can be caught and transformed into other types of energy: electrical, mechanical or thermal. Thus, the solar energy can find its use in different domains, from agriculture to research.

Its main usage types are the following:

1) The producing of thermal energy: heating the water, heating the houses or the greeneries, etc.

2) The producing of electrical energy through the photovoltaic cell. This is the purpose of a long evolution, from the alimentation of pocket calculators to solar power plants, which can supply entire neighborhoods.

But this doesn’t stop here, evidence being the scores of solar devices found on the market, from watches to artificial satellites.

The solar energy could assure five thousand times more energy than the actual level of consumption! This is a significant number. For now, we only exploit five thousand megawatts, number that represents only 0.15% of the total energy produced by the mankind. You can easily remark that the solar energy is, as yet, a low used resource.

Actually, the increment rate for the usage of solar energy constantly accelerates. By now, the main conversion method of the solar energy into electrical energy is the solar panel. It has two big disadvantages: it has a low efficiency (10-20%) and it’s very expensive. But the things are on the right way. Photovoltaic cells with an efficiency of 40% already are in the experimental phase and sustained efforts are made for reducing their prices. But the Photovoltaic cell is not the main thing we want to talk about. In this section, as we told you before, we’re trying to look to the future, to the solutions that barely appear on the designer's board.

One of the solutions would be the one proposed by the “Stirling Energy Systems” company. It searched for another way to produce energy, starting with the solar one. Because, at least for now, the solar panels are inefficient, the researchers from “Stirling Energy Systems” suggested the transformation of the solar energy into mechanical energy (a “Stirling” engine must be used) and only after that the electricity generator to be operated. As concerns the engine, it’s a very simple one, based on the dilatation of a previously chosen gas (in case of “Stirling Energy Systems”, the gas was hydrogen). This kind of system will have a bigger efficiency, compared with the one obtained by the solar panels. According to the data provided by the company, a big project is developing in the Mojave Desert. This project consists in building a 400 megawatt solar power plant, which will cover an area of 1,600 hectares. Here, 20,000 curved mirrors will be arranged such as each one to focus the entire solar light on one “Stirling” engine, which, as we said before, will operate an electricity generator. If the results will be those expected, the power plant will become operational and the amplification of its power to 850 megawatts will be considered. One kilowatt produced with solar energy will cost somewhere around 13 cents, but it’s expected that once with the mass production, the cost will drop to 6 cents.

However the performances of the solar power plants placed on the ground, they stay at the mercy of the clouds. From this simple phrase results the idea for the new solar power plant: we’ll have to move it into space. Let’s not forget that exactly the cosmic space was the location in which the conversion of the solar energy into electrical energy was firstly used at a large scale. It’s sufficient to have a view of the “International Space Station” (ISS), whose energy is entirely assured by the sun, to understand we are right. But, for now, the generated power is too little and wouldn’t even partially satisfy the needs of the humanity. A technological through cut is needed. One of the ideas is proposed by “Martin Hoffert”, physics teacher within the New York University. He led a study team, whose conclusions were made public in the November 2006 number of the “Science” magazine. His study shows us that the intensity of the solar radiation is eight times more pronounced in space than on the ground, the problem of the clouds being totally solved. Hoffert’s proposal could be described this way: huge solar panels are placed on a low orbit around the Earth, panels which will convert the solar radiation into electricity and, in the next phase, this energy is converted into a microwave fascicle and sent to Earth.

Other methods imply the application of some mirrors around the Moon or in the Lagrange points, mirrors which will reflect the sun light into the solar panel power plants, placed on the low orbit of the Earth. According to an interview offered to “Space.com” internet site, Hoffert says that he recommends this simple way, with stations placed on the low orbit, which have relatively low costs and can direct the microwave fascicles to multiple locations on the ground. The stations can also be positioned as a constellation, for constantly energy delivery. Later, when the technology will advance, says the same Hoffert, we can think about more efficient systems, which we can place on geosynchronal orbits. This way, the power plant will not change its apparent position on the sky, fact that means it can constantly assure energy for any location in its visibility range. Of course, the space electrical power plants represent a big technological challenge, but the effort will surely be lesser than the one implied by the constructing of a reactor based on nuclear fusion

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It looks like the space power plants don’t pollute and they may represent the ideal solution for this century. Only that the situation isn’t so simple. This kind of power plant would have an area of at least two or three square kilometers and would luminously pollute the sky on night time. Just try to keep an eye on the International Space Station when it passes over you and think that it’s minuscule in comparison with what would be a power plant. Then think about the microwave flux sent to the ground. How dangerous would it be for the creatures that will interfere with it?