Parabolic solar collector making CONCEPT

This article offers an illustrated description of a method to produce a closed parabolic trough solar energy collector box based on the elasticity of the material. What is described here is basically a manual method to make high efficiency solar collectors against very low cost, which is particularly suited for teaching, research or demonstration purposes. But it is hard for a manually made collector to match the efficiency, lifetime and water tightness standard of an industrial product using the same method. It will also cost more than the industrial collector.

The method for industrial production of elastic closed parabolic trough boxes will be described in another article later. A parabolic trough solar collector uses a mirror in the shape of a parabolic cylinder to reflect and concentrate sun radiations towards a receiver tube located at the focus line of the parabolic cylinder. The receiver absorbs the incoming radiations and transforms them into thermal energy, the latter being transported and collected by a fluid medium circulating within the receiver tube. This method of concentrated solar collection has the advantage of high efficiency and low cost, and can be used either for thermal energy collection, for generating electricity or for both, therefore it is an important way to exploit solar energy directly.

Known methods to form the parabolic cylinder reflective surface consist either of forming a curved plate material under high temperature, or of adding pre-formed ribs at the back of a flat reflective plate, then force the plate to follow the curve of the ribs. Both methods are expensive, and both have difficulties to reach a high precision. Our method uses the natural elastic deformation of a planar plate to form a curved surface close to a parabolic cylinder, then redress the approximation error of this surface, again using elasticity. As it is easier to get higher precision by natural elastic deformation, this method has the following advantages.

1. Simplicity and low cost. It is actually the only known method for home making high performance parabolic trough solar collectors without any special tools. Not only the production cost drops to far below the other manufacturing methods of parabolic troughs, but also it makes the solar energy collecting cost substantially lower than any fossil fuel. The economic and social signification of the method may be huge.

2. Better performance and quality of the product. It is a general understanding that the smaller a parabolic trough is, the lower is its performance, although smaller parabolic troughs are much more useful than bigger ones. The fundamental characteristics of the performance of a parabolic trough solar collector are its concentration ratio and its optical efficiency. Today, the concentration ratio of a parabolic trough collector of width between 1m and 2m is limited to about 50 times under industrial manufacturing conditions and with high cost, while our method can achieve an effective and efficient concentration ratio of over 80 times for a manually made parabolic trough of width less than 1m, together with a higher efficiency.

The solar collector described here has several usages, and changing the usage amounts simply to replacing the receiver tube. Beside the simple low-temperature receiver described in this article that can be used for water heater, space heater or heat source for an absorption cooler, there are also tubes covered by photovoltaic cells useful for combined heat and electricity generation, and evacuated high-temperature receivers. The latter can be combined with thermal storage devices to be described in a coming article, to form round the clock electricity generating systems of sizes ranging from individual home energy systems to large solar power plants.

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The low costs of the collector and the storage device guarantee that all these applications will lead to an energy cost significantly below that of fossil fuels. The theoretic design principle of a closed parabolic trough box can be found in MIT.

The method described here is patent pending. But the patent assignee allows royalty-free manual use of this method for non-profit purposes. For commercial exploitation of the method or product, please contact the author.