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Solar collectors and their types 15.03.2018

Solar collectors and their types

 

The basis of many solar energy systems is the use of solar collectors. The collector absorbs the light energy of the Sun and turns it into heat that is transferred to the coolant (liquid or air) and then used to heat the buildings, heating water, producing electricity, drying agricultural products or cooking. Solar collectors can be used in almost all processes using heat.

The production technology of solar collectors has reached a practically modern level in 1908, when William Bailey of the American company Carnegie Steel Company invented a collector with a heat-insulated body and copper tubes. This collector is very similar to the modern thermosyphon system. By the end of the First World War, Bailey sold 4,000 such collectors, and a businessman from Florida who bought his patent, sold nearly 60,000 collectors by 1941.

A typical solar collector saves solar energy in roof-mounted modules of tubes and metal plates painted black to maximize radiation absorption. They are enclosed in a glass or plastic case and are tilted to the south to capture maximum sunlight. Thus, the collector is a miniature greenhouse that accumulates heat under a glass panel. Since solar radiation is distributed over the surface, the collector should have a large area.
There are solar collectors of different sizes and designs, depending on their application. They can provide a household with hot water for washing, washing and cooking, or used to pre-heat the water for existing water heaters. Currently, the market offers many different models of collectors.

 

Integrated collector

 

The simplest form of a solar collector is the "capacitive" or "thermosyphon collector", which received this name because the collector is also a heat-storing tank in which the "one-time" portion of water is heated and stored.


Such collectors are used for preliminary heating of water, which then heats up to the desired temperature in traditional installations, for example, in gas columns. In household conditions preheated water enters the tank-drive. This reduces energy consumption for further heating. Such a collector is an inexpensive alternative to an active solar water-heating system that does not use moving parts (pumps) requiring minimal maintenance, with zero operating costs.

 

Flat solar collectors

 

Flat collectors are the most common type of solar collectors used in household water heating and heating systems. Typically, this collector is a heat-insulated metal box with a glass or plastic cover, which is placed in a black colored absorber (absorber) plate.

The glass can be transparent or matte. Flat panels usually use matt, only light, low-iron glass (it passes a significant part of sunlight entering the collector). The sunlight enters the heat-absorbing plate, and due to the slip the heat loss is reduced. The bottom and side walls of the collector cover with a heat-insulating material, which further reduces thermal losses.

Flat collectors are divided into liquid and air. Both types of collectors are glazed and unclosed.

 

Solar tubular evacuated collectors

 

Traditional simple flat solar collectors have been designed for use in regions with a warm sunny climate. They dramatically lose their effectiveness on adverse days - in cold, gloomy and windy weather. Moreover, due to weather conditions condensation and humidity lead to premature wear of internal materials, which, in turn, leads to deterioration of the operational qualities of the system and its breakdowns. These disadvantages are eliminated by the use of vacuumed collectors.

Vacuum collectors heat water for domestic use where water is needed at a higher temperature. Solar radiation passes through the outer glass tube, gets to the absorber tube and turns into heat. It is transmitted through the fluid flowing through the tube. The collector consists of several rows of parallel glass tubes, each with a tubular absorber (instead of an absorber plate in flat collectors) with a selective coating.

A heated liquid circulates through a heat exchanger and gives heat to the water contained in the tank-storage.

The vacuum in a glass tube - the best possible insulation for the collector - reduces heat loss and protects the absorber and heat-pipe from adverse external influences. The result is excellent performance that exceeds any other type of solar collector.

 

Focusing collectors

 

Focusing collectors (concentrators) use mirror surfaces for the concentration of solar energy on a sink, also called "heat receiver." The temperature which they reach is much higher than that of flat collectors, but they can only concentrate direct solar radiation, which will negatively affect accessibility indicators in dull or cloudy weather. The mirror surface focuses on sunlight, reflected from a large surface, to a smaller surface of the absorber, which results in a high temperature.

In some models, solar radiation concentrates at the focal point, while in others, the rays of the sun are concentrated along the fine focal line. The receiver is located at the focal point or along the focal line. Liquid-coolant passes through the receiver and absorbs heat. Such collector-concentrators are most suitable for regions with high insolation - close to the equator and in desert areas.

There are other inexpensive technologically simple solar collectors of narrow purpose - solar stoves (for cooking) and solar distillers, which allow you to get distilled water cheaply from almost any source.

 

Solar stoves 

 

They are cheap and easy to make. They consist of a spacious well-insulated box, pasted light-reflecting material (for example, foil), covered with glass and equipped with an external reflector. The black pan is an absorber, heating faster than conventional aluminum or stainless steel utensils. Solar stoves can be used to disinfect water if brought to boil.

There are box and mirror (reflector) solar furnaces.

True, there are exceptions, in the photo below: Large Solar Oven (VSP) with a capacity of 700 kilowatts, located in Uzbekistan. There are two such ovens in the world, the second one in France. 

The Great Solar Oven is a complex optical-mechanical complex with automatic control systems, consisting of a heliostat field and a paraboloid concentrator, forming a stationary high-energy energy stream in the focal zone of the concentrator. Surface area reflecting heliostat field - 3020 m², concentrator - 1840 m². The focal point of the concentrator rays exceeds 3000 degrees Celsius. It is the largest solar furnace in the world.

 

Solar distillers

 

Solar distillates provide cheap distilled water, with the source can serve even salty or heavily contaminated water. They are based on the principle of evaporation of water from an open container. The solar distiller uses the sun's energy to accelerate this process. It consists of a thermally insulated container of dark color with a glass that is inclined so that the condensate from fresh water flows into a special container. A small solar distiller - the size of a cooker - can produce up to ten liters of distilled water on a sunny day.

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