Home Solar Thermal Collector Systems - Turning Heat into Free Energy

There are two ways of converting the sun's rays into usable energy for your home. One is by using the sun's photons to generate an electric current, known as the photovoltaic process. The other is by harnessing the sun's heat using solar thermal collectors.

Evacuated Tube Collectors for Solar Energy
 
 

Obtaining the sun's heat energy this way is a lot less complicated than with photovoltaics. Designing PV cells and installing solar panels made up of such cells requires delicate multi-stage processes. Collecting heat is a lot easier, but the tricky part is maximizing that solar warmth. Systems designed to absorb sunlight can come in many different forms, from the simplest flat plate collector to more complex solar pyramids and parabolic dish arrays.

In the end, solar collectors can be categorized as either concentrating or non-concentrating. This depends upon whether or not the solar radiation is being used at the point at which it's physically gathered. Systems that are non-concentrating transfer the heat energy directly, whereas concentrating solar collectors are designed to direct the energy to another central point where it will then be absorbed and used.

While there are significant advantages to thermal solar energy systems when compared to PV-type processes, the major disadvantage is that a solar collector only works in direct sunlight. Cloudy and hazy conditions cause a diffusion in light that makes them a lot less efficient. They still may be able to provide small amounts of power, but for the most part they're designed to work in conjunction with a solar tracker - or to be installed in climates and conditions when direct sunlight is almost always possible.

Types of Solar Thermal Collectors - Home Energy Systems and Commercial Applications

Flat Plate Collector - Perhaps the most common of all types, the flat plate solar collector is usually produced in a box-shaped design. Colored black for highest heat absorption, the box is highly insulated and usually contains a glazed absorption sheet that reaches the highest temperatures. Sometimes the box is covered or encased in transparent glass - this allows the light to penetrate the box in order to heat up the absorption plate, but allows the box to retain much of the escaping radiant heat. Many flat plate collectors are used in solar hot water or swimming pool heating systems.

Evacuated Tube Solar Collector - Another popular method of obtaining heat energy, an array of glass tubes are evacuated, vacuum-sealing them to protect against conducive heat loss. As sunlight strikes the tubes they can reach hotter temperatures than non-evacuated tubing, and since the tubes are rounded the surface area of each tube is more exposed to direct sun exposure. Some systems are designed with curved reflective surfaces beneath each tube in order to capture and redirect sunlight that falls between the tubes themselves. Another advantage evacuated tubes have over flat plate collectors is the ability to produce energy even when colder temperatures occur. The heat generated for each tube is directly related to the amount of sunlight it receives, and not the tube's surrounding air temperature.

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Parabolic Dish Collector - While not exactly ideal for home use, the parabolic dish type thermal collector is designed to capture the sun's rays and project them to a single focal point. The parabola of such a dish must be specifically designed so that incoming sunlight always reflects off the surface of the dish to arrive at the same focal point no matter what part of the dish the sunlight first hits. Since solar light waves essentially travel parallel to each other, this type of collector can be pointed directly into the sun and still achieve total focal output from all parts of the dish. The parabolic dish is the most efficient collector there is, and is often used in commercial applications and power plants.

Solar Power Tower - Essentially this configuration acts the same as a parabolic dish, only instead of a solid parabola reflecting the sunlight the reflecting is done by hundreds or even thousands of small mirrors. The mirrors are constructed so that each can pivot and rotate on it's own axis, and together they are programmed to track the same focal point. This focal point is the top of a large tower - the power tower - and enormous amounts of usable energy can be directed at this one structure.

Solar Pyramids - A newer type of collection technology, the solar pyramid acts by drawing air into the structure and heating it up before moving it through electrical turbines. The best techniques to maximize the benefits of this process are still being investigated.



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