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Types of Solar Collectors
Written by Geoff Jones   
Wednesday, 22 November 2006 19:00

Solar Collectors

Not only are there many different ways that solar energy can be applied, but there are also many different methods for collecting the solar energy from incident radiation.  Below is a listing of some of the more popular types of solar collectors.  

  • Glazed flat-plate solar collectors
  • Unglazed flat-plate solar collectors
  • Unglazed perforated plate collectors
  • Back-pass solar collectors
  • Concentrating solar collectors
  • Air based solar collectors
  • Batch solar collectors
  • Solar cookers
  • Liquid-based solar collectors
  • Parabolic dish systems
  • Parabolic trough systems
  • Power tower systems
  • Stationary concentrating solar collectors
  • Vacuum tube solar collectors

More information about collectors can be found at the  U.S. Department of Energy – Solar Energy Technologies Program: Solar Heating.                

For a list of suppliers within Canada, contact the Canadian Solar Industries Association (CanSIA)

Glazed flat-plate collectors 

Glazed flat-plate collectors are very common and are available as liquid-based and air-based collectors.  These collectors are better suited for moderate temperature applications where the demand temperature is 30-70C and/or for applications that require heat during the winter months. The liquid-based collectors are most commonly used for the heating of domestic and commercial hot water, buildings, and indoor swimming pools. The air-based collectors are used for the heating of buildings, ventilation air and crop-drying.

image001.jpg

Glazed flat-plate collector
[courtesy of Natural Resources Canadaan (RETScreen)

In this type of collector a flat absorber efficiently transforms sunlight into heat. To minimize heat escaping, the plate is located between a glazing (glass pane or transparent material) and an insulating panel. The glazing is chosen so that a maximum amount of sunlight will pass though it and reach the absorber. 

Unglazed flat-plate solar collectors

In North America unglazed flat-plate collectors currently account for the most area installed per year of any solar collector. Because they are not insulated, these collectors are best suited for low temperature applications where the demand temperature is below 30C. By far, the primary market is for heating outdoor swimming pools, but other markets exist including heating seasonal indoor swimming pools, pre-heating water for car washes and heating water used in fish farming operations. There is also a market potential for these collectors for water heating at remote, seasonal locations such as summer camps.

image002.jpg

Unglazed flat-plate collectors

Unglazed flat-plate collectors are usually made of black plastic that has been stabilized to withstand ultraviolet light. Since these collectors have no glazing, a larger portion of the sun’s energy is absorbed.  However, because they are not insulated a large portion of the heat absorbed is lost, particularly when it is windy and not warm outside. They transfer heat so well to air (and from air) that they can actually ‘capture’ heat during the night when it is hot and windy outside! 

Unglazed perforated plate collectors 

The key to this type of collector is an industrial-grade siding/cladding that is perforated with many small holes at a pitch of 2-4 cm. Air passes through the holes in the collector before it is drawn into the building to provide preheated fresh ventilation air. Efficiencies are typically high because the collector operates close to the outside air temperature. These systems can be very cost-effective, especially when they replace conventional cladding on the building, because only incremental costs need be compared to the energy savings.The most common application of this collector is for building ventilation air heating. Other possible components for this system are: a 20-30cm air gap between the building, a canopy at the top of the wall that acts as a distribution manifold, and by-pass dampers so that air will by-pass the system during warm weather.Another application for this collector is crop drying. Systems have been installed in South America and Asia for drying of tea, coffee beans, and tobacco. Currently there is a project underway with funding through the Technology Early Actions Measures (TEAM) for the monitoring of 10 crop drying systems in 8 countries in South and Central America and Asia. 

Back-pass solar collectors 

Air-based collectors use solar energy to heat air.  Their design is simple and they often weigh less than liquid-based collectors because they do not have pressurized piping.  Air-based collectors do not have freezing or boiling problems.  In these systems, a large solar absorber is used to heat the air. The simplest designs are single-pass open collectors.  Collectors that are coated with a glaze can also be used to heat air for space heating.  This type of collector may be integrated in the building and combined with thermal mass such as in the Trombe wall described at the National Renewable Energy Laboratory.  

Concentrating solar collectors 

By using reflectors to concentrate sunlight on the absorber of a solar collector, the size of the absorber can be dramatically reduced, which reduces heat losses and increases efficiency at high temperatures. Another advantage is that reflectors can cost substantially less per unit area than collectors.This class of collector is used for high-temperature applications such as steam production for the generation of electricity and thermal detoxification. These collectors are best suited to climates that have an abundance of clear sky days and therefore are not so common in Canada.  Stationary concentrating collectors may be liquid-based, air-based, or even an oven such as a solar cooker.There are four basic types of concentrating collectors:

  1. Parabolic trough
  2. Parabolic dish
  3. Power tower
  4. Stationary concentrating collectors

Air based solar collectors 

The energy collected from air-based solar collectors can be used for ventilation air heating, space heating and crop drying. The most common application in Canada is for ventilation air heating. Three types of air-based collectors and their corresponding suitably for three applications are listed: 

 

Type of collector Ventilation Air Heating Space Heating Crop Drying
Unglazed perforated plate Very Good Poor Very Good
Glazed flat-plate Good Poor Good
Back Pass Fair No Fair-Good 
Trombe wall No  Good  No 

 

  

 

 

 

 

 

Designs for the first three collector types are simple.  The collectors usually weigh less than liquid-based collectors because they do not have pressurized piping.  Another advantage of air-based collectors is that they do not have freezing or boiling problems. All four of these air-based collectors can be integrated into buildings and form part of a building’s envelope. These first three collectors are described in more detail on each of their own pages; the trombe wall is described in detail at the U.S. National Renewable Energy Laboratory  web site. NRCan has developed two free software programs for analysis of solar air heating systems.  SWIFT (Solar Wall International Feasibility Tool) can be used for job quotations and system design for ventilation air heating and crop drying applications for the first three system types.   RETScreen is useful for conducting quick pre-feasibility studies of the cost effectiveness of proposed unglazed perforated plate collector installations. 

Batch solar collectors  

One hundred years ago, water tanks that were painted black were used as simple solar residential water heaters. Today their primary market is for residential water heating in warm countries. In Canada, they can be effectively used in campgrounds and for residential water heating in temperate climates such as Vancouver Island; during winter the tanks must be protected from freezing or they must be drained. Modern batch collectors have a glazing that is similar to the one used on flat plate collectors and/or a reflector to concentrate the solar energy on the tank surface.  Because the storage tank and the solar absorber act as a single unit, there is no need for other components. On an area basis, batch collector systems are less costly than glazed flat-plate collectors but also deliver less energy per year. 

Solar cookers   

Though there are many types of solar cookers, all of them have a couple of basic components:

  • Concentrator or lens to increase the available solar energy and insulation to reduce heat loss.

Often there is also an oven type cavity to place food into for cooking.  Hot dog cookers, which do not need an 'oven' can also be made.Solar cookers are commonly able to reach cooking temperatures of 90-150 C (200-300 F) and some can even reach 230 C (450 F)! With these temperatures, it is possible to cook virtually any food as long as it is sunny outside.Making and using solar cookers can be a fun and educational school project.

Liquid-based solar collectors 

Liquid-based collectors use sunlight to heat a liquid that is circulating in a "solar loop". The fluid in the solar loop can be water, an antifreeze mixture, thermal oil, etc. The solar loop transfers the thermal energy from the collectors to a thermal storage tank. The type of collector you need depends on how hot the water must be and the local climate. The most common liquid-based solar collectors are:

  • Glazed flat-plate              
  • Unglazed flat-plate              
  • Vacuum tube              
  • Batch collector  
  • Concentrating  

 

Parabolic dish systems 

A parabolic dish collector is similar in appearance to a large satellite dish, but has mirror-like reflectors and an absorber at the focal point. It uses a dual axis sun tracker. 

A parabolic dish system uses a computer to track the sun and concentrate the sun's rays onto a receiver located at the focal point in front of the dish.  In some systems, a heat engine, such as a Stirling engine, is linked to the receiver to generate electricity. Parabolic dish systems can reach 1000 °C at the receiver, and achieve the highest efficiencies for converting solar energy to electricity in the small-power capacity range. 

image003.gif

Parabolic dish collector with a mirror-like reflectors and an absorber at the focal point
[Courtesy of SunLabs - Department of Energy]
 

Parabolic trough system 

Parabolic troughs are devices that are shaped like the letter “u”. The troughs concentrate sunlight onto a receiver tube that is positioned along the focal line of the trough. Sometimes a transparent glass tube envelops the receiver tube to reduce heat loss. Parabolic troughs often use single-axis or dual-axis tracking. In rare instances, they may be stationary. Temperatures at the receiver can reach 400 °C and produce steam for generating electricity. In California, multi-megawatt power plants were built using parabolic troughs combined with gas turbines.

image004.gif

Parabolic trough system
[Courtesy of SunLabs - Department of Energy]

Power tower system 

A heliostat uses a field of dual axis sun trackers that direct solar energy to a large absorber located on a tower. To date the only application for the heliostat collector is power generation in a system called the power tower. A power tower has a field of large mirrors that follow the sun's path across the sky. The mirrors concentrate sunlight onto a receiver on top of a high tower. A computer keeps the mirrors aligned so the reflected rays of the sun are always aimed at the receiver, where temperatures well above 1000°C can be reached.  High-pressure steam is generated to produce electricity. 

image005.gif

Power tower system
[Courtesy of SunLabs - Department of Energy]
 

Stationary concentrating solar collectors 

Stationary concentrating collectors use compound parabolic reflectors and flat reflectors for directing solar energy to an accompanying absorber or aperture through a wide acceptance angle. The wide acceptance angle for these reflectors eliminates the need for a sun tracker. This class of collector includes parabolic trough flat plate collectors, flat plate collectors with parabolic boosting reflectors, and solar cookers. Development of the first two collectors has been done in Sweden.  Solar cookers are used throughout the world, especially in the developing countries. 

image006.jpg

Vacuum tube solar collectors 

Vacuum (also “evacuated”) tube solar collectors are amongst the most efficient and most costly types of solar collectors. These collectors are best suited for moderate temperature applications where the demand temperature is 50-95C and/or for very cold climates such as in Canada’s far north. Like with glazed flat-plate solar collectors, applications of vacuum tube collectors include heating of domestic and commercial hot water, buildings, and indoor swimming pools. Due to their ability to deliver high temperatures efficiently another potential application is for the cooling of buildings by regenerating refrigeration cycles. Vacuum (also “evacuated”) tube solar collectorsVacuum tube solar collectors have a selective absorber for collecting sunlight that is in vacuum-sealed tube. Their thermal losses are very low even in cold climates. 

Information from CanREN (www.canren.gc.ca) 

Comments (4)add
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what r u doing
written by me , January 27, 2014
u r lame
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types of collecters
written by Svm.Suresh , September 10, 2013
very usefull......smilies/cool.gif
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gooood
written by bull , March 11, 2013
smilies/grin.gifsmilies/grin.gifsmilies/grin.gifsmilies/grin.gif
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solar thermal collectors and their industrial applications
written by norman , February 27, 2012
the information was very helpful
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Last Updated on Saturday, 02 May 2009 19:55