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Green Collar Careers - Solar Collectors

A solar collector is a device that collects the energy from the sun and transfers that energy to a different media in the form of heat.  Most of the heat comes from the longer wavelength light in the Infra-Red (IR) range.  Infra Red is the reason you feel the warmth of the sun through a window. 

A system can either be passive, meaning it doesn't move, or active such as a solar concentrator that tracks the sun.  Not all experts may agree on the definitions of active and passive systems as there are so many different designs that may use various mechanisms to move fluid exchange mediums or move the collector to track the sun. 

Typical Non-Tracking Systems

Flat-plate collector
Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors—typically used for solar pool heating—have a dark absorber plate, made of metal or polymer, without a cover or enclosure.  While these are the least expensive systems, they are also the the least effective at capturing heat.  Typically the peak water temperature will only rise about 30-50° warmer then the ambient air with a ceiling of about 140° F.

Integral collector-storage systems
Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. If water is the fluid exchange medium they should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.  Typically the peak water temperature will only rise about 60-70° warmer then the ambient air with a ceiling of about 150° F.

Simple evacuated-tube solar collectors
They feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin's coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.  While being the most expensive, the lack of thermal convection losses also make them the most efficient.  Typically the peak water temperature will 180° F. and ambient air temperature has very little effect if the manifolds are properly insulated.

Water is not the only fluid exchange medium used, its just the one most people think of.  Some evacuated tube systems may use air, helium, or some other gas and due to the lower mass, the temperatures can easily reach 400° F.  Non-evacuated systems lose too much heat to convection to take advantage of this characteristic.

Sealed condensate evacuated-tube solar collectors
Similar to the evacuated-tube solar collectors the difference is they work on the principal of boiling the primary fluid medium in the absorber tube causing it to rise to the top, and then exchanging the heat in the boiled liquid with a second medium.  After the primary medium exchanges the heat it liquefies and falls back to the bottom of the absorber tube to repeat the process.  The primary medium is sealed in the absorber tube and since the heat exchange takes place only at the highest point it needs only one manifold.  

Solar Concentrator Tracking Systems

Solar concentrators focus a large area of sunlight on a small target concentrating a large area of energy on a small collector.  Solar concentrators offer some advantages in temperatures and performance although the cost is higher due to the required tracking system.  Two types of solar concentrators are available today:
 

Parabolic dish Every satellite dish uses a parabolic shape to reflect concentrated radio waves on a receiver and given a highly reflective surface, they could also reflect sunlight.  There are several designs of systems ranging from perfectly curved mirrors to an arrangement of tiny flat mirrors mounted to a curved surface of an engineered parabolic shape.  These mirrors can concentrate an incredible amount of heat on a small area.  Recalling that a square foot of sunlight in Kansas City will provide about 205 BTU's/hour, a parabolic mirror of 8 feet in diameter will produce over 10,000 BTU's in an hour.  Focus that energy on a sphere large enough to hold 1 gallon of water and it will boil a gallon of tap water in 5 minutes.

Parabolic trough
Where a parabolic mirror is shaped to focus energy onto a sphere, a parabolic trough works much better with tubes and are much easier to manufacture.  Coupled with an evacuated tube collector and Stirling engine the parabolic has a very bright future in solar energy. 

Use the Search Tool below to research existing systems that may fit your local market needs best.