In large applications of solar hot water, there are 3 types of collectors; concentrating collectors, flat panels and evacuated tubes.
This article will discuss the pros and cons of each type of collector when used in large solar hot water and solar heating applications
Concentrating collectors in Solar Heating ApplicationsConcentrating solar collectors use reflectors either as a trough to focus on a line absorber or a dish to focus on a point absorber. They can reach far higher temperature levels than non-concentrating collectors. Concentrating collectors will collect only direct radiation (the solar energy coming directly from the sun) and consequently perform better in areas with predominantly clear sky (not cloudy) conditions.
An innovative parabolic concentrator is called the SolarBeam Concentrator. This parabolic dish is 15 feet wide and is a solar hot water concentrator that can track the sun on 2 axis (horizontal and vertical). This system has been tested to SRCC standards for rebates.
To see how the SolarBeam tracks the sun, check out the solar heating videos.
When it comes to concentrating collectors common systems include the parabolic trough, linear Fresnel, parabolic dish and central receivers (solar tower). These collectors are typically used where temperatures above 100°C are needed, i.e. process heat or electricity generation.
Concentrating collectors are typically specified by their concentration ratio. The concentration ratio is the ratio of the area of the reflector to the absorber area. High concentration ratios are used for higher temperature collectors, but require more accurate tracking of the sun’s path.
In regards to the SolarBeam, the system provides solar hot water up to 205 F since it’s applications Include residential and commercial applications,
Flat plate Collectors in Solar Heating Applications
Flat plate collectors can be constructed from a variety of materials and different construction methods are possible. As a result, they may have different performance and costs and be designed for different applications. For example, two layers of glazing are sometimes used to improve thermal performance.
Some of the other variations are discussed below.
Unglazed collectors have no glazing or insulation, and usually consist of extruded polymer tubes. Their use in large solar hot water installations is rare, although they have been used in the horticultural sector for greenhouse heating and swimming pool heating where lower water temperatures are required. These collectors have the largest
share of the flat plate solar collector market, particularly in Australia.
Evacuated tube collector in Solar Heating ApplicationsThere are two common types of evacuated tube collectors: heat pipe and U-tube. Both collector types are formed from an array of evacuated tubes joined to a manifold through which the heat transfer liquid (water or water/glycol) flows.
The solar absorber is located inside a double glass tube with a vacuum between the two tubes, similar to an elongated thermos flask. The tubes are connected to a manifold through which the heat transfer fluid is passed. The inner glass tube has a selective surface facing outward to absorb the sun’s energy. The heat is transferred into the inner glass tube and removed by a heat pipe or a copper tube through which the heat transfer fluid flows. The loss of heat from the absorber by natural convection is eliminated by the vacuum and, as a result, high operating fluid temperatures of up to 120ºC can be achieved. The possibility of higher temperatures is of particular importance for solar industrial process heating application because it increases the number of applications where solar energy can be used.
Collector performance comparison
Various types of solar collectors have been briefly described above. How do they compare with each other and what might be their areas of application? The standard method to evaluate the performance of solar collectors is to compare:
instantaneous efficiency curve
annual heat output.
When determining the annual heat output of a solar collector, the efficiency equation used must be consistent with the collector area used by the test laboratory to compute efficiency from the collector test results. It is distinguished between three collector areas:
gross collector area
The area basis for defining solar collector efficiency can be on the basis of gross, aperture or absorber area. If alternative solar collectors are compared on the basis of efficiency, care must be taken to use the efficiency with the collector area that was used by the test laboratory to compute the efficiency.
The SolarBeam Concentrator was testing by a board certified lab. Its efficiency is at 72% at 1000w/m2 solar radiation. At this radiation level, It will provide 11kWh of solar thermal energy. The collector area is 171 sq.feet and the absorber area is 10″ x 10″.
The SolarBeam is sold through distributors around the world.