Transpired Solar Collector

Technology Marketing SummaryUnglazed solar collectors have been used in the past for preheating ventilation air for a building. These solar collectors typically include a dark absorber panel, positioned to face the sun, and a plenum or air collection space into which the heated air is drawn through perforations or holes in the absorber panel. The movement of air is often aided by fans or some source of suction to draw the air into the plenum and distribute it throughout the building. It was believed that absorbers had to be constructed of high thermal-conductivity materials such as copper or aluminum to avoid overheating in regions away from the holes, which would reduce overall efficiency due to radiative loss of heat.DescriptionNREL researchers have discovered that high thermal-conductivity materials are not necessary for the construction of absorber panels, and that the presumed loss of efficiency is dramatically overestimated. Simulation and experimental data both show that styrene plastic (with a conductance more than 1000 times lower than that of aluminum) performs with an efficiency within 10% of that of an equivalent aluminum absorber. It is expected that absorbers having a thermal conductance even less than 1 x 10-2 W/°C would be efficient in unglazed transpired solar collectors. In fact, simulation has shown that even an absorber with a conductance 14 million times smaller than that of aluminum yields results only 32% less efficient.

The present invention, therefore, describes an unglazed transpired solar collector with an absorber formed of rigid or pliable or flexible sheet, foil, film membrane or fabric, having a relatively low thermal-conductance. Low thermal-conductance may result from inherent properties of the material or through the use of high conductivity metal foils which have low overall conductance because of their thinness. The front surface of the absorber is substantially flat (not corrugated) but the absorber itself may be curved or shaped to suit a particular application.

Because of the use of low thermal-conductance materials, a wider range of perforating methods may also be employed, including laser perforating or hot punching, which may not be suitable to typical absorber materials. The use of flexible absorber materials allows for more deployable solar collectors for temporary or intermittent applications.Benefits

• Reduced cost through use of less expensive absorber materials
• Material flexibility allows for deployable, temporary use
• More options for methods of perforation/hole creation

Applications and Industries

• Heated air for building
• Heated air for temporary structures
• Crop drying

Patents and Patent Applications

ID Number	Title and Abstract	Primary Lab	Date
Patent 5,692,491	Unglazed transpired solar collector having a low thermal-conductance absorber An unglazed transpired solar collector using solar radiation to heat incoming air for distribution, comprising an unglazed absorber formed of low thermal-conductance material having a front surface for receiving the solar radiation and openings in the unglazed absorber for passage of the incoming air such that the incoming air is heated as it passes towards the front surface of the absorber and the heated air passes through the openings in the absorber for distribution.	National Renewable Energy Laboratory	12/02/1997 Issued

Technology Status

Development Stage	Availability	Published	Last Updated
Development	Available	01/14/2010	02/02/2010