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Solar Thermal 101: Flat Plate Solar Collectors

This is the second in a series of posts written by Free Hot Water’s co-founder and senior mechanical engineer, Gal Moyal. We’ll be posting this series every Wednesday, so please make it a date. Some of the information in future posts may be very technical, but if you have any questions at all, please feel free to contact us. We sincerely want to help. If you would like to have a more hands-on experience, explore our certified Free Hot Water training courses.  –Solar Fred.


The principal component of a flat plate solar collector is the absorber plate, which consists of an assembly of a copper sheet and copper tubing.

The top surface of the absorber plate is coated with either a dark colored material or with a selective absorbent coating that is designed to extract as much as 15% more heat for the same active area.  The solar radiation that strikes this surface is converted to thermal energy that’s used to heat the fluid flowing through the tubes.

To ensure extended service life, Free Hot Water collector parts are housed inside an anodized Aluminum case that’s capable of withstanding many years of exposure to the elements. The components inside and the back of this enclosure are insulated in order to minimize potential heat loss.

Anatomy of a Solar Flat Plate Collector (click for larger photo)

The upper surface of the collector is covered with tempered glass with low iron oxide content. The glass is designed to withstand high thermal stress (heat from the sun!) as well as impact from hailstones.

Free Hot Water’s Flat Plate Solar Collectors are  high performance thermal collectors certified by the Solar Rating and Certification Corporation (SRCC) as OG-100, appropriate for large installations such as apartment buildings, hospitals,restaurants, retirement homes, and other businesses.

That’s it for this Wednesday. Return next Wednesday, when Gal will continue Solar Thermal 101 with a description of Evacuated Tube Solar Collectors.  If you have any questions and want to skip ahead, please contact us.

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