Building Solar Heating Panels - Flat Black Paint Vs Thurmalox 'Selective Surface' (?) Coating

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I needed a small array of solar thermal panels for some process heating projects around home, and thought it would be a good opportunity to compare the performance of standard flat black stove paint vs a selective surface coating. A selective coating has high absorbence and low emittance properties to help maximize the amount of solar energy the collector captures. Flat black paint has high absorbence, but also high emittance properties, so it 'reflects' more solar energy away from the collector than a selective surface coating would. Exactly how much depends on the manufacturer. Most selective surface coatings aren't available to the general public to use, however, I came across ThurmaIox 250 sold as a selective surface coating in a spray can, and thought I'd give it a try and compare it with standard Tremclad stove paint to see if there's much difference in performance and if the extra cost is worth it. Thurmalox is claimed to have an absorptivity value of 0.95 and emissivity value of 0.65. For context, black chrome - typically used on commercial evacuated tube solar collectors - has an absorptivity of 0.9 and emissivity of 0.09, and black paint has an absorptivity of 0.9 and emissivity of 0.9. So Thurmalox isn't necessarily a selective surface coating since the emissivity value is still relatively high compared to common commercial selective surfaces, but will it work better than standard paint? More details about the heaters and the results of the performance comparison can be found at the link below.

See the results: https://www.resystech.com/collector-coating-comparison.html

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