Solar DHW Collector Thermal Performance Ratings
Florida Solar Energy Center
FSEC-GP-14-81
Last update: December 2007

Thermal performance ratings, derived from the FSEC testing and certification program, are a useful tool in comparing the efficiency and economics of various flat-plate solar collectors. Since collectors used in domestic hot water (DHW) systems typically operate in the intermediate temperature range (120°F-160°F), this is the rating provided for comparisons. It must be stressed that these comparisons are only a guide and should not be considered as a rank ordering of collectors. Such considerations as component sizing and proper installation procedures are equally important in determining a system's overall efficiency. In addition, because of the variability of weather conditions, instrumentation accuracies, and other test condition constraints, the thermal performance of any two collectors should be considered approximately the same if their ratings are within 25 Btu/(ft²day) of each other. Bear in mind that comparisons based on these ratings address thermal efficiency and energy output per investment dollar only; they do not imply equivalent reliability or durability among collectors.

Approximate Comparison Model

1) To compare the thermal efficiency of different collectors, look at the Btu/(ft²day) rating (last column); the higher the number, the better the solar energy collection efficiency (which means it will require fewer square feet of collector area to do the job).

2) To determine the collector that supplies the most energy per investment dollar, divide the Btu/day rating (next to last column) by the total installed cost of the system, then multiply the result by the number of collectors used. Example: Collector X has a Btu/day rating of 25,000. Your dealer has given you a price of $2,000 for an installed system consisting of two collectors. Calculate as follows: 25,000 ÷ 2,000 = 12.5, 12.5 x 2 = 25 Btu/day per dollar invested.

This listing of collectors is provided in alphabetical order, by manufacturer name.

A    B-R    S    T-Z