Equation 6 – Simple payback period

Another system sizing analysis would be:

For a location receiving 2,220 – 2,854 Btu/sq ft (7–9 kWh/m2) on a high-radiation day a system that will provide heat for a domestic hot water system located will have a degree of utilization of ~50%. The result is 1,110 to 1,427 Btu/sq ft (3.5 to 4.5 kWh/m2) of collector area provided as useful heat for generating the hot water. The value of 4.0 kWh/m2 is equal to 13,650 Btu/m2 or 1,270 Btu/sq ft of collector. This amount of heat can raise 19.2 gal water/m2 from 55 to 140 °F. A sq ft of collector area can heat 1.8 gal. A solar storage system for this application should be in the range of 60 to 70% of the normal daily use. If the daily use is 1.8 gal/sq ft, then the storage tank size would be ~1.2 gal per sq ft