Calibrated simulation of a solar hot water system to match degraded performance over a 22-year period using two models

This paper reports on the measured performance of a residential solar water heating system over a period of 22 years and the modeling of the system to simulate its degradation over that period. The system consists of three fixed flat-plate collectors with a total of 5 m2 of double-layer glass cover plates and black aluminum fin-tube absorber plates. The solar storage tank capacity is 303 L, which is used as a pre-heater to a 114-L conventional electric water heater. Measurements and simulations indicate that fogging of the glass cover plates has reduced the transmissivity by around 63% over the 22 years.