Calibrated simulation of the degradation of a solar hotwater system performance over a 22-year period of operation

This paper reports on the measured performance of a residential solar water heater 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 liters, which is used as a preheater to a 114-liter conventional electric water heater. Measurements and simulations indicate that the degradation is mainly due to fogging of the glass cover plates, reducing the transmissivity by around 63 percent over the 22 years.