We are using Solar Water heater from last 11 years and find no degradation in the heating. Following care has been taken.
1. Clean the top transparent glass(?) with flowing water and rubber wiper.
2. See that hot water pipe has not exposed outside of heat coating. It may be very near to storage tank or inside bathroom. If it gets corroded (mostly near up-stare tank) then it will leak hot water and cold water will fill in.
3. See Copper tube inside heat collector. There must not be any hard deposition (white buildup of calcium etc) on inside surface of tube. If it is there then there is need of some acidic solution which is dissolves hard build up when added into that water and kept for prescribed time. This was some blue solution added to our tank and kept overnight. This is routine after 3-4 years interval. And increase efficiency of heat transfer. Take manufacturer's service for this. They know best.
