... , 1000W-1500W Our special heating tube can keep the solar water heater on working order ,When the cloudy sky or clouded or ... , this heating tube can put into the tank of solar water heater , When the cloudy sky or clouded or sunshine shortage , ... automatic , when the water is heating up to 90 centigrade , it will turnoff automatic . Life time : 5000 hours assistant heating tube for solar water heater ...