Solar Thermal Panel Section Detail, 15mm dia. galv. sheet metal, upvc or copper pipe to be conected to bottom of solar panel & to bottom of water tank. this pipe provides the cold water to the solar panel and as it gets hot, the water rises up in the serpentine pipe. 15mm dia. upvc, galv metal or copper pipe connected to top 1/4 of water tank and to top of solar panel. this pipe comes from the serpentine collector and should, on a sunny day contain warm water which is supplied to the top of the tank.