How to drain photovoltaic panels

When the pump is not running in a drain-back solar system, all of the liquid is inside the building and the solar panels are empty of fluid. A small tank (the drain-back vessel) holds the liquid so that the resting fill level is above the pump. If there is heat to be collected from the solar panel, the pump is energised by the solar. . In a pressurised solar system, the solar circuit is completely filled with liquid at all times, including overnight in freezing weather and during. . A re-start of the solar pump following stagnation will result in steam being pushed out of the solar panel and down the pipes to the cylinder.