When there is enough sunlight, the water will usually be warm within two to three hours.
Does solar water heater heating require sunlight? If it is ordinary solar energy, it certainly needs sunlight, but some solar energy can be used for heating. Electric water heaters don't need sunlight in theory. However, current solar energy is electrically assisted heating only. If there is no sun. It is heated by electricity. Same as electric water heater. This does not necessarily cost much in electricity, but the temperature is high.
Should a solar water heater be installed on the roof of the building? It depends on the ground level. Generally, small high-rise buildings can be installed on the roof, but they can also be installed on the balcony wall. The solar water heatere vacuum tube machine (all-in-one vacuum tube machine) does not need to be installed on the roof.