One of the most common solar water
heating systems is the pre-heat solar tank system. This system uses two
tanks. The first tank is known as a solar pre-heat tank which works like
a supplemental source of warm water for an existing hot water tank.This solar water heater needs very less
plumbing retrofit and the existing main supply line is connected to the
pre-heat tank. This solar water heating system works on the efficient
stratification principle. This principle states that the top layers of
water in the solar hot water tank are always the hottest, readily
available to meet the daily hot water requirements of households. https://www.solartubs.com/