Solar Domestic Hot Water Drain-back System

The starting point for using solar thermal energy is to heat domestic hot water, as it is used year-round.
Solar panels are usually mounted on the roof while a small storage tank is installed in the basement. Other options exist if necessary or desirable. Usually 2 to 4 panels and 80 to 160 gallons of stored hot water compose a system. The solar system preheats the cold water before it gets to the existing gas or electric water heater. Our systems typically reduce the hot water bill by 80% or more.
In our drain-back system, system water is pumped through the panels and the heat exchanger only when the panels are hotter than the solar tank. A Heat exchanger  allows optimal contact for heat exchange between the system water, which goes through the panels, and the fresh water, which you use in your house. A differential controller makes this flow fully automatic.
With the simple effect of gravity, the system water safely returns to the drain-back tank inside the house before the panels get cold. This system does not need to be pressurized. The only requirement for this system is that all pipes and panels must be sloped and above the tank, so that gravity empties the panels when the pump turns off.
The absence of pressure makes for a system which is virtually maintenance free, in stark contrast to the pressurized glycol and oil systems of the early 80s. If properly maintained, the typical life span of our system is over 50 years. The water tank might require changing after 15 to 25 years, just like any water storage tank. Typically our drain-back systems require service every 5 to 10 years.