Gravity System

There are two tricks to the high efficiency of this solar heater.  First, a vacuum prevents any conductive or convective heat loss to the environment from the absorber.  Second, heat pipes ensure one-way heat transfer from the absorber to the water: the water can not heat the absorber. The selective coating in the inner cover of the evacuated tubes ensures high energy absorption and low heat radiance losses. The liquid in the inner glass heat pipes changes into vapor which then rises up the heat pipe. When heat is exchanged between the condenser end of the heat pipe and the cold water in the tank, it turns into liquid again, then comes down to the base of the heat pipe. This cycle continuously repeats as long as the sun shines. Hot water can be obtained by injecting cold water into the bottom of the tank, with the hot water being forced out the top.

The evacuated tubular collector with heat pipes are quasi-tracking in four seasons, which is to say that as the sun tracks across the sky, about the same absorber area is facing the sun all the time, since the absorber surfaces are cylindrical. The collector will be in operation as long as sun shines. The solar water heater can be in service all year round even in cold climate areas since heat pipes transfer heat in one direction only within the collector and the vacuum prevents convective heat losses.