See the schematic and photos of my prototype all-polypropylene solar hot water system.
This was first made public when I posted it on http://www.Sol-Y-Agua.com on April 10, 2009 (confirmation of registration with GoDaddy.com available.)
First, I am using an all-polypropylene solar panel that has historically only been used for heating swimming pools. To the best of my knowledge no one else has ever used an all-polypropylene solar panel to make hot water.
Second, I am using an all-polypropylene, internally insulated (through a special roto-molding process) 150 gallon water tank to hold the water as it is continually heated by the water circulating through the plastic solar panel.
The circulation is accomplished through the natural process of thermal hydronic siphoning: hot water rises, colder water sinks. This process is known in the solar hot water industry. To accomplish this, the hot water tank must be higher than the top of the solar panel, which is set at an angle approximately the same as the latitude to which is being placed. (If you are in a 13 degree latitude in Puerto Rico, the angle of the solar panel should be set at 13 degrees.)
The outlet of the solar panel should be at the top of the panel and should go into the upper third of the plastic tank. Adjacent to or near this tank inlet should be the outlet for the domestic hot water supply to the house.
In line and after the exit from the tank, the hot water passes through a mixing valve to reduce the possibility of scalding by ensuring that the resultant domestic hot water to be used is never above 101 degrees F.
This water can then be passed through an auxiliary in-line hot water heater or an existing hot water heater in the rare event that the water exiting the tank is below 95 degrees F due to an onset of cloudy days.
It is important to note that since the water tank has such a large capacity (150 gallons) this water is continually being heated and re-heated through the thermal siphoning process, the hot water actually acting as a battery reserve for excess hot water being continually produced.
The colder circulating water exiting the tank should exit near the bottom of the tank and enter at the bottom of the solar panel. At the bottom of the solar panel is also the supply of the replenishing water source, either from the city water supply or a cistern.
Also in the system are a series of drain valves, check valves, on/off by-pass isolating valves, air release valves, temperature/pressure release valves and vacuum breakers which all add to the safety and efficiency of the design.
