Energy  from sunlight in the form of heat is  transferred to a water/antifreeze solution is circulated through insulated pipes from the collector to the heat storage tank or vault.  Note the red bubbles leaving the collector. These represent  a hot water/antifreeze.  As this mixture is circulated around the solar storage tank it gives up it's heat to the supply of domestic hot water. On the  return trip to the collector the water/antifreeze mix has been cooled by releasing it's heat to the domestic hot water supply.  It is at this point that you see the red bubbles turn blue. As soon as the temperature of the collector is less than the storage tank water sensors relay this message to shut off the pump.

The storage tank water is used to preheat water used for domestic hot water. If the temperature of storage tank water is heated sufficiently additional conventional heating would not be required. The temperature difference between  the solar storage tank water and the desired water temperature would determine the amount of conventional energy required to heat your domestic hot water. 

To calculate  the yearly energy savings from a solar hot water system you must know the temperature difference between incoming water and outgoing water and the quantity of water under consideration. A unit of heat known as a British Thermal Unit or BTU is the energy required to raise one pound of water one degree F.

 Lets say that over the period of one year your household raises 500,000 lbs. of water 100 degrees F. This would be the equivalent of (500,000  lbs of water )X (100 degrees F). or 50,000,000 BTU.  So what is the value of  50 million BTU's. The quantity of heat in a gallon of fuel oil should shed some light on this problem. Any ideas?

Well let's see. A 100 % efficient oil burner is capable of extracting 150,000 BTU's of heat energy per gallon of number 2 fuel oil. If we assign a value of $1.50 to a gallon of oil than  1,000 BTU's of heat are worth about a penny, and 50 million BTU's are worth about $500.


What does all this mean?
Is  a solar hot water system practical?
Would it be more practical when combined with a home heating system?
How much energy is available from the sun anyhow?

The answer to these questions will of course depend on location,  cost and life expectancy of the system. 

Domestic Solar Hot Water and  Solar Heating Systems

Swimming Pool Heating System Kits

Hexagonal Housing Active Solar   Books
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