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Education on Solar Hot Water Heating

Its fuel, sunlight, is limitless,
free and emits nothing when converted into energy.  

A solar water heater does one thing:
It uses sunlight to warm water.

12% of your Electric Bill

is Heating Water


Heating water for personal use,
dish washing & laundry takes an
average of 12% of your
household electric bill in the U.S., 

 more than Lighting at 11%.


  A solar water heater is typically used in conjunction with a traditional heater for backup, since weather affects solar hot-water production. 

The traditional heater supplements the solar heater & is used as a backup. 

Adding a solar water heater to a water-heating system can reduce energy bills and corresponding CO2 emissions by 50 % - 80%.


Solar Hot Water in the World


  • save electric cost to heat water 50% - 80%

  • China produces 70% of the world’s solar hot water heaters (180 GWth)

  • Israel also has a high per-capita production of hot water from solar

  • in the US, solar hot water is used mainly to heat pools

  • Return on Investment is 7.7%

  • payback in Huntsville is 13 yrs

  • Life of system is 40 yrs.


 2 Flat Plate Collectors on Roof

Solar Hot Water

is about as

green as
hot water

can get.

Total Installed Cost of a 2 Flat Plate Collector Hot Water system in 2016 is


 about  $5600.

{after 30% Federal Tax Credit}

How does it work?


  1. The sun's thermal energy heats the fluid in the solar collectors on the roof.

  2. Then, this fluid passes through a heat exchanger in the storage tank, transferring the heat to the house water.

  3. The Exchange Fluid then cycles back to the collectors. 

A small pump circulates household water through the collectors and into the storage tank.

A collector holds just a gallon of Exchange Fluid, so the pump & the electricity used by the pump is very small.

Direct Heating vs.
Indirect Heating


There is Direct Heating system where the actual water to be used by house is heated in the Collector and

In an Indirect Heating system, the Heat Exchange Fluid used in the Collectors is ‘treated’ when the system is installed and kept separate from the ‘house’ water. 

The treatment includes addition of a liquid to prevent this fluid from freezing while on the roof in very cold outside temperatures.

Types of Collectors


  1. Flat Plate Collector  
    (best for N. AL)  

  2. Evacuated Tube Collector  
    (used when higher H2O temp is required or in colder climates or less sunlight)

Flat-plate Collectors

( best for N. AL )


Flat-plate Collectors typically consist of copper tubes fitted to flat absorber plates. The most common configuration is a series of parallel tubes connected at each end by two pipes, the inlet and outlet manifolds. The flat plate assembly is contained within an insulated box, and covered with tempered glass. 

Flat plate collectors are typically sized to circulate 40 gallons of water.

2 flat plate collectors provide 80% of hot water needs for family of 4.

  • In warm climates with lots of sun, flat plate is better for the money. 

  • 30% cheaper than Evacuated Tube Collector

  • less efficient than Evacuated Tube, especially winter months & cloudy days

Evacuated Tube Collectors


Each evacuated tube is similar to a thermos in principle. A glass or metal tube containing the water or heat transfer fluid is surrounded by a larger glass tube. The space between them is a vacuum, so very little heat is lost from the fluid.
These collectors can even work well in overcast conditions and operate in temperatures as low as -40°F.

Individual tubes are replaced as needed.

  • most efficient collectors available

  • 30% more expensive than Flat-Plate

  • a must for freezing climates

  • works well in cloudy days & winter

  • easier to repair & install


The evacuated tube 

works like a thermos.


The vacuum between the outside, larger glass tube

and the inner tube (containing the Exchange Fluid) buffers the temperatures from the outside air, as low as -40°F.

Evacuated Tube

Solar Hot Water Heating in China & other Countries
Much More Popular than U.S.

 "In China, the system used is a thermosiphon, a passive system without a pump," said Tim Merrigan, a researcher at the National Renewable Energy Laboratory (NREL).

"The thermosiphon system requires that you have a storage tank on the roof.

The drawback in the U.S. is that typically people have water tanks in their basements or garages. 

The most common technology in the U.S. is an indirect system which has a pump."



90% of Israeli homes already have solar
water heaters


  • In 1980, the Israeli Parliament passed a law making solar heating mandatory for new residential buildings.

  • If you use up all the hot water in the tank or there was not enough sunlight to warm the water, you can turn on the heating element.


From a distance, solar collectors on a roof look similar to PV / Solar panels.  Collectors heat water and solar panels create electricity.

for more detail, see this .pdf

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