Solar Water Heating

 Solar water heaters -- also called solar domestic hot water (DHW) systems -- can be a cost-effective way to generate hot water for your home. They can be used in any climate, and the fuel they use -- sunshine -- is free.


How They Work - click on video on right:

Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don't. 


There are two types of active solar water heating systems:

  • Indirect circulation systems (Closed-loop active systems)

Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.


a)  Not susceptible to freeze damage in our geographical area

b)  Very little heat loss or thermosiphoning 

c)  No calcification inside collectors due to glycol/distilled water mixture

d)  OG-300 rated and therefore eligible for CSI-Thermal rebate as well as Federal Tax Credit!

  • Direct circulation systems
    Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.


​a) Prone to freeze damage (yes, even in SoCal) - systems can sustain freeze damage at an ambient temperature of 42F.  We diagnose dozens of systems each year.

b) High rate of heat loss during the night - due to thermosiphoning, which allows the hot water to circulate back to the roof.

c) Calcification inside collectors.

d) At this time eligible for incentives or tax credit for commercial systems only.



Passive solar water heating systems are typically less expensive than active systems, but they're usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:

  • Integral collector-storage passive systems (ICS)
    These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.

  • Thermosyphon systems -
    Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.


Source: PG&E

Active, Indirect Circulation System​

Thermosyphon System

Solahart & Sunsiphon

Discontinued in U.S.

Integral Collector-Storage Systems

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