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The Basics of Solar Hot Water Heaters

Updated on July 9, 2013

Next to HVAC systems, hot water heaters are the second largest users of energy in a typical American home. Traditional water heating methods use considerable amounts of natural resources and generate pollution because of the amount of energy that they require. Fortunately, the sun has a plethora of free energy that can be easily utilized by consumers. By switching to a solar hot water heater, you'll have highly sustainable water heating system that could save you more than 20% off of your utility bill while also reducing negative impacts to the environment.

Solar hot water heaters use the sun's heat energy to warm water for your home. There are a variety of low maintenance methods and systems available today that can efficiently and reliably accomplish this task. Each method of solar water heating has it's advantages and disadvantages. In general, all solar hot water heaters can be categorizes as being active or passive systems.

Passive Systems

A passive solar hot water heating system is one that does not use a pump to circulate fluids. If installed in the proper climate, they rarely require human intervention to operate either. A passive solar hot water heating system may be the solution you are looking for if you want a low maintenance system to supplement your regular hot water heater.

Batch Systems - Batch solar hot water heaters (also known as Integral Collector-Storage Systems or ICS) are simple, inexpensive, and require no pump to transfer fluid. Batch systems basically allow your water to be heated by being storing it in a black tank that is enclosed in a high temperature "greenhouse" type of box. The box that has a transparent double or triple glazed glass window on it. As the sun warms the box, the pressure and temperature inside the tank rises. This eventually causes water to circulate into and out of this tank. Water that leaves the tank can flow into the plumbing fixtures or to a secondary storage tank located inside the home. The disadvantages to this type of system are that they are inefficient, bulky, and require protection from freezing temperatures.

Thermosyphoning Systems - This method of heating water is very similar to the batch style solar hot water heaters. The main difference is in the design of the heat collection box. In a thermosyphoning system, the collector box contains a serpentine or parallel pattern of water pipes instead of a tank. As the water is heated, it expands and is naturally circulated back into the storage tank located inside the home. The main disadvantage to these systems is the you have to have a water tank installed at a higher elevation than the collector box for it to function properly. This typically means having a water tank located in your home's attic or on the roof. In addition to this, the system should not be installed in cold climates.

Example of a roof mounted evacuated tube solar hot water heater system.
Example of a roof mounted evacuated tube solar hot water heater system. | Source

Evacuated Tube Thermosyphoning Systems - This method is same as the thermosyphoning system, except it uses a collector box filled with evacuated tubes (airless tubes). The advantage to this is that the suns radiation can penetrate them and heat the water, yet the heat cannot readily escape back into the atmosphere. This improves the thermal efficiency of the system while also preventing the water from being frozen if installed in a cold climate. Naturally, an evacuated tube system is more expensive than a standard system.

Active Systems

In an active solar hot water heater, a pump is used to move fluid throughout the system. These systems are the most common form of solar water heaters available today. This is because they are generally more efficient then their passive counterparts and afford the owner with some control over their use. There are two main types of active solar water heaters:

Direct (Open Loop) Systems - In a direct heating system (also called an open loop system) water is heated directly by the sun. Water used for drinking and bathing is circulated through the pipes and a collector box using a pump. The pump can be power by a standard electrical connection to the home or an additional solar collector comprised of photo-voltaic cells. The pipe network can also be arranged into a draindown or a drainback configuration. In a draindown system, sensors and special valves allow the water to drain from the collectors if freezing temperatures are approaching. In a drainback system, the pump automatically shuts down to allow water to drain back into the storage tank in the event freezing temperatures are imminent. Obviously the drainback system is much more reliable.

Diagram of a closed loop solar hot water heater
Diagram of a closed loop solar hot water heater | Source

Indirect (Closed Loop) Systems - In an indirect system (also called a closed loop system), a water/glycol solution (anti-freeze) is circulated through pipes instead of water. This fluid is warmed by the sun and is used to heat the home's water by passing it through a heat exchanger. Due to the properties of the water/glycol mixture, this system would be the best choice for colder climates. A disadvantage of indirect systems is that they are expensive and sometimes require more than one pump to operate efficiently.

Thinking About Getting a Solar Hot Water Heater?

Thinking about getting a solar hot water heater? Here are a couple of additional things that you should be aware of:

  • Most solar water heating systems still require that you have a backup water heater in your home. This is necessary to account for the fact that the sun may not be available at all times to heat your water.
  • Each square foot of collector area can typically heat about 1.5 gallons of water. Consider reducing your hot water usage so that you can get a smaller solar heating system. This will reduce your upfront costs and also conserve water.
  • Take action to reduce the amount of heat lost in your water pipes and storage tanks. Consider insulating these so that your solar water heating system will be more efficient.
  • Solar water heaters are expensive to purchase and install ($3,000 to $6,000 for a typical residential installation). They can usually pay for themselves in about 5-15 years depending on various factors. Check with your local and state government agencies to see if a tax credit or rebate is available for solar hot water heaters.
  • Need another reason to get a solar water heater? Installing a solar hot water heater can prevent up to 5,000lbs of carbon dioxide (CO2), 20lbs of sulfur dioxide (SO2), and 12 lbs of nitrogen oxide (NO) from being released into the atmosphere annually.


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    • poppi profile image

      poppi 6 years ago


      I just put Solar on my house two years ago. Then last year I went Solar for the pool. Now I'm thinking which way to go with the hot Water System "Open/Closed or can I connect to the house system and "forgetaboutit" now that I'm living in Arizona.

    • CWanamaker profile image

      CWanamaker 6 years ago from Arizona

      Stephaniedas - Yeah it's crazy to think about the economics of solar energy. With all the tax deductions and credits available, the initial investment could be very small. This would just be another reason why solar energy is the way to go.

    • stephaniedas profile image

      Stephanie Das 6 years ago from Miami, US

      Great hub. This is really important. I figured out that if my parents had made the initial investment in solar power for their house, which they had built 25 years ago, and if they had paid for the solar power system every month with the same amount of money that they actually spent on the electric bill every month, they could have paid it off in 16 years. That would be 9 years of NO electric bills.

      Plus- Better for the environment, and that's less money going into Exxon's pocket!

    • CWanamaker profile image

      CWanamaker 6 years ago from Arizona

      Mama Told Me - Yes you are correct! This is one of the many great features of solar water heating systems. Yet another reason why they are a really good investment for homeowners.

    • Mama Told Me profile image

      Mama Told Me 6 years ago from Anchorage AK

      Side note: They hardly ever break down since it's a passive system. Once installed, they are pretty much maintenance free unless you leave in Tornado Alley or where there is a lot of heavy hail.