Solar Water Heaters

Classic image of rooftops in Turkey... solar water heaters and satellite dishes.

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In my travels overseas, I occasionally come across things that make me say, "Why in the world do we not do this in the United States?"  Solar Water Heaters are one of them.  Yes, there are some people (mostly corporations) who are utilizing solar water heaters in the U.S., but it is nothing like the common everyday use like in Turkey, South Africa, Germany, and India.

I think the biggest reason why the U.S. is not utilizing this technology more is because of the photo at the top of this article. Home owners associations do not want their roofs to look cluttered like this... it's unattractive. Who cares about the monetary savings and reduction in pollution to generate the energy to heat the water conventionally? But in reality, they do not have to look bad. German rooftops seem to integrate the solar systems into the design a lot more.

Solar water heating systems in Germany are a bit more aesthetically pleasing.

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According to 2010 data, it would take over 12 years to have the initial system's cost paid back in energy savings in the United States. In Brazil and South Africa, the payback time is 5 years or less. However, this is for a purchased system. There are many systems that can be designed, built, and installed for only a few hundred dollars (if that) if we are willing to do a little scrounging and do-it-yourself work. I'll try to highlight some of these systems in future posts.

Passive (A) and Active (B) Solar Water Heating Systems.

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There are two basic design types of solar water heating systems, passive and active. Passive Systems (aka Thermosiphon Systems) allow the natural properties of water (hot rises and cold sinks) to run the system. This is not as efficient a system, but it is cheaper and is often more reliable as it contains no moving parts and has no electronics that could break. Active Systems (aka Forced-Circulation Systems) utilize an electric pump and an electric controller to maximize the sun's heating power, and well designed systems also use solar energy to power the electric pump and controller.

Another way to categorize solar water heating systems is Direct Circulation vs. Indirect Circulation systems. Simply put, direct circulation systems heat up your home's water directly. Indirect circulation systems will heat up some sort of anti-freeze fluid that then runs through coils of pipe (a heat exchanger) that heats up your home's water indirectly. I always think of an indirect system like an electric blanket... the wires heat up the blanket which heat me up. Indirect circulation systems are good for areas that freeze frequently or severely; the anti-freeze fluid won't freeze and crack the pipes which could happen with a direct circulation system in colder climates.

A Direct Circulation Solar Water Heating System (this one is a passive design type).

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An Indirect Circulation Solar Water Heating System (this one is an active design type).

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Finally, there is a choice of solar collector types. The solar collector is the heart of the system, it is how solar energy is actually captured. There are three basic solar collector design types:

• Batch or Integral Collector-Storage (ICS) - These systems utilize one or more tanks, painted black or coated with a "selective absorber" finish, which is inside an insulated box with a clear top often made of glass. This design uses the same concept as solar ovens. Cold water flows into the black tank which is "cooked" by the sun to fairly high temperatures. The water is heated and returns either actively or passively back to the home. These systems are probably the most common do-it-yourself types of systems. Old refrigerators with the door removed and glass placed on top are frequently used.
• Flat-Plate Collector - This is a very similar design to the Batch or ICS system. However, instead of large tanks inside the sealed box, there is a tube that slowly winds its way back and forth through the flattened box.
• Evacuated-Tube Collector - This collector design relies on the fact that heat cannot be lost easily through a vacuum. This is basically a tube within a tube. The space between the inner and outer tubes is "evacuated" of all air (made into a vacuum). The outer tube is clear, typically glass, and the inner tube is painted black. The sunlight passes through glass tube and heats up the black tube, but the heat cannot escape back out through the vacuum. These systems are almost always an indirect circulation design where an anti-freeze liquid is circulated through the inner black tube. The heated anti-freeze then flows back to a heat exchanger and heats up the home's water. Evacuated-Tube Collectors are very efficient, but much more expensive.

The last thing to consider with solar water heaters is how they will be integrated into the home. Some people choose to utilize the solar water heating system as the home's primary water heating system. If the sun is out, they you have hot water. If the sun does not come out, then within hours to days, depending on the size of your storage system and its ability to retain heat, you will be out of heat. Homes that are completely "off-grid" often do not have, or do not want to use, extra electricity or gas to heat water on cloudy days.

Another way to integrate solar water heating systems, and one that is most often used, is to have the solar water heating system pre-heat water going to a conventional water heater (either electric or gas). Newer constructs are using on-demand water heaters that have no hot water storage tank. The pre-heated water then needs significantly less energy (sometimes none) to heat it up for the home's needs. This allows a home greatly reduced energy costs, but still provides hot water on cloudy days.

Solar water heating systems will become more and more popular in the U.S. as people start to understand their benefits and start to feel the pain of increased energy costs.