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Solar Q&A “Solar Uncertainty”

Q&A with Howie Michaelson, Sun Catcher

There are many questions and concerns that repeatedly come up around Solar Energy and its day-to-day functioning. In this column, Howie Michaelson (who has lived in a solar, off-grid home for 14 years) will try to answer those questions in a simple, clear fashion. Please submit your questions to: uncertain@catamountsolar.com  for inclusion in future editions!

I’m interested in a Solar Hot Water system for my home, and have gotten different designs from installers. Is it better to collect solar energy into the same tank that I have for my existing domestic hot water system or a totally separate collection tank?

There are definitely different approaches to designing Solar Hot Water systems and more than one design is likely to be applicable to any scenario. So what design you choose should take into account all the existing circumstances and equipment (age, fuel type, system location, etc.), as well as possible solar collector and storage tank locations, and choices about efficiency of the system versus overall cost. Your designer/installer needs to know all of these factors in order to make the best recommendation.

While there are many possible solar hot water (SHW) storage designs, there are 2-3 basic options normally considered for northern climates like ours. If you have an existing domestic hot water (DHW) tank that you do not want to replace, you can choose to add a separate SHW storage tank that to preheat the water supplying your DHW tank. The other basic option is to store heat from your solar collectors directly into your existing DHW tank. The first scenario is usually more expensive, but is almost always more efficient at solar collection/storage and it potentially provides more overall hot water capacity. In general, it is the most common SHW storage design.

If you are installing a new DHW system at the same time (because you have a new house or it is time to replace your existing system), you may also consider pairing your SHW storage system with an instantaneous (or tankless) DHW system. Often this may be the most efficient and cost effective design choice. The major advantage of this combination is that the tankless heater only needs to turn on to heat the water the difference between SHW storage tank temperature and the 120-130 degrees desired for your hot water.

As with all systems, for the DHW and SHW to play nicely together, they must be designed with whatever existing system is already in place and remaining. Be sure to have your system designer explain the economic and efficiency costs and benefits of the possible choices before installing a solar hot water system tailored to your needs.

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