Solar Water Heater | Know What You Are Buying

A typical glazed flat plate solar water heating collector in Florida.
A typical, traditional, and proven glazed flat plate solar water heating collector in Florida.

I was recently contacted by a homeowner in Georgia who was seeking my advice about a product they had introduced to them by a solar dealer. The product was called a solar dome. I didn’t really know what it was at first, so I set out to research the product and it’s performance. The product is intended to heat and store water for domestic use. It looks like a radar antenna with a glass bubble over it and integrated underground storage.

It actually looks pretty neat, space age perhaps. There are some ingenious features. It probably even works. Unfortunately, things start to break down when you start comparing it to the alternatives. The solar energy buying decision is often based largely on efficiency, and by that I mean how much are you going to spend, and what benefit will you get from your investment.

For equivalent solar technologies, you can usually get a pretty good idea of how much energy you can harvest based on the area of solar panels, but that is not always the case. For solar pool heating, similarly constructed panels will perform within a 15% range of each other, but not all panels have the same design. For solar electric panels, some manufacturing techniques can make solar panel power outputs up to 25% greater. For glazed solar water heating collectors, the area of the panel will give you a pretty good idea of the average energy output. In the case of the solar dome design, the particular collector pitched to my new Georgia friend had an area of 28 square feet. I was immediately suspicious because we normally install residential solar panels of 40 square feet, or 43% larger.

Upon consulting the SRCC rating data sheets for the two products, my suspicions were confirmed. Our collector output rating is literally double the rating of the solar dome in warm climates and four times the rating in cool climates. But that’s just part of the story. The dealer wanted double our installed price for half to one quarter the performance! My answer to the nice man was, “run like hell!”

Fortunately we can usually make efficiency comparisons that are much closer when comparing similar technologies. Comparing a domed collector to a flat plate collector is not going to yield a great comparison. When looking at a flat plate collector vs another flat plate collector, we can look at equivalent surface areas and make a valid comparison. For example, we previously offered a nominal 40 square foot solar water heating collector that is rated with a net area of 37.4 square feet. Our new 40 square foot offering is 37.12 square feet, so essentially the same area. The new collector’s warm climate rating is 42.6 BTU/sf/day and the old one was 41.7 BTU/sf/day. These are hardly wide gaps in performance characteristics, so it comes down to a cost and quality comparison.

When comparing both similar and disparate technologies, it is important to consider performance, cost, and quality. If you can take at least one factor out of the mix, and preferably two, the decision becomes much easier. In the case of solar water heating systems, we have elected to offer a system with similar performance and cost to our competition. The remaining factor is quality. I’m not going to give up all of my secrets right now, but if you are interested in solar water heating, we will be happy to compare the remaining factor of quality with you one-on-one!

Before your make a decision on a solar water heater, know what you are buying. Consult with a reputable dealer that will be up front about solar panel ratings from a trusted third party. When comparing different technologies, take extra care to be sure what you are buying is a proven type of system with a good track record and lots of existing owners. Your solar water heater buying decision will be yours to live with for well beyond a decade, so make the right choices from the beginning!

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