Choosing Your Solar Hot Water Heater

Open loop. Closed loop. Active. Passive. Single tank or dual tank. Purchasing a solar hot water heater is a task full of choices. Choices that often go unrecognized as we scramble to explain how it works or what incentives may or may not be available. Knowing and understanding those two variables are vital to any water heater buy, but doing so is not like a trip to the appliance store, where you might walk in, peruse the aisles, and walk out with whatever clothes dryer fit your budget.

Photo Credit: r_neches

Shopping for solar hot water heaters requires a little extra research. There are different designs whose relevance to you will vary based on several factors, including local climate, water needs and more. There are also many manufacturers that should be researched as well. We’ll now dive a bit deeper into some of these key factors…

Local Climate

The vital factor here is the threat of freezing temperatures in winter. In warm and sunny climates, such as those enjoyed by Florida and southern California, open loop systems are most common. In these systems, water is heated directly by the solar collectors. Passive integral collector storage (ICS) systems are a possibility for these residents.

For those in cold or mild but freeze-threatened regions, such as the northern states and the Pacific Northwest, a closed loop system is most viable. There are also drain back system that drain the water from the collector into a separate tank when not in use, or when temperatures approach freezing (using a sensor). In closed loop systems, instead of running the water itself through the solar collectors, an antifreeze solution (propylene glycol or ethylene glycol) is passed through the collector. Once heated, this transfer fluid passes that heat along to the water supply by way of a heat exchanger.

Even among closed and open loop systems, there are a number of different designs. These are expertly explained in this article from the American Solar Energy Society. However, your best resource for discovering which systems are best suited to your local climate will be a local and reputable solar thermal installer.

Water Needs

Some solar water heaters use pumps to move water or transfer fluids throughout the system. Others simply use the pressure of the city water supply. Most solar hot water systems will contain one or more storage tanks to hold heated water until it’s needed within the home. Tankless systems are also available.

The size of the water tank and the square footage of the collector space on your roof will be largely determined by your family’s hot water needs. Larger families will obviously need a bigger tank to meet demand. The average 40 square-foot group of solar collectors provides nearly 40 gallons of hot water per day – roughly 60 percent of what the average family of four requires.

Factoring your daily water usage will have an effect on which solar hot water heater you choose.

Collectors

There are three types of solar hot water collectors. As mentioned above, integral collector storage systems, in which storage tank itself is the collector, are passive systems. More common are flat plate collectors and evacuated tube collectors. The former is cheaper and more common in warm and sunny climates. The latter is more expensive but also more efficient and recommended for those who live in Northwestern, Northeastern, and similar climates. Evacuated tube collectors are able to heat and function at higher temperatures than flat plate collectors and are better suited for families seeking year-round water or space heating. Solar hot water collectors are best explained here and here.

Manufacturers

Solar-rating.org is the home of the Solar Ratings and Certification Corporation (SRCC). Every solar water heater manufacturer must register with this organization in order for their products to be eligible for federal tax incentives. SRCC is step number one in researching who to buy your solar water heater from. There, you’ll find a list of water heaters as well as performance ratings for each. There’s a system designed for every climate, and once again, your solar thermal contractor will have extensive knowledge of which manufacturers and which systems will work best for you.

Budget

Solar hot water heaters cost upwards of $6,000 before any incentives or rebates are factored in. That’s no small chunk of change (although it should be noted that solar water heaters will last over 40 years with routine maintenance). There are several variables that affect price. Closed loop systems will naturally cost more on average than open loop due to the addition of parts. Active systems with their pumps will cost more than passive systems. Two storage tanks will cost more than one. You get the idea.

With the renewal of solar tax credits at the end of last year, a federal tax credit of 30 percent of total costs is now available to everyone. Many states have their own incentives as well, which bring down the end costs even more. Also look into utility and local city or county incentives as well. There is much out there to help ease the financial burden on solar hot water heaters, and the amount of aid available may not only determine which system you buy, but whether you buy at all.

Installer

Not only will a solar thermal installer get the system up and running after you’ve chosen, he or she will also be a valuable consultant during the choosing process. Reputable installers will have valuable knowledge about all the above factors. Finding installers is as easy as ever. The American Solar Energy Society allows you to search by zip code, and of course, Calfinder Solar lists local installers and connects you with them for free estimates.

All this may seem like a lot of information to swallow, but that’s what makes local solar professionals such a valuable resource. All it takes is a little research and a few phone calls before you’re enjoying a hot shower, low carbon footprint and greatly reduced water bills locked in for the next 30-40 years.

Posted on January 14th in Solar Products by Dan.