Solar water heating systems for homes are not new. The increasing cost for energy, and growing concerns for the environment have caused more and more homeowners to think about installing a solar water heating system. Advances in technology, which make the solar collectors much more efficient, have resulted in reduced cost of these systems. In addition, federal tax credits are available to defray some of the cost, provided your solar hot water system supplies 50% or more of the domestic hot water requirements.
Two kinds of solar hot water heating systems are used for homes: open loop systems or closed loop systems. Open loop systems are installed in areas where temperatures stay above freezing and where the water is soft. In an open loop system, the incoming cold water is circulated through the solar collectors, and then stored in the solar hot water storage tank from where it goes to the water heater. In the closed loop system, a heat exchanger isolates the domestic water from the solar collector loop. The fluid running through the loop is usually a freeze-proof glycol solution. Because of the added heat exchanger and a bit more piping, the cost of a closed loop system is higher than that of a comparable open loop system.
Size and number of collectors depend on the type of collector you decide to install, for a given hot water load. Flat plate collectors and evacuated tube collectors are the two most frequently used types. Evacuated tube collectors are more efficient than the flat plates, especially in colder or foggy weather and climates. It is generally just fine to use flat plate collectors in sunny and warm climates, as long as your water is soft. The more expensive, but also more efficient, evacuated tube collectors are a better option in colder, cloudy or foggy areas.
It is important to know that a solar water heating system must have a regular water heater as a backup to make sure that you have enough hot water during, and after, a number of days of overcast conditions. I like to look at a residential solar water heating system as a system that PRE-heats the incoming cold water on most days and on some days it heats all your hot water up to the required 130degF. The water heated in the solar collectors is stored in the solar storage tank from where it flows into your regular water heater to be fully heated as needed. With a well designed system, enough hot water will be produced in the solar collectors on clear days so that you don’t need the regular water heater.
The most important decision made for a solar water heating system installation is the location of the solar collectors. Even the best flat plate or evacuated tube collectors will perform poorly if they are mounted in an area that is shaded many hours each day. Tools are available to measure or calculate the solar radiation in your location. Some calculation programs, available online, are free. All will require you to do some of the work yourself, such as collecting some data and entering it into tables or forms. You can also buy an instrument to measure the solar radiation at your location. Or you can try your friendly local solar system installer. They might give you a free analysis.
Once you know where on the roof you want to put the solar collectors, talk to a contractor about the requirements for strengthening needed to install the collectors and frames. And ask the contractor about the roofing. Several roof penetrations will have to be made. These must be sealed at the end to keep your roof absolutely waterproof.
Ok, let’s look what is needed in the house. Here you will need space for the solar storage tank, pump and maybe a small expansion tank, if you end up with a closed loop system. How much space? For initial planning purposes, allow at least 2 1/2 times as much space as your existing water heater uses. This needs to be adjacent to the water heater. Allow enough space for easy access for maintenance.
All right, the collectors are on the roof, the solar storage tank is in the basement. How will the pipes be run between the two? You will need to run two 3″ pipes. That is based on 1″ pipes with 1″ insulation. Scout out which walls you can use to run the pipes up through, all the way from the basement, or first floor, to the roof. If possible, avoid having to build pipe enclosures. That gets costly and might not look very nice. Corners in built-in closets are great places to to hide pipes.
You are on the way. Once you have the answers to all the issues mentioned above, you can move to the next level: serious, detailed planning and design. Either make it a do-it-yourself solar project, or use your knowledge to negotiate and work with a contractor to have them install the solar hot water heating system for your home.
Avoid the same mistakes other folks have made in the past when they were building a solar hot water system. Get educated and learn how to do a successful system.
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