This summer is a great time to get a good deal on a solar water heating or solar-electric (photovoltaic) system for your home. While I argued a few months ago in this column that the 30% federal solar tax credit has some flaws–key among them being that it’s based on the dollar value rather than performance and that there’s no cap on the cost of the system (and credit you can earn)–these aren’t reasons not to take advantage of it.
While the are scheduled to be in place until 2016, I won’t be at all surprised to see them scaled back or eliminated well before then. If you haven’t noticed, the political pendulum is swinging, and incumbents who supported the stimulus funding are now being cast as reckless spenders and are losing primaries. I think we’ll see a growing focus on deficit control–and that could well include scaling back on incentives like the solar tax credits. The bottom line is that now’s the time to benefit from the solar tax credit.
For most homeowners, installing a solar water heating system will have a more rapid return on investment (ROI) than installing an electricity-generating photovoltaic (PV) system, so I’ll focus on the former. Most solar water heating systems for typical homes have two flat-plate solar collectors. Either water or an antifreeze solution is pumped through the collectors during the day and heat is transferred from the absorber plate to that fluid. A glass cover plate on the collector, insulation behind the absorber plate, and pipe insulation all help to improve efficiency and direct more heat into the circulating fluid.
While the collectors sit on your roof (or on a separate rack outside the house), there are also solar water heating components inside the house. Most systems have a separate solar hot water storage tank in the basement or utility room that serves as a preheater for the standard water heater. A heat exchanger in this tank transfers heat from the fluid circulating through the collectors into the storage tank. Rather than a preheater tank, some systems have a single tank containing both the heat exchanger from the solar collectors and a standard heating element.
Controls and a pump round out the system. The conventional approach is to have a differential thermostat that senses temperatures both in the collectors and storage tank, and then switches on the circulator pump when the collectors are warmer than the water in the storage tank. Some systems, however, now use a simpler control system: a separate PV module powers the circulating pump, operating only when the sun is shining.
Solar water heating systems vary a great deal in their cost, depending on the size, type of system, added features like digital monitoring, and challenges of the installation. The typical price range for a residential system is $5,000 to $8,000, installed. With new construction, costs can be lower, especially if a lot of identical systems are being installed on multiple tract homes.
To function efficiently, solar panels must be installed on a good site. The sun traverses the southern sky during the day, rising in the east and setting in the west, so the best site for solar is a south-facing roof. The pitch of the roof isn’t critical. A steeper pitch will be a little better in the winter (when the sun is lower in the sky), while a shallower pitch is better in the summer (when the sun is higher in the sky), but most standard roof pitches will work all right. There should be as few obstructions as possible, so cutting or pruning nearby trees is often an important part of a solar installation.
A properly sized and well-sited solar water heating system should satisfy most of your hot water needs during the summer months, but it may provide less than half in the winter, when there is less sunlight. To maximize the percent of hot water provided by the solar system, you should carry out appropriate water conservation efforts, such as installing low-flow showerheads and washing laundry in cold water.
Contact a local or regional solar installer for more information and to schedule a site visit. Be sure the contractor you pick is more interested in a quality, reasonably priced installation than on maximizing the tax credit. (Be aware of scams in which roofing or other costs unrelated to the solar system are added into the installation price so that Uncle Sam will pay you more–an indicator that the contractor’s motivations are misplaced.)
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Alex Wilson is the executive editor of and founder of BuildingGreen, LLC. To keep up with his latest articles and musings, you can .