BASICS Energy-Efficiency Basics By Seth Masia and Carly Rixham Solar Water-Heating Basics Edited by Barry Butler, Liz Merry and Diana Young I t’s cheaper to save energy than to make energy. If you want to offset $100 a month in utility bills, the right place to start is not with a solar array on the roof, but with insulation under it. I n most parts of North America, the best bang for your solar energy buck is with domestic solar water heating (DSWH). It’s a no-brainer in the desert Southwest and in semitropical Florida and Hawaii. A complete DSWH system can be installed for $4,000 to $7,000, depend-ing on its size, complexity and the climate. These systems are now eligible for the 30 percent federal tax credit. At today’s energy prices, over the life of the system, the cost to operate is about 20 percent lower than a conventional gas water heater and 40 percent lower than an electric one. As gas and electricity prices rise, DSWH will look like a better and better deal. The benefits are much greater since solar energy avoids 2,400 pounds of CO 2 per year and provides a secure domestic source of hot water. Solar water-heating systems come in two flavors: passive and active. In warm climates, a simple passive system can provide plenty of hot water. First, Look at Your Heating and Cooling Bills Whether you battle high heating or cooling expenses, a quality roof and windows, good insulation and proper sealings are important in maintaning a controlled climate. Most homeowners can save 20 to 25 percent by caulk-ing air leaks around windows, doors, foundations and soffits. Check the attic insulation, too. It’s cheap to add an extra layer of batting or blown-in cellulose. It’s more expensive to swap out old single-pane or metal-frame windows for more efficient modern insulated triple-pane wood-or vinyl-frame windows. The cheapest fix of all is to renew weather-stripping around all doors and window sashes, and put insulating covers on pet doors. Spending $2,000 on insulating upgrades may cut heating costs by 50 percent and pay for itself in about three years. The U.S. Department of Energy (DOE) website (energysavers.gov) includes interactive worksheets to help you figure out how much more insulation you may need (depend-ing on your climate), how much it may cost and, depending on what you’re paying for heat energy today, how long the payback period may be. Heating and cooling systems can usually be improved. Be sure to change the furnace air filter quarterly. Get ductwork cleaned and air leaks sealed, and make sure that ducts are insulated at least to local codes. Your ductwork should be set up to heat (or cool) recirculated air from inside the house, but the furnace should draw combustion air from outside — you don’t want to burn fuel using air you’ve already paid to heat. If you heat with oil or electricity, consider installing a modern high-efficiency gas furnace or ground-source heat pump. A $6,000 investment in insulating and HVAC improvements might pay for itself in five or six years. Not sure where to start? The most direct way to find cost-effective fixes, especially in an older house, is with a professional energy audit. Check with your utility company to see if they offer free or reduced-cost audits. Standard price for this service is $200 to $400. It may include a blower-door test to locate air leaks. Passive Solar Water-Heating Systems Passive systems are installed in areas where freeze protection is not an issue. The most common types are integral collector storage (ICS) and thermosiphon systems. In an ICS (or breadbox) system, cold city water flows into a rooftop collector. The collector holds 30 to 50 gallons of water in a serpentine pipe with a heat-capturing coating. Hot water from the collector flows directly to a conventional water heater; in effect the sun does most of the work usually performed by the water heater’s burner. As hot water is withdrawn from the water heater, cold water is drawn into the collector, driven by pressure in the city water pipes. A thermosiphon takes advantage of the fact that water rises as it ’s heated. Solar-heated water in a flat-plate collector rises through tubes and flows into the top of an insulated storage tank. Colder water at the bottom of this tank is drawn into the lower entry of the solar collector. Water thus flows in a continu-ous loop, continually reheating during daylight hours. When a hot water tap is opened in the house, hot water flows from the top of the storage tank, and is replaced with cold city water flowing into the bottom of the storage tank. Although the system is simple, thermosiphons put an 800-lb storage tank high on the roof, which should be reinforced to support it. Other solar water-heating systems put the storage tank at ground level or in the basement, where it ’s not a structural challenge. Look Into Energy-Efficient Appliances The typical refrigerator built in 1980 costs about $154 in electricity to run for a year, at today’s average rate of 11 cents per kilowatt-hour. A modern high-efficiency refrigerator runs for about $55 a year. The average home-owner would save $99 a year — enough to pay for the refrigerator in a few years. A new water-heating system may be cheaper still. 12 FALL 2017 SOLAR TODAY Active Solar Water-Heating Systems Active systems use an electric pump to circulate water through the collector. In warm climates, a direct (or open-loop) system is practical: City water goes into an insulated storage tank. A pump draws water out of the storage tank to pass through the solar collector and go back into the tank. Copyright © 2014 American Solar Energy Society. All rights reserved.