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FAQ on using solar energy for heating space and water

Source: US DOE

Q: What are the benefits of using solar energy to heat water in my home?

A: First, the fuel is free! Once you recover the higher initial costs of a solar system through reduced or avoided energy costs (that is, lower utility bills), your solar system will require expenditures only for maintenance. And when you include the cost of a solar water heater in a mortgage on a new home, the system often provides a positive monthly cash flow from the first day of ownership. US Solar Buildings Program offers a free software program that allows you to determine how much money you'll save by installing a solar water heater in your new home.

Second, solar water heaters and other solar technology applications do not pollute. They do not add to the carbon dioxide, nitrogen oxides, sulfur dioxide, and other air pollutants and wastes produced by most of today's power plants, even those that run on natural gas. And they allow you to burn less natural gas in your home, as well.

Q: Are there any disadvantages to using solar energy?

A: The energy in sunlight can be used for many purposes, including heating water for a building or swimming pool. And using solar energy has many environmental and life-cycle economic benefits. However, solar energy heating or solar electric products often have higher "first costs" than other, similar products do. This means it will probably cost more initially to purchase and install a solar system than it will to purchase and install another kind of heating or electric system. Still, in nearly all cases, you will recover your initial costs through substantial fuel savings (as shown in lower utility bills) over the life of the product. Many solar systems last from 15 to 30 years.

Q: Can a solar water heater replace an electric or gas water heater?

A: Not completely. Conventional electric or gas water heating systems are still necessary as a supplement to the solar water heating system, largely because the sun might not shine in a particular area for several days at a time. However, because solar water heaters are designed provide hot water directly to the tank of a gas or electric water heater, they reduce the need for the water heater to run on conventional fuels. And this in turn reduces your gas or electric bill. Depending on where you live, solar water heaters can provide up to 80% of your home's annual water-heating needs.

Q: Can solar water heaters be used in northern states and other colder climates?

A: Yes. Solar water heating technology is effective regardless of the outside temperature. In colder climates, more energy is required to heat cold incoming ground water, so using solar energy in such conditions could dramatically lower a consumer's utility bills. In addition, colder incoming ground water helps solar water heaters to operate at higher efficiencies.

Q: Can I use a solar water-heating system to heat my swimming pool?

A: Using a solar system to heat a swimming pool is the most common use for solar energy in the United States today. Solar pool-heating systems increase an unheated pool's water temperature by 10 degrees or more, and they can extend the swimming season by two to three months. Solar system prices range from $2,500 to more than $5,000, depending on the size of your pool and other conditions, such as shading from nearby trees and buildings and how close the pool is to the ocean. When solar systems replace a conventional gas or electric swimming pool heater, the initial investment can usually be recovered in about three years or less, because of reductions in subsequent utility bills.

Q: Can solar power be used to heat my home and business?

A: No pre-engineered residential solar space heating systems are readily available to consumers today. But many solar energy professionals can engineer a system for you, on request. However, solar space-heating systems are considerably more expensive than solar water-heating systems. Depending on the size of the space that needs heating, a solar system could cost anywhere from $3,000 to more than $10,000. A solar energy professional in your area can explain what would be involved to purchase this type of solar system. You may want to consider increasing your insulation and using passive solar technologies—such as large, energy-efficient, south-facing windows—as an alternative.

Q: How much does a solar water-heating system cost?

A: Unfortunately, there is no one answer to this question. The cost of a solar system depends on a number of factors, such as the size of the system and the particular system manufacturer, retailer, and installer. However, any solar rebates and other incentives available in your area will reduce that total cost.

For solar water heaters and space heaters, you will also be taking into consideration the price of the fuel used to back up the system. In most cases, you will have to add in the cost of supplemental natural gas or electricity to get a fairly accurate estimate of how much you can expect to pay for a solar system.

Installed costs vary widely, from $1,500 to more than $3,000. Some home builders are beginning to list solar water heaters as an option for their homes. Others include them as a standard feature in every home. In some cases, the builder or mortgage company may offer a lower interest rate when solar water heaters or other energy-efficient features are built into a new home, because the buyer can expect to save a significant amount of money on future energy bills. Although a solar water-heating system still costs more than a conventional electric or gas water heater, some states and utilities offer rebates that can reduce the total cost appreciably.

Other Resources: To learn more about financial incentives in your area, please visit the Database of State Incentives for Renewable Energy (DSIRE) and contact your State's Energy Office . One caveat: any time you work with a contractor, it is wise to check references.

Your U.S. Department of Energy (DOE) regional support office may also be able to provide guidance.

To find a solar energy system designer or installer in your area, please visit our solar yellow pages for a list of sources of solar professionals.

To learn more about financing opportunities, please see The Borrower's Guide to Financing Solar Energy Systems: A Federal Overview, September 1999 (PDF 501 KB).
Download Acrobat Reader.

Q: How much money will a solar water-heating system save on my utility bill?

A: It is difficult to say how much you will save with a solar system. That depends on several factors, including how much you already pay your local utility for electricity or natural gas. You can ask your solar system professional how much heat your new system will produce on an annual basis and then subtract that number from your current annual consumption—the total amount of electricity and gas you use—to get an idea of how much you will save. Data on your current annual consumption should be available from your utility.

Q: Since concentrating solar power plants are reliable, why haven't more been built in the last few years?

A: One reason is the relatively low cost of fossil energy in most areas of the United States. The majority of today's power plants run on inexpensive coal. And the current utility environment generally favors new natural gas power plants, which have comparatively low initial costs (first costs). With fossil fuel plants, however, customers (ratepayers) must bear the risk of higher fuel costs in the future.

In contrast, the fuel needed to run a concentrating solar power (CSP) plant is sunlight, which is free. A CSP plant uses its field of mirrors to deliver the thermal energy that's provided by the fossil fuels burned in a conventional (e.g., gas- or coal-powered) plant. So, investing in a CSP plant is the equivalent of buying a lifetime supply of fuel. But the first costs associated with CSP plants can be high. To guarantee that they'll recover their first costs, most CSP plant operators would probably want to have some long-term power purchase agreements lined up, to minimize the financial risk.

Other factors could also play a role in delayed investment in CSP. These include the perceived risks associated with new technologies and a need for tax equity with conventional technologies. Financial and regulatory incentives, advances in CSP technologies, and cost reductions resulting from economies of scale are just some of the things that could help to increase investments in CSP.

Q: Do concentrating solar power (CSP) plants require a lot of land? How much, exactly?

A: Relatively speaking, no. Consider Hoover Dam, for example. Nevada's Lake Mead, which is home to the dam, covers nearly 250 square miles. In contrast, a CSP system occupying only 10 to 20 square miles could generate as much power annually as Hoover Dam did in one recent year. And if we take into consideration the amount of land required for mining, CSP plants also require less land than coal-fired power plants do.

It's hard to say exactly how much land is required for a CSP plant, however, because this depends on its generating capacity and the particular technology used. For example, a 250-kilowatt plant composed of ten 25-kilowatt dish/engine systems requires less than an acre of land. And a parabolic trough system uses about 5 acres for each megawatt of installed capacity. But in any case, the solar resource needed to generate power using CSP systems is quite plentiful. Imagine being able to generate enough electric power for the entire country by covering about 9 percent of Nevada — a plot of land 100 miles on a side — with parabolic trough systems!

Q: What are the environmental impacts of concentrating solar power plants (CSP)?

A: Concentrating solar power plants have few environmental impacts; land use is the primary one. Although a CSP plant's "footprint," or the amount of land it occupies, is larger than that of a fossil fuel plant, the two actually use about the same amount of land. This is true because fossil fuel plants require a significant amount of land for exploration, mining, and road-building purposes. And CSP plants have the advantage in that they produce no environmental contaminants or greenhouse gases. However, the fossil fuel component of a hybrid power plant does not have the same benefits.

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