Active Solar Water Heating

Nearly 300 homes in this San Diego development have solar water heating systems, and some have solar electric systems. The solar water heating collectors on the roof look like skylights.

One of the most cost-effective ways to include renewable technologies into a building is by incorporating solar hot water.

A typical residential solar water-heating system reduces the need for conventional water heating by about two-thirds. It minimizes the expense of electricity or fossil fuel to heat the water and reduces the associated environmental impacts.

Solar Water Heating for Buildings

Most solar water-heating systems for buildings have two main parts: (1) a solar collector and (2) a storage tank. The most common collector used in solar hot water systems is the flat-plate collector.

Solar water heaters use the sun to heat either water or a heat-transfer fluid in the collector. Heated water is then held in the storage tank ready for use, with a conventional system providing additional heating as necessary. The tank can be a modified standard water heater, but it is usually larger and very well insulated. Solar water heating systems can be either active or passive, but the most common are active systems.

Active solar water heaters

Active solar water heaters rely on electric pumps, and controllers to circulate water, or other heat-transfer fluids through the collectors. These are the three types of active solar water-heating systems:

1. Direct-circulation systems use pumps to circulate pressurized potable water directly through the collectors. These systems are appropriate in areas that do not freeze for long periods and do not have hard or acidic water. These systems are not approved by the Solar Rating & Certification Corporation (SRCC) if they use recirculation freeze protection (circulating warm tank water during freeze conditions) because that requires electrical power for the protection to be effective.

2. Indirect-circulation systems pump heat-transfer fluids through collectors. Heat exchangers transfer the heat from the fluid to the potable water. Some indirect systems have "overheat protection," which is a means to protect the collector and the glycol fluid from becoming super-heated when the load is low and the intensity of incoming solar radiation is high. The two most common indirect systems are:

   • Antifreeze. The heat transfer fluid is usually a glycol-water mixture with the glycol concentration depending on the expected minimum temperature. The glycol is usually food-grade propylene glycol because it is non-toxic.

   • Drainback systems, a type of indirect system, use pumps to circulate water through the collectors. The water in the collector loop drains into a reservoir tank when the pumps stop. This makes drainback systems a good choice in colder climates. Drainback systems must be carefully installed to assure that the piping always slopes downward, so that the water will completely drain from the piping. This can be difficult to achieve in some circumstances.

Passive solar water heaters

Passive solar water heaters rely on gravity and the tendency for water to naturally circulate as it is heated. Because they contain no electrical components, passive systems are generally more reliable, easier to maintain, and possibly have a longer work life than active systems. The two most popular types of passive systems are:

1. Integral-collector storage systems consist of one or more storage tanks placed in an insulated box with a glazed side facing the sun. These solar collectors are suited for areas where temperatures rarely go below freezing. They are also good in households with significant daytime and evening hot-water needs; but they do not work well in households with predominantly morning draws because they lose most of the collected energy overnight.

2. Thermosyphon systems are an economical and reliable choice, especially in new homes. These systems rely on the natural convection of warm water rising to circulate water through the collectors and to the tank (located above the collector). As water in the solar collector heats, it becomes lighter and rises naturally into the tank above. Meanwhile, the cooler water flows down the pipes to the bottom of the collector, enhancing the circulation. Some manufacturers place the storage tank in the house's attic, concealing it from view. Indirect thermosyphons (that use a glycol fluid in the collector loop) can be installed in freeze-prone climates if the piping in the unconditioned space is adequately protected. Learn more about freeze-protected piping and research being conducted at the National Renewable Energy Laboratory.

U.S. Department of Energy

Active Solar for Lighting

Solar lighting Basics

Solar hybrid lighting system.

Research under way at Oak Ridge National Laboratory (ORNL) could lead to entirely new, highly energy-efficient ways of lighting buildings using the power of sunlight. This new technology, called Hybrid Solar Lighting, (HSL) would use sunlight to simultaneously light interior spaces and generate electricity.

Hybrid solar lighting makes better use of sunlight in its natural form and specifically targets the energy consumed by electric lights—the largest consumer of electricity in commercial buildings. Electric lighting accounts for more than a third of all electricity consumed for commercial use in the United States.

HSL, currently in the research and development phase, would use a specially designed collector to focus natural, full-spectrum sunlight into optical cables while simultaneously converting otherwise wasted infrared energy into electricity. The optical cables would then deliver the full-spectrum sunlight to light fixtures throughout a building. Additionally, HSL would convert sunlight to electricity much more efficiently than conventional solar technologies.

In a solar lighting and power system, the roof-mounted concentrators collect sunlight and distribute it through the optical fibers (enlargement) to hybrid lighting fixtures in the building's interior. The system also produces electricity for supplemental lighting or other uses.

Solar hybrid lighting system in commercial building.

There are currently two proposed applications for hybrid solar lighting systems. First, hybrid lighting systems are being developed for use in commercial buildings to displace electric lighting, which consumes a large portion of electricity in commercial buildings. The figure below illustrates one system configuration being developed for this application.

Second, researchers are investigating the use of HSL as a key component in new hybrid solar photobioreactors that sequester carbon via enhanced photosynthetic-based bio-processing at power plants, illustrated below. This concept is explained in further detail in the Hybrid Solar Lighting for Photosynthetic-based Carbon Sequestration at Power Plants poster.

U.S. Department of Energy

How Solar Collectors Work

This home in Nevada has an integral collector storage (ICS) system to provide hot water.

Solar collectors are the key component of active solar-heating systems. Solar collectors gather the sun's energy, transform its radiation into heat, then transfer that heat to water, solar fluid, or air. The solar thermal energy can be used in solar water-heating systems, solar pool heaters, and solar space-heating systems. There are several types of solar collectors:

• Flat-plate collectors
• Evacuated-tube collectors
• Integral collector-storage systems

Residential and commercial building applications that require temperatures below 200°F typically use flat-plate collectors, whereas those requiring temperatures higher than 200°F use evacuated-tube collectors.

Flat-plate collectors

Flat-plate collectors are the most common solar collector for solar water-heating systems in homes and solar space heating. A typical flat-plate collector is an insulated metal box with a glass or plastic cover (called the glazing) and a dark-colored absorber plate. These collectors heat liquid or air at temperatures less than 180°F.

Flat-plate collectors are used for residential water heating and hydronic space-heating installations.

Liquid flat-plate collectors heat liquid as it flows through tubes in or adjacent to the absorber plate. The simplest liquid systems use potable household water, which is heated as it passes directly through the collector and then flows to the house. Solar pool heating also uses liquid flat-plate collector technology, but the collectors are typically unglazed as in figure below.

Unglazed solar collectors typically used for swimming pool heating.

Air flat-plate collectors are used primarily for solar space heating. The absorber plates in air collectors can be metal sheets, layers of screen, or non-metallic materials. The air flows past the absorber by using natural convection or a fan. Because air conducts heat much less readily than liquid does, less heat is transferred from an air collector's absorber than from a liquid collector's absorber, and air collectors are typically less efficient than liquid collectors.

Air flat-plate collectors are used for space heating.

Evacuated-tube collectors

Evacuated-tube collectors can achieve extremely high temperatures (170°F to 350°F), making them more appropriate for cooling applications and commercial and industrial application. However, evacuated-tube collectors are more expensive than flat-plate collectors, with unit area costs about twice that of flat-plate collectors.

Evacuated-tube collectors are efficient at high temperatures.

The collectors are usually made of parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin is covered with a coating that absorbs solar energy well, but which inhibits radiative heat loss. Air is removed, or evacuated, from the space between the two glass tubes to form a vacuum, which eliminates conductive and convective heat loss.

A new evacuated-tube design is available from the Chinese manufacturers, such as: Beijing Sunda Solar Energy Technology Co. Ltd. The "dewar" design features a vacuum contained between two concentric glass tubes, with the absorber selective coating on the inside tube. Water is typically allowed to thermosyphon down and back out the inner cavity to transfer the heat to the storage tank. There are no glass-to-metal seals. This type of evacuated tube has the potential to become cost-competitive with flat plates.

Integral collector-storage systems

Integral collector-storage systems, also known as ICS or "batch" systems, are made of one or more black tanks or tubes in an insulated glazed box. Cold water first passes through the solar collector, which preheats the water, and then continues to the conventional backup water heater.

ICS systems are simple, reliable solar water heaters. However, they should be installed only in climates with mild freezing because the collector itself or the outdoor pipes could freeze in severely cold weather. Some recent work indicates that the problem with freezing pipes can be overcome in some cases by using freeze-tolerant piping in conjunction with a freeze-protection method.

What Are Sun Spaces ?

Homeowners with a sunspace frequently cite it as their favorite room of the house. Sunspaces provide light, warmth, aesthetics, and a healthy environment for plants and people. Sunspaces can also save money on home heating costs. In fact, well-designed sunspaces can provide up to 60% of a home’s winter heating requirements.

Elements of Sunspaces

Sunspaces contain the following elements:

• Glass panels, or "glazing," permit light to enter a room, but prevent infrared heat from escaping. This process warms the interior space.

• Thermal mass, such as masonry or water, absorbs heat and releases it into the room during extended cloudy weather or at night.

• Insulation in ceilings, walls and windows retard heat loss at night and during cold weather.

• Climate control features such as operable windows, vents, and fans keep the sunspace from overheating and move warm air to other parts of the house.

Design Considerations

When designing a sunspace, there are several important factors that must be taken into consideration. Your planned primary use of the sunspace will influence some planning decisions:

• A sunspace must face south. Due south is ideal, but 30 degrees east or west of south is acceptable. If the south side of the house faces the street, the sunspace must be integrated into the house to avoid a "tacked-on" look.

• The sunspace must receive direct sunlight between the hours of 10:00 a.m. and 3:00 p.m. Any object over 10 feet tall within 15 feet of the south glazing is likely to block solar gain.

• If the primary function of the room is to provide heat, you can maximize heat gain by using sloped glazing, few plants, little thermal mass, and insulated, unglazed end walls. However, compared to vertical glazing, sloped glazing loses more heat at night, can be covered with snow in the winter, and can cause overheating in warmer weather. Vertical glazing can maximize heat gain in winter, and yields less heat gain in the summer. A well-designed overhang may be needed to shade the glazing in the summer.

• If the space is to be used as a greenhouse, remember that plants require lots of light, fresh air, water, and protection from extreme temperatures. Plants consume energy that would otherwise be available as heat. Plants require overhead glazing, which complicates construction, and glazed end walls, which are net heat losers.

As most homeowners wish to use their sunspaces year-round as living areas, the rooms should be designed to have minimum glare and moderate humidity. Carefully sized thermal mass materials will improve comfort levels by stabilizing temperature extremes.

US Department of Energy’s Energy

What Is Solar Electricity ?

Q: What is photovoltaics (solar electricity), or "PV"?

A: What do we mean by photovoltaics? The word itself helps to explain how photovoltaic (PV) or solar electric technologies work. First used in about 1890, the word has two parts: photo, a stem derived from the Greek phos, which means light, and volt, a measurement unit named for Alessandro Volta (1745-1827), a pioneer in the study of electricity. So, photovoltaics could literally be translated as light-electricity. And that's just what photovoltaic materials and devices do; they convert light energy to electricity, as Edmond Becquerel and others discovered in the 18th Century.

Other Resources:

Q: How can we get electricity from the sun?

A: When certain semiconducting materials, such as certain kinds of silicon, are exposed to sunlight, they release small amounts of electricity. This process is known as the photoelectric effect. The photoelectric effect refers to the emission, or ejection, of electrons from the surface of a metal in response to light. It is the basic physical process in which a solar electric or photovoltaic (PV) cell converts sunlight to electricity.

Sunlight is made up of photons, or particles of solar energy. Photons contain various amounts of energy, corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, they may be reflected or absorbed, or they may pass right through. Only the absorbed photons generate electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the PV cell (which is actually a semiconductor).

With its newfound energy, the electron escapes from its normal position in an atom of the semiconductor material and becomes part of the current in an electrical circuit. By leaving its position, the electron causes a hole to form. Special electrical properties of the PV cell—a built-in electric field—provide the voltage needed to drive the current through an external load (such as a light bulb).

Other Resources:

Q: What are the components of a photovoltaic (PV) system?

A: A PV system is made up of different components. These include PV modules (groups of PV cells), which are commonly called PV panels; one or more batteries; a charge regulator or controller for a stand-alone system; an inverter for a utility-grid-connected system and when alternating current (ac) rather than direct current (dc) is required; wiring; and mounting hardware or a framework.

Other Resources:

Q: What's the difference between PV and other solar energy technologies?

A: There are four main types of solar energy technologies:
1. Photovoltaic (PV) systems, which convert sunlight directly to electricity by means of PV cells made of semiconductor materials.
2. Concentrating solar power (CSP) systems, which concentrate the sun's energy using reflective devices such as troughs or mirror panels to produce heat that is then used to generate electricity.
3. Solar water heating systems, which contain a solar collector that faces the sun and either heats water directly or heats a "working fluid" that, in turn, is used to heat water.
4. Transpired solar collectors, or "solar walls," which use solar energy to preheat ventilation air for a building.

Other Resources: For tips on saving energy and using solar and other renewable energy technologies in your home, please visit the U.S. Department of Energy's consumer information Web pages

To learn more about PV and solar hot water systems, please visit the Florida Solar Energy Center site.

Q: How long do photovoltaic (PV) systems last?

A: A PV system that is designed, installed, and maintained well will operate for more than 20 years. The basic PV module (interconnected, enclosed panel of PV cells) has no moving parts and can last more than 30 years. The best way to ensure and extend the life and effectiveness of your PV system is by having it installed and maintained properly.

Experience has shown that most problems occur because of poor or sloppy system installation. Failed connections, insufficient wire size, components not rated for dc application, and so on, are the main culprits. The next most common cause of problems is the failure of the electronic parts in the balance of systems (BOS): the controller, inverter, and protection components. Batteries fail quickly if they're used outside their operating specification. For most applications (uses), batteries should be fully recharged shortly after use. In many PV systems, batteries are discharged AND recharged slowly, perhaps over a period of days or weeks. Some batteries quickly fail under these conditions. Be sure the batteries specified for your system are appropriate for the application.

Other Resources:

Q: How does sunlight effect life on Earth?

A: All life on earth is supported by the sun, which produces an amazing amount of energy. Only a very small percentage of this energy strikes the earth but that is still enough to provide all our needs. A nearly constant 1.36 kilowatts per square meter (the solar constant) of solar radiant power impinges on the earth's outer atmosphere. Approximately 70% of this extraterrestrial radiation makes it through our atmosphere on a clear day. In the southwestern United States, the solar irradiance at ground level regularly exceeds 1,000 w/m². In some mountain areas, readings over 1,200 w/m² are often recorded. Average values are lower for most other areas, but maximum instantaneous values as high as 1,500 w/m² can be received on days when puffy-clouds are present to focus the sunshine. These high levels seldom last more than a few minutes. The atmosphere is a powerful absorber and reduces the solar power reaching the earth at certain wavelengths. The part of the spectrum used by silicon PV modules is from 0.3 to 0.6 mirometers, approximately the same wavelengths to which the human eye is sensitive. These wavelengths encompass the highest energy region of the solar spectrum.

Talking about solar data requires some knowledge of terms because on any given day the solar radiation varies continuously from sunup to sundown and depends on cloud cover, sun position and content and turbidity of the atmosphere. The maximum irradiance is available at solar noon which is defined as the midpoint, in time, between sunrise and sunset. Irradiance is the amount of solar power striking a given area and is a measure of the intensity of the sunshine. PV engineers use units of watts (or kilowatts) per square meter (w/m²) for irradiance. Insolation (now commonly referred as irradation) differs from irradiance because of the inclusion of time. Insolation is the amount of solar energy received on a given area over time measured in kilowatt-hours per square meter (kwh/m²) - this value is equivalent to "peak sun hours". Peak sun hours is defined as the equivalent number of hours per day, with solar irradiance equaling 1,000 w/m², that gives the same energy received from sunrise to sundown. In other words, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the sun shone for six hours with an irradiance of 1,000 w/m². Therefore, peak sun hours corresponds directly to average daily insolation given in kwh/m². Many tables of solar data are often presented as an average daily value of peak sun hours (kwh/m2) for each month. Insolation varies seasonally because of the changing relation of the earth to the sun. This change, both daily and annually, is the reason some systems use tracking arrays to keep the array pointed at the sun. For any location on earth the sun's elevation will change about 47° from winter solstice to summer solstice. Another way to picture the sun's movement is to understand the sun moves from 23.5° north of the equator on the summer solstice to 23.5° south of the equator on the winter solstice. On the equinoxes, March 21 and September 21, the sun circumnavigates the equator. For any location the sun angle, at solar noon, will change 47° from winter to summer.

The power output of a PV array is maximized by keeping the array pointed at the sun. Single-axis tracking of the array will increase the energy production in some locations by up to 50 percent for some months and by as much as 35 percent over the course of a year. The most benefit comes in the early morning and late afternoon when the tracking array will be pointing more nearly at the sun than a fixed array. Generally, tracking is more beneficial at sites between 30° latitude North and 30° latitude South. For higher latitudes the benefit is less because the sun drops low on the horizon during winter months.

For tracking (structures that follow the sun across the sky by various mechanisms, thereby increasing the energy captured from the sun) or fixed arrays, the annual energy production is maximum when the array is tilted at the latitude angle; i.e., at 40°N latitude, the array should be tilted 40° up from horizontal. If a wintertime load is the most critical, the array tilt angle should be set at the latitude angle plus 15° degrees. To maximize summertime production, fix the array tilt angle at latitude minus 15° degrees.

Using inaccurate solar data will cause design errors, so you should try to find accurate, long-term solar data for your system location. These data are becoming more available, even for tilted and tracking surfaces. Check local sources such as solar system installers, universities, airports, or government agencies to see if they are collecting such data or know where you might obtain these values. If measured values on a tilted surface are not available, you may use the modeled data here. Data for fixed and single-axis tracking surfaces at three tilt angles (latitude and latitude ±15°) are provided. Two-axis tracking data are given also, as well as a set of world maps that show seasonal values of total insolation at the three tilt angles. All data are in units of kilowatt-hours per square meter. This is equivalent to peak sun hours—the number of hours per day when the sun's intensity is one kilowatt per square meter.

Other Resources:

Q: How long do PV systems last?

A: A well-designed and maintained PV system will operate for more than 20 years. The PV module, with no moving parts, has an expected lifetime exceeding 30 years. Experience shows most system problems occur because of poor or sloppy installation. Failed connections, insufficient wire size, components not rated for dc application, and so on, are the main culprits. The next most common cause of problems is the failure of electronic parts included in the Balance of Systems (BOS) - the controller, inverter, and protection components. Batteries will fail quickly if they are used outside their operating specification. In most applications, batteries are fully recharged shortly after use. In many PV systems the batteries are discharged AND recharged slowly, maybe over a period of days or weeks. Some batteries will fail quickly under these conditions. Be sure the batteries specified for your system are appropriate for the application.

Other Resources:

Q: How much electricity does a photovoltaic (PV) system generate?

A: A 10% efficient PV system in most areas of the United States will generate about 180 kilowatt-hours per square meter. A PV system rated at 1 kilowatt will produce about 1800 kilowatt-hours a year. Most PV panels are warranted to last 20 years or more (perhaps as many as 30 years) and to degrade (lose efficiency) at a rate of less than 1% per year. Under these conditions, a PV system could generate close to 36,000 kilowatt-hours of electricity over 20 years and close to 54,000 kilowatt-hours over 30 years. This means that a PV system generates more than $10,000 worth of electricity over 30 years.

Other Resources: Consumer's Guide to Buying a Solar Electric System. September 1999. NREL. (PDF 704 KB). Look on page 9 for a map titled, "Calculating Electricity Bill Savings for a Net-Metered PV System".
Download Acrobat Reader.

Q: What does energy conversion efficiency mean?

A: Some of the following documents are available as Adobe Acrobat PDFs. Download Acrobat Reader.

Energy conversion efficiency is an expression of the amount of energy produced in proportion to the amount of energy consumed, or available to a device. The sun produces a lot of energy in a wide light spectrum, but we have so far learned to capture only small portions of that spectrum and convert them to electricity using photovoltaics. So, today's commercial PV systems are about 7% to 17% efficient, which might seem low. And many PV systems degrade a little bit (lose efficiency) each year upon prolonged exposure to sunlight. For comparison, a typical fossil fuel generator has an efficiency of about 28%.

We're working on ways to convert more of the energy in sunlight to usable energy and increase the efficiency of PV systems, however. Some experimental PV cells now convert nearly 40% of the energy in light to electricity. In solar thermal systems (like solar water-heating roof panels), efficiency goes down as the solar heat is converted to a transfer medium such as water. Also, some of the heat radiates away from the system before it can be used.

Other Resources: EERE's Solar Yellow Pages. A list of directories of companies that make solar products, design, install solar systems, and companies that provide training and consulting services

DOE's Building America Program site provides information about how to reduce energy use in homes.

Links to DOE sites that provide information about solar energy.

NREL's High-Performance Building Research provides information about efforts to reduce energy consumption in residential and commercial buildings by integrating passive solar, energy efficiency, and renewable energy technologies.

Energy Savers: Tips on Saving Energy and Money at Home. (Brochure) August 1998. You can download copies of the brochure from this location. Hard copies of the brochure are also available through the EERE Clearinghouse, 1-800-DOE-3732.

Consumer's Guide to Buying a Solar Electric System. September 1999. NREL (PDF 155 KB).

SNL's Photovoltaic Program site provides information about the various applications of PV systems.

The Solar Electric House: A Design Manual for Home-Scale Photovoltaic Power Systems by Steven Strong and William Scheller. Sustainability Press. 1993. To order contact NC Solar Center at Box 7401, NCSU, Raleigh, NC 27695, 919-515-5778. The fee for the book is $21.95.

Home Power Magazine: The Hands-On Journal of Home-Made Power

ASES's Solar Today Magazine

The New Solar Electric Home: The Photovoltaics How-To Handbook — Joel Davidson. 1990. To order contact American Solar Energy Society, 2400 Central Ave., G-1, Boulder, CO 80301, 303-443-3130. The fee for the book is $18.95 for members and $16.95 for non-members.

Florida Solar Energy Center.

Solar Energy Industry Association.

Sustainable Buildings Industries Council – 202/628-7400

Passive Solar Energy for cooling

The following techniques use passive solar strategies to provide cooling:

Passive solar cooling can reduce or even eliminate the need for air conditioning in homes. At its simplest, passive cooling includes overhangs for south-facing windows, few windows on the west, shade trees, thermal mass and cross ventilation. Some of the same strategies that help to heat a home in the winter also cool it in the summer. For example, with a well-designed overhang, the south-facing windows that admit the low-angled rays of the winter sun are shaded from the high-angled summer sun. Thermal mass, which stores heat in the winter to release in the evening, works in reverse in the summer. The mass cools down in the evening and retains that coolness the next day, moderating the effects of high daytime temperatures.

Graphic courtesy of North Carolina Solar Center.

Passive solar design works by utilizing overhangs to shade a house during the heat of the summer and allow sunlight to penetrate the interior of the house during the winter.

Passive solar design utilizes energy efficiency

Energy efficiency minimizes the need for heating, cooling and electricity, solar or otherwise. Designers of solar homes use insulation levels that are higher than those found in typical construction and energy efficiency appliances and lighting.

Windows are up to twice as resistant to heat loss as those used in conventional construction. Air infiltration is also reduced by carefully sealing and caulking around window and door openings and under sill plates.

Adapted from "Consumer Guide to Solar Energy," K. Sheinkopf and S. Sklar, Bonus Books, Inc. and "Buildings for a Sustainable America Case Studies," Burke Miller Thayer, American Solar Energy Society.nesea.org

Passive Solar Energy For Heat

A "passive" solar house provides cooling and heating to keep the home comfortable without the use of mechanical equipment. This style of construction results in homes that respond to the environment.

For passive heating and cooling, the plan of the house, careful site selection and planning, construction materials, building features and other aspects of the home are designed to collect, store and distribute the sun's heat in winter; and to block the sun's rays in summer. Passive solar houses can be built in any architectural style and in any part of the country.

The following techniques use passive solar strategies to provide heat:

Direct Gain is radiant heat resulting from sunlight admitted directly to the living spaces through south-facing windows, which warms the interior surfaces (walls, furniture, floors, etc.). For direct gain, the south-facing window area must be sized for the climate, the type of window used and the amount of thermal mass in the home.

Graphics courtesy of North Carolina Solar Center.

Indirect Gain In a design that employs indirect gain, an attached sunspace or Trombe wall collects heat from the sun before transferring it to other spaces within the home. The air heated in a sunspace circulates naturally or with the aid of fans to other rooms.

Thermal Mass is any material in the home that absorbs and stores heat. Concrete, brick, tile and other masonry materials are the most common choices for thermal mass in a passive solar home, these materials absorb and release heat slowly and are easily and inexpensively integrated into the house design. They are most effective when dark colored and located in direct sunlight. The addition of thermal mass allows saved solar energy to heat the house at night or on cloudy days. The combination increases the performance and energy-saving characteristics of the home, generally for only a modest cost increase.

Adapted from "Consumer Guide to Solar Energy," K. Sheinkopf and S. Sklar, Bonus Books, Inc. and "Buildings for a Sustainable America Case Studies," Burke Miller Thayer, American Solar Energy Society.

Complete "How to" Use Wind Energy

We have harnessed the wind's energy for hundreds of years—from windmills that pump water or grind grain to today's wind turbines that generate electricity.

If you live on at least one acre of land with an ample wind resource, you can generate your own electricity using a small wind electric system. You can also use a small wind turbine for pumping water.

You may have the opportunity now or in the future to buy clean electricity from a wind power plant.

Small Wind Electric Systems

Small wind electric systems are one of the most cost-effective, home-based renewable energy systems. These systems are also nonpolluting.

If a small wind electric system is right for you, it can do the following:

• Lower your electricity bills by 50–90%
• Help you avoid the high costs of having utility power lines extended to a remote location
• Help uninterruptible power supplies ride through extended utility outages.

How a Small Wind Electric System Works

Wind is created by the unequal heating of the Earth's surface by the sun. Wind turbines convert the kinetic energy in wind into clean electricity.

When the wind spins the wind turbine's blades, a rotor captures the kinetic energy of the wind and converts it into rotary motion to drive the generator. The manufacturer can provide information on the maximum wind speed at which the turbine is designed to operate safely. Most turbines have automatic overspeed-governing systems to keep the rotor from spinning out of control in very high winds.

A small wind system can be connected to an electric distribution system (grid-connected) or it can stand alone (off-grid).

Evaluating a Potential Small Wind Turbine Site

A small wind energy system can provide a practical and economical source of electricity if the following apply to you:

• Your property has a good wind resource

• Your home or business is located on at least one acre of land in a rural area

• Your local zoning codes or covenants allow wind turbines

• You can determine how much electricity you need or want to produce

• It works for you economically, and you're comfortable with long-term investments

• Your average electricity bills are $150 per month or more

• Your property is in a remote location that does not have easy access to utility lines.

  Small Wind Electric System Components

  To capture and convert the wind's kinetic energy into electricity, a home wind energy system generally comprises the following:

  • A wind turbine (blades) attached to a rotor, generator/alternator mounted on a frame, and usually a tail

  • A tower

  • Balance-of-system components, such as controllers, inverters, and/or batteries.

    Installing and Maintaining a Small Electric Wind System

    With proper installation and maintenance, a small wind electric system should last up to 20 years or longer.

    Installation

    Before installing your system, you first need to do the following:

    • Find the best site
    • Size your wind turbine
    • Decide whether you'll have a grid-connected or stand-alone system
    • Understand your local zoning, permitting, and neighborhood covenant requirements.

    The manufacturer/dealer should be able to help you install your small wind electric system. Many people elect to install the systems themselves. Before attempting to install your wind turbine, ask yourself the following questions:

    • Can I pour a proper cement foundation?
    • Do I have access to a lift or a way of erecting the tower safely?
    • Do I know the difference between alternating current (AC) and direct current (DC) wiring?
    • Do I know enough about electricity to safely wire my turbine?
    • Do I know how to safely handle and install batteries?

    If you answered no to any of the above questions, you should probably choose to have your system installed by a system integrator or installer.

    Contact the manufacturer for help, or contact your state energy office and local utility for a list of local system installers. You can also check the yellow pages for wind energy system service providers.

    A credible installer may provide additional services such as permitting. Find out if the installer is a licensed electrician, and ask for references and check them. You may also want to check with the Better Business Bureau.

    Maintenance

    Although small wind turbines typically are sturdy and reliable machines, they do require some annual maintenance.

    • Check and tighten bolts and electrical connections as necessary.
    • Check machines for corrosion and the guy wires for proper tension.
    • Check for and replace any worn leading edge tape on the turbine blades, if appropriate.
    • Replace the turbine blades and/or bearings after 10 years if needed.

    If you do not have the expertise to maintain the system, your installer may provide a service and maintenance program.

U.S. Department of Energy