Energy from the sun can be used for many practical purposes, including generating electricity and heating water. In fact, using solar energy instead of fossil fuels to meet some of our energy needs reduces emissions of greenhouse gases and other pollutants. These emission savings depend upon many factors, including where you live, the type of solar technology used, and the amount of energy provided by these technologies. You can estimate the emissions benefits of using photovoltaics, solar water heaters and solar heated swimming pools.
When solar energy displaces other energy sources with higher emissions levels, it produces a benefit in the form of reduced emissions of pollutants. Take the case of a solar water heater displacing an electric water heater. In producing the electricity needed to operate an electric water heater, SO2, NOX, and CO2 are emitted.
However, since solar heating creates no emissions,replacing an electric water heater with a solar water heater reduces emissions by the amount that would have been generated in providing power to the electric water heater.
The Solar Power Calculator estimates SO2 and NOX emission reduction benefits using information from the Emissions and Generation Resource Integrated Database (E-GRID), which provides data on actual emissions associated with electric power generated by US utilities. Carbon dioxide emission reductions are based on a model that simulates marginal reductions in electricity use. In the calculator, emission factors (expressed in terms of pounds of pollutant per kWh of electricity) are multiplied by reduced electricity use.
Solar Energy Technologies
One technology for transforming the sun's energy into electricity is photovoltaic (PV) panels. Sunlight strikes the panels, causing electron movement between different types of materials within them, thus producing electricity.
PV panels can be used for both small and large applications. Many residential and commercial consumers have chosen to install PV panels on the roofs of their homes and buildings, generating electricity for their own use. On average, each kW of installed PV capacity can generate 150 kWh of electricity each month1.
Some electricity providers use PV panels to generate electricity, which is then sold to customers. These PV panels are the same technology installed on the roofs of homes and businesses, but electricity providers connect many cells to form large "arrays" of photovoltaics with greater capacity to produce electricity.
Solar Water Heaters
Solar water heaters harness the sun's energy and use it directly for heating water. The solar energy reduces the need for electricity and other energy sources traditionally used for this purpose. Heating water is very energy intensive – about 25 percent of an average household's electricity consumption is devoted to this purpose2.
Solar water heaters are typically intended for use in individual homes or businesses. According to the Florida Solar Energy Center, a water heater's capacity should be sufficient to provide 20 gallons of hot water per day for each adult and 15 gallons per day for each child living in the household. Water heaters are available in standard sizes of 40, 52, 66, 82, 100, and 120 gallons.
Visit DOE for more information on solar water heaters.
Solar Heated Swimming Pools
Solar heated swimming pools make use of the sun's energy to maintain a comfortable temperature for swimming, typically about 78 degrees Fahrenheit. For most applications, simple solar panels are located on a roof or adjacent to the pool, facing within 45 degrees of due south. The pool's filtration system pumps water from the pool through pipes in the solar collection panels, heating the water before its return to the pool. An array of solar panels approximately equal to half the surface area of the pool should raise the pool temperature by about 5 degrees Fahrenheit, and larger arrays can be expected to provide greater temperature increases.3
When using the solar heated swimming pool option in the Environmental Benefits Calculator, please remember that the resulting emission savings are only estimates, which are based upon regional climatic conditions. Many factors will affect the actual energy savings realized at your pool, including the intensity of solar radiation, weather conditions, and length of your swimming season. To review the assumptions used in calculating the estimates provided by this calculator, please visit our background section. You can improve the quality of energy savings estimates by downloading the Department of Energy's Energy Smart Pools
software, which allows you to enter specific information about your pool, location, and swimming habits, and calculates your energy savings based upon those factors; or, you can contact a local pool care professional for information about solar pool heating in your area.
Using solar water heaters to heat swimming pools and spas is very cost-effective. Payback can be as low as 2 years, and utility bills are much lower than they would be using a conventional heating system.
The pool's existing filtration system pumps water through the solar collectors, and the collected heat is transferred into the pool. Because solar pool-heating collectors operate just slightly warmer than the surrounding air temperature, these systems typically use inexpensive, unglazed low-temperature collectors made from specially formulated plastic materials. Glazed (glass-covered) solar collectors usually are not used in pool-heating applications, except for indoor pools, hot tubs, or spas in colder climates. In some cases, unglazed copper or copper-aluminum solar collectors are used.
Off-the-shelf packages are generally appropriate, and maintenance of solar pool-heating systems is minimal. The systems are pre-engineered, and can be sized for any pool by adding additional solar panels until an adequate square footage of solar collector area is achieved.
The only moving part on a solar pool-heating system is the diverting valve. This valve controls whether or not the water circulates through the collector loop. When the collector temperature is sufficiently greater than the pool temperature, the water is diverted from the filter systems through the collector loop. The water bypasses the solar collectors during nighttime or cloudy periods. Some smaller systems are operated manually or with timers, but larger systems are operated by electronic sensors and controls.
Adding a swimming pool cover will further enhance the temperature of a swimming pool, and should be considered along with the solar pool-heating system to prevent loss of heat to the atmosphere.
The market for solar pool-heating systems has been strong over the years, with approximately 25,000 systems sold in the United States This number represents about one-fifth of all pool heaters sold annually. Solar pool heaters often pay for themselves in 2–4 years when replacing a conventional pool heater. However, in many cases solar systems are added to existing unheated pools, allowing the owners to make use of their pool for several additional weeks or even months each season
Written by: Environmental Protection Agency
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