Solar Power
Anyone who has visited Florida in July knows that the sun can produce heat. And in 1839, French physicist Edmund Bequerel discovered that sunlight could also produce electricity (known as the photoelectric effect). Knowledge of the sun’s ability to produce both heat and electricity has led to the invention of numerous technologies for capturing the sun’s energy. The most common technologies produced and used in the United States today include photovoltaics, concentrating solar power (also known as solar thermal electric) systems, solar hot water systems, and passive solar building design.
Photovoltaics
Photovoltaic (PV) cells, also known as solar cells, produce electricity directly from sunlight. When a PV cell is exposed to the sun, the cell, which is made of semiconductor materials, absorbs a portion of the light that strikes it. If the energy from the absorbed light strikes electrons in the outer shell of an atom, these electrons are freed from their parent atoms. Free electrons can then travel into a circuit in the form of electricity. PV cells can be hooked together to meet many different types of electricity requirements, from pumping water to operating calculators and watches, and lighting homes and communities.
PV has traditionally been used in locations where it is expensive or impossible to send electricity through power lines. An increasing number of utility companies are experimenting with using PV to fill their small or more expensive power needs. Some homeowners and commercial building owners are integrating PV systems into their building designs to offset utility power demand and improve power reliability.
The growing demand for reliable electricity internationally has contributed to the growth of the U.S. PV industry—approximately 70 percent of PV systems manufactured in the United States are sold to other countries.
Concentrating Solar Power
Although the mechanics of each method differs, all three concentrating solar power (CSP) technologies—parabolic troughs, power towers, and parabolic dishes—use mirrors to focus incoming sunlight onto a receiver. The receiver collects the sun’s energy in the form of heat, which can then be used directly or converted into electricity using a generator.
These technologies are currently in different stages of development. Troughs have a proven track record as a technology that can function effectively for large-scale power needs (such as those of a utility company) and are currently the least expensive way to produce solar electricity. Power towers have also demonstrated an ability to function on a large, utility scale, while parabolic dish systems, still under development, show promise for small-scale projects.
CSP technologies have caught the attention of some U.S. utility companies, as well as others interested in tapping into the projected consumer demand for green power supplies, even though the cost of using these technologies to generate electricity is still somewhat high.
Solar Hot Water
Energy from the sun can also be used to heat water for buildings and swimming pools. Solar water heating systems for buildings typically include a solar collector, in which fluid is heated by the sun, and a storage tank, which holds the hot fluid after it has been heated by the collector. Systems using fluids other than water require the additional step of passing water through a heat exchanger to heat the water. Swimming pool systems are very simple; they generally consist of collectors made of black plastic or rubber through which pool water is pumped to be heated.
Advances in solar hot water technology for buildings have dramatically cut the cost of solar water heaters from about $.20 per kilowatt-hour (kWh) in 1980 to $.08 to $.10 per kWh in 2000. As a result, solar hot water systems are increasingly being installed in schools, hospitals, prisons, and other government-owned facilities across the country. However, the number of solar hot water systems purchased in the United States is still quite small compared to the number purchased in the rest of the world. In 1997, for example, Americans purchased approximately 25,000 systems. Of the systems purchased, the majority were for heating residential swimming pools.
Passive Solar Building Design
Building orientation, types of construction materials, glass selection, and architectural features all affect the overall energy performance of a building. For a passive solar building, designers consider these features early in the design process along with taking advantage of solar energy to heat and light a building. They also design the building to be cool in summer.
It may cost more to design a passive solar building, but the savings achieved from decreasing the size of the mechanical and electrical systems to heat/cool and light the building, as well as energy cost savings, more than make up the difference.
Jobs in Solar Power
Growth of the solar power industry creates high-wage, skilled jobs throughout the country for individuals with many different types of training. R&D groups at national laboratories, universities, and private companies develop and continually improve solar products to lower their costs and improve their reliability. Individuals employed in solar R&D generally have professional degrees in electrical, mechanical, and chemical engineering; materials science, and/or physics. Many of the people involved with technologies that are still under development, such as parabolic dish systems, focus on R&D.
As each technology progresses from the R&D phase toward full-scale commercialization, an increasing number of both professional and skilled workers are needed to sell, manufacture, design, install, and maintain equipment. The PV and solar hot water industries currently employ the majority of these workers, including electricians, engineers, technicians, and technical managers. As utility-scale CSP technologies become commercially viable, the CSP industry will eventually require an increasing number of these workers, as well as engineers and construction workers to design and build power plants. The passive solar industry involves many of these professions as well, but also employs architects and builders.
