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.

Q: What is concentrating solar power?

A: The real powerhouse in CSP plants is focused sunlight. CSP plants generate electric power by using mirrors to concentrate (focus) the sun's energy and convert it into high-temperature heat. That heat is then channeled through a conventional generator. The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity. Within the United States, over 350MW of CSP capacity exists and these plants have been operating reliably for more than 15 years.

CSP systems can be small enough (Stirling systems as small as 10 kilowatts are under development) to help meet a small village's power needs. (For comparison, a typical U.S. home might require a system generating about 5 to 15 kilowatts to meet most of its power needs, according to some renewable energy experts.) CSP systems can also be much larger, generating up to 100 megawatts of power for use in utility-grid-connected applications. Some CSP systems include thermal storage to provide power at night or when it's cloudy. Others are combined with natural gas systems in hybrid power plants that provide power on demand.

The amount of power generated by a concentrating solar power plant depends on the amount of direct sunlight at the site. CSP technologies make use of only direct-beam (rather than diffuse) sunlight.

The amount of power generated by a concentrating solar power plant depends on the amount of direct sunlight at the site. CSP technologies make use of only direct-beam (rather than diffuse) sunlight.

Today's CSP systems can convert solar energy to electricity more efficiently than ever before. Utility-scale trough plants are the lowest cost solar energy available today and further cost reductions are anticipated to make CSP competitive with conventional power plants within a decade. So, CSP is a very good renewable energy technology to use in the southwestern United States as well as in other sunny regions around the world.

Q: How does a hybrid solar lighting (HSL) system work?

A: Imagine being able to light your home or office most of the day, and on most days, with sunlight, but not the kind that comes through the windows. That's what hybrid solar lighting (or HSL) systems are being developed to do. Prototype HSL systems are made up of roof-mounted concentrators that collect and separate the visible and infrared portions of sunlight. The visible portion of the light is distributed through large-diameter optical fibers to hybrid luminaires. (Hybrid luminaires are lighting fixtures that contain both electric lamps and fiber optics to distribute sunlight directly.) Unlike conventional electric lamps, the solar component of HSL produces little heat.

The remaining "invisible" energy in the sunlight, mostly infrared radiation, is directed to a concentrating thermo-photovoltaic (solar) cell that very efficiently converts infrared radiation into electricity. The resulting electric power can be directed to other uses in a building. When sunlight is plentiful, the fiber optics in the luminaires can provide all or most of the light needed in a particular area. But when there is little or no sunlight, sensor-controlled electric lamps turn on to maintain the desired illumination level.

Independent cost and performance models suggest the overall affordability of solar energy could be doubled or tripled by using this new hybrid approach. The multidisciplinary R&D effort involved in developing HSL includes several industrial and university partners. Other Resources: