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

A: 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 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.

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.

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.

Q: How is a solar electric system designed, installed, and maintained?

A: You could install a photovoltaic (PV) or solar electric system yourself. But to avoid complications or injury, you will probably want to hire a reputable professional contractor with experience in installing solar systems. PV systems have few moving parts, so they require little maintenance. The components are designed to meet strict dependability and durability standards so they can stand up to the elements. However, they are fairly sophisticated electric systems, so installation usually requires the knowledge and experience of a licensed electrical equipment contractor. Although the initial cost for a PV system can be relatively high, by taking advantage of available financing, a complete system will pay for itself in a short time. Many PV panels have a life expectancy of 30 years or more! And many utilities are realizing that reduced utility-generated electricity demand is one of the benefits of PV systems, and some offer incentives to building owners to install PV.

 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 exist and these plants have been operating reliably for more than 15 years.

Q: What's the difference between concentrating solar power (CSP) and other solar technologies?

A: They all make use of the abundant energy of sunlight. But they differ in the ways that they capture and use solar energy to produce heat or electricity. Most solar water- and space-heating technologies, for example, use sunlight directly to produce heat rather than using the sun's heat to produce steam that drives a generator to produce electricity, the way CSP does. Electricity can also be generated by photovoltaic (PV) systems. These technologies convert sunlight directly to electricity using the semiconductor materials in solar panels.

Q: How often do you have to clean the collector?

A: In January 2003, an experimental hybrid solar lighting (HSL) system was cleaned for the first time. It had been installed in September 2002. The system's performance improved approximately 5% after the primary mirror, secondary mirror, and fiber end-faces were cleaned (about a 5-minute task). This indicates that cleaning the mirrors and end-faces at six-month intervals should be sufficient to keep a typical installation operating well.

Source: US Dept. of Energy