Photovoltaic (PV) devices can be made from various types of semiconductor materials, deposited or arranged in various structures, to produce clean electricity at the buildilng site. There are two main types of materials used for solar cells: crystalline silicon -- by far the most common structure -- and thin films. PV devices capture the sun's energy and convert it directly to electricity.

• Grid-connected PV systems--the most common configuration--allow building owners to supply some of the power they need and use utility-generated power at night and on cloudy days. When the PV system supplies power to the grid as well as to a specific building or piece of equipment, the utility becomes a kind of storage device for PV-generated power. When that building requires less electricity than the PV array is generating, the excess can often be sold back to the utility through net metering, which is becoming more and more common throughout the nation. At the end of the month, a credit for electricity sold is deducted from charges for electricity purchased.
• PV with battery storage systems supply electricity in areas where utility power is unavailable or utility line extensions would be too expensive. PV systems with storage are a reliable source of power all over the world, providing electricity for critical loads such as computers, communications, emergency lights, sensors, switches, pumps, etc.
• Stand-alone PV systems are often best for buildings that don't have access to grid power or where it is too costly to hook up to because of the price of extending power lines. Stand-alone systems are also excellent for uses that don't require a lot of power, and for peak shaving air conditioners during high insolation periods.