Solar energy

Solar energy refers to the light and heat carried by solar radiation and the technologies that capture it for human use. Two major approaches to producing electricity are photovoltaics (PV) and concentrating solar-thermal power (CSP). PV makes electricity directly from light; CSP first gathers sunlight as heat. Solar technologies can be built in small systems serving individual buildings or in large plants connected to an electricity network, and solar heat can also support industrial processes.

A PV cell is a semiconductor device. When it absorbs photons from sunlight, electrical charges are set in motion and a voltage develops across the cell. Individual cells produce modest amounts of power, so manufacturers connect them into protected modules; modules can then be arranged into larger arrays. A complete system also includes mounting and electrical equipment. Since PV modules produce direct-current electricity, an inverter or other power electronics convert it to the alternating current used by most buildings and electricity grids. This modular design allows PV to serve anything from small off-grid uses to rooftop and utility-scale systems.

CSP plants use mirrors to direct sunlight onto a receiver, where a fluid or other medium is heated. The captured heat can produce steam to turn a turbine and generator, or supply heat directly to some industrial processes. Unlike PV, which converts light into electrical current at the cell, CSP converts sunlight to heat before producing electricity. Thermal storage can retain some collected heat for later use, including periods after sunset; the amount of heat available depends on system design and the sunlight collected.

The amount of solar energy available changes with time of day, season, cloud cover, dust and shading. As a result, solar generation does not always coincide with demand. Batteries and thermal storage can shift some energy to other times, while broader power-system measures—such as stronger grids, flexible generation and demand response—help balance variable supply. The International Energy Agency emphasizes that integrating growing shares of solar and wind requires planning across the power system rather than relying on a single storage technology.

Photovoltaic panels generate electricity without air emissions while operating, and solar heat can displace heat otherwise supplied by burning fuels. These operational benefits do not mean that solar equipment has no lifecycle impacts: panels and associated components must be manufactured, maintained and eventually retired. The U.S. Environmental Protection Agency notes that end-of-life panels need safe management and that some may be subject to hazardous-waste rules under U.S. law. Reuse, material recovery and recycling can reduce waste, but collection systems and regulations differ by place.