What Is Solar Power?

Solar power is electricity generated from sunlight through the conversion of solar radiation into electrical energy. It encompasses two principal technology branches: photovoltaic (PV) systems, which convert light directly to electricity via the photovoltaic effect in semiconductor cells, and concentrating solar-thermal power (CSP) systems, which focus sunlight to heat a working fluid that drives a conventional steam or gas turbine. Both approaches exploit the same primary resource, incoming solar irradiance, but differ fundamentally in their physical mechanisms, cost profiles, and grid-integration characteristics. Solar power has become the fastest-growing source of new electrical generation capacity globally, driven by sustained cost reductions in PV module manufacturing and the scaling of utility-level installations.

The disciplines informing solar power include semiconductor physics, power electronics, thermodynamics, and electrical grid engineering. Solar power connects closely with energy storage, since its output is intermittent, and with transmission infrastructure, since the best solar resources are often geographically distant from major load centers.

Photovoltaic Power Systems

Photovoltaic power systems assemble solar panels, inverters, racking, and grid-interconnection equipment into installations that range from a few kilowatts on residential rooftops to hundreds of megawatts at utility-scale solar farms. Individual PV cells produce DC current; string, central, or microinverters convert this to AC at grid-compatible voltage and frequency. Modern monocrystalline silicon modules achieve commercial efficiencies of 20-23 percent, while emerging perovskite-silicon tandem cells have exceeded 30 percent in research conditions. Maximum power point tracking (MPPT) algorithms, implemented in inverter firmware, continuously adjust the operating point of the PV array to extract maximum power under varying irradiance and cell temperature. Single-axis tracking systems, which rotate panels to follow the Sun's daily path across the sky, increase annual energy yield by 15-25 percent compared to fixed-tilt installations at similar cost.

Concentrating Solar Power

Concentrating solar-thermal power systems use mirrors or lenses to focus direct normal irradiance (DNI) onto a small receiver, generating heat at temperatures from 300 to over 1000 degrees Celsius depending on the collector design. Parabolic trough systems, the most commercially mature CSP technology, focus sunlight onto a linear receiver tube carrying synthetic oil or molten salt; this heated fluid generates steam to drive a Rankine cycle turbine. Power tower systems (central receivers) use a field of individually tracking flat mirrors called heliostats to concentrate DNI onto a centrally located receiver atop a tower. The U.S. Department of Energy's Concentrating Solar-Thermal Power program is pursuing Generation 3 CSP designs that target system costs below $0.05 per kilowatt-hour by operating at supercritical CO2 power cycle temperatures. DOE CSP Basics provides a foundational overview of collector types, working fluids, and power cycle configurations.

Grid Integration and Storage

Integrating large quantities of solar power into electricity grids requires managing the variability introduced by cloud cover, diurnal cycles, and seasonal changes in solar angle. Battery storage, particularly lithium-ion systems, is increasingly paired with utility-scale PV to provide several hours of dispatchable generation. CSP systems offer an intrinsic advantage in this respect: thermal energy storage using molten salt can hold heat at high temperature for 10 or more hours, allowing CSP plants to generate electricity after sunset and shift output to evening peak-demand periods. NREL's CSP research program investigates advanced storage media, receiver designs, and power cycles to improve CSP dispatchability and reduce costs. On the transmission side, high-voltage direct-current (HVDC) lines are used to move solar generation from sunny, land-rich regions to distant urban load centers.

Applications

Solar power has applications across a wide range of sectors, including:

• Utility-scale electricity generation through photovoltaic farms and CSP plants
• Residential and commercial rooftop PV with grid interconnection
• Off-grid power for remote communities, communications, and water pumping
• Space power systems for satellites and planetary missions
• Hybrid microgrids combining solar, storage, and diesel backup for island grids
• Solar-powered desalination for freshwater production