How Solar Panels Work: From Photons to Electricity

The Photovoltaic Effect

A solar panel generates electricity through the photovoltaic effect — the production of voltage and electric current in a material when it is exposed to light. This phenomenon was first observed by French physicist Edmond Becquerel in 1839 and explained by Albert Einstein in 1905 (the work for which he received the Nobel Prize in Physics in 1921). At its core, the photovoltaic effect is a quantum mechanical process: photons — particles of light — carry energy that can be transferred to electrons, exciting them to higher energy states and making them available to do electrical work.

The most important material for practical photovoltaics is silicon — the second most abundant element in Earth's crust. Silicon's semiconductor properties make it ideal: it can be engineered to absorb sunlight efficiently and to support the directional electron flow that constitutes an electric current. Silicon solar cells power everything from pocket calculators to utility-scale power plants generating hundreds of megawatts.

How Silicon Solar Cells Work

A silicon solar cell is a p-n junction — a sandwich of two types of silicon with different electrical properties. In pure crystalline silicon, each atom shares electrons with four neighbors in a symmetric lattice. Solar cells use doped silicon: small amounts of impurity atoms are added to modify the electrical properties.

• N-type silicon: Doped with phosphorus (which has five outer electrons rather than silicon's four), creating excess electrons — negative charge carriers.
• P-type silicon: Doped with boron (which has three outer electrons), creating electron deficiencies called holes — positive charge carriers.

When n-type and p-type silicon are joined, electrons from the n-side diffuse across the junction and fill holes on the p-side, creating a thin region depleted of charge carriers — the depletion zone. This produces a built-in electric field pointing from n to p across the junction. When a photon with sufficient energy strikes the cell, it knocks an electron free from a silicon atom — creating an electron-hole pair. The built-in electric field sweeps the electron toward the n-side and the hole toward the p-side, preventing them from recombining. Connecting the two sides through an external circuit allows these charge carriers to flow as useful electric current.

From Cell to Panel to System

An individual silicon solar cell produces only about 0.5 to 0.6 volts — far too little for most applications. Practical solar panels are built by connecting many cells in series (to increase voltage) and parallel (to increase current). A standard residential solar panel contains 60 to 72 cells and produces around 300 to 400 watts under ideal sunlight conditions.

The solar cells are encapsulated between a tempered glass front (which must be transparent, durable, and anti-reflective), an ethylene vinyl acetate (EVA) encapsulant, and a polymer or glass back sheet, all held in an aluminum frame. The encapsulation protects the delicate cells from moisture, mechanical stress, and UV degradation — giving modern panels lifetimes of 25 to 30 years or more.

Panels produce direct current (DC), but the electrical grid and most appliances use alternating current (AC). An inverter converts DC to AC. Modern string inverters, microinverters (one per panel), and power optimizers offer different trade-offs between cost, efficiency, and performance under partial shading. A complete rooftop solar installation includes panels, mounting hardware, inverter(s), wiring, and often a meter that tracks energy produced and exported to the grid.

Types of Solar Cells

Several types of photovoltaic technology are commercially available, with different performance characteristics and applications:

• Monocrystalline silicon: Made from single-crystal silicon wafers, offering the highest efficiency (typically 20 to 23 percent for commercial panels) and the sleekest appearance. More expensive to manufacture than polycrystalline.
• Polycrystalline silicon: Made from multiple silicon crystals, producing the characteristic blue mottled appearance. Slightly lower efficiency (16 to 18 percent) but lower manufacturing cost. Market share has declined as monocrystalline prices have dropped.
• Thin-film technologies: Cadmium telluride (CdTe), copper indium gallium selenide (CIGS), and amorphous silicon deposited as thin layers on glass, plastic, or metal foil. Lower efficiency but lower material costs, better performance in diffuse light and high temperatures, and flexibility for applications on curved surfaces. CdTe panels from First Solar are price-competitive at utility scale.
• Perovskite solar cells: An emerging technology based on perovskite crystal structures that has achieved laboratory efficiencies exceeding 33 percent (in tandem with silicon). Not yet commercially available at scale due to durability challenges with moisture and heat, but the subject of intense research and development.

Efficiency: How Much Light Becomes Electricity?

Solar cell efficiency is the fraction of incident sunlight energy converted to electrical energy. Commercial silicon panels achieve 20 to 23 percent efficiency; laboratory records for single-junction silicon cells reach about 26 percent. These values are constrained by fundamental physics described by the Shockley-Queisser limit (about 33 percent for a single p-n junction under standard illumination) — photons with too little energy to excite electrons are wasted, and photons with too much energy lose their excess as heat.

Multi-junction solar cells stack multiple p-n junctions, each optimized for a different part of the solar spectrum, achieving efficiencies above 40 percent in laboratory conditions. These are currently too expensive for most terrestrial applications but are used in satellites and concentrated photovoltaic systems. Perovskite-silicon tandem cells are promising a near-term route to high efficiency at lower cost than multi-junction III-V semiconductor cells.

Solar Energy's Global Growth

Solar photovoltaics have experienced one of the fastest cost reductions in technology history. The cost of solar electricity has fallen by more than 90 percent since 2010, making solar the cheapest source of electricity ever produced in much of the world. Global installed solar capacity reached over 1,600 gigawatts by 2024 and is growing by hundreds of gigawatts per year. Solar now provides about 5 to 6 percent of global electricity, but its growth trajectory makes it central to the decarbonization of the power sector.

The integration of large amounts of variable solar generation into electricity grids creates challenges — particularly the need for storage or demand flexibility to balance supply and demand when the sun is not shining. Battery storage (primarily lithium-ion), grid interconnection, demand response, and ultimately green hydrogen are among the solutions being developed to manage a grid powered predominantly by solar and wind. The physics of photovoltaics makes solar energy fundamentally abundant: Earth receives approximately 10,000 times more solar energy each year than total human energy consumption.