How Solar Power Works

Two ways to use sunlight

The sun delivers energy to the earth continuously, and there are two main ways to put it to use. Photovoltaic (PV) technology converts sunlight directly into electricity. Solar thermal technology uses sunlight to produce heat. Both are called solar power in everyday speech, but they work differently and suit different jobs.

How photovoltaic panels work

A solar panel is made of many solar cells, most commonly built from silicon, a semiconductor. The idea behind them is the photovoltaic effect:

1. Light hits the cell. Particles of light carry energy, and some of that energy is absorbed by the semiconductor.
2. The absorbed energy frees electrons from their atoms, allowing them to move.
3. The cell is built with a built-in electric field, created by treating two layers of silicon differently. This field pushes the freed electrons in one direction.
4. Metal contacts collect the moving electrons as an electric current, which flows through a circuit and can do work.

There are no moving parts and no fuel. The cells produce direct current (DC). Because homes and the electricity grid use alternating current (AC), an inverter converts DC into AC. A typical system therefore includes panels, mounting hardware, wiring, an inverter and often monitoring equipment. Some systems also add a battery so that surplus daytime energy can be used later.

Rooftop and utility-scale

PV comes in a range of sizes. Small rooftop systems supply a home or business, and what they do not use can sometimes be exported to the grid, depending on local rules and net metering arrangements. Large solar farms feed power into the grid at scale. The underlying technology is the same, but planning, cost and grid connection differ. Those thinking about a home system will want to look at the questions raised about rooftop solar before deciding.

How solar thermal works

Solar thermal captures heat rather than making electricity directly.

• Water heating. Collectors on a roof, often dark panels or glass tubes, heat a fluid that passes through a tank to warm domestic water. This is a long-established, relatively simple use.
• Concentrating solar power. Mirrors focus sunlight onto a receiver, heating a fluid to a high temperature. That heat creates steam to drive a turbine in the same way as a conventional power station. Some plants store the heat, for example in molten salt, so they can keep generating after sunset. This approach needs strong direct sunlight and is mainly built in sunny regions.

What affects how much a system produces

Output is never constant. The main influences include:

• Time of day and season. Panels produce nothing at night and less when the sun is low. Winter output at high latitudes is much lower than summer output.
• Weather. Clouds reduce output, though panels often still produce something in diffuse light.
• Angle and direction. Panels facing the sun at a suitable tilt gather more energy. The best direction depends on the hemisphere.
• Shade and dirt. Even partial shading of a panel can reduce output, depending on how the system is wired. Dust, snow and leaves matter too.
• Temperature. Panels typically become slightly less efficient when they get very hot, so a cool, sunny day can be better than a scorching one.
• Panel efficiency and aging. Commercial panels convert only a fraction of the light that hits them into electricity, and performance generally declines slowly over decades.

Because of these factors, solar farms tend to have a lower capacity factor than sources that can run around the clock. That figure describes yearly output compared with a theoretical maximum, and it varies by location.

Common limits and trade-offs

Solar is variable and follows the sun rather than demand, so it is often paired with energy storage, flexible plants and transmission to move power around. As more solar joins a grid, midday supply can exceed demand in some regions, while evening peaks must be met by other sources. Managing this is a task for grid operators and a significant planning topic.

Other considerations include the land needed for large installations, the materials and energy used in manufacturing, and the management of panels at the end of their life. Recycling methods are developing, and life cycle assessments are used to compare impacts, though results vary with the manufacturing location and energy mix used. Costs for panels have fallen substantially over the past decades, but total project costs still depend on installation, grid connection and local rules.

Safety and working with solar

Solar panels produce electricity whenever light reaches them, and systems can carry high direct-current voltages that are dangerous. Installation and repair should be done by qualified, authorized people following local electrical codes. Work at height on roofs adds further risk. If you want to understand the career side, a solar installer role is described in general terms elsewhere on this site, and training routes vary by country.

This article is general information, not engineering, financial or safety advice. Performance depends heavily on location and equipment.