Solar cell technology

Solar cell technology generates electricity from sunlight using the photovoltaic effect, in which light absorbed by a semiconductor frees electrons and drives them through an external circuit. Because the conversion is direct and involves no moving parts, photovoltaic systems are quiet, low-maintenance and produce no emissions while operating. They have grown from a niche power source for spacecraft and remote equipment into a major form of renewable energy generation.

The most common cells are made of crystalline silicon, available as single-crystal (monocrystalline) and multi-crystal (polycrystalline) types, which differ in appearance, cost and efficiency. Thin-film technologies use much thinner layers of light-absorbing material deposited on glass or flexible backing, trading some efficiency for lower material use and flexibility. A key figure of merit is efficiency: the fraction of the sunlight's energy that a cell turns into electricity, which for typical commercial silicon panels falls in roughly the high teens to low twenties as a percentage.

Cells produce only a low voltage individually, so they are connected in series and parallel to build modules, and modules are joined into larger arrays sized for the job, from a single rooftop installation to a utility-scale power station. Because a cell produces direct current, most systems include an inverter to convert it to alternating current for use in homes and the grid, and stand-alone systems may add batteries to store energy for night-time or cloudy periods. The electricity a panel yields depends on the available sunlight, the angle and orientation toward the sun, temperature and shading, all of which installers take into account when designing a system.

Frequently asked questions

What are solar panels usually made of?

Most panels use crystalline silicon, either monocrystalline or polycrystalline. Thin-film panels use thinner layers of other light-absorbing materials on a backing.

What does solar cell efficiency mean?

Efficiency is the percentage of the energy in the sunlight reaching a cell that is converted into electricity; typical commercial silicon panels convert roughly a fifth of it.

Why do solar systems need an inverter?

Solar cells produce direct current, but homes and the grid use alternating current, so an inverter converts the cell output into a usable form.