How Do Solar Panels Work? Turning Sunlight Into Electricity

On rooftops, in fields and even on calculators, dark blue and black panels quietly turn sunlight into electricity, with no moving parts, no noise and no fuel. Solar power is now one of the cheapest sources of electricity in history. But how can a flat sheet of glass and silicon make electricity from light?

The photovoltaic effect

Light is made of tiny packets of energy called photons. When a photon hits certain materials, it can transfer its energy to an electron and knock it free from its atom. If those freed electrons can be pushed to flow in one direction, you have an electric current. This is the photovoltaic effect, “photo” meaning light and “voltaic” meaning electricity.

Inside a solar cell

Most solar cells are made of silicon, the same element used in computer chips and found in sand. A cell is a thin wafer with two layers:

• The top layer is treated, or “doped”, with a small amount of an element such as phosphorus, which gives it extra electrons. This is the n-type layer.
• The bottom layer is doped with an element such as boron, which leaves gaps, called holes, where electrons are missing. This is the p-type layer.

Where the two layers meet, the p-n junction, electrons and holes rearrange themselves and create a built-in electric field. It acts like a one-way gate.

When sunlight knocks electrons loose, this field sweeps them towards the top of the cell and holes towards the bottom. Thin metal lines on the surface collect the electrons, which then flow through an external circuit, powering a lamp or charging a battery, before returning to the bottom of the cell. As long as light shines, the flow continues.

From panel to plug

A single cell produces only about half a volt. A panel connects dozens of cells to produce a useful voltage. Panels produce direct current (DC), while homes use alternating current (AC), so an inverter converts it. Extra electricity can charge batteries or be fed into the power grid.

How efficient are solar panels?

Not every photon produces electricity. Some light is reflected, some photons have too little energy to free an electron, and photons with too much energy waste the excess as heat. Typical rooftop panels today convert about 20 to 23% of sunlight into electricity. The best single silicon cells in the laboratory reach about 27%, close to silicon’s theoretical limit of about 30%.

To go higher, researchers stack layers of different materials, each tuned to a different part of the spectrum. Such multi-junction cells have passed 47% in the laboratory, but they are expensive and used mainly in spacecraft and special systems. Newer materials called perovskites are being combined with silicon to raise efficiency at lower cost.

Light, not heat

Solar panels need light, not warmth. In fact, they become slightly less efficient as they heat up, so a cold, bright spring day can be better than a scorching summer afternoon. They still produce some electricity on cloudy days, but none at night.

In short

• Solar panels use the photovoltaic effect: light knocks electrons loose.
• Cells are made of two layers of silicon that create a built-in electric field.
• The field pushes electrons one way, producing direct current.
• An inverter converts it into the alternating current used at home.
• Rooftop panels convert about 20–23% of sunlight; lab cells have passed 47%.
• Panels need light, not heat, and work best on cool, sunny days.