How does a solar panel work?

Energy arriving

How does light become electricity without anything spinning?

A solar panel does not need a turbine or moving engine. Sunlight arrives in packets of energy called photons. When a solar cell absorbs a photon with enough energy, that energy can free an electron to move through the material.

Electrons are tiny particles with electric charge. The light supplies energy to charges already in the cell; it does not deliver a stream of new electrons from the Sun.

Inside the cell

What stops those charges from just wandering around?

Most solar cells use silicon, a material called a semiconductor. Carefully made layers create a built-in electric field that helps separate charges. Metal contacts collect them so they can travel through an outside circuit.

The light connection

Does a hotter panel mean more electricity?

It is the absorbed light that gives electrons energy, not the panel simply getting hot. Under otherwise similar conditions, stronger sunlight can free more charges each second and produce more current.

Shade reduces the light reaching the cells. Clouds can reduce output too, although scattered daylight can still produce electricity. Solar panels often work less efficiently when very hot, so sunny and hotter are not the same thing.

Completing the path

Why won’t a loose wire power the lamp?

Charges need a complete route through the wires and the device, then back to the cell. That closed path is a circuit. The flow of electric charge is called electric current. Open the circuit and the useful flow stops.

1. Absorb lightPhotons transfer energy.
2. Separate chargesThe cell’s field guides them.
3. Close the loopCurrent flows through a device.

The lamp receives energy and gives off light and heat. It does not use up the electrons: charge continues around the circuit.

Building bigger

Why is a rooftop covered in little rectangles?

One cell makes only a small amount of power. Connect many cells and you get a solar panel. Connect multiple panels and you get a solar array. Working together, they can supply more power than one cell alone.

That is why a small solar-powered gadget may need only a few cells, while a building needs much more collecting area. The required size depends on both the available sunlight and how much power the devices need.

Power at home

Can the panel’s electricity go straight into a wall outlet?

There is a conversion step. Panels produce direct current (DC), which flows in one direction. Homes and the power grid use alternating current (AC), which repeatedly changes direction. An electronic device called an inverter converts DC to AC.

A brief history of solar power

Solar cells had a space adventure before they became a rooftop sight.

Imagine sending a machine into space and then remembering you cannot pop over to change its batteries. Sunlight offered engineers a way to keep some spacecraft equipment powered.

1. 1839 · A laboratory clueScientists observed that light could produce an electrical effect. Turning that discovery into useful power would take more than a century of experiments.
2. 1954 · A useful silicon cellResearchers at Bell Labs demonstrated a silicon solar cell that converted about 6% of the sunlight’s energy into electricity. A laboratory effect was becoming a working power source.
3. 1958 · Sunlight goes to work in orbitVanguard 1 became the first solar-powered satellite. Its solar-powered radio kept transmitting for about six years. That is a long shift for a tiny power supply!

The same basic idea connects that satellite to a rooftop panel: light gives charges energy, and a circuit lets that energy do a job. Engineers kept improving the cells and finding new places to use them.