Topics Physics and everyday science

How do solar panels make electricity?

Solar panels make electricity by using the energy in sunlight to push electrons through a circuit. Each panel is made of cells, usually silicon, built with two layers that are slightly different. When a photon of light with enough energy hits the silicon, it frees an electron. The built-in electric field where the two layers meet sends that electron one way, and a wire lets it travel around a loop and come back. That moving charge is direct current. This is called the photovoltaic effect.

What makes it interesting is how little moves and how much has to go right. There are no spinning parts and no fuel burned. But not every photon is useful: some lack the energy to free an electron, and others carry extra energy that is lost as heat. That is one reason a typical panel turns only a modest fraction of sunlight into electricity. Then there is the question of why the electrons do not simply fall back where they started.

An episode would start with the atoms in silicon and follow the energy to the outlet, including what the inverter does and where the losses are. It would also say what is still debated or depends on the setup. bre is an app whose hosts are AI, so they can be wrong, and you can press Talk to ask your own question mid-episode.

What a bre episode would cover

An outline of the episode bre would make for this question. Every episode is written fresh when you ask, so yours will differ.

  1. What sunlight actually carriesLight arrives as photons, each with a fixed amount of energy depending on its color. That energy is what a solar cell has to catch.
  2. Why silicon is the usual choiceSilicon holds its electrons loosely enough that light can free them, but tightly enough that they stay put in the dark. Other materials work too, with different trade-offs.
  3. The two layers and the built-in fieldThe cell has layers treated differently so an electric field forms where they meet. That field gives freed electrons a direction to go.
  4. A loop, like a pumpLight supplies the push, much as a pump drives water around a closed loop. The electrons circulate through the circuit and return to the cell; they are not used up.
  5. What gets lost along the wayPhotons without enough energy pass through unused, and extra energy in stronger photons turns into heat. This is a big part of why panels have limited efficiency.
  6. From panel to wall outletPanels make direct current, and an inverter converts it to the alternating current most homes use. We also look at why panels still work on cloudy days, only less well.

How the episode might open

A sample exchange between two of bre’s AI hosts, bre and Cal. Both are AI; this is written by AI, as every bre episode is.

  1. breAI host

    Here's the picture I keep coming back to: a flat, silent slab on a roof, no moving parts, and somehow your kettle boils. So where does the electricity actually come from?

  2. CalAI host

    The light. Sunlight is a stream of photons, and each one carries a little packet of energy. If a photon hits the silicon with enough energy, it knocks an electron loose. That's the whole trigger.

  3. breAI host

    But loose electrons just wander. Why don't they bump around and settle back where they started?

  4. CalAI host

    Because the cell is built in two layers, treated a bit differently, and an electric field forms where they meet. A freed electron gets steered one way across that boundary instead of falling back.

  5. breAI host

    So the field is the direction. What happens next?

  6. CalAI host

    You connect a wire from one side to the other, and the electrons travel around it as a current, then return to the cell. Think of a pump pushing water around a closed loop. Light supplies the push, and the electrons circulate rather than get used up.

  7. breAI host

    Okay, here's the part nobody tells you: I assumed every bit of sunlight gets used. Does it?

  8. CalAI host

    Not close. Some photons lack enough energy to free an electron, so they pass through. Others carry extra energy, and the surplus is lost as heat. That's a big reason panels convert only a fraction of the light.

Questions people also ask

Do solar panels work on cloudy days?
Yes, but they produce less. Clouds block part of the sunlight, so fewer photons reach the cells and less current flows. Panels also respond to light that is scattered through the clouds, so output drops rather than stopping. Exact output depends on the panel and how thick the cloud is.
Why do solar systems convert direct current into alternating current?
The panels themselves only produce direct current. A separate device called an inverter does the conversion. Homes and the power grid mostly use alternating current, so the inverter changes the panels' output to match what appliances and the grid expect.
What are solar panels made of?
Most are made of silicon, a common element found in sand, purified and shaped into thin cells. The cells are treated to form two layers and wired together under glass in a frame. Other materials exist, including thin-film types, with different costs and efficiencies.
Do solar panels make power at night?
No. Without light, there are no photons to free electrons, so a panel produces essentially nothing. Systems that supply power after dark rely on stored energy, such as batteries, or on a connection to the wider grid.

Related topics

More: all 300 topics, physics and everyday science, or the longer reads on /learn.

bre’s hosts are AI, and every episode is generated, so they can be wrong: check anything that matters. This page outlines what an episode would cover. It is for interest and learning, not medical, financial or legal advice.