How Do Solar Panels Work? The Photovoltaic Effect Explained

A solar panel has no moving parts, makes no noise and consumes nothing. Light goes in and electricity comes out. The mechanism responsible is over a century old in principle and still slightly surprising when you look at it closely.

Start with silicon

Silicon is a semiconductor — neither a good conductor like copper nor a good insulator like glass, but something in between whose conductivity can be controlled.

In pure crystalline silicon, each atom shares electrons with its neighbours in a rigid lattice. Those electrons are held in place. Nothing flows.

To make a solar cell, manufacturers deliberately introduce impurities. The process is called doping, and it is the foundation of the whole device.

Two types of doped silicon

N-type silicon is doped with an element having one more outer electron than silicon — phosphorus, typically. Each phosphorus atom slots into the lattice and contributes a spare electron with nowhere to bond. The material has surplus mobile negative charge.

P-type silicon is doped with an element having one fewer outer electron — usually boron. Each boron atom creates a vacancy in the bonding structure, called a hole, which behaves like a mobile positive charge.

Neither material is electrically charged overall. Both are neutral. The difference is what can move within them.

The junction: where the magic happens

Place n-type and p-type silicon in contact and something immediate occurs.

Surplus electrons from the n-side diffuse across into the p-side, where they fill holes. This leaves the n-side slightly positive near the boundary, having lost electrons, and the p-side slightly negative, having gained them.

The result is a built-in electric field across the junction — a permanent, self-established field that requires no battery and no external input. It exists purely because of how the two materials were joined.

This field points in a specific direction, and that direction determines everything that follows.

Adding light

Now shine light on the cell.

Light is made of photons. When a photon with sufficient energy strikes a silicon atom, it can knock an electron free from its bond, creating a mobile electron and leaving a hole behind. This is the photovoltaic effect.

Without the junction, that electron would simply wander and eventually recombine with a hole, releasing its energy as heat. Nothing useful would happen.

But the built-in field is there. It pushes the freed electron in one direction and the hole in the other. Charge accumulates on opposite sides of the cell, creating a voltage difference.

Connect a wire between the two sides and electrons flow through it to reach the holes. That flow is electric current, and anything placed in that circuit — a light, a pump, an inverter — is powered by it.

Why it is direct current

The field always points the same way, so electrons are always driven in the same direction. Current flows one way only: direct current.

Grids and most appliances use alternating current, which reverses direction many times per second. Bridging that gap is the inverter's job — which is why the inverter is a mandatory component of every grid-connected system and, as we discuss in our guide to choosing an inverter type, a decisive one.

The efficiency ceiling, and where losses come from

A silicon cell cannot convert all incoming sunlight, and the reasons are physical rather than engineering shortcomings.

• Low-energy photons pass straight through. A photon must carry at least the silicon bandgap energy to free an electron. Anything less contributes nothing.
• High-energy photons waste their excess. A photon with far more energy than required frees one electron and dumps the remainder as heat.
• Reflection. Some light bounces off the surface, which anti-reflective coatings reduce but never eliminate.
• Recombination. Some freed electrons meet holes before reaching the circuit.
• Resistance. The metal contacts collecting current have resistance, and they also shade part of the cell.

These combine into a theoretical limit for single-junction silicon cells in the low thirties of a percent, with commercial modules today typically in the low twenties. The remaining gap is narrower than most people assume, which is why efficiency improvements now come in fractions of a percent rather than leaps.

Heat is not the friend it appears to be

A common misconception deserves correcting: panels are powered by light, not warmth. Rising temperature actually reduces a cell's voltage and therefore its output.

This matters enormously in hot climates, where cell temperatures routinely run far above ambient. We cover the numbers in our explainer on solar panels in extreme heat.

From cell to module to array

A single cell produces a low voltage — roughly half a volt. Useful systems need much more, so:

• Cells are wired in series into a module, adding their voltages together.
• Modules are laminated behind glass with a backsheet and frame, for decades of weather protection.
• Modules are wired into strings, and strings into an array.
• The array feeds an inverter, which converts DC to AC for use or export.

The bottom line

A solar panel works because two deliberately contaminated pieces of silicon, placed in contact, create a permanent electric field — and because light can knock electrons loose for that field to push. There is nothing consumed and nothing moving. Everything else in a solar system exists to manage, convert and deliver what that junction produces.

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