How do solar panels work?

The photovoltaic effect is at the root of how solar cells turn sunlight into electricity. Here's a simplified explanation of how it all works.

Photo of a solar panel farm
Solar panels in Lincoln, Nebraska. (American Public Power Association)

If you stick some solar panels on your roof, they’ll generate clean electricity for 25 years or even more.

They don’t make noise, generate smoke, or move. All they do is silently turn sunlight into electricity. Seems pretty magical, no?

It is a little bit magical, but it’s also good old physics and chemistry. Here’s a quick explanation of how it works.

How is a solar cell constructed?

The essential component of a solar panel is the solar photovoltaic cell. Edmond Becquerel discovered the photovoltaic effect in 1839 using silver bromide. Today, most solar cells are made using crystalline silicon.

Here’s a basic diagram of a solar photovolatic cell:

Example of solar conduit
Diagram of a solar cell

Here’s a few terms to know:

Sunlight is made of photons, which are elementary particles.

An electron is also an elementary particle, and the outermost part of an atom. Electricity is simply the movement of electrons through a conductor.

A semiconductor is a material with electrical conductivity between that of an insulator and a conductor. A solar cell consists is made of two types of semiconductors: a p-type semiconductor has a positive charge while an n-type semiconductor has a negative charge.

The p-n junction prevents movement of electrons between the two semiconductor layers.

The top and bottom electrical contacts are conductors typically made of aluminum or copper. The top contacts often consist of very thin wires known as fingers and a few thicker wires known as busbars. These are the visible lines you may see on the front surface of a solar cell. These need to be thin in order to block as little incoming light as possible.

How does a solar cell make electricity?

Incoming photons from sunlight supply the energy needed to turn the semiconducting material of a solar cell into a conductor. When photons strike the cell, they excite electrons in the semiconducting material. If a wire is connected to the top and bottom conductors, the electrons are able to move between the p and n layers of the cell.

Those excited electrons are electricity, which you can use to do useful work, like charge a battery. If you have a few million cells, you can power a whole city.

How is a solar panel made?

A solar panel is made of dozens of individual solar cells. For a panel intended for the residential market, there might be 60 cells, but it depends on the size and voltage of the cells.

A single solar cell might produce only half a volt of electricity, which isn’t high enough to be useful for household use. When dozens of them are wired in series, their voltages are combined so that the panel might end up between 40 and 70 volts.

The top layer of a solar panel is tempered glass which usually includes an anti-reflective coating to allow more light through. Beneath that are the solar cells, which are laid out in a grid and wired together.

This electrical layer is sandwiched by a clear encapsulant, which might be made of acetate.

All of this sits on top of a backsheet which is usually made of plastic. The backsheet is usually white but is sometimes black for aesthetic reasons.

A durable metal frame holds these layers together. Corrosion-resistant and lightweight aluminum is the material of choice, but some manufacturers are exploring lower cost stainless steel as an alternative.

Finally, a junction box with industry-standard MC4 connectors provides the electrical connection to the panel.

It’s not actually magic, but is still pretty magical

Solar cells seemingly create electricity out of nothing, which is why some people are enthusiastic about making more electricity this way versus digging stuff out of the ground and burning it.

And the technology keeps getting better. The diagram of the solar cell above is a simplified view of one type of silicon cell, but there’s always new developments happening. Click on the panel technology tag below to read articles about some of the latest ways that solar manufacturers are trying to create cheaper and more efficient panels.

#Panel Technology #Basics

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