How Does Sunlight Become Electricity?

Step 1 of 5

Light arrives in packets, not as a stream.

Sunlight behaves like a hail of tiny parcels of energy. That matters here, because one parcel can do one specific job inside the cell.

Step 2 of 5

A packet can knock one electron loose.

Silicon holds its electrons at a fixed price. A packet carrying at least that much energy frees one; a weaker packet does nothing at all.

Step 3 of 5

The layers make loose electrons go one way.

The silicon is deliberately spoiled with different impurities top and bottom. That builds a one-way slope, so freed electrons drift in a single direction.

Step 4 of 5

Cells are wired in long rows to be useful.

A single cell only manages about half a volt, which runs nothing. Sixty of them in series add up to a voltage worth wiring into a house.

Step 5 of 5

Shade and heat both cut the output.

Cells in series all carry the same current, so one shaded cell throttles the whole row. Heat separately weakens the voltage each cell can produce.

A good rooftop panel converts about 20% of the sunlight landing on it, and bright midday sun delivers roughly 1,000 watts per square metre.