How Solar Works

Sunlight becomes direct current

A solar panel is a sheet of individual cells wired together. Each cell is two ultra-thin slices of silicon, one treated so it has spare electrons and one so it is short of them, pressed together at a boundary called a p-n junction.

Sunlight arrives as photons — discrete packets of energy. When a photon reaches that junction it knocks an electron loose. Do that across billions of cells at once and the loose electrons flow in one consistent direction: a direct current. That is the whole photovoltaic effect. There are no moving parts, which is why panels are close to maintenance-free and silent.

Direct current becomes the electricity your house actually uses

Sockets and appliances run on alternating current, so the direct current from the panels has to be converted. That is an inverter's only job.

Where the inverter sits is one of the real design choices in a system. A string inverter is a single box, usually near the main service panel, handling the whole array. Microinverters or power optimizers sit behind each individual panel instead, so one shaded panel does not drag down its neighbours. Which approach suits a roof is a design decision, not a preference — the next module covers the trade-off.

What happens to the power you do not use

This is the part almost everyone has backwards. Solar production peaks in the middle of the day, which is often when a house is empty. The surplus is not wasted, and it does not mean going off-grid.

It flows back out to the grid, and a meter records it. Under net metering the utility credits you for what you exported and bills you only for the difference — hence "net". A system typically runs a surplus in summer and falls short in winter, and net metering is what lets those cancel out across a year.

The terms are set by each utility and each state, and they change. That is a question for the installation partner about your specific address and provider, not something any general page can answer.

Cloudy days, night, and winter

Output is roughly proportional to the light landing on the panels. Cloud reduces production; it does not stop it. Night stops it completely — there is nothing to convert.

"Peak sun hours" is the useful unit here: hours in which sunlight exceeds about 1,000 watts per square metre. A day with twelve hours of daylight might contain only four to six peak sun hours, and that middle block is where the great majority of a system's annual production comes from. In this region that is roughly 10am–5pm in summer and 11am–3pm in winter.

One practical consequence: shade outside those windows matters far less than people assume. A lot that is wooded on its eastern edge can still be a perfectly reasonable candidate.

The parts, named

Useful vocabulary for reading a proposal, and for knowing which question belongs to whom.

Modules (panels)

The sheets of solar cells. Rated in watts; an array is described by the sum, in kilowatts.

Racking and mounts

The hardware fixing the array to a roof, a ground frame, or a carport. Tilt legs can angle panels off a surface that is flatter or facing worse than ideal.

Inverter, microinverters, or optimizers

Direct current in, alternating current out. One central box, or one device per panel.

Main service panel

Your fuse box. A system needs free breaker slots and an adequate amperage rating; upgrading it is a real and sometimes surprising line item.

Meter

The utility's equipment. Under net metering it records energy flowing both directions.

Battery (optional)

Storage for use at night or during an outage. Not required for a grid-tied system, and it changes the economics — covered in the next module.