Cover: power and energy in one picture. The height of the curve is power, in kilowatts. The area under it is energy, in kilowatt-hours.

Let's get technicalNo. 03 · Language2 min read

The words, explained.

Solar has its own vocabulary. Here are the terms worth knowing, in the order you'll meet them.

01Power and energy

Nearly every confusion about solar starts with two units that sound alike and mean different things.

Kilowatt (kW): Power: how fast electricity is being made or used right now. A kettle draws about two kilowatts while it's on.
Kilowatt-hour (kWh): Energy: an amount. One kilowatt running for one hour. It is what your bill counts and what a battery holds.
System size: The rated power of all the panels added together, in kilowatts. A roof reaches it only briefly, in ideal conditions.

Kilowatts are how fast. Kilowatt-hours are how much.

Five words describe everything that happens between your roof, your home and the street.

Generation: What your roof makes. Also called production.
Consumption: What your home uses, wherever it came from.
Self-consumption: The part of your generation that your home uses as it's made. This is where most of the saving is.
Export: Generation your home didn't need, sent out to the grid.
Import: Electricity bought from the grid when the roof and the battery aren't enough.
Feed-in tariff: The credit your retailer pays for each kilowatt-hour you export. Far less than the price you pay to import one.

Sunshine is measured, and the measurements explain why the same system behaves so differently in January and June.

Peak sun hours: A day's sunshine expressed as hours of full-strength sun. Five peak sun hours doesn't mean five hours of daylight: it means the whole day delivered as much energy as five hours at full strength would.
Yield: Kilowatt-hours made for each kilowatt installed, over a day or a year. It lets you compare systems of different sizes fairly.
Bell curve: The shape of a clear day's generation: rising from sunrise, peaking around the middle of the day, falling away to sunset.

You don't need to be an electrician, but four terms come up in every design conversation.

DC: Direct current. What panels make and batteries store.
AC: Alternating current. What your home and the grid run on.
Inverter: The unit that turns DC into AC. A hybrid inverter also manages a battery.
DC-coupled and AC-coupled: Two ways to connect a battery. DC-coupled shares one inverter with the panels. AC-coupled has an inverter of its own, which makes it easier to add to a system that's already there.
Single-phase and three-phase: How your home is connected to the street. Three-phase homes can connect larger systems.

And three that appear on forms rather than on the roof.

Distributor: The company that owns the poles and wires in your street. It approves your connection and sets how much you may export.
Retailer: The company that sends your bill. You choose your retailer. You don't choose your distributor.
Export limit: The most your system may send to the grid at once, set by the distributor.

The terms make more sense with your own numbers beside them. Your project brief puts them there.