kWh kWp, kW vs kWh: What do these terms mean?

kWh kWp, kW vs kWh: We see these terms in solar related content ALL the time. But are you 100% certain about what do they stand for?

kW: A solar system’s capacity (or how much energy it can make) will be rated in kilowatts (kW)…

So a larger system, one that is capable of powering a higher amount of electricity consumption, will have a higher capacity, quoted in kW. There will be more panels needed to make more power and therefore they will take up more space on the roof.

A kilowatt (kilo – means a thousand) is 1,000 watts so 1 kW (one kilowatt) is usually about 4 panels. That’s because these days a typical panel often has a capacity of 250 watts, and 4 X 250=1,000 watts; 1 kW.

(But plenty of panels are also made with a 200-watt capacity, in which case and so you would estimate five 200 watt panels for each kW of capacity you want.)

This ball park view is useful in sizing up your roof for solar. Since panels are about 3 feet by 6 feet, and a foursome – or say a 6 foot by 12 foot area – make 1 kW; you can get a pretty general sense for how much capacity, in kW (or how many kilowatts) your roof could handle.

So a bigger solar “power station” takes more space, and makes more power, and has a higher number in kW.

Got that, right?

What does kWh stand for?: ….we produce electricity in units called kilowatt-hours (kWh)

So now for the tricky part…. The word kilowatt-hours has confused many, with its suggestions of some kind of fancy math, and algebraic equations involving candle power etc, leading to complete brain shutdown, and it is really not necessary.

Try to substitute the word “units” for kWh, and you will have no trouble understanding kWh. You use power in units. If you run 9 big screen TVs full time all month, you’ll use more units of power than if you have one. Duh.

Most electric utilities charge you by how many kWh units you use each month (or in Australia, each quarter, one big reason that so many Australians go solar: once you see how this money racks up, it kind of compels action to get solar instead!)

Sometimes utilities reveal that info on the bill, in kWh, and separately list all the other things you are charged for, like them taking apart their old nuclear plants, or fixing wires when a squirrel eats them (No kidding. Squirrels are worse than terrorists when it comes to causing blackouts).

But other power companies use the much less confusing term “units” of electricity.

More: details on solar panel kWh.

kW vs kWh

The difference between kW and kWh is simply adding a time dimension. kW is a measure of how much energy can be produced, and kWh is what we end up with after some amount of time. 10 kW of power output over 10 hours is 100 kWh.

kWp: …and it will have a maximum power rating in peak kilowatts (kWp)

This has been likened to the horsepower rating in cars.

The peak power rating on a solar panel represents the most power that it would produce under ideal conditions for solar production; in other words, between 11 and 1PM on a sunny day, when the temperature is not too hot – solar panels would really to be no more than 110 degrees F and ideally between 65 and 85 degrees, and of course, when there is no snow cover.

Manufacturers put the kWp on the data specs for the panels, so you can compare between manufacturers for the best kWp ratings. A higher number is better.


  • by Understand Solar
  • |
  • February 2, 2016

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