Kilowatts and kilowatt-hours sound almost the same. They're on every solar quote, battery brochure, EV spec sheet and power bill, and most people quietly mix them up. Here's the difference in about three minutes, followed by the same explanation in writing, with a few extras the video didn't have time for.
The short version
- A kilowatt (kW) is power: how fast energy is flowing right now.
- A kilowatt-hour (kWh) is energy: how much has flowed in total.
- kW × hours = kWh. Two kilowatts for three hours is six kilowatt-hours.
Tap and bucket
Think of a tap filling a bucket. The kilowatts are how far the tap is open. The kilowatt-hours are how much water ends up in the bucket.
A typical kettle draws about 2 kW while it's on. Boil it for three minutes, which is a twentieth of an hour, and you've used about 0.1 kWh. A 10-watt LED light uses very little power, but leave it on for a hundred hours and it has also used a full kilowatt-hour.
So power is the rate, and energy is the amount. Kilowatts multiplied by hours gives kilowatt-hours.
Solar panels: kW is the size, kWh is what you get
Fifteen panels at 440 watts each make a 6.6 kW system. That's the rate: the most they can produce at any moment, in strong midday sun, and heat and dust usually keep them a little below even that.
But the sun doesn't stay at full strength all day. On a clear day, that 6.6 kW system might make around 30 kWh. On a dull winter's day, maybe 8 kWh. Same panels, same kilowatts, very different kilowatt-hours. We go through the real numbers in how much power a 6.6 kW solar system produces per day, and how to size a system for your own home in what size solar system do I need?
You'll also see kWp, kilowatts peak, on solar quotes. It's the panels' rated output under standard test conditions: the same idea as kW, with the "peak" there to remind you it's a best case.
Home batteries: check both numbers
A home battery has both:
- kWh is the size of the bucket: how much energy it can store.
- kW is the size of the tap: how much it can power at once.
A battery with plenty of kWh but a small kW rating can run your house all evening, but not the oven, kettle and air conditioner at the same time. Check the usable kWh, not just the headline figure. We work through whether one pays for itself in is a home battery worth it?
Electric cars: kWh in the battery, kW at the charger
The car's battery is measured in kilowatt-hours. The charger is measured in kilowatts. A 7 kW home charger adds about 7 kWh to the battery every hour, a little less in practice because some energy is lost as heat. That makes charging times simple arithmetic: see how long it takes to charge an EV at home.
EV efficiency is usually given in kWh per 100 km (or miles per kWh): the energy it takes to travel a set distance, the electric version of litres per 100 km.
Your power bill: mostly kWh
Your electricity bill mostly charges for kilowatt-hours: the amount you used, not the rate. A few tariffs also charge for your peak kilowatts (a "demand charge"), which is where the difference really starts to cost money. Our guide to reading your electricity bill goes through every line.
kVA, for completeness
Some inverters, generators and business tariffs quote kVA (kilovolt-amperes). For most household equipment it's close to kW. The difference matters for motors and some commercial tariffs, but you can safely treat kVA as "roughly kW" at home.
One idea, every spec sheet
Rate and amount. Tap and bucket. Once that clicks, almost every number in home energy starts to make sense.
If there's a term that still confuses you, leave a comment on the video on YouTube and it might become the next one.