This is the one that confuses everyone in my DMs, so let's sort it in plain English.
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kW = how fast. kWh = how much.
Think of it like a shower.
It's the size of your shower head, how hard the water can come out. Your solar system might be 5kW, your kettle is 3kW. That's how much muscle they have at any one second.
It's how much water actually ended up in the bath. If your 5kW system runs full whack for 1 hour, you made 5kWh. That's what fills your battery, runs the house, and what ESB Networks measures on your bill.
Big kW means nothing if it's cloudy and you get no kWh.
So: kW is the speed. kWh is the distance. One looks good on Facebook; the other one pays your bill.
☕ Solar Sid's Tip: When you download your ESB Networks usage file it's in kWh - that's the real stuff that decides your bill. Your inverter shows kW right now, but the kWh total is what saves you money.
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