Offtake vs injection: why selling your solar power back is a bad deal

Your digital meter keeps two tallies. Offtake: every kilowatt-hour you pull from the grid, billed at the full retail rate — energy, network costs, taxes, the works. Injection: every kilowatt-hour your panels push out, credited at… considerably less. How much less varies by country and contract, but "a quarter of the offtake price" is often optimistic. Sometimes it's closer to a sixth.

That asymmetry isn't a scam; it's unbundling. When you buy, you pay for the electron and the wires and the taxes. When you sell, you're paid wholesale for the electron only — at noon, when every solar roof in the country is selling too and wholesale prices are at their daily low.

The kitchen-table maths

Say offtake costs €0.32/kWh and injection pays €0.05/kWh (adjust for your own contract — the shape of the argument doesn't change). Now follow one kilowatt-hour from your roof on a sunny noon:

What you do with it	What it's worth
Inject it at noon, buy one back at 19:00	€0.05 − €0.32 = −€0.27
Use it yourself the moment it's made	€0.32 avoided = +€0.32

Same kilowatt-hour, same roof, same weather. The only difference is when you switched things on. A self-consumed kilowatt-hour is worth roughly six times an injected one in this example — that ratio is the single most useful number a panel owner can know about their own contract.

Self-consumption: the only lever that's free

You can attack this with a home battery, and increasingly people do — but batteries cost real money and have their own payback maths. Load shifting costs nothing:

• Dishwasher, washing machine, dryer: they all have delay buttons nobody uses. Use them.
• Electric boiler: a simple timer moves hundreds of kilowatt-hours per year into the sun.
• EV charging: the biggest movable load in most homes — charge at noon, not at midnight, whenever the car is home.

Typical households self-consume around a third of their solar production without trying. With deliberate shifting, half or more is realistic — and every shifted kilowatt-hour banks the full offtake-minus-injection spread.

You can't shift what you can't see

Two pieces of information make the habit stick. The forecast tells you which hours will be green: that's the Solar Forecast tool, and here's how to plan a day around it. And the live state tells you whether now is the moment: your meter's P1 port broadcasts it every second, and an €8 LED strip turns it into a colour the whole household reads without thinking. Green light, big loads on. Red light, they wait.

Injection isn't evil — unplanned injection is

You'll always inject something; noon production on a July day will beat any household's appetite, and those cents are still better than nothing. The point isn't zero injection — it's zero accidental injection while the boiler sits on a 21:00 timer out of habit. Sell your surplus, by all means. Just stop selling at €0.05 what you're about to buy back at €0.32.

Prices above are worked examples, not quotes — tariffs differ per country, region, supplier and month, and capacity tariffs (like Flanders') add their own wrinkle by rewarding flat, sun-timed consumption too. Check your own contract; the asymmetry will be there, only the ratio changes.