The €8 light that trims your electricity bill (by making you look at it)

Here's an uncomfortable fact about home energy: your meter knows everything, and you look at it roughly never. The data is perfect — every watt you draw, every watt your solar panels push back — and it lives in a grey box you visit twice a year, usually because a fuse tripped.

The cheapest energy-saving device I know of is not a battery, not a smart thermostat, not a new appliance. It's a WS2812B LED strip — about €8 — glued somewhere you can't avoid seeing it, showing your live power flow as colour. Green: your panels are exporting, electricity is effectively free right now. Red: you're buying. The redder, the faster the money leaves.

Why an ambient display works when an app doesn't

You've probably got an app from your inverter or utility. Apps have a fatal flaw: you have to open them. Nobody opens an energy app before switching on the dishwasher — checking is a chore, so it doesn't happen, so the information might as well not exist.

An ambient display flips that. The light is simply there, in the corner of your eye, all day. You stop reading numbers and start absorbing a state: "we're green right now." And once the whole household absorbs it, behaviour follows without anyone making a spreadsheet about it:

• The dishwasher starts when the strip is green, not at 21:00.
• The tumble dryer waits for a sunny afternoon.
• The EV charges when the light says the sun is paying for it.
• Someone finally asks why the strip glows red at 2 a.m. (Hello, forgotten patio heater.)

Does it actually save money?

Honest answer: it saves what your behaviour saves — the strip itself consumes a watt or two and produces zero kilowatt-hours. But the research on in-home energy displays has been fairly consistent for years: making consumption visible typically shaves a few percent off household usage, with bigger effects when the feedback is real-time and always visible — which is exactly what an ambient light is.

Do your own maths: a few percent of a €1,200–1,800 annual bill is €40–90, every year, for an €8 strip and an evening of tinkering. And if you have solar panels, the load-shifting effect is where the real money is — more on that below.

What you need

• A digital meter with a P1 port (standard in Belgium and the Netherlands).
• A HomeWizard P1 dongle plugged into it — it puts your live readings on your WiFi.
• An ESP32 (a few euros) running WLED with the HomeWizard P1 usermod.
• The €8 LED strip.

The usermod polls the dongle and paints the net flow onto the strip. No cloud, no subscription, no account: the data does one hop across your living room and becomes light. Flashing the firmware happens straight from your browser with the WLED P1 Flasher — the build story is in this earlier post.

The solar multiplier

If you have panels, visibility pays double. In Belgium and most of Europe, the electricity you inject earns you a fraction — often a quarter or less — of what the electricity you buy costs you. Every kilowatt-hour you manage to consume while the sun produces it, instead of exporting it at noon and buying it back at 19:00, is worth the full difference. That's the whole game of self-consumption, and it starts with knowing when you're green.

The light tells you now. For planning the rest of the day — will 14:00 be better than 16:00 for the laundry? — you want a solar production forecast. And for the economics of offtake versus injection, read why selling your solar power back is a bad deal.

No affiliations, nothing to buy from me: the flasher tool, the usermod and this blog are free. The €8 goes to whoever sells you the LED strip.