Dynamic tariffs & battery arbitrage

A dynamic electricity tariff (e.g. Tibber, aWATTar, Rabot) gives you hourly prices that follow the wholesale market. Combined with a battery, a new saving lever appears: charge when cheap — use when expensive.

How arbitrage works

The price swings noticeably across the day (often cheap at night and midday, expensive morning and evening). The idea:

• Cheap hours: charge the battery from the grid (or run the heat pump).
• Expensive hours: live off the battery, avoid grid draw.
• Sunny hours: store PV surplus anyway.

The battery thus becomes not just a PV buffer but a price buffer.

Requirements

• A dynamic tariff (usually needs an intelligent metering system / iMSys).
• A controller that can shift battery charging into cheap/green hours — either the manufacturer's bundled energy management, or (locally) evcc / Home Assistant.
• A battery whose grid charging power is controllable (not every brand allows this equally well — see the controllability checklist).

Who becomes the battery manager?

This is the decisive point. By default the inverter manages the battery itself (self-consumption mode). The moment you actively send charge commands, you take on the battery-manager role — and must then think about three things yourself:

1. Keep serving self-consumption sensibly (not just arbitrage).
2. Respect the minimum state of charge (don't over-discharge the battery).
3. Failsafe behaviour: what happens if your controller crashes? Ideally the inverter reverts cleanly to self-consumption mode.

That's why evcc is the recommended solution: it takes on exactly this manager role and handles the interplay, instead of you programming it all yourself.

Is it worth it?

The saving depends on the price spread and your consumption. In many cases it's a few hundred euros a year — enough to justify the setup effort, but not automatic. Important: grid charging adds wear to the battery — a good controller weighs the saving against the cycle cost.

In short: dynamic tariff + battery = charge when cheap, use when expensive. Once you steer, you become the battery manager (mind self-consumption, min SoC, failsafe) — evcc handles this cleanly.

On to the second big control lever: coupling PV surplus with the heat pump.