The house as a heat battery

A house with waterborne heating is sturdier than it looks. The floors, walls and the water in the hot water tank all hold heat for hours - and that can be used to shift electricity use to the cheapest hours without it being noticeable indoors.

EnergyWizard has a rule (Priority 4.5 in the control engine) that raises the hot water tank to 60°C as soon as the electricity price is low or the solar panels are producing a surplus - "charging the battery". When electricity becomes expensive again, output is reduced, and the house "discharges" what was stored: the water cools slowly, the floor heating releases the heat it already absorbed, and no compressor needs to run right then.

There's also a predictive variant: if a price spike is known within the next few hours (MAX_COAST_HOURS in the heating engine, set to 6 hours), the house is heated extra just before - so it can coast straight through the expensive period without the compressor needing to start.

This isn't a guess - it's the same rule engine controlling real houses right now, and the same principle shows up in the heat battery numbers on the front page, pulled straight from the operational log.