A Dublin home, run as one system.

A semi-detached house with a heat pump, solar panels, an electric car and a battery on the way. Everything worked, but nothing worked together.

The brief

The household had five apps for one house, and none of them knew what the others were doing or what electricity cost at that moment. They wanted one place to see it all, the house run on the cheap hours, and to hear about problems before they noticed them on the bill.

What we did

• Installed a Home Assistant hub and connected the inverter, car charger, thermostat and heat pump metering.
• Set the heat pump to pre-heat on the night rate when a cold morning is forecast.
• Kept the car charging at night only.
• Set up alerts for the things that matter: the inverter going offline, the car not charging, solar well below forecast, an overdue backup. At most three a day, and none at night unless urgent.
• Added a morning briefing on the kitchen screen: yesterday's cost, the weather and the day ahead.

What we found

The heat pump is most of the bill

Over last winter (November to March) the heat pump used 2,693 kWh and cost €693. That is 66% of the electricity bill, excluding the car. About half already ran on the night rate.

Turning the heating down at peak saves almost nothing and makes the house cold when people get home, so we didn't do it.

Solar stored in a battery isn't free

Each kWh stored from the panels is a kWh not exported at 18c. After losses, a kWh from the battery costs about 20.0c from solar and 20.3c from the night rate. So the battery fills every night, keeps a reserve for the 5–7pm peak, and never exports. Leaving it empty overnight to "make room for solar" loses money on most Irish winter days.

Expected value: about €180 a year. This is modelled from a year of the home's hourly data; we will publish the measured figure after the winter.

Forecasts can't be trusted with money

Over 46 days the free solar forecast ran 16% low on average and was more than 40% out on 9 days. The home now uses a better forecast, and forecasts only make low-stakes decisions, like whether to pre-heat at 11am.

Wash temperature is what costs money

Across 456 washes, the eco and quick programmes cost the same, about 21c. Nearly all the energy goes on heating water. The monthly report covers things like this so the household can stop thinking about them.

The result

The schedules are worth €150–300 a year in this home. The household values the rest more: one view of the house instead of five apps, alerts only when something is actually wrong, and nobody changing the inverter settings when the clocks change.

The pilot home belongs to our founder. Figures are measured from its Home Assistant data, except the battery figure, which is modelled.