Heat pump + battery + EV: why a smart tariff alone is not enough

Adding a heat pump to a home that already has solar, a battery, and an EV is presented as the logical next step toward full electrification. The installers are right that all the pieces fit together technically. What they rarely explain is how these devices behave when they are all running on the same smart tariff, competing for the same stored energy, at the same time.

What each device needs

To understand the conflict, it helps to think about what each device is optimising for independently.

Your heat pump is optimised for comfort. It wants to run during the coldest parts of the day and night — typically early morning before the house wakes up and early evening when occupants are home and temperatures are dropping. A well-configured heat pump on Octopus Go or Agile will try to pre-heat the home during cheap overnight periods and run a top-up in the evening if needed.

Your battery is optimised for bill savings. It wants to charge from cheap overnight grid power or daytime solar, then discharge to offset expensive peak-rate imports in the early evening. Its job is to be full at around 07:00 and empty by 23:00.

Your EV is optimised for convenience and cost. It wants to charge overnight when rates are cheapest. On Intelligent Go, Octopus controls when that happens — usually overnight but sometimes during cheap daytime windows.

Each of these devices has a coherent individual strategy. The problem is that they share a battery and a grid connection, and their strategies can directly conflict.

The three-way conflict

Here is a realistic winter morning in a home with all three:

00:30 — The cheap overnight window begins (standard Go, 00:30–05:30). Your battery starts charging from cheap grid power. Your EV is also charging via the scheduled Go window. The heat pump runs its overnight low-power cycle. Everything — heat pump, household loads — runs from cheap grid electricity while the battery fills. Battery reaches 85% by 05:00.

05:30 — The cheap overnight window ends. Your battery switches from charge mode to discharge mode. The EV has finished charging. The heat pump starts its morning pre-heat cycle and draws 2.5kW. The battery begins discharging to supply this load — that is what it is there for. Battery drops from 85% to 70%.

06:15 — Grid rate has jumped to 30p/kWh (the overnight window ended at 05:30). The heat pump is still running. The battery continues discharging to offset the peak-rate grid.

07:00 — Battery is at 55%. The house is warm. Heat pump switches to standby. Everything looks fine.

08:30 — You check the inverter app. Battery is at 35%. Winter solar generation is weak — maybe 1–2kWh by midday. The battery will not recover much today.

16:30 — The heat pump starts its evening cycle. Outside temperature is 3°C. It runs at 3kW for two hours. Battery drops to 10%. Grid imports at 30p/kWh fill the gap.

17:45 — Your EV needs topping up. Octopus dispatches a 45-minute Intelligent Go session. The battery is at 8% — effectively empty. The full EV load comes from the grid.

The result: you spent money on a battery, but the battery spent its entire cycle on heat pump support and never had enough charge left to do what it was installed to do: offset peak-rate imports in the evening.

Why a smart tariff does not solve this

A smart tariff like Octopus Intelligent Go, Agile, or Flux optimises the scheduling of one controllable device — typically the EV charger. It does not:

• Know how much energy the heat pump consumed last night
• Know what the battery's state of charge is before dispatching an EV session
• Adjust the heat pump's schedule to protect battery charge
• Coordinate morning pre-heat with expected solar generation

Octopus's system sees your home as a single electricity meter. It dispatches cheap energy to your EV charger when prices are low. That is all it was designed to do, and it does it well.

The heat pump has its own controller — a manufacturer app or a Modbus interface — that has no connection to Octopus. The battery has its own management system that responds to loads without knowing what caused them. These three systems have no shared coordination layer.

What whole-home coordination adds

The missing piece is a system that can see all three devices simultaneously and make sequencing decisions:

• Before an EV session: check battery state. If the battery is below a threshold that will be needed for heat pump support in the next 6 hours, hold the battery rather than letting it supply the EV load.
• Before the heat pump's evening cycle: check whether the battery has recovered from overnight discharge. If not, allow a partial grid import rather than running the battery below minimum useful charge.
• During overnight cheap periods: prioritise battery charging to cover both heat pump and EV needs before the window closes.

This is not a dramatic algorithmic overhaul. It is sequencing and awareness — decisions that a person could make manually if they had real-time data on all three systems at once, but that no individual device's controller can make because none of them can see the others.

The Daikin and Solis example

1app.energy's current private beta is built specifically around homes with this combination: Daikin heat pumps, Solis inverters with battery storage, Zappi or similar EV chargers, and Octopus smart tariffs.

Daikin's cloud API provides visibility into heat pump operating mode, current draw, and scheduled cycles. Solis's API provides battery state, solar generation, and grid flow. Octopus's API provides dispatch signals and upcoming cheap windows. Zappi provides EV session state.

With all four data sources visible, the coordination decisions become straightforward: the battery is protected before known heat pump cycles, EV sessions are allowed to proceed without draining the battery below its useful floor, and solar generation is preserved for evening demand where it has the highest value.

Is this for every home?

No. A home with just an EV and no battery or heat pump benefits mainly from a good smart EV tariff. The conflict described here only applies when multiple high-draw devices are sharing the same stored energy.

The more devices you add, the more the individual optimisation strategies start working against each other — and the more valuable whole-home coordination becomes.

If your home has a heat pump, battery, and EV, see how 1app.energy coordinates all three — or tell us your exact device and tariff combination and we will review whether the current foundation can support your setup.