Where you live

Prices load live from Octopus for your region. Your postcode is only sent to Octopus to look up the region, and isn’t saved.

Solar panels

Generation is estimated when you change the size or direction. If you have the figure from your MCS certificate or quote, enter it after those.

Battery and inverter

The fastest charge or discharge is usually the inverter’s size. The export limit is 3.68kW unless your installer got approval for more under G99.

Heat pump and hot water

Heat demand and SCOP come from your heat pump survey or design. Heat demand covers heating and hot water.

Electricity use

Your yearly use is on your bill or in the Octopus app. Leave out the heat pump, which is worked out from the heat demand above, and the car, which goes below.

Electric car

Leave car charging at 0 if you don’t have an electric car. Each 1,000 miles is roughly 300kWh, and the car’s app or dashboard shows its miles per kWh. Most home chargers are 7.4kW, and a three-pin plug is about 2.3kW. The EV charging tab shows when to charge.

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Save to your account

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1. Octopus app: switch to Cosy Octopus, variable version. Keep or rejoin Outgoing Octopus export.
2. Duracell app, Schedule Control: edit Charge 1 to 04:00–07:00 at . Turn on Charge 2 (13:00–16:00, ) and Charge 3 (22:00–23:59, ). Turn off Discharge 1.
3. Battery app: set timed charges for 04:00–07:00, 13:00–16:00 and 22:00–23:59 at . Turn off any timed discharge or export.
4. Heat pump: to 04:00–07:00 and 13:00–16:00.
5. Leave the heating running steadily. The battery covers the 4–7pm peak.

• Charge 1: 04:00–07:00, , every day, on
• Charge 2: 13:00–16:00, , every day, on
• Charge 3: 22:00–23:59, , every day, on
• Discharge 1, 2 and 3: off

End Charge 3 at 23:59, not 00:00, because times around midnight can be misread. Between windows, the battery runs the house by itself.

• : 04:00–07:00 and 13:00–16:00. Target .
• Anti-legionella: .
• Heating: steady, on weather compensation. Don’t turn it off for the 4–7pm peak, because the battery covers it.
• Cold-weather option: if the battery runs empty before 22:00 on cold days, set the comfort temperature 1°C higher (say 21°C) for a 13:00–16:00 slot in the . Keep the setback temperature at your normal 20°C for the rest of the day. Try +0.5°C first, and go back to steady heating when the cold spell ends.
• How to tell: on cold evenings, check the battery level between 19:00 and 22:00 in the .

• Battery: no changes, whether you’re out for the day or on holiday. It only tops up what it used, and Cosy’s cheap rate is about the same as what export pays.
• Out all day: leave the heating steady. A setback of no more than 3°C is fine.
• Holiday: turn on with your dates. Drop about 1°C for each day you’re away, no lower than about 15°C.
• Hot water: if the cylinder keeps reheating while is on, set hot water to Off for the trip.
• Coming home: end the day before you’re back, at about 13:00. The weekly anti-legionella heat-up can run as soon as it ends, so this keeps it in the cheap window.

1. Octopus app: switch to Octopus Flux. It replaces your import and export tariffs.
2. Duracell app, Schedule Control: edit Charge 1 to 02:00–05:00 at this month’s rate from the table below. Turn off Charge 2 and Charge 3. Turn on Discharge 1: 16:00–19:00 at .
3. Battery app: keep one timed charge, 02:00–05:00, at this month’s rate from the table below, and turn off the others. Add a timed discharge or export from 16:00–19:00 at .
4. Heat pump: to 12:00–15:00, so it reheats on solar.
5. On the 1st of each month, change the Charge 1 rate using the table.

• Charge 1: 02:00–05:00, rate from the table, every day, on
• Charge 2 and 3: off
• Discharge 1: 16:00–19:00, , every day, on
• Discharge 2 and 3: off

for three hours sells about and leaves about for the evening. Ask your installer to confirm that the discharge powers the house first and exports the rest.

• : 12:00–15:00, on solar. Target .
• Anti-legionella: .
• Heating: leave weather compensation on for cool spells.

• Out all day: set Charge 1 500W lower than the table. You use less during the day, so more solar goes into the battery. Keep Discharge 1 as it is.
• Holiday: set Charge 1 to 1000W, which adds about 3kWh. That’s enough for the fridge, freezer and standby until the sun is up, and the battery fills from solar during the day.
• Holiday: keep Discharge 1 at 16:00–19:00, , so the solar you’ve stored sells at 30.3p.
• If several dull days are forecast while you’re away, set Charge 1 back to the table rate. Grid power bought at 16.2p still makes about per kWh when sold at the peak.
• Heat pump: turn on with your dates. If the cylinder keeps reheating, set hot water to Off for the trip.
• Coming home: end the day before you’re back, around midday. The anti-legionella heat-up can run as soon as it ends, so this keeps it on solar.

• Charger schedule: 22:00–23:59 and 04:00–07:00, every day, at .
• That’s 5 cheap hours a night at 14.1p, adding up to about , or .
• If the car is at home in the afternoon, 13:00–16:00 is cheap too.
• Don’t charge from 16:00–19:00. It’s the 43.2p peak, and the home battery is running the house.

• Charger schedule: 02:00–05:00, every day, at .
• That’s 3 cheap hours a night at 16.2p, adding up to about , or .
• On sunny days when the car is at home, charge it from spare solar if the charger has a solar or eco mode. That solar would only earn 11.1p as export, so it saves about per kWh on charging from the grid at night.
• Never charge from 16:00–19:00. Import is 37.4p, and the home battery is selling to the grid at 30.3p.

• Charge the car only in the times above. At other times the home battery can end up powering the car, and run flat before the evening peak.
• In those times the home battery is charging from the grid itself, so it won’t discharge into the car.
• If you need to charge at another time, pause the home battery’s discharge in the while the car charges, then turn it back on.
• Some chargers and inverters can be wired so the battery ignores the car completely. Ask your installer how yours is set up.

Will your supply cope?

• If it’s parked for a few weeks, leave the car about half charged. Most car batteries last longest part-charged, not full or nearly empty.
• Turn the charger schedule off, or leave the car unplugged, so it doesn’t top up every night for nothing.
• Plug in the night before you get back, and the schedule will charge it in the cheap window.

• Join Octopus with Outgoing Octopus export first. You need an Octopus import and export tariff before you can move to Flux.
• Choose the variable version of Cosy, so you can switch freely.
• On the last Sunday of March and of October the clocks change. Check the inverter time in the , because Octopus’s windows follow UK clock time.

• Open the menu (or tap the battery on the home screen), then Schedule Control, then Charge / Discharge.
• You get up to three charge and three discharge sessions, each with a start, end, power and frequency.
• Each session needs its toggle switched on, and sessions mustn’t overlap.
• Outside the scheduled sessions, the battery charges from spare solar and runs the house by itself.

• Most battery apps let you set timed charge and discharge (or export) slots, each with a start, end, power and days.
• Each slot needs switching on, and slots mustn’t overlap.
• Outside the slots, the battery should be in its normal self-use mode, where it charges from spare solar and runs the house. Some apps call this eco or self-consumption mode.
• These guides call the slots Charge 1–3 and Discharge 1–3. Your app may name or number them differently.
• Some batteries, such as Tesla Powerwall, don’t use fixed slots. Give them Octopus’s times and prices in their time-of-use settings instead.

• Weather compensation on, with the heat curve taken from your heat pump design. To fine-tune it, lower it in 0.05 steps a few days apart until the house is slightly cool, then go back up one step.
• Adaptive heat curve: off.
• Room temp mod: Active. Switch it to Inactive while you’re tuning the curve.
• Maximum flow temperature: your design flow temperature, so it never caps the curve.
• Setback: no more than 3°C below your comfort temperature, or none at all.
• Hot water: Time-controlled mode, target , cylinder charging hysteresis 7K.
• Maximum cylinder charging time: 120 minutes. Anti-cycle time: 60 minutes.
• Anti-legionella: .
• Hot water mode: start on Normal. Eco roughly halves compressor output, so a full reheat could run past a 3-hour window. Try Eco once you know your reheats finish well inside the window.
• In myVAILLANT, the curve is under Heating, then Heat curve settings, then Heating curve (expert). Menu names can vary between app versions.

• Weather compensation on, with the heat curve taken from your heat pump design. To fine-tune it, lower it one small step every few days until the house is slightly cool, then go back up one step.
• Maximum flow temperature: your design flow temperature, so it never caps the curve.
• Setback: no more than 3°C below your comfort temperature, or none at all.
• Hot water: on a schedule, target .
• Anti-legionella: .
• A reheat needs to finish inside a 3-hour cheap window. If your heat pump has an eco or quiet hot water mode that lowers its output, check that a reheat still finishes in time before you rely on it.
• Ask your installer where each of these settings is in your heat pump’s app or controller.

Legionella bacteria grow in water between about 20°C and 45°C and die above 60°C. The target keeps most of the cylinder too hot for them, but the bottom, where cold water comes in, runs cooler. Once a week the heat pump heats the whole cylinder to 60°C or more to clear anything that has grown.

• When: .
• Cost: from , the cylinder needs about of heat to reach 60°C, or about to reach 70°C. That’s roughly of electricity if the heat pump does it all, up to about if the immersion heater does. At the cheap rate that’s between about and a week.
• Leave it on all year. It’s the one hot water setting that isn’t worth trimming to save money.
• Hot taps run hotter than usual on . Take care with the first bath or shower, especially if there’s no mixing valve on the cylinder.
• Away: the heat-up can run as soon as ends, so end it at the time the away sections suggest. That’s about 13:00 in winter and around midday in summer.
• Ask your installer what temperature the cycle heats to and whether it uses the immersion heater.