Operating guide · Battery storage

Home battery tariff charging

A tariff schedule needs enough time and charge power to store the required energy, while leaving the intended backup reserve and solar headroom. Import, export and battery losses all belong in the cost comparison.

14 minutes to read

Published 23 July 2026

Reviewed 23 July 2026

Key points

  • Use the household’s interval data to set the energy target. Do not fill the battery by default if the stored energy will not be used.
  • Check usable kWh, charge kW, the cheap-period duration, household demand during charging and the configured import limit.
  • The grid-charge target also sets the headroom available for later PV. The appropriate target changes with season and expected demand.
  • Use one primary scheduler and record the reserve, charge, discharge, export and failure-state settings.
On this page
  1. Record the tariff and operating objective
  2. Calculate the energy target
  3. Check the charging window
  4. Leave headroom for PV
  5. Reserve and backup
  6. Discharge period and household loads
  7. Import and export limits
  8. Export tariffs and battery energy
  9. One primary scheduler
  10. Grid charging with solar self-use
  11. Commissioning the schedule
  12. Interval data and schedule revisions
  13. Related knowledge-base entries

Record the tariff and operating objective

Save the current tariff terms before changing the battery:

  • cheap and expensive periods
  • import rates
  • standing charge
  • export tariff
  • fixed, variable or dynamic structure
  • battery or grid-export restrictions
  • contract end and rate-change terms

Choose the main operating objective. It may be to cover household use through an expensive period, preserve a backup reserve, reduce grid import at a peak time or use expected solar later in the day.

Compare the cheap rate, day rate, standing charge, export terms and the periods in which the household will use the stored energy.

If the tariff is dynamic, use the supplier’s actual interval prices and rules. Do not treat a previously cheap clock period as a permanent schedule.

Calculate the energy target

Use recent half-hourly household data to find the energy normally required between the end of the cheap period and the next opportunity to charge. Exclude loads that will be met directly by expected PV where that expectation is reasonable, then allow for the intended reserve and conversion loss.

Keep these quantities separate:

  • nominal battery capacity
  • usable capacity
  • minimum operating SoC (state of charge)
  • protected backup reserve
  • target SoC after grid charging
  • energy expected to be used before the next charge

The displayed percentage is a BMS estimate within the battery’s protected operating window.

Avoid setting 100% simply because it is available in the app. If the household normally uses less than the available energy, the remaining stored electricity may provide no extra tariff value and can remove space for solar.

A useful starting calculation is:

target stored energy = expected expensive-period demand + reserve − expected direct solar contribution

Apply the product’s conversion efficiency and usable-capacity definition when translating this into an app target. The exact setting should come from the installed system data rather than a generic percentage.

Check the charging window

The maximum energy the battery can take during a window is constrained by time and power:

maximum charge energy before losses = available charge power × charge time

Available charge power may be lower than the product headline because of:

  • battery or inverter limit
  • current SoC
  • temperature
  • number of battery modules
  • configured import limit
  • simultaneous household demand
  • DNO import-limitation scheme
  • phase limit

A nominal 5 kW charge path cannot necessarily add 5 kWh in every clock hour. Power may taper and household loads may share the supply headroom.

Check the result in actual session data. If the target is repeatedly missed, determine whether the window, charge-power setting, household demand or a system limit is responsible before increasing anything.

Do not alter a commissioned import limit or electrical protection to reach a tariff target.

Leave headroom for PV

Grid charging fills space that could otherwise accept solar. The appropriate target therefore changes through the year and with the next day’s expected demand.

On a winter day with low expected PV, a higher overnight target may cover more expensive-period use. On a clear summer morning, a lower target may leave room for the array. The decision also depends on the export payment given up when solar is stored.

Forecast-based modes can change the target automatically. Check:

  • weather and generation data used
  • household-demand forecast
  • minimum reserve
  • response to forecast error
  • internet or cloud dependency
  • manual override

A forecast is an input to the schedule rather than a guaranteed amount of PV. Review actual grid import, export and battery SoC after days when the forecast was wrong.

Reserve and backup

A backup reserve prevents all usable energy being allocated to normal tariff operation. It should be based on the backed-up loads and intended outage duration rather than one standard app percentage.

The reserve may behave differently across products:

  • unavailable for normal discharge
  • preserved until a grid outage
  • released under a low-price or emergency command
  • automatically changed by a storm or resilience mode

Test the documented behaviour with the installer. A displayed reserve does not establish that backup wiring, island-mode earthing or changeover has been installed.

If no backup arrangement exists, a high reserve can still keep energy unused without providing outage power. The home battery backup guide explains the required system boundary.

Discharge period and household loads

Set the discharge period around the tariff and household demand. Avoid exporting or discharging during a cheap import period unless that is an intentional and permitted strategy.

Large loads can empty the battery faster than the energy plan assumes:

  • EV charging
  • immersion heating
  • heat pump
  • electric shower
  • cooking

The battery may also have a lower continuous discharge power than the combined load. The grid supplies the difference even while the battery is discharging.

Where practical, schedule EV charging directly from the cheap grid period rather than routing it through the battery. This can avoid an extra conversion cycle and preserve battery energy for loads that occur at the expensive rate.

A home-energy controller may coordinate the loads. Check which one has priority when the battery, EV charger and heat pump all respond to the same price period.

Import and export limits

G100 can control net import or export at the grid connection. It is a commissioned electrical function, separate from a tariff schedule.

The control system may reduce battery charging if household import approaches the agreed limit. It may reduce battery or PV export if net export approaches another limit.

Ask for:

  • agreed import and export limits
  • CT (current transformer) or meter position
  • battery power limit
  • response after sensor or communications failure
  • priority between PV curtailment and battery charging
  • commissioning result

A CT must measure the intended conductor and direction. A schedule based on the wrong grid reading can import or export when the owner expects the opposite.

The tariff cannot authorise flow above a DNO or electrical limit. A supplier instruction remains subject to the local controller and installed protection.

Export tariffs and battery energy

Compare the value of storing, using and exporting one unit of energy.

For grid-charged energy:

gross tariff spread = later import rate avoided − charging import rate

Then account for conversion loss, standing-charge differences between tariffs and any battery-warranty or service conditions relevant to the chosen operation.

For solar energy, the alternative value is the export payment. Storing a solar kWh for later use gives up that export.

SEG licensees can treat mixed-source export differently where a meter also records grid-charged battery energy. A tariff may pay it, require additional evidence, apportion it or exclude it. Check the current supplier contract before enabling battery export.

Legacy FIT (Feed-in Tariff) installations need accurate generation and export measurement. Battery control and wiring changes should preserve the accredited measurement boundary and be notified where current FIT guidance requires it.

One primary scheduler

Commands can come from:

  • inverter or battery schedule
  • supplier tariff integration
  • aggregator or flexibility service
  • home-energy platform
  • manual app mode

Choose one primary scheduler for ordinary operation. Disable or widen conflicting local windows in line with the product instructions.

Keep electrical import, export, battery and reserve limits active. These are constraints rather than competing tariff schedules.

Record the order of authority. A supplier service may temporarily take control during an event. The owner should know how to opt out, what local setting remains and whether the command changes the backup reserve.

After a firmware, router, supplier or account change, confirm that the intended controller still has access. A schedule displayed in one app may no longer be the schedule being followed.

Grid charging with solar self-use

Solar self-use mode often tries to keep grid flow near zero by charging from surplus and discharging into household demand. A separate tariff schedule can override or modify that behaviour.

Check the transition at:

  • start of the grid-charge window
  • end of the window
  • start of PV generation
  • expensive-period start
  • backup-reserve threshold

The battery should not immediately discharge grid-charged energy into the EV during the same cheap period unless that is deliberate. It should not export in breach of the tariff or DNO setting.

If two controllers repeatedly change the battery direction around zero grid flow, adjust their priority or thresholds through the supported configuration. Do not move a CT or change a protection setting as a software workaround.

Commissioning the schedule

Use a complete charge and discharge cycle under normal household conditions. Record:

  • starting SoC
  • target SoC
  • charging power
  • energy imported
  • household load during charging
  • end time and achieved SoC
  • discharge power and energy
  • grid import during the expensive period
  • PV generation and export
  • reserve reached

Test loss of internet or supplier control if the integration depends on it. The fallback should maintain the electrical limits and leave the owner with a documented local mode.

Confirm clock, time zone and daylight-saving behaviour. A schedule can move by an hour after a clock change if the product and tariff use different time bases.

Save the commissioned mode and settings outside the app. The record is needed if a service visit or update resets them.

Interval data and schedule revisions

Compare intervals rather than only the battery’s daily saving estimate. Check:

  • cheap-rate import
  • expensive-rate import
  • export
  • battery charge and discharge
  • conversion loss
  • missed targets
  • unused stored energy
  • backup reserve

Recalculate when the tariff, household occupancy, EV, heat pump, PV system or battery firmware changes. Seasonal revisions can be useful because both solar generation and household demand move.

If the financial result differs from the app, check its tariff entries, standing-charge treatment, export value and measurement boundary. The supplier’s bill and settlement readings determine the energy charge.

Keep the documented schedule where it meets the intended target. Add further control only where the installed data shows a better result.

Related knowledge-base entries