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Home battery charge priority limit configuration

This page contains instructions for configuring
chargers with Charge HQ
Please refer to our
charger listing for details on supported models and charger specifications.

Note: if your EV charger is wired such that the load is not visible to your home battery, and you are using the "Consumption Excludes Charging" setting, it's not possible to use the battery priority charge limit and the information on this page is not applicable. In such cases, as the load from the EV charger is not visible to the home battery, it does not know that the EV is charging and cannot react to the reduction in true excess solar.

Charge HQ integrates with home batteries to provide flexible control over how excess solar energy is shared between your EV charging and home battery charging.

When used with a compatible EV & home battery, you can set the charge priority to control how you want excess solar to be used.

In home battery priority mode, you can also nominate the home battery priority charge limit.

Once set, EV charging will commence once the home battery reaches the configured charge priority limit.

Recommended Setting

We recommend setting Battery Priority Charge Limit to between 75% and 90%.

The aim is to have a bit of empty space in the home battery while the EV is charging so it can absorb the excess solar that the EV does not use, whilst still reaching the desired state of charge by the end of the day. This approach maximises the amount of solar which is used to charge the EV or battery, and minimises exports to the grid.

You can experiment with different values to see what works best for your situation.

Details

In practice once the EV starts charging, there will almost always be some excess solar available which the home battery can absorb if still has spare capacity to charge.

This occurs because:

  • Charge HQ only updates every 1+ minute, with excess solar availability changing every second
  • EV charging can only adjust in 1/3 Amp increments (for single phase / 3 phase) leaving small amounts of excess
  • The excess solar may exceed the maximum charge rate of the EV. For example, a 10 kW solar system with a 7kW EV charger will still see up to 3kW of excess solar whilst the EV is charging at full speed.
  • The EV is disconnected at times during the day.

The charge priority limit takes advantage of the rapid response of the home battery, allowing it to act as a buffer to frequent changes in the available excess solar. This minimises both exports and imports of energy to and from the grid whilst solar charging.

This example, shows home energy consumption in blue (including EV charging) and home battery charging in green. The EV starts to charge earlier in the day with home battery continuing at a low rate in parallel. In the afternoon the EV is used and so the home battery returns to max charge rate until full.

In situations where the preference is to fill the home battery each day to cover overnight energy use in the home, setting a charge priority below 100% lets you use more of your own solar, whilst still filling the home battery.

Each home has a different energy use and charging pattern, so experiment with different charge priority limits at different times of year to optimise your solar self-consumption.

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