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Using Export Limited Solar for EV Charging

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

In many locations, limits are placed on how much excess solar can be exported to the grid.

The amount of exported energy is equal to the total production minus and energy that is being used in the home.

In most cases Charge HQ will work automatically where export limits are in place, making full use of any solar production that may otherwise have been curtailed.

How it works

Provided your export limit is not less than 1.5 kW, your solar system will be able to produce sufficient excess solar for Charge HQ to detect it and commence charging.

Once charging starts, more of your solar will be self-consumed, your exports will be reduced and your solar inverter will be able to ramp up production.


System configuration:

  • 10 kW solar system
  • 5 kW solar export limit
  • 7 kW EV wall charger

Consider a day when you’re at peak solar production of 10 kW and your home is only using 2 kW. Your solar system is able to create 8 kW of exports, but with a 5 kW export limit, it will ramp down total production to 7 kW  to comply with the 5 kW export limit, with 3 kW of production being lost.

  • 10 kW available solar production
  • 2 kW home load
  • 5 kW exports
  • 3 kW curtailed
  • 7 kW actual solar production

Using Charge HQ, your EV will see 5 kW of excess and start charging at 5 kW. Your inverter will now see that your exports have reduced to 0 kW so it will begin ramping up production until it reaches full output of 10 kW, initially with 3 kW of exports.

  • 10 kW available solar production
  • 2 kW home load
  • 5 kW EV charging
  • 3 kW Exports
  • 0 kW curtailed
  • 10 kW actual solar production

Charge HQ will now see that there’s more excess available and increase the EV charging up to the 7kW limit of the charger. You’ll now have:

  • 10 kW available solar production
  • 2 kW home load
  • 7 kW EV charging
  • 1 kW exports
  • 0 kW curtailed
  • 10 kW actual solar production

All of this will happen automatically every time you're charging from solar, with adjustments to your EV charging rate being made as often as every minute.

Charge HQ configuration for export limited sites

If your export limit is greater than 1.5 kW, there are no special configuration requirements for Charge HQ on export-limited sites. The default configuration will automatically make use of all available solar production and minimise curtailment whilst charging your EV.

If your export limit is less than the minimum charge rate of your EV or charger (often around 1.5 kW) Charge HQ may not detect sufficient excess to commence charging. In such cases, you may need to set a small negative solar tracking margin.

Maximising feed-in tariffs with export-limited rooftop solar

If you have a large solar system and regularly export a lot of your generation, or only have relatively small EV charging loads which are readily met with solar charging you may look at ways to reduce the curtailment caused by export limits.

The less time your solar output is curtailed, the more production you have, which reduces fossil fuel use in grid generation and may earn additional credits from feed-in tariffs.

Whilst Charge HQ will automatically utilise solar production that may have been curtailed due to export limits, it won’t optimise your charging to also maximise your exports. There are some steps you can take though.

To minimise curtailment you want to align any flexible loads such as EV and home battery charging to occur with periods that would otherwise be curtailed.

A few options are presented that need to be adapted to your individual circumstance. They may also need adjusting as your solar generation varies with the seasons.

  1. Set Min Solar Generation to say 5 kW. In our example above with a 10 kW solar system with a 5 kW export limit, this would stop your EV from charging at the start and end of the day when solar production is low and concentrating charging to periods where it may be otherwise curtailed.
  2. Set Blockout periods from 6 am to 10 am and 4 pm to 8 pm. This will override solar tracking and prevent EV charging from occurring before 10 am and after 4 pm. Similar to option 1 but using time-clock based constraints.
  3. Set your Max Charge Amps to say 5 kW. Again using our example system above, a 10 kW system with 5 kW of EV charging should never be exporting more than 5 kW allowing for some minimal home loads. By using a slightly reduced charging speed your EV charging will be spread out over a longer period of the day, reducing the period the export limit may apply.