Slow down battery charge when solar is good.

[searlecom]

How about an option to slow down the charge rate of a battery when the solar forecast is good?

On a good day, even in winter, my battery is charged by 13:00, if not before, but I still have hours of good solar power to come. If Predbat could slow down the charge rate to allow a more even export of excess power, that would help the grid and due to the slower charge rate, may even extend the life of my battery.

This would also allow people with export limits to gain extra time to export excess power while charging up if their array can produce more power than they can export.

I ran this past DeepSeek

Example:

Approach 1: Spread charging over the entire solar window

Approach 2: Charge the battery to 100% first, then export everything else.

We’ll analyze both approaches using the same parameters:

PV Generation: 40 kWh over 6 hours (~6.67 kW average).

Battery Capacity: 10 kWh.

Max Export to Grid: 5 kW.

Inverter Limit: 8 kW.

Approach 1: Spread Charging Over the Entire Solar Window

Battery Charge Rate: 1.67 kW.

Export Rate: 5 kW.

Totals:

    Battery Charging: 1.67 kW × 6 hours = 10 kWh (100%).

    Export: 5 kW × 6 hours = 30 kWh.

Approach 2: Charge the Battery to 100% First, Then Export

Step 1: Charge the Battery to 100%:

    Energy needed to charge the battery: 10 kWh.

    Charge rate: Let’s assume you charge at the maximum rate the PV system can support (6.67 kW).

    Time required to charge the battery:
    Time=10 kWh6.67 kW=1.5 hours.
    Time=6.67 kW10 kWh​=1.5 hours.

    During this 1.5-hour period:

        Battery Charging: 6.67 kW × 1.5 hours = 10 kWh (100%).

        Export: 0 kW (since all energy is used to charge the battery).

Step 2: Export for the Remaining Time:

    Remaining solar window: 6 hours - 1.5 hours = 4.5 hours.

    PV energy available during this time: 6.67 kW × 4.5 hours = 30 kWh.

    Export at the maximum rate of 5 kW:

        Export: 5 kW × 4.5 hours = 22.5 kWh.

Totals:

    Battery Charging: 10 kWh (100%).

    Export: 22.5 kWh.

Comparison:

Approach 1 (Spread Charging):

    Export: 30 kWh.

    Battery Charging: 10 kWh.

Approach 2 (Charge First, Then Export):

    Export: 22.5 kWh.

    Battery Charging: 10 kWh.

Conclusion:

Approach 1 (Spread Charging) allows you to export more power (30 kWh) compared to Approach 2 (22.5 kWh).

By spreading the charging over the entire solar window, you can maximize export while still ensuring the battery reaches 100% by the end of the window.

Approach 2 (charging first) limits your export potential because you’re not exporting anything during the initial charging phase.

Therefore, spreading the charging over the entire solar window is the better strategy for maximizing export while still fully charging the battery.

[gcoan]

There has been other similar discussions about Predbat being able to handle battery clipping and spread solar charging across the day, see #1206 for example.

At the moment you can programatically control battery charge rate yourself with an automation to set battery charge rate via the predbat manual API which should get to what you are asking for