Solar tracking reserved amount as amps or watts

As an owner of a heat pump and other appliances drawing power from my solar array during the day
I want to be able to set aside a specified amount of power for these devices and the car to be charged with whatever else is available
So that I don’t start paying for electricity that I used to get free from solar when my car is charging.

During the morning I have a heat pump in operation until about midday (or whenever the hot water tank fills up) that draws about 1kW plus a background load of about 4-500watts. I want to be able to easily configure a figure that reserves this amount and lets me change it later once the heat pump has finished so that I can release the heat pump’s allocated solar power for charging the car again.