Heating buffer tank with excess solar energy – peak-power problem

Configuration
1

I’m trying to heat my 1000 L buffer tank using excess solar energy, among other things, via a 3-phase 9 kW heating element that’s controlled by a Carlo Gavazzi RGC3P60V30C16DM (proportional burst-firing SSR).
If I have, for example, 4.5 kW of excess solar energy, I drive the SSR at 50% (0–10 V signal via KNX connected to Home Assistant).
But because of the burst-firing principle (8 cycles on, 8 cycles off), my SlimmeLezer (P1) sometimes shows 9 kW consumption during the “on” phase.
My control logic then thinks there’s no more surplus and ramps down.
Since I’m in Belgium, I also want to avoid those short peaks that might increase my capacity tariff.

Question:
How do you solve this?
• Do you work with an averaged P1 value instead of the instantaneous one?
• Are there any examples of how to control this ideally in Home Assistant?

All tips welcome!

2

Are you being billed by average or peak demand consumption? How do you determine ‘surplus’ solar energy?

Not sure about the SlimmeLezer (P1) and your comment about polling - does it accurately reflect the meter reading your utility supplier uses to bill you?

Show your code and sensors. Are you filtering or smoothing?

Can your smart SSR controller be configured for upper limits, or does it just blindly follow analog inputs? How is it (logically) connected to KNX?