I want to optimize the use of my photo-voltaic production by redirecting the remaining unused energy to electric heaters in winter, or something else in summer (given that fans are inductive loads and would make the problem worse). Note due to the (insulting) comment below: I obviously do not want to waste energy uselessly! My panels covers at most 75% of my needs, so I do have a use for the energy I produce cleanly!
The question is how to drive variable loads in such a way as to achieve a near-zero net meter reading. To be clearer if I can: if my smallest heater is 1000W, and the remaining power I have from my panels (after driving whatever I could fully) is 800W, then I want to feed them to the heater, without having to pay for the "missing" 200W. The net energy shows zero, and I am fully using my solar grid.
On/off strategy: easy but non optimal
Until now I only used on/off modes. I compute the best combinations of heterogeneous heaters to use my production in the best way. This is a classic packing problem, and the effect is easy to understand on my electricity bill.
But when the solar production is lower than the smallest load I have (<800W), then my best option is to give it for free to my electricity provider (which resells it to my neighbors... huh). Else I would be paying by importing energy.
So I need to be able to drive loads more gradually and have my energy meter integrate the kWh correctly (from my viewpoint!).
Skip half mains cycles: would it really improve my bill?
I could skip half mains cycles by driving a TRIAC or a solid state relay thanks to a Bresenham algorithm (i.e. switch it on only for N half-cycles out of each repeated M half-cycles).
But I doubt that such uneven AC waveform use would work on my electronic meter. May be it would if it was integrating my need over a significant time interval, like the old spinning disk meters.
Instead, I suspect that every peak I use would still overshoot my instantaneous production, count as an import of energy, and be detected as so (which is fair). But during the cycles I do not use I would again over-produce electricity for free, back into the public grid.
Switching the load at high speed (chop the AC)
I can otherwise rely on a much higher switching frequency (e.g. hashing the 50Hz AC waveform with a 100KHz PWM). Technically, it should still be fairly easy with a microcontroller and a TRIAC.
But still, I wonder if the electricity meter would count it the way I would like. As a side note, even with a zero-cross detection, would I pollute the mains with electromagnetic noise (even for resistive loads? my micro-inverters are quite sensitive to noise on the AC waveform and may shutdown as a protection!).
More complex control?
Still in order to use my excess of energy, as measured by my electricity meter, I could also try and drive the heaters with variable voltage instead of chopped AC.
It may be the only real way to have the electricity meter behave as I expect (instantaneous P=UI ?). But I have no clue how to do this with loads up to 2KW . Would adding high power coils smooth the chopped AC waveform?
So far my weirdest idea would be to try and add a servomotor to set the potentiometer of a 4KW AC motor controller in order to drive my heaters... but this sounds like a bad idea :D