My goal is to regulate loads in my offgrid inverter-powered system.
I moved to a fully offgrid house with batteries and a pure sine inverter. I would like to control how much I dump of my solar production into my water heater, like when I was grid-tied: meter the house net and use a basic zero-crossing TRIAC to regulate the heater anywhere from 0 to 100% according to my will.
Eg. with a 2.1kW production and a 3kW heater set at 30% I would have 1.1kW left for other appliances.
However I am not knowledgeable enough to make my mind regarding the impacts on the off-grid inverter and/or on the noise on the mains, without the backing of an external electricy supply (and pretty long cables, ie. using the grid as a regulating flywheel...)
I keep on fearing worst case scenarios. Say, with a 2.6kW inverter, I could theoretically have two 2.6kW heaters at 50% duty cycle (one cycle on, one cycle off, the average being 2.6kW). But how true is it with an off-grid inverter? Because if both of them fire in sync, it would be 5.2kW half of the time and 0W the other half. Instant peak vs fast average...
My swiss-made inverter seems robust (studer compact 2600-24) but I fear it is not designed to work like this (I have RTFM twice). Or it might reduce its lifespan, or switch to protection mode, or make other devices fail all around the house with severe voltage spikes and drop downs.
As a final remark, I obviously favor zero-crossing because of possible inductive loads like pumps. May be I might better focus on resistive-only loads like heaters and opt for higher frequency PWM switching (like, 500Hz or more?). But would it really be kinder to the inverter and overall noise, how much would such PWM interefer with the inverter correct operating mode?
All in all:
- feasability of PWM zero-crossing regulation on an offgrid inverter?
- impact of higher frequency PWM?
- other? (eg. use an expensive, slow motorized variac, or try to add some inertia/smoothing via kers or motor+alternator seem all overkill). Bypass the inverter and try to connect directly to the low-voltage batteries (unsuitable existing cable size) ?
Nb: When using conventional means to control a heating element, how does it affect the peak required VA? is pretty close but does not answer my need to regulate smoothly from ~0 to 100%