Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 20,497
What do you mean by "rotating machinery"?
A generator, which spins at somewhat higher RPM under no load.
SMA in describing use of generators feeding Sunny Island indicate that with such behavior, as generator gets loaded down Sunny Boy would start producing full power, and unloaded Sunny Boy respond to increased frequency by ceasing to deliver power.
While battery needs a charge, Sunny Island would suck down whatever Sunny Boy produces and more if needed from generator. If it detects Sunny Boy backfeeding into generator (because producing more power than needed), it would disconnect from generator (or grid, if told not to backfeed.)
Maybe you could get away with just a rotating generator. Need to avoid backfeed.
It would be enough to use a relay to disconnect the solar panels from the heating rods, right? The problem is, I can't find a suitable DC relay for the 5 kW I need per heating element, e.g. 200-250 volts at 20 amps.
Yes, just need to connect/disconnect. Probably existing thermostat and overtemperature switch could handle pilot duty.
Somewhere on the forum there is a posting for an electronic controller which drives water heater with PWM. This can accomplish MPPT without needing inductors.
If you have 12 kW of PV and 3 Sunny Boys, that could be handled off-grid by one Sunny Island and an auto-transformer. I would set up the PV array 6 kW SE and 6 kW SW orientation, maybe 4 strings, with one SE and one SW string feeding of two each Sunny Boys. Wouldn't need the 3rd one.
That would give a full system, and use a SoC based control relay to switch AC to your water heater as a dump load.