Hi everybody.

I am thinking about a way to use any extra power an offgrid solar system can generat at a certain time, in space heating or water heating.

The heating power could be variable using pwm for the heating resistive element, think about dimming the resistive load as coulds passes and turn off the load when the generated power became less than or equal the normal load+charging power for batteries.

We have, I believe, to read the input power continuously, and both the normal load and charging power continuously too, and it's like trying to drain more power to the new resistive load without affecting neither the charging current nor the normal load itself as it's power is purely from solar panels.

Just any extra power the panels can deliver is to be used to heat the water or power some radiant space heater with the all remaining extra power but surely with maximum power the new load can drain. Hope you understood my point.

I thought about using wireless RF control switches to turn on the heaters when the batteries are fully charged, but what I explained above is much better if can be really implemented.

 

An alternative arrangement is to regard the water heater (plus any other loads) through the inverter as a shunt regulator across the batteries. Regulating the heating power draw via triac controller or even relay switching, the inverter loading can function as a charge controller if it is set to voltage points below the solar controller settings. If the water storage reaches maximum temperature the shunt regulation will have to cease but the solar controller will take over the regulation.