A (really) dumb question

[mike cunningham]

I have a Kid controller and three arrays with total 250 watt output.

When my batteries are charged and I am in float I see about 10-15 watts at the Kid.

When I place a load on the system I see wattage increase at the Kid display.

All good.

But where does the SA power go when there is minimal load on the system? Obviously the Kid dishes out as much power as is required by loads up to the point where the panels are maxed out and then starts pulling supplemental power form the batteries. It is also obvious when there is minimal load the controller reduces output to the load. But how the heck does this work?

Are there any explanatory materials on the site which would help me understand this process?

Many Thanks,
Mike

[mcsarge]

Where does the power inside a battery go when it is not connected to a circuit? The power from the panels is potential, if you don't connect a circuit that it can push the electrons through, there there is nothing to get rid of. You may be confused with things you have read like diverting the power to a water heater - this is to capture as many watts that are being converted from sunlight as possible. One of the functions of the solar controller is to disconnect the panels from your batteries when they are full, or only provide a trickle charge when needed.

[mike cunningham]

Mcsarge,

OK, thanks for the response, I am laughing at myself. The comparison to a battery helps me understand the general concept. I definitely need to spend some time gaining a better understanding of PV panel and battery tech.

The alternative, I guess, is too just accept Arthur C, Clark's aphorism: "any sufficiently advanced technology is indistinguishable from magic." Next person comes aboard my boat and asks how the solar works, I answer "it's magic, next topic".

[boB]

This is actually a pretty good question !  Not dumb at all !
I also sometimes try to explain how this works just so they might sort of understand.

So, when you need all the power you can get, the Kid (or any other MPPT controller) will find and keep the PV input voltage at its Vmp or maximum power point voltage.  This is NORMALLY around 80% of its Voc or open circuit voltage, which is the highest voltage you will see.  Just like the battery that is disconnected, its voltage is open circuit.  Open circuit meaning nothing connected to it.  The switch is off (if there was a switch)

So, as the battery gets to its absorb or float voltage, the Kid will go off of that max power point voltage and let it rise just enough to keep the voltage at the battery terminals constant.  Whatever that constant voltage needs to be at that time. (float, absorb, or EQ)

So loading the PV input to higher than Vmp but lower than Voc (between 80% and 100% of Voc) it is like a volume control.   Operating at Voc is volume turned all the way down.

It could also drop the voltage below the Vmp max power point voltage to turn down the power but it can only go as low as the battery voltage itself which isn't low enough in most cases.    So, up it goes towards open circuit.