Where can I find a description of how an off grid inverter routes PV panels input DYNAMICALLY to the load and battery for charging . I have a Kodak OGS 5.6 which seems to indicate power USED from PV panel and not Power available , on the display . The power used seems to be controlled depending on the load at any point in time , where load is a ‘ combo meal ‘ of the pylontech battery that may require recharge / top up  and the load . During the day the PV panels “in theory” can supply more than we need and due to conservation of energy this excess available power can’t just disappear so - does the inverter dynamically change the load resistance ? . I have trawled the internet for internal schematics or theory of operation with no success , only suggestions of how to wire up and set up . Some texts refer to load diversion , or load shifting . 
 

any links or clarification welcomed 

7 hours ago, Hedley said:

does the inverter dynamically change the load resistance ?

Yes, more or less. The solar charger is usually a boost converter (in some it's a buck converter down to battery voltage), and the inverter's processor(s) has(have) control over the pulse width of the gate voltage fed to the boost or buck transistor(s). With this, the inverter can control the current through the converter, either to find the maximum power point when load exceeds available solar power, or to cut back the current so as not to over-voltage the DC bus or the battery (depending on where there output of the solar charger is connected).

When the power drawn from the panels is less than the maximum power available, the difference causes the panels to heat up slightly. If you think of the panel as a variable current source with a diode across it, the excess solar current flows through the diode. If no power is drawn from the panels and they are in sun, all the current generated from the solar energy flows through these diodes. These diodes aren't separate components (don't confuse with the panels' bypass diodes); each solar cell is an actual silicon diode. If you push power into a cell, it actually becomes an infra-red "light" emitting diode and emits infra-red light.

The display doesn't show the available solar power (unless it happens to be the same as the used solar power), because it's impossible to know what the available power is unless you try to use it all. In many circumstances, you can't use it all, so the maximum available power is unknown.

As for where you might be able to find a better description of solar chargers, sorry, I don't know.

Thanks for reply - I purchased a spare Inverter  unit to do a teardown on,  and try and understand how it works . One of the interesting things I did not expect is that the Inverter portion  is Bi-directional so when grid power is available the AC is converted to dc to charge the battery and also routed to the AC output,  BUT if solar is available and set as a preference then utility power is only ' mixed in'  if the load is greater than the available PV power . I'm starting to view this off grid inverter ( Kodak / Voltronic / Axpert ) like an audio mixing desk one would find in a recording studio. 

As a separate task I am trying to model a buck/boost converter in LT spice so I can simulate to extract a graphical plot of how the input impedance changes when the variable (load ) is changed - For the sim the load will just be a resistor whose value I can sweep in the sim . 

 

The journey continues 

On 2023/06/18 at 7:17 PM, Hedley said:

I have trawled the internet for internal schematics or theory of operation with no success , only suggestions of how to wire up and set up . Some texts refer to load diversion , or load shifting . 

Hi Hedley,

you don't need to scratch your head. For me it's straight forward. I have 2 Off grid Axpert/Voltronic in parallel. Look at the 48V bus with the batteries as a water container with input and drain pipes. PVs input as much they can. From there the inverter drains what's needed for the AC load, the rest goes into recharging (refilling) the batteries. However there is a max level watch. If the bus with the batteries reach the level set in the inverter (Bulk charge voltage, floating charge voltage) it reduces the input from the PVs in order to not overflow the "container" (similar to the WC flush tank input valve). The MPPT does this with its pulse width control. As Coulomb explained, the excess energy goes into heating the panels. As soon as the load drain increases such that lowers the level in the container, the MPPT resumes PV input as available.