My system consists of 3 by 10kVA Quattro's, Venus, Fronius Grid tie inverter downstream of the Quattro's and a 15kVA diesel generator (3ph) connecyed directly to the Quarttro's. My battery is a Freedom Won 30/21 lithium Ion battery. The primary back-up supply is the Grid with secondary back-up the generator.
The Quatros are used to prevent grid feedback because my grid consuption meter consist of 3 single phase "impulse" meter that measure both forward and backward energy flow as consumption.
The battery management of the Freedom won battery does not always alow the battery to discharge the same SOC (State of charge). If the battery was not fully charged the previous day the minum state of charge is increased so that (I think) the averge state of charge is maintained at a specific level. This makes it difficult to use the state of charge setting to optimally start the generator when the grid fails and the batteries reach their minumum SOC.
If the generator starting is set to battery voltage - the generator starts irrespective of the actual battery voltage when the grid fails and irrespective if the sun is shining and I am harvesting energy from the sun! (Defeating the purpose of using the sun). and shuts the Fronius down.
What is the correct way to set this system up?
If I download all datat from VRM I see that there is a variable "#1 SOC Low" which changes to On just before the supply is changed from battery to grid. Is this not a variable that can be used to start the generator and then use say a SOC of 50% or some other value to switch the generator off.
How do you change from generator back to solar once solar is again avalable but the generator has not yet reached it switch-off value?