Optimal distance between batteries
- Thread starter Bob Smith
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arwooldridge
Well-known member
The Solax inverters can be configured in master slave mode (up to several slaves in fact) if all the same generation. Not quite set this up properly yet. One unit controls the other inverter(s) and all batteries via the CAN bus links, but I think you need equal battery string lengths for the all inveters hence my 4+4+4 topology. Might need an EPS parrallel box to make that work according to manual, but not sure if this applies if not using EPS mode.
arwooldridge
Well-known member
One thing I discovered is that any excess PV power exported whether by hybrid or AC inverters (actually any source eg windmill etc) will be used to charge any other inverter/ batteries whether Hybrid or Retrofit AC provided on the same grid circuit of course. Seems the hybrid inverter works three ways: pv-batt, batt-grid, grid-batt. Not sure if this applies to all hybrids but confirmed works on Solax.
Only problem is can cause hunting between two if both on self use mode, when not master/slave. But temporary fix if one set to backup mode and the other to self use. i have to alternate them when the backup on is fully, not ideal but ok for winter, will sort M/S by spring.
arwooldridge
Well-known member
Obviously grid-batt works on most hybrid inverters (for example charging overnight) but was not sure it could act as a Retrofit AC inverter does too ie if you leave off the PV inputs it acts exactly as an AC retrofit unit utilising excess exportable power. Ditto with PV connected. The takeaway from this is if anyone is considering an AC retrofit inverter battery system they should seriously consider the small cost upgrade to a Hybrid inverter (even if no PV) which does exactly the same job but allows you to add more PV panels whether now or in future hence potentially saving an inverter.
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Unless your existing system is with FiT
I had concerns with my DIY AC Coupled battery, wondering how it would deal with excess solar PV, loads greater than the inverter power and interaction between the two differing makes of inverter. I'm happy to say it just sits there and does it, works as expected. The only oddity is that the original install (Growatt SPH6000 / Growatt 7 kWh Battery) seems to want to charge the battery on the new system whenever it's not 100% SOC. Ive got a workaround.
arwooldridge
Well-known member
You can add AC (or Hybrid as discussed above) inverter battery systems to existing FIT (assuming on a deemed 50% export basis) systems. You are just using part of your deemed export quite legitimately. What is more debatable is any change to the existing FIT system by adding batteries before the generation meter of the FIT system, which must be covered by a change in the agreement. There are ways to do it but best avoided. (Edited export to generation)
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That is what I meant and understood when you say about replacing the inverter.
I agree downstream of the inverter you can add batteries no problem. I think we have the same understanding wrt FiT System
arwooldridge
Well-known member
Not familiar with the Growatt system. However two inverter battery systems can react incorrectly due to the two sets of grid sensors (CT or meter) working on different thresholds of import/export. Ie one can think it's importing but the other thinks it's exporting. Even if the difference in threshold is just a few Watts. One answer is to put a small bias say equivalent to 100watt into one or other. Ideally in software but can be done externally by adding a small bias current to the CT via very low voltage transformer. There is a way to do this using around 1watt only. Or some manufactures have master slave modes. If it's possible to use a digital meter output to both inverters, it may remove the problem assuming both inverters use the same digital threshold.(would be true of identical inverters with same software)
In my case it's two different inverters, 1 Victron and 1 Growatt. My quick workaround was to pram the relay in the Victron to energise at 95% charge. When the relay energises the contacts can programmed to turn off the charger, it works for me.
