We have completed several totally different AC coupled systems using different inverters, due to large ground mounted arrays that had to be located a great distance from inverter-battery-generator-grid BAS, which are working just fine even with the mis-match of inverter brands. The SunnyBoy seems to not care what its connected to or how, as it just keeps doing what it does and if a relay cuts off its connection to the grid when the battery voltage goes high then it just waits and re-connects when the grid is back or the battery voltage drops.
What I am bothered by is the need to custom design a power relay circuit on each project which takes lots of fine-tuning of setpoints to get everything to work correctly. If you have not done one the problem is simple - when you backfeed the AC output from a remote grid-tie inverter "through" the AC side of a battery based inverter, everything works great and the solar AC just passes straight through the sub-panel, back throught the battery inverter, back into the grid. However, when the grid is down and the battery-inverter is no longer receiving (or sending) power from the grid, for some reason I cannot begin to understand, any AC being fed from the solar inverter goes straight into battery charging with absolutely no limit on charge rate or charge limit, and if you do not add a relay to dis-connect or shut-down the solar inverter you can quickly destroy a bank of AGM batteries if there are no major system loads as it just keeps charging and charging.
I am not an electronics engineer, but if the battery is being charged by the battery charger built into the inverter, I just do not see why the same battery charger suddenly has no clue that the battery is being overcharged when its now receiving AC power from a different source. I think with larger and larger arrays being installed as module costs fall, higher DC array string voltges to reduce wire costs, and more people worried about grid reliability, there would be a good market niche for an inverter that can properly charge a battery bank regardless of which way the AC power comes into the charger section. Whats the problem?
Jeff Yago
DTI Solar
Netscape. Just the Net You Need.
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