Post #9744

Had a conversation with a group member today about an issue he's having with his solar that reared it's ugly head after he had the utility remove power from his house. He has two separate hybrid inverters that are completely separate from each other. Each one feeds a different part of his house, each one is connected to half the solar panels on his roof, and each one is connected to two proprietary HV batteries. For the sake of simplifying this I'm going to make up some parts of this to make it more clear.... one inverter runs 20% of his house but the loads it does run are high power loads. The other inverter runs the rest of the house, 80% of his daily usage. Two separate systems feeding two separate load centers. I need to go off on a tangent for a moment to make sure that everyone is up to speed.... When a hybrid inverter wants to connect to the grid to export power, it will monitor the grid for 5 minutes for stability, then at the last instant it will come in phase with the grid and connect. It's not like DC where it can just connect any time.... the incoming utility grid and the inverter's grid frequency, voltage and phase must match precisely for the connection to work. Once connected the inverter can import or export power to/from the grid..... back to the post. How it worked before.... the inverter that runs 20% of his house only gets a workout when the hot water and the clothes dryer run (I'm making this up as I go). So each day, it begins with full batteries and starts selling to the grid. The other inverter has run the house all night and it's batteries need charging. So it charges batteries from solar and also connects to the grid. In reality, it's importing 240v from what the other inverter is exporting. This exchange happens within his house and never makes it to the grid despite both inverters being actively connected to the grid. But each inverter must see a pilot signal of 50/60hz steady state before it will connect to what it calls "the grid". Once connected , one of them is exporting and the other is importing. They are sharing each other's solar panels. How it works now..... The inverter that runs 80% of his house wakes up in the morning with a low battery and uses half the solar panels on the house to charge the batteries. The inverter that runs 20% of his house wakes up with a full battery and charges for a few moments and stops using solar. There is no grid for it to synchronize to, so it has nowhere to export power.... so it just sits idle. So now we have one inverter that's trying to charge a battery with half the panels for 80% of his daily usage. As you can imagine this is no beuno. The 80% loaded inverter can't call for help because there's no grid for it to connect to... so neither of these inverters is able to connect to each other because there's no grid for them to sync with.... and that "grid" connection is their lifeline to each other. No grid, no connecting together. The installer says these two inverters cannot be "stacked". This is crazy to me because even "chinese" eg4 and growwatt inverters can be stacked. So there's no way to combine these two 5kw inverters into one "super inverter". I suggested he bridge the two batteries together but otherwise leave the two systems separate.. then atleast they could share power thru the battery bussbars instead of the "grid connection". Any of this will void the warranty from his installer. Sadly, his solution is to spend about $2500 and get a 10kw inverter to replace the two 5kw units. Moral of the story.... do like MasterBrains says.... kill your main breaker for a weekend and see what doesn't work. A plan that has not been tested is no plan at all. Something will always come out of left field and smack you in the head.