this post was submitted on 27 Sep 2023
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That doesn't really make sense, since an off-grid inverter literally cannot backfeed. It's essentially just a computer UPS on steroids. It accepts the grid as an input that it can pass through but it's not possible for it to push energy back to the grid.
I mean yes if you decided to hook its output directly up to your Mains panel without separation you would be back feeding. But only for maybe a few minutes at most as you would also destroy your inverter because it has no mechanism to synchronize the output with the mains since it's not designed to backfeed
It's 120v, there's nothing to synchronize? Not sure what you're talking about here. Same power is coming from the inverter, battery, grid, generator...
This is standard practice. Inverter - > monitoring - > maybe a knife disconnect - > main panel.
I'm not really sure what you are talking about, you need to synchronize both the phase of the power and the frequency. If they differ even slightly you damage your equipment. This is why when running multiple inverters in parallel they require both a Communication cable and a power sharing Cable in order to ensure that they stay perfectly synchronized. Inverters capable of doing grid tie have equipment in them to monitor the mains power and make sure that they stay synchronized with it. Whereas an off-grid inverter does not contain that equipment which is why they are generally cheaper
There are several different possible phases for 120 volt they are not all the same. And while hooking to the mains may be standard practice for something that can grid tie it is not standard practice for an off-grid inverter. You are specifically expected to have a secondary panel specifically for that inverter. The mains power will reach that secondary panel through the inverter when it's in pass through but the panel should in no way be connected to the mains directly (other than a ground bond between the secondary panel and the mains)
With that having been said, I have no doubt that solar installers have instead opted to continue to use inverters that are capable of grid tie even in a installation that will not be backfeeding. Probably just to reduce the amount of inventory required so that they can get full purchase orders. But that doesn't change the fact that a proper true off-grid inverter is not capable of tying into the mains without destroying itself
The fact that you say you were a solar installer, but you're not even aware of something as simple as phases and frequency synchronization is part of the reason I feel like solar installers are wildly overpaid. You're basically doing the bare minimum without really understanding what it is you're doing
I mean, the other option is you're pulling things out of your ass like every other armchair expert on the internet.
Like...no. You get 240v 2p incoming with a split bar. 120v is 120v is 120v. Maybe you're dealing with 3 phase power but a residential building is not. And I have no idea why you'd have an inverter that outputs 3 phase power in a residential building.
https://youtu.be/NKIbR69opgc?si=kbp9mLaAZ5brQTxf
This is a nice little experiment to show you what happens when you try to parallel two inverters that are not synchronized. Just because the voltage matches does not mean they are in the same phase or synced up with their sine waves. You can also just look at the manual for any dedicated off-grid only solar inverter and they will make it very clear that you are not supposed to hook the output up to the mains panel and doing so will void your warranty and damage the unit. But I'm sure that those inverter manufacturers have no idea what they're talking about /s
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