Why are they deceptive? They are just following UL standards. Why does UL allow them if they are not safe?
I have seen a few cheap inverters that say "Designed to meet UL-1741 standards". Now that is being a bit deceptive as they say this without ever having an independent testing lab verify that it meets those rules.
The Schneider SW and XW series inverters use a very similar circuit design. They both use an "H" bridge between the battery and the transformer, and a contactor can connect the transformer 120/240 windings to the grid. The XW is UL listed and tested and has the software to allow it to export to the grid. The SW is not able to export to the grid. The SW is also UL listed and tested, but without grid export functions. I almost went with an SW, but decided on the XW line because I wanted to be able to push power back to my main panel.
Most of the "Off Grid" inverters that include a grid input are not able to ever sync with the incoming grid. They only close the grid input contactor when the inverter is shut down. And once on grid, it can only run as a battery charger. If it senses a grid failure, it still has to open the contactor before it can switch to inverting mode.
The Schneider SW is a bit unique in that it can sync with the grid and help power loads by using PV solar and/or battery power to reduce the current needed from the grid. But if the current coming in from the grid falls below a minimum threshold, the inverter again shuts off to be sure it never exports from battery power. A few newer hybrid inverters ae claiming similar functionality, but these tend to also be the ones that can also be configured for grid tied operation.
Under NEM 2.0 it only made sense to get the interconnect agreement for my initial PV solar install. I looked into batteries back then, but the cost was way too high. But when I decided to add batteries later, I looked at many options. I did look into using some of the cheaper stuff off Ally Express and having a controller switch it from charging to inverting. But as I thought about it, the idea of having some cheap non listed equipment shuttling around upwards of 4,000 watts of power was just a bit scary. At that point, I decided any solution I bought to push current to my main panel had to be built and independently tested to meet the UL standards. Even if something goes very wrong, it has a very good chance of failing in a safe manner. That is the main thing UL tests for. They know shit happens. Their job is to try and make the worst case failure still not ever hurt anyone.
Strict legality is a separate issue. I knew of several ways I could make a completely safe system, but the rules can be a fine line with some limits that are really there just to be able to charge fees. I have an interconnect agreement with an NEM 2.0 agreement that allows me to back feed up to 16 amps and up to 900 KWHs a month. As long as I stay under both of those, I am not breaking my agreement with So Cal Edison. And since I added the battery bank, both my peak export and total monthly export have decreased vastly. And every KWH I am no longer exporting, is also matched by a KWH I no longer have to import back later. If someone really wanted to carefully look over my hourly energy usage, it is quite obvious that I am now storing energy and using it in house later, but there is nothing in my NEM 2.0 or interconnect agreements that prohibit what I am doing. In reality, I have vastly reduced my impact on the grid. For less current ever goes to or from my house. The only real thing they can whine about is that I am now paying them far less money. They still hit me with about $12 a month in "non bypassable charges" and taxes. My exported energy credits all get used up in the hot summer and short winter months, so they never have to pay me. I still end up owing them about $250 per year to keep the grid available as my backup when the PV solar falls short. It did that for about 30 minutes this morning, and will likely do it again tomorrow. This "May Grey" weather has reduced my normal May 29-30 KWHs a day to just 13 KWHs a day. And even with my extra 2,000 watts of panels charging the battery, I fell to my low volt cutoff this morning as the clouds stayed too heavy to cover the loads. Yesterday, I had to buy 0.31 KWHs from the grid, and today, I am sure it will be even a little more. Hopefully we get some sun tomorrow to get the battery SoC back up.
I'm neck deep in Enphase, Schneider & tons (literally) of LiFePO hardware plus the utility caps me at a paltry 10kw, else I need to load up with a $1M home policy (they copied the FL solar regulations) for export. No thanks - I decided to go off grid. So now I just need to be where you are, but with different hardware and unattached.
