Inverter terminology and usage case

[doc3g]

I was recently watching a video from Beene Energy to try and get a sense of the different inverter types (

), and I had a very basic question about something that I think I've never realized.

With the caveat that I realize, there are safety issues that need to be addressed for real-world applications. In the simplest terms, feeding power into a main panel via a branch circuit will energize the panel, correct? For example, the Vevor microinverters that plug into a regular outlet simply backfeed the panel?

Given that basic premise, I see terms like "off grid" and "grid tie" and "all in one" but then when I look at 3 different inverters with the same label, they all seem to do different things. Hence, I would like to know what "type," or, more ideally, what specific inverter would be the best for my desired usage case (assuming that what I hope to do would be feasible).

I have roughly 10 KW hrs of Li-Ion 18650 batteries that I plan to configure in a 48V system. If I had it to do over, I would have purchased Lithium iron phosphate but here we are. Given the limited cycles of the Li-Ion batteries, I would prefer to keep from cycling them except for when the power is out. Hence, the batteries will serve as an emergency power backup only, rather than a part of the daily system.

I would then like to add ~ 4k watts of PV and use it to offset some of my daily usage (as opposed to being totally off grid). However, in the event of extended downtime, I would like to be able to have the PV charge the batteries. What type of inverter can accomplish this?

 

[Mattb4]

Understand that inverters do not charge batteries. Charge controllers or Solar Charge controllers "SCC" (commonly referred to as MPPT inaccurately) do. Inverters take DC and output AC.* Grid tie inverters parallel with a grid in order to function. Various Hybrid AIO (All in ones) can parallel as well as charge a battery for use when PV is not available to feed inverter. This type can be setup to export via their AC in as well as a AC output. Off grid styles can only power loads from the AC output. The AC in for them is used as a power supply to charge batteries or bypass the inverter and feed the AC out.

Exporting (paralleling) to your Main panel from a grid tie is often not allowed by your utility or local code. Those plug in 120vAC microinverters you see are not approved anywhere for use in the US.

* Inverters can act as chargers working in reverse in some cases but they have a circuit controlling charging.

 

[50ShadesOfDirt]

The type of inverter that most likely will meet your needs is an "off-grid" inverter (no grid-tie functions, no sell-back, etc.). Because it doesn't have all the bells and whistles for those grid-tied capabilities, it should theoretically be less expensive.

The "installation" type (especially for this very custom battery-bank you are envisioning) might best be "parallel" (it doesn't touch the existing house wiring).

Build the system of your dreams, using all the stuff you have laying around and want to incorporate, and test, test, test ... when you think it is working right, and safely, then start hooking stuff up to it, not by going thru the main service panel, but by installing separate feed panels, circuits (or even suitable extension cords). This requires no permits or inspections, because it is parallel. Very similar to a DIY solar generator (components) on a hand-truck, without the hand truck.

You can reach over to the grid with a single supply cord that will tie into inverter to recharge (I'd use an extension cord to start). Your inverter is acting like any other electrical device at that point, and is just pulling power from the grid to recharge its battery.

One day, when it all works right, have an electrician stop by and review things and figure out how to tie it in cleanly. Then you can roll with integration.

Hope this helps ...

 

[doc3g]

Thank you for the replies. Below, I have sketched out what I think was suggested, but I would appreciate confirmation.

1. Inverter has 3 options to draw current: Grid, Solar, Battery
2. Branch circuit (for example, kitchen lights) has been moved from the main panel to a sub panel (I guess this is called the "critical loads" panel)
3. Ideally, what should happen is:
   1. Sun is shining and the lights are powered by solar
   2. Sun is down (night time, cloudy day, etc), then the lights are powered by the grid (mains -->inverter -> lights)
   3. Sun is down, grid is down, then lights are powered by battery via route of inverter (battery -->inverter -> lights)