Grid Tie Inverter without Built-in Charge Controller?

[stojo107]

I was hoping to build a system with discrete charge controllers on each string, 48v battery system, and grid tied inverter. This allows me to decouple the solar facing specs (number of MPPTs / MPPT voltage range / etc) from the inverter specs. One motivation is to be able to scale up or down my solar generation capability (and maybe battery) without needing to change inverter size. I'm having a hard time finding grid tie inverters that don't have built in MPPTs though. Ideally there would be grid tie inverters which take in 1x ~48v DC battery bus only. Maybe there are some products I'm missing? Thanks in advance for the help!

 

[BentleyJ]

Schneider Conext SW and XW series inverters.

 

[SeaGal]

Maybe there are some products I'm missing?

Victron, surely?

MultiPlus-II - Victron Energy

The MultiPlus-II is ideally suited for professional marine, yachting, vehicle and land based off-grid applications. Learn more now.

www.victronenergy.com

 

[stojo107]

Thanks! Schneider has what I'm looking for. It has a built in charge controller for pulling data from the AC side and storing it. But Schneider inverters (and charge controllers) seem to be quite expensive, are they mostly used in commercial settings? Any thoughts on whether they're worth the price premium??

Victron appears to only have off-grid inverters.

 

[SeaGal]

Victron appears to only have off-grid inverters.

The Victron I linked to supports grid-tied configuration...

 

[400bird]

Outback and Midnight Solar also have separate component based systems.

However, it sounds like you're comparing the cheap import AIO (all in one, combined MPPT and inverter in one box) with quality, tier one hardware.
They products aren't in the same category.
Sure, the cheap import stuff will work, but every corner was cut and no-one expects them to last a long time. It's like electronics from Harbor Freight, it will probably work a couple times, but that's all you can trust it for.

 

[stojo107]

Thanks, not sure how I missed that victron option. Victron Multiplus 2 is the only model with a UL1741 listing, though its not clear to me that a UL1741 is actually required? From digging through the NBT Rate Schedule , "Special Condition 7", it seems like UL1741 listing is one option, but not a strict requirement. Maybe I'm interpreting it wrong though?

Related: based on the NBT schedule it seems the best way to maximize the export credits / feed in tariff revenues is to keep your storage system max capable discharge rate below 10 kW, and to go with an inverter without "power control system (PCS)" features. This allows you to both charge battery from grid energy, and export stored energy to the grid (up to a certain amount). The approach appears to allow you to export 100% of the theoretical generation capacity of the solar system (as calculated by CSI EPBB) you have attached to your battery before export credits cap / cutoff. This seems like the best config to me, where there is more room to export. Any NBT experts have thoughts? Next step is to model/simulate to see if its true. This NBT system is even more complex than I thought!

Screenshot of how export credits are capped for small (<10kW) systems which don't have PCS features built in:


EDIT: I had mistakenly called out UL1741 in the comment above, but have since replaced that with "PCS" which I've since learned is a separate set of features not directly related to the UL1741 certification/listing.

 

[stojo107]

@400bird thanks, makes sense. the less reliable stuff seems suited well to non-mobile cases where the grid is the reliable backup and the solar is more about saving money/environment. This mostly applies in residential areas where the grid is very stable I suppose.

 

[wpns]

UL1741

What grid-tie inverters don’t have UL1741? Isn’t that the anti-islanding thing where they shut down when the grid goes away?

 

[stojo107]

I came across a few out there which are grid tie capable but are not UL certified. But yeah my understanding is: UL1741 ~= California Rule 21 compliant ~= anti-islanding features for improved grid stability.

After more reading, I've realized that UL1741 has nothing to do with Power Control System (PCS) features. PCS is a set of settings which can disable certain modes of operation like "no grid charging" or "no storage export". These modes allow utilities (like the big CA utilities) to restrict homeowners from playing the energy triage game (buying electricity from utility when its cheap and selling it back to utility when export rates are high.