Need to convert Grid-Tie to Battery with Net Zero export (Sol-Ark, Fortress)

[wpns]

You have to be careful about charging current. Otherwise inverters see voltage, and are happy.

Even with two of them at max output (which can't happen with these generators) that's only 100A into the batteries, and I'm looking at 2-3 of the Fortress or 4-6 of the EG4, so well under their charge currents. I just need to have the Chargeverter stop charging at an appropriate voltage. I take it there's no communications capability with the Chargeverter, it's just 'charge at this power level until the batteries are full (have reached the appropriate voltage) or the generator runs out of fuel'?

 

[DIYrich]

Chargeverter charges up to a fixed voltage. It will stop at that voltage. It starts at a lower voltage up to the amp setting, and will increase the voltage to keep the amps. When voltage is reached, it will hold as amps decline.

 

[wpns]

Also looks like I can use the Generator Start output of the EG4 inverter to shut the generator down when the battery SOC reaches some programmed value, even if the generator's connected to a Chargeverter and then directly to the batteries, so then it's a simple matter of finding the constant-current setting on the battery. side that'll load the generator without overloading it as the voltage changes during the charge cycle.

BTW: Many thanks for all the feedback here, the plan for the new system is coming together, and I really appreciate your help with all the details!

 

[wpns]

Chargeverter charges up to a fixed voltage. It will stop at that voltage. It starts at a lower voltage up to the amp setting, and will increase the voltage to keep the amps. When voltage is reached, it will hold as amps decline.

So it's a constant-current output with a voltage limit, essentially? Good to know.

 

[Rusty959]

I've got the 18kpv and LL batteries. I don't know of any issues with the 18kpv that would cause me to not recommend it for your purposes. There is potential to maximize your MPPTs in different combinations depending on exactly what your max voltage and current of your panels are, but otherwise they have very few functional differences. I was deciding between the sol-ark and eg4 when I did my upgrade (also came from a sunny boy grid tie) and decided the eg4 was the way to go.

Now for some more details, the first month or two the 18kpv was out there were some export issues where it took way too long to cut export and would therefore export a bit. That's been fixed for a long time. The good news is that scenario is only really a problem for people trying to hide their solar system from the utility. You aren't trying to do that, you just want to zero out your export. Plus it's not even a problem anymore.

It's a good unit.

 

[Rusty959]

I'll have two dig up the details, but the ground-mount array is (45) 260W panels in 3 strings to a DC combiner and then the SMA grid-tie inverter, and the roof-mount is (38) 405W panels in 4 strings into the two GoodWe inverters. Too much to put them all into a single 15K inverter, which is why I think I need two. Two would give me 6 MPPT inputs, but I have 7 strings...

Both the sol ark 15k and eg4 18kpv have the ability to hook multiple strings in parallel to one MPPT. There are limitations of course but since you're already using a DC combiner you probably are already meeting these limitations. Check out the MPPTs on the 18kpv - of the 3 one has 10A extra capacity so you can parallel a string.

 

[Rusty959]

Also looks like I can use the Generator Start output of the EG4 inverter to shut the generator down when the battery SOC reaches some programmed value, even if the generator's connected to a Chargeverter and then directly to the batteries, so then it's a simple matter of finding the constant-current setting on the battery. side that'll load the generator without overloading it as the voltage changes during the charge cycle.

BTW: Many thanks for all the feedback here, the plan for the new system is coming together, and I really appreciate your help with all the details!

You may have already seen this but you should be able to set this very easily


I'd highly recommend just reading the manuals for the sol ark and 18kpv top to bottom. It's a lot of information but will do a good job of keying you in on the unique differences and capabilities of each.

 

[wpns]

Both the sol ark 15k and eg4 18kpv have the ability to hook multiple strings in parallel to one MPPT.

I finally had time to sit down this morning and confirm that my strings match the MPTT inputs of the EG4 18Kpv, and determined that if I combine 2 strings of the ground array I can reduce my string count to 6, which fits fine with (2) 18kpv in parallel, so that's the current plan. A bit of time with a spreadsheet and I discovered I can connect the strings to each of the inverters on a 15K/12K split, so that's not awful. Thanks!

 

[wpns]

You may have already seen this but you should be able to set this very easily
View attachment 194948

I'd highly recommend just reading the manuals for the sol ark and 18kpv top to bottom. It's a lot of information but will do a good job of keying you in on the unique differences and capabilities of each.

The issue I found with the EG4 generator input was that the manual says:
Generator requirements:
1. Generator should be a 120/240VAC, 60 Hz generator.
2. Generator capacity should be between 6 – 21.6kW.
And I'll be running one or two UE3000is (2500W continuous) 120V generators in parallel, so it seems 'better' to get one or two EG4 Chargeverters and use them to charge the batteries in the daytime on cloudy weeks when the grid is down. SWAG: I can put 54KWHR into the batteries in one 7-hour run on 3.4 gallons of fuel (Fermi 50 cents per KWHR) with one generator, which ought to suffice as long as I can manually reduce optional loads.

 

[wpns]

I'd highly recommend just reading the manuals for the sol ark and 18kpv top to bottom. It's a lot of information but will do a good job of keying you in on the unique differences and capabilities of each.

Yes, indeed, working on that, there's a lot of info there!