Designing a 20kW Commercial System

[InPhase]

I've just received plans for a new off grid commercial project. By plans I mean just a floor plan 😂. This is a design-build, so it's up to me to figure it out. 20 kW solar, maybe two 800 Ah forklift batteries, 12 tons of total A/C. Your inverters are the first thing that popped in my mind. Is this a job these inverters can handle?

[Sid Genetry Solar]

26 minutes ago, InPhase said:

I've just received plans for a new off grid commercial project. By plans I mean just a floor plan 😂. This is a design-build, so it's up to me to figure it out. 20 kW solar, maybe two 800 Ah forklift batteries, 12 tons of total A/C. Your inverters are the first thing that popped in my mind. Is this a job these inverters can handle?

What are the power requirements on the AC side of things.  Do you happen to know the LRA of the A/C units?

2 forklift batteries...are we talking 12v, 24v or 48v?

[InPhase]

They haven't finalized the air conditioning but at this stage it look like there may be three 4 ton units. Those are typically under 120 LRA. I would also interlock the controls so that units can't start simultaneously. I'm also looking into DC solutions for air conditioning.

Batteries will be 48 volt. As far as AC loads, there is probably less than 1000 connected watts of lighting. A commercial refrigerator that pulls about 13 amps at start. A low heat dishwasher that pulls 11 amps continuous @120 volts. A 1 HP well pump @240 V. Two 3000 watt water heaters. I think I will interlock those as well. Besides air conditioning, I don't expect the instantaneous draw to be more than 10000 watts at any given moment, almost certainly less. 

[Sid Genetry Solar]

1 hour ago, InPhase said:

I'm also looking into DC solutions for air conditioning.

Surprisingly, I haven't found a DC-powered A/C (all Chinese made) that's worth the expense--or for that matter, uses less power than a similarly sized AC version.  All of the Chinese 48v DC mini-splits I was checking on Alibaba...convert the power to 360vDC for a regular inverter A/C compressor in the first place.  They also used significantly more power than an off-the-shelf Pioneer mini-split of the same size (and less cost).

Absolute best bet would be inverter-based A/C units--the startup surge is completely eliminated, and you could technically power them on 360vDC.

 

Obviously, this project sounds like a job for 2 12kw GS inverters (whether split-phase or parallel...not sure yet)--that is once we finally get the design proofed and ready for manufacturing.  Awaiting a transformer test at the moment.

[Joe S]

Ok, so how many say 6K's can be paralleled? If this has been covered somewhere else in forum, then my apologies.

[InPhase]

My thoughts are to split the system up across several panels, each powered by its own inverter. That way, a single inverter failure won't black the whole place out. Two lighting and general purpose receptacle panels can be fed from one 6kW each. Then, maybe the mini splits share two parallel inverters and a control system staggers their start up.

[Sid Genetry Solar]

4 hours ago, InPhase said:

My thoughts are to split the system up across several panels, each powered by its own inverter. That way, a single inverter failure won't black the whole place out. Two lighting and general purpose receptacle panels can be fed from one 6kW each.

Fair enough 😉

 

4 hours ago, InPhase said:

Then, maybe the mini splits share two parallel inverters and a control system staggers their start up.

If you're using "inverter compressor"-based units, you do not need to be concerned about startup surges.  (It's just the old-as-dust synchronous AC compressors that have the ginormous startup surge.)  I have a Pioneer 1-ton mini-split (12kbtu)...and for startup, it literally starts at under 1A (120v)...and slowly ramps up to full 8A load if required over 30 seconds' time.

[Sid Genetry Solar]

5 hours ago, Joe S said:

Ok, so how many say 6K's can be paralleled? If this has been covered somewhere else in forum, then my apologies.

Parallel functionality is (like I've told Sean) very difficult to handle...at least via the "no comm harness" method I've been trying to do.  At the moment, the theoretical limit for paralelling inverters would be your wallet...but this has not been tested.  Max testing has only been on 2 units thus far.

We may have to add a (hardwired) inter-inverter comm method, as much as I don't like to--but if properly implemented, that'd handle surge loads as well.  It would connect to an existing port on the control boards, so the only difficulty would be mounting said connector in the chassis (and as they're stainless steel chassis, that's easier said than done).

[dickson]

We may have to add a (hardwired) inter-inverter comm method, as much as I don't like to--but if properly implemented, that'd handle surge loads as well.  It would connect to an existing port on the control boards, so the only difficulty would be mounting said connector in the chassis (and as they're stainless steel chassis, that's easier said than done).

I  would  buy  2  GS 6kw  if  parallel  2  GS  240 vac  can  handle the surge of a  4 ton heat pump .   

[Sid Genetry Solar]

10 minutes ago, dickson said:

I  would  buy  2  GS 6kw  if  parallel  2  GS  240 vac  can  handle the surge of a  4 ton heat pump .

Not at the current time...at least in parallel mode.  The 6k seems to be able to reach a 77A surge...which is a solid 3x surge.  (Limit there is a hardware limitation.)

If the 2 GS inverters are internally set to 120vAC single-phase output, and run in split-sync...they should be able to handle the startup surge of a 4-ton A/C.  (This has not been tested, however.)

[InPhase]

2 hours ago, Sid Genetry Solar said:

Fair enough 😉

 

If you're using "inverter compressor"-based units, you do not need to be concerned about startup surges.  (It's just the old-as-dust synchronous AC compressors that have the ginormous startup surge.)  I have a Pioneer 1-ton mini-split (12kbtu)...and for startup, it literally starts at under 1A (120v)...and slowly ramps up to full 8A load if required over 30 seconds' time.

OK. That can be done. I suggested mini-split systems from the beginning. We'll use inverter based systems if the 6 kW will supply it comfortably. I think four 6 kW units will probably be sufficient.

[Sid Genetry Solar]

12 minutes ago, InPhase said:

We'll use inverter based systems if the 6 kW will supply it comfortably. I think four 6 kW units will probably be sufficient.

As long as the full load is under 6kw, a 6kw GS inverter should do just fine.  There's no startup surges to be concerned with inverter-based A/C compressors; the water heaters are just instantaneous loads (no surge).

Balancing the loads out across the inverters would be kinda important so you can run everything without overloading any of them.  Another possibility would be running 2 6kw inverters in split-sync mode (one per AC phase) for a 12kw circuit.

[Joe S]

4 hours ago, Sid Genetry Solar said:

Parallel functionality is (like I've told Sean) very difficult to handle...at least via the "no comm harness" method I've been trying to do.  At the moment, the theoretical limit for paralelling inverters would be your wallet...but this has not been tested.  Max testing has only been on 2 units thus far.

We may have to add a (hardwired) inter-inverter comm method, as much as I don't like to--but if properly implemented, that'd handle surge loads as well.  It would connect to an existing port on the control boards, so the only difficulty would be mounting said connector in the chassis (and as they're stainless steel chassis, that's easier said than done).

OK so a hole punched out for a future connector might be worthwhile. 

[dickson]

OK so a hole punched out for a future connector might be worthwhile.

To  parallel  2 GS  6kw inverter by  punching  2 holes  to hardwired  is a lot cheaper than  buying  a 12kw  GS  inverter . 

[Sid Genetry Solar]

9 hours ago, Joe S said:

OK so a hole punched out for a future connector might be worthwhile. 

Yeah...in the NEXT run of inverters.  Chassis are stainless steel, so drilling holes by hand is next to impossible.

[Sid Genetry Solar]

4 hours ago, dickson said:

To  parallel  2 GS  6kw inverter by  punching  2 holes  to hardwired  is a lot cheaper than  buying  a 12kw  GS  inverter . 

We don't know that; as of yet, we still don't have a price.

[InPhase]

So, next question is what kind of lead time is there on 4 inverters? And Ben told me that if I buy four, you'll throw a fifth in free.😏

[Sid Genetry Solar]

2 hours ago, InPhase said:

So, next question is what kind of lead time is there on 4 inverters?

At the moment...I don't know.  I'm sending Sean another box of assembled and tested Rev. C boards hopefully Monday--it's up to him from there.

 

2 hours ago, InPhase said:

And Ben told me that if I buy four, you'll throw a fifth in free.

I wish we had profit margins through the roof and we could make deals like that.  But unfortunately due to our competitive pricing on the inverters, we would be selling at a loss to do that.

[InPhase]

7 hours ago, Sid Genetry Solar said:

At the moment...I don't know.  I'm sending Sean another box of assembled and tested Rev. C boards hopefully Monday--it's up to him from there.

 

I wish we had profit margins through the roof and we could make deals like that.  But unfortunately due to our competitive pricing on the inverters, we would be selling at a loss to do that.

Ben said you'd say that!

 

What is the best means to go through with this order? I need to speak with Sean about lead time. Should I message him from the forum?

[Sid Genetry Solar]

7 minutes ago, InPhase said:

Ben said you'd say that!

Doesn't sound like Ben is giving you very pertinent info, hehe.

 

 

8 minutes ago, InPhase said:

What is the best means to go through with this order? I need to speak with Sean about lead time. Should I message him from the forum?

Texting Sean @ 833-436-3879 is probably the best way to contact him.

[InPhase]

Looking for high voltage input charge controllers that have arc fault protection and ground fault protection. There doesn't seem to be much of a market for off grid stuff, everything is geared toward grid tie. The Magnum PT-100 is my best candidate so far, accepting an absolute max of 240 VDC. I can make that work... But it would be much more convenient if I could find something that would work at 350+ V. Any ideas?

[TheButcher]

I looked into that for someone a couple of years ago and there was pretty much nothing available.  Well at least nothing that wouldn't require life support for you wallet.  Even just getting a standalone PV HV charger without fault protection is hard.  All-in-one inverters go up to about 450VDC and I've seen grid tie go up to around 800VDC (mppt range, Vmax is around 950VDC) but standalones...  just doesn't seem to be something the market is interested in producing.

[Sid Genetry Solar]

43 minutes ago, InPhase said:

Looking for high voltage input charge controllers that have arc fault protection and ground fault protection. There doesn't seem to be much of a market for off grid stuff, everything is geared toward grid tie. The Magnum PT-100 is my best candidate so far, accepting an absolute max of 240 VDC. I can make that work... But it would be much more convenient if I could find something that would work at 350+ V. Any ideas?

Definitely isn't cheap, but Morningstar makes a 600v MPPT: https://www.morningstarcorp.com/products/tristar-mppt-600v/

 

While I don't have one of those 600v MPPTs, I DO have one of their regular TS-MPPT-60 units (150v PV input max).  It is a GREAT little MPPT, as close to perfection as I've yet seen for a 150v input MPPT.  No fans, extremely efficient (full 3200W power load and the heatsink isn't much over 100F), very good MPPT tracking, solid performance, exemplary voltage regulation (doesn't "overshoot" if you instantly go from full load to no load), easy MODBUS comm via RS-232 or LAN (if you get the 60A unit), configurable, etc.

Only issue I had with it was...well...having one blow up when I was trying to adjust the battery charge settings via MODBUS.  Changed the settings (for the 7th time in a row I think)...turned it off via MODBUS command, and then restarted it (via MODBUS command).  It restarted, did the power-up LED sequence...and then blew up with a bright orange flash (simultaneously tripping the battery/solar tandem breakers.)  However, Morningstar's customer service was beyond exemplary--so I am not complaining at all.  If it weren't for the cost, I'd have bought more when I added more solar--but cost and the 150v input limit meant that I ended up with 2 Epever Tracer 8420AN units (200v max).  Very crude and inefficient by comparison--but hey, they get the job done.

 

My current TS-MPPT-60 has 43,045 hours of flawless operation and 8,489kWH of power (connected to 2,940W of solar).  If I had a deeper pocketbook, I'd have exclusively Morningstar MPPTs 😉.

[TheButcher]

I guess the 600V could be used to restart your wallet's heart after it sees how much that thing costs   😆  I use Victron as my primary charger and like your experience with the Morningstar, these things just work.  24 x 7 no issues.  Quite nice these days.  I've pulled 3.07MWh through it to date.   Only disappointment is there doesn't seem to be a self-destruct facility like your Morningstar has.  I guess every silver lining comes with a cloud.  😉

[InPhase]

Morningstar does 600 VDC but doesn't have arc fault protection. The NEC requires arc fault protection on PV over 80 volts if mounted on the building. I guess the Magnum controllers are what I have to go with. There are ways to use an external arc fault detector and shunt trip breakers, but it gets hairy quickly with multiple strings. More expensive than using the Magnums and shorter strings. The manufacturers just aren't interested in stand alone off grid systems apparently.