I've looked at AC coupling for years, and it makes lots of sense if
retrofitting battery backup to an existing GT system. Its # 1 reason
its so popular I think, is that it allows install crews that are only
used to GT wiring to use the same methods off grid. Otherwise, its
really way more expensive.
Just compare the costs of an 80 amp MPPT charge controller at 48 v to an
4000 w GT Inverter. The inverter is almost 4 times the cost.
The extra surge capability is interesting and would help in my
situation, but we're in trouble if a cloud passes over when the air
conditioning kicks on.......
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 3/25/2014 8:53 PM, William Miller wrote:
Ray:
I went through the same set of mental Q&A you are when I was exposed to my
first AC coupled system. That was at least a week ago so I've forgotten almost
everything I learned except two things:
1. The distance thing you brought up.
2. If you perchance need extra AC wattage during sunny hours, you have it
because you have the GT inverters creating AC and helping the GT inverters.
This may be a rare load profile, but the possibility does exist.
The SMA white paper proposed by another wrench sums up the Pros pretty well.
Let me know if you need a copy.
William
Miller Solar
On Mar 25, 2014, at 5:42 PM, Ray Walters <[email protected]> wrote:
I had another related question to add to using the SMA SI inverters: Can't we
still use regular charge controllers to charge the battery, and just use the
SIs as inverters, and gen in charging only?
I don't see justification for the extra cost of an AC coupled system here. The
array will be on the garage roof, with equipment below. Only 50 ft run for the
PV, so I was planning on using Midnite Classics.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 3/25/2014 4:21 PM, Kevin Pegg wrote:
Hi Ray,
I have several 3-phase off-grid inverter/battery/generator systems out there.
- SMA Sunny Island is the best. Can scale to at least 180 kW, maybe more. Reliable
& very solid. I have several sites going over 2 years without a single second
of power outage.
- Xantrex XW. It can work in a 3-ph config, but it's not as stable system. We
have taken to preventatively rebooting the systems every 4 months and that
helps a lot - at least the outage can be planned and on our terms.
- Outback has had so many power quality nightmares I won't go there anymore.
- I believe Magnum has a 3-ph option but haven't installed one yet.
SMA inverters are more expensive. And they work very well. They also have a
very good battery charging algorithm and integral gen start control.
Kevin
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Ray
Walters
Sent: March 24, 2014 6:44 PM
To: RE-wrenches
Subject: [RE-wrenches] 208 3 phase Off Grid Inverter
Hi All;
I'm exploring options for an off grid project with an existing 30 Kw
Kohler wired for 208 vac 3 phase. The generator runs some 8 hp air
compressors, so rewiring it is not an option. We're primarily
interested in reducing gen run time from the current situation: 14 hrs/ day.
So far, only the Outback VFX inverters seem capable of being wired in
208, 3 phase, but according to the manual they can only be stacked 1
inverter per leg. This limits the system to only 3 inverters total, or
10.8 kW. I would like expandability beyond this.
1) are there any other inverters available that I'm over looking?
2) Should I consider a transformer to convert from 208 vac/3phase to 240
vac/ singe phase?
We're not going to even try to run the compressors, just the other
single phase loads, mostly 120 vac, but we have a couple of small air
conditioners, that are currently running on 208 single phase. I believe
they would run fine on 240 vac, as they have a name plate rating at 230 vac.
3) We may possibly run 2 separate 3 inverter stacks and only tie
together at the battery, but otherwise they would not be connected. This
seems inefficient, and would require some load balancing of the various
inverters.
All help and discussion is greatly appreciated as always,
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