[RE-wrenches] 208 3 phase Off Grid Inverter

Ray Walters ray at solarray.com
Tue Mar 25 21:07:04 PDT 2014


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 <ray at solarray.com> 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: re-wrenches-bounces at lists.re-wrenches.org
>>> [mailto:re-wrenches-bounces at lists.re-wrenches.org]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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