[RE-wrenches] central vrs string inverters

Marco Mangelsdorf marco at pvthawaii.com
Sat Jun 27 09:57:01 PDT 2015


Hey Al,

 

I had a similar choice to make several months ago.  There are not that many options out here in Hawaii—given the more demanding utility requirements for grid-tie inverters—for string inverters that are true 3-phase 120/208 while the choices are more abundant if you have 277/480 as the service voltage.  The Fronius Symo has a 12 kW @ 120/208 model which I plan to use soon.

 

For this last ~ 100 kW system we did, we used five SMA Tripowers and a step-down x-former to bring the voltage down to 120/208.  As for transformers, note that Dongan (made in the U.S.) offers such high-efficiency x-formers even in stainless steel enclosures at a very reasonable price.  Given the 1,000V DC max input possible for the Tripowers, we went into unknown territory with the AHJ here on the Big Island.  While I spec’ed out 1 kV-rated conductors for the + and – DC conductors, I realized late in the game that I needed to use 1 kV-rated EGC wire from the roof as well.  D’oh!  Trying finding some of that at your local electrical supply.  Finally, to my surprise and somewhat annoyance, we are being required to erect a protective barrier, i.e., fence, around the inverters—which are mounted on the exterior wall of a medical professional building—in order to keep them beyond the reach of the public, even though one would have to take covers off in order to expose the conductors.

 

Always an adventure.

 

marco

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jason Szumlanski
Sent: Friday, June 26, 2015 9:39 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] central vrs string inverters

 

I don't have anything in terms of advice on the Tri-Power, but I have done microinverters on straight 208V three-phase and also 480V with a step-down transformer. While there are more potential points of failure, future service is straightforward. There are lots of capable people who can swap a micro. We have been called out to several 20-100kW central inverters that were essentially unserviceable due to obsolescence, bankruptcy, parts availability, and lack of qualified personnel. That could be a function of the crummy Florida commercial solar market, but it's something to consider. Lifetime service and replacement costs need to be considered in the ROI analysis, and despite micro's higher initial cost, there is a good argument to be made...

 

On the other hand, while I have never used a Tri-Power, SMA's Sunny Boy's have been rock solid around here in demanding conditions.

 

Jason Szumlanski


 

 

On Fri, Jun 26, 2015 at 9:26 AM, Allen Frishman <amfrish at aeonsolar.com> wrote:

Hi Wrenchers,

I am considering using 8 SMA Tri-power Inverters for a project with a 3 phase 208V Grid which means I have to add a step down transformer (480V to 208V).    I am comparing this option to a central inverter.    I have done many of the central inverter systems at the 208V but have yet to try the 20+ KW string inverters with the addition of a step down transformer.

 

I know that both systems have there own pros and cons and I will really appreciate some feedback from those that have experience doing both types.   

 

For the central inverter there are fewer inverters to malfunction however when one does the entire system is down.   In my experience the Central Inverters that I have used have been very reliable.       

- Anyone seeing reliability issues with the SMA Tri-power 20KW and 24KW string inverters?

 

Note:   My project is under NEC 2008.

 

All feedback is appreciated.

 

Al Frishman
AeonSolar

(917) 699-6641 <tel:%28917%29%20699-6641>  - cell
(888) 460-2867 <tel:%28888%29%20460-2867> 
www.aeonsolar.com <http://www.aeonsolar.com/> 

 

 

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