SB Disco for 2 strings (was RE: ST XR series, anyone tried on yet? )[RE-wrenches

Fri Jun 21 12:27:57 PDT 2002

In my opinion a really nice dc disco would also have a
combiner box built in.  So, if you are running two
strings of 24vdc panels you can combine them before
the SB, provide string fusing, and have only a single
disco to contend with.  Is my thinking flawed -- any
other suggestions??  We are doing quite a bit of 2
string installs with a single SB.

Thanks!
Mo
--- jberdner at sma-america.com wrote:
> William:
> 
> Two of our customers have been testing the new XR's
> which are
> replacements for older ST's.
> They both tell me they are better than the ST in
> steady state conditions
> (clear sky) but still have trouble if there are any
> clouds in the sky.
> This is really key since we don't all have perfectly
> clear sky days.
> The MPPT seems to get lost if the irradiance is
> changing.
> Now the XR's are only 10 to 15% behind the Sunny Boy
> instead of 20 to
> 25% for the older ST's.
> 10% does not seem like much but would you seriously
> consider an inverter
> that was 80 to 85% efficient instead of one that was
> 94.4 ?
> By the way - I use 92.5% for design by the way not
> 94.4 peak as in the
> CEC calculation
> 
> To address the comment re: internal disconnects.
> We tried to put one in but we can't' get a
> conclusive go ahead from UL.
> The inverters are considered serviceable items and
> therefore you have to
> be able to remove it form the installation and leave
> things in a safe
> condition.  
> Right now this means an external disconnect until UL
> says otherwisw.
> I know the ST /XR does it but that does not mean we
> want to do it too.
> We operate at higher voltages and I want to be safe
> rather than sorry.
> I am working on lower cost disconnects and will let
> you know when we get
> one.
> 
> If you have any questions, or if I can be of any
> further assistance,
> please do not hesitate to contact me.
> 
> Best Regards,
> 
> John Berdner
> 
> SMA America, Inc.
> 20830 Red Dog Road
> Grass Valley, CA  95945
> 530.273.4595 (voice)
> 530.274.7271 (fax) 
> 
> 
> -----Original Message-----
> From: William Miller [mailto:wrmiller at slonet.org] 
> Sent: Thursday, June 20, 2002 9:32 PM
> To: RE-wrenches at topica.com
> Subject: Re: ST XR series, anyone tried on yet?
> [RE-wrenches]
> 
> Bob-o:
> 
> We used to joke that the person who recommended the
> meters on the ST was
> bound to get fired.  I guess he or she did get
> fired.
> 
> I am not impressed that the STs no longer have the
> metering we were used
> to.  I thought this was one of only two advantages
> the ST had over the
> Sunny Boy (the other is built in disconnects).
> 
> Also, it sounds like you are assuming the shut-downs
> are caused by grid
> problems.  Do you have evidence of that?  (After
> watching the original
> ST
> inverters shut down hundreds of times, I am
> convinced it was because the
> MPPT algorithm was too aggressive and, after loading
> the panels too
> much,
> the voltage collapsed.  You could see the PV volts
> cave just before the
> shutdown.)
> 
> I did a  back-to-back comparison between the
> original ST2500 and the
> SB2500
> and found the ST to be about 10% less efficient than
> the SB.  Sounds
> like
> we may be in the same ballpark.  This comparison was
> relevant for the
> periods of time that the ST was running.  Frequent
> shut-downs and the
> subsequent time-outs could reduce the efficiency
> significantly.
> 
> This was actually a trick question as I installed
> two XRs yesterday, but
> wanted to reserve judgement until I heard from
> others.  One of my two
> inverters had a missing lower line on the display. 
> This was also
> disappointing as I have many of display failures in
> the original STs.
> 
> I'm looking for a reason to use STs rather than
> Sunny Boys and I haven't
> found one yet.  With the SB1800s now shipping (they
> are shipping, aren't
> they?) the 1500 no longer fills any kind of gap in
> the product line.
> 
> Thanks for your responses,
> 
> William Miller
> 
> 
> 
> At 10:20 AM 6/20/02 -0700, you wrote:
> >William,
> >We probably ARE all fiends, at that!
> >I've got six of the STXR 2000 in parallel on a big
> system in Redding. 
> >We had a few fits and starts, but at this point
> they all seem to be 
> >playing nicely. I'm seeing about 65-68% conversion
> from PV nameplate 
> >watts to ac watts out. That's about 10% less than
> the Sunny Boy will 
> >give you, but you've got to figure that 48V to 240V
> step up is going 
> >to be less efficient anyway.
> >Roy,
> >Yes, the meter built into the XR shows cumulative
> DAILY watts (resets 
> >every night) ONLY. If you want instantaneous watts,
> volts, etc., you 
> >have to have the STXR remote. Xantrex claims that
> they changed the 
> >display because they were getting too many calls
> from end users 
> >reading it and being confused. Yeah, yeah... maybe.
> On the other 
> >hand, Xantrex is a MARKETING company, so....
> >One cool thing about the remote is the error codes
> feature. It will 
> >tell you how many times the inverter has gone off
> line for 5 minutes 
> >due to poor grid voltage, frequency, overheating,
> etc. It's amazing 
> >how often that happens. So much for grid stability.
> Unfortunately, 
> >the codes are not resettable to zeros (dumb) so you
> have to keep a 
> >running tally from looksee to looksee.
> >Bob-O
> >
> 
>
__________________________________________________________________
> William Miller
> Miller Power and Communications
> PO Box 50, Santa Margarita, CA 93453
> Voice :805-438-5600		Fax: 805-438-4607	VMail:
> 805-546-4875
> email: wrmiller at slonet.org
> http://millerpowerandcomm.com
> License No. C-10-773985
>
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=====
Mo Rousso
Urban Refuge, Inc.
760.451.9374 (v) 760.451.9784 (f)
mrousso at urbanrefuge.com
www.urbanrefuge.com

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