Re: [RE-wrenches] Supply side connection to a dedicated panel

[Mark Frye]

It doesn't sound like you have a "supply side connection". It sounds like
you have a "load side connection" which is upstream of the transfer switch
but still downstream of the service disconnect.

Mark Frye 
Berkeley Solar Electric Systems 
303 Redbud Way 
Nevada City,  CA 95959 
(530) 401-8024 
  www.berkeleysolar.com  
 

  _  

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dave Palumbo
Sent: Monday, October 11, 2010 9:15 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Supply side connection to a dedicated panel



We are installing a 8kW grid tied PV system for a commercial client.  There
is an auto start generator on the premises, therefore we will be utilizing a
supply side AC point of connection. Inverter is an SMA SB8000. System owner
plans on adding to system in the next few years. We are designing for a
total of 24kW  of PV.

 

We will install a 200A fused disconnect off the grid feed (line side of the
generator transfer switch). My plan is install a dedicated breaker panel for
the inverter 240VAC output(s). The SB8000 is rated at 29 Amps, so a 40A DP
breaker will do for the point of connection. This panel will eventually have
a total of (3) 40A DP breakers each with 8kW of inverter output. 

 

My question has to do with the interpretation of the 120 percent rule of the
rating of the busbar in the panel. Do I need to use a 225 Amp rated panel
with a downsized 150A main breaker? 225A busbar x 1.2 = 270 Amps -150A MB =
120A total of inverter output allowed. Or, since this panel will only be
used for inverter AC point of connection, and not for loads, is it allowable
to label this panel as a "Dedicated Panel - connect no loads". If that is
the case we could use a 200A panel, or even a 150Amp panel. A local
electrician proposed this "dedicated panel" to avoid the larger load center
panel. I cannot find any mention of "dedicated panel" in the NEC. 

 

I think what I am proposing follows 690.64. Any opinions, or advice would be
appreciated.

 

Dave Palumbo

Independent Power LLC 

www.independentpowerllc.com 

NABCEP Certified PV Installer

Vermont Solar Partner

802.888.7194 

 

 

 

 

 

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Re: [RE-wrenches] Supply side connection to a dedicated panel

[Jason Szumlanski]

That sounds right, which means that the existing wiring between the service 
disconnect and the transfer switch may also need to be evaluated since it will 
now have sources available at both ends. The rule applies to all bus bars and 
conductors "upstream" of the interconnection point  as I understand it.

Jason Szumlanski
Fafco Solar

On Oct 12, 2010, at 6:25 AM, "Mark Frye"  wrote:

> It doesn't sound like you have a "supply side connection". It sounds like you 
> have a "load side connection" which is upstream of the transfer switch but 
> still downstream of the service disconnect.
> 
> Mark Frye 
> Berkeley Solar Electric Systems 
> 303 Redbud Way 
> Nevada City,  CA 95959 
> (530) 401-8024 
> www.berkeleysolar.com 
>  
> 
> From: re-wrenches-boun...@lists.re-wrenches.org 
> [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dave Palumbo
> Sent: Monday, October 11, 2010 9:15 PM
> To: 'RE-wrenches'
> Subject: Re: [RE-wrenches] Supply side connection to a dedicated panel
> 
> We are installing a 8kW grid tied PV system for a commercial client.  There 
> is an auto start generator on the premises, therefore we will be utilizing a 
> supply side AC point of connection. Inverter is an SMA SB8000. System owner 
> plans on adding to system in the next few years. We are designing for a total 
> of 24kW  of PV.
> 
>  
> 
> We will install a 200A fused disconnect off the grid feed (line side of the 
> generator transfer switch). My plan is install a dedicated breaker panel for 
> the inverter 240VAC output(s). The SB8000 is rated at 29 Amps, so a 40A DP 
> breaker will do for the point of connection. This panel will eventually have 
> a total of (3) 40A DP breakers each with 8kW of inverter output.
> 
>  
> 
> My question has to do with the interpretation of the 120 percent rule of the 
> rating of the busbar in the panel. Do I need to use a 225 Amp rated panel 
> with a downsized 150A main breaker? 225A busbar x 1.2 = 270 Amps -150A MB = 
> 120A total of inverter output allowed. Or, since this panel will only be used 
> for inverter AC point of connection, and not for loads, is it allowable to 
> label this panel as a “Dedicated Panel – connect no loads”. If that is the 
> case we could use a 200A panel, or even a 150Amp panel. A local electrician 
> proposed this “dedicated panel” to avoid the larger load center panel. I 
> cannot find any mention of “dedicated panel” in the NEC.
> 
>  
> 
> I think what I am proposing follows 690.64. Any opinions, or advice would be 
> appreciated.
> 
>  
> 
> Dave Palumbo
> 
> Independent Power LLC
> 
> www.independentpowerllc.com
> 
> NABCEP Certified PV Installer
> 
> Vermont Solar Partner
> 
> 802.888.7194
> 
>  
> 
>  
> 
>  
> 
>  
> 
>  
> 
> 
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Re: [RE-wrenches] need Sanyo HIP modules

[Dan Fink]

Bruce;

Let me know if you find any. I have a client in need of a single 200.
I'm talking the 68 Voc type.
DAN FINK



Bruce Erickson wrote:

Hello Wrenches,
 
Does anyone know of a source for Sanyo HIP 190's, 195's, or even 200's? We have a customer who would like to add 4 to an existing array of 190's.


Thanks,
Bruce

Bruce Erickson
Mendocino Solar Service
PO Box 1252
Mendocino, CA 95460
707-937-1701


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Re: [RE-wrenches] Supply side connection to a dedicated panel

[Mark Frye]

Well yes but, 690.64 (2) is titled and reads "Bus or Conductor Rating". The
"or" is important and the 120% requirement does not apply to the upstream
conductors, in this case.
 
In general, if the sudpanel of 225A where backfeed with the 120A of PV and
had a 150A breaker on its feeder from the main panel, the conductor between
the main panel and the sub need be rated only for the 150A feeder conductor.
 
The size of the feeder tap between the transfer switch lug and the new sub
panel needs to be evaluated differently.
 
I myself am a big fan of 240.21 (B), even when it comes to feeders with PV
on them. I guess some folks are not, but other than the expression of
opinion, I don't see anything to prohibits the use of downsized feeder taps
in PV circuits. I think most folks would go for a downsized conductor to
connect up the new subpanel, so long as it was located right next to the
transfer switch equipment.

Mark Frye 
Berkeley Solar Electric Systems 
303 Redbud Way 
Nevada City,  CA 95959 
(530) 401-8024 
  www.berkeleysolar.com  
 

  _  

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jason
Szumlanski
Sent: Tuesday, October 12, 2010 4:05 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Supply side connection to a dedicated panel


That sounds right, which means that the existing wiring between the service
disconnect and the transfer switch may also need to be evaluated since it
will now have sources available at both ends. The rule applies to all bus
bars and conductors "upstream" of the interconnection point  as I understand
it.

Jason Szumlanski
Fafco Solar
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Re: [RE-wrenches] Supply side connection to a dedicated panel

[Glenn Burt]

There is a good Technical Note on the SMA website that talks about sizing an
AC combining panel that may provide some guidance on this.

 

http://download.sma.de/smaprosa/dateien/4307/Multiple%20SB%20Installation%20
on%203%20Phase%20Utility%20Tech%20Note%20V21.pdf

 

 

-Glenn Burt

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Dave Palumbo
Sent: Tuesday, October 12, 2010 12:15 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Supply side connection to a dedicated panel

 

We are installing a 8kW grid tied PV system for a commercial client.  There
is an auto start generator on the premises, therefore we will be utilizing a
supply side AC point of connection. Inverter is an SMA SB8000. System owner
plans on adding to system in the next few years. We are designing for a
total of 24kW  of PV.

 

We will install a 200A fused disconnect off the grid feed (line side of the
generator transfer switch). My plan is install a dedicated breaker panel for
the inverter 240VAC output(s). The SB8000 is rated at 29 Amps, so a 40A DP
breaker will do for the point of connection. This panel will eventually have
a total of (3) 40A DP breakers each with 8kW of inverter output. 

 

My question has to do with the interpretation of the 120 percent rule of the
rating of the busbar in the panel. Do I need to use a 225 Amp rated panel
with a downsized 150A main breaker? 225A busbar x 1.2 = 270 Amps -150A MB =
120A total of inverter output allowed. Or, since this panel will only be
used for inverter AC point of connection, and not for loads, is it allowable
to label this panel as a "Dedicated Panel - connect no loads". If that is
the case we could use a 200A panel, or even a 150Amp panel. A local
electrician proposed this "dedicated panel" to avoid the larger load center
panel. I cannot find any mention of "dedicated panel" in the NEC. 

 

I think what I am proposing follows 690.64. Any opinions, or advice would be
appreciated.

 

Dave Palumbo

Independent Power LLC 

www.independentpowerllc.com 

NABCEP Certified PV Installer

Vermont Solar Partner

802.888.7194 

 

 

 

 

 

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[RE-wrenches] insolation v. actual output

[Marco Mangelsdorf]

Could someone please provide me with that generally accepted equation when
it comes to estimating AC output from a PV array versus the STC rating?

 

That is, I'm looking for that equation which estimates the losses due to mod
mismatch, soiling, wire losses, etc., etc.  I've got someone who mistakenly
expects their PV array to put out 90 or more percent of the STC rating.

 

Thanks,

marco

 

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Re: [RE-wrenches] insolation v. actual output

[Mike Nelson]

Marco
I use 75% as a general rule, it seems to work out well. I've gotten upwards
of 80% on certain enphase & sanyo installations.

Mike Nelson
MD Electric & Solar, Inc.
Gualala, Ca. 95445

On Tue, Oct 12, 2010 at 6:17 PM, Marco Mangelsdorf wrote:

>  Could someone please provide me with that generally accepted equation
> when it comes to estimating AC output from a PV array versus the STC rating?
>
>
>
> That is, I’m looking for that equation which estimates the losses due to
> mod mismatch, soiling, wire losses, etc., etc.  I’ve got someone who
> mistakenly expects their PV array to put out 90 or more percent of the STC
> rating.
>
>
>
> Thanks,
>
> marco
>
>
>
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Re: [RE-wrenches] insolation v. actual output

[Marco Mangelsdorf]

Yeah, but I'm looking for the equation as to how you get to that 75-80
percent figure.

 

marco

 

Marco

I use 75% as a general rule, it seems to work out well. I've gotten upwards
of 80% on certain enphase & sanyo installations.

 

Mike Nelson

MD Electric & Solar, Inc.

Gualala, Ca. 95445

On Tue, Oct 12, 2010 at 6:17 PM, Marco Mangelsdorf 
wrote:

Could someone please provide me with that generally accepted equation when
it comes to estimating AC output from a PV array versus the STC rating?

 

That is, I'm looking for that equation which estimates the losses due to mod
mismatch, soiling, wire losses, etc., etc.  I've got someone who mistakenly
expects their PV array to put out 90 or more percent of the STC rating.

 

Thanks,

marco

 

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Re: [RE-wrenches] insolation v. actual output

[Kent Osterberg]

Marco,

This may be what you are looking for:
http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/derate.cgi

Kent Osterberg
Blue Mountain Solar


Marco Mangelsdorf wrote:

  
  
  

  
  Could someone please provide me with that
generally accepted
equation when it comes to estimating AC output from a PV array versus
the STC
rating?
   
  That is, I’m looking for that equation which
estimates
the losses due to mod mismatch, soiling, wire losses, etc., etc.  I’ve
got someone who mistakenly expects their PV array to put out 90 or more
percent
of the STC rating.
   
  Thanks,
  marco
   
  
  

  



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Re: [RE-wrenches] insolation v. actual output

[Kent Osterberg]

Marco,

Just playing around with these factors a bit shows you can get 90%, if
the modules have -0% tolerance and they are spotless clean.  

Kent


Kent Osterberg wrote:

  
Marco,
  
This may be what you are looking for:
  http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/derate.cgi
  
Kent Osterberg
Blue Mountain Solar
  
  
Marco Mangelsdorf wrote:
  




Could someone please provide me with that
generally accepted
equation when it comes to estimating AC output from a PV array versus
the STC
rating?
 
That is, I’m looking for that equation which
estimates
the losses due to mod mismatch, soiling, wire losses, etc., etc.  I’ve
got someone who mistakenly expects their PV array to put out 90 or more
percent
of the STC rating.
 
Thanks,
marco
 

  



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Re: [RE-wrenches] insolation v. actual output

[Peter Parrish]

Hi Marco,

First off, the P-ptc/P-stc ratio is 90% if you have a high-quality module.
>From their things get progressively worse.

IMHO it is like peeling an onion. From the outside it can be reduced to one
simple statement. Then you can investigate some of the simplifying
assumptions and make more sophisticated calculations based “actual data”. I
won’t start with an “equation” but a “rule of thumb”.

In Southern California 20-60 miles east from the ocean, with a roof facing
South and pitched at 5:12, with 3-6” of air space between the roof and the
modules, no shading, a good inverter (weighted 95% efficiency), and modules
with a PTC/STC rating of 90%, and all dc and ac runs using #10 wire...

One (1) kW-stc should produce 4.25 kWh per day, averaged over a year.

Less than optimum orientation, closer to the ocean and say a 3:12 roof
pitch, less than or equal to 3” off the roof, maybe an inverter with a 93%
efficiency, 50’ plus of #12 wire runs…

The number drops to 3.9 kWh per kW-dc averaged over a year.

I am surprised how well the two numbers bracket the actual numbers.

If you want an “equation” with a dozen independent parameters that you can
set…ask yourself how many of those parameters you actually have independent
verification and can “plug and chug” with any confidence? 

You can try PVWatts (which takes into account everything you have asked for)
or the EPBB calculator and compare them. 

PVWatts breaks everything down into two steps: (1) the microclimate,
orientation, array type (fixed, or tracking) and P-stc, and (2) inverter
efficiency, ac and dc losses, module mismatch, soiling, shading, etc. I
think that the algorithms behind PVWatts are pretty straightforward, and in
the case of step #2, it is pretty much a series of multiplicative factors.

Let me drop in one question, "If PV mfgr XYZ says that their P-stc numbers
are +0 / -3%, how do you translate that into a "module mismatch" percentage?

But ultimately you have to take into account that a given year’s weather
differs from the 30 year mean by +/- 6% (experts correct me here, and if you
do please introduce the concept of standard deviation), so don’t let your
customer pin you down based on 1 year’s data.

Bottom line: take a close look at PV Watts and consult with the folks at
NREL.

- Peter

 
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parr...@calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

 

From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Marco
Mangelsdorf
Sent: Tuesday, October 12, 2010 6:17 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] insolation v. actual output

Could someone please provide me with that generally accepted equation when
it comes to estimating AC output from a PV array versus the STC rating?

That is, I’m looking for that equation which estimates the losses due to mod
mismatch, soiling, wire losses, etc., etc.  I’ve got someone who mistakenly
expects their PV array to put out 90 or more percent of the STC rating.

Thanks,
marco



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