[RE-wrenches] String Combiners for a-Si modules

Wed Jul 22 12:11:32 PDT 2009

Peter,

The fact that the cut sheet does not have that information should be an
indicator to you. EPV has never manufactured modules much above 42
watts-that's what is currently listed. 

8 in parallel sounds very suspect. They would have to have a series fuse
rating of about 35 amps to pull that off. Remember that the parallel module
currents must be subtracted from the fuse size to determine the final fuse
size when paralleling strings before going to a fuse.  Lots of folks are
claiming to start production on a-Si arrays, and few people have a clue on
how to design arrays for them-least of which are most of the manufacturers. 

Minimum fuse size for 8 strings in parallel:

Isc = 1.49 A

Imax = 1.49 A x 1.25 = 1.86 A

Minimum fuse size for parallel strings = 8 x 1.86A x 1.25 = 18.6 A (20A next
available size)

Fault analysis:

7 strings (n-1) plus series fuse = total current into faulted string

7 x 1.86 = 13.02 A

Total current in fault condition = 13.02A +20 A = 33.02 A (35A next
available size)

I sincerely doubt they are going to come out with a 35A max series fuse
rating for their module. Many PV module manufacturers have done the fault
analysis wrong and only included the fuse as the source of current. I would
expect them manufacturer to say that their max series fuse rating is 20 A
and that 8 strings can be paralleled. That is clearly wrong. From the
previous analysis, it is clear that much fewer than 8 in parallel would be
allowed (maybe 3 or 4 would work-you do the math).

To answer your original question, SMA makes a 52-string combiner box with a
max series fuse of 8 amps. This would be an ideal box for an a-Si array. The
other issue that is often not understood is that most glass a-Si modules
should have blocking diodes for each series string. Broken modules produce
high currents that become pyrovoltaic without diodes.

Bill.

Bill Brooks, PE

Brooks Engineering

873 Kells Circle

Vacaville, CA 95688

Office and Mobile: 707-332-0761

Office Fax: 707-451-7739

email: Bill at BrookSolar.com

www.BrookSolar.com

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Peter
Parrish
Sent: Tuesday, July 21, 2009 5:52 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] String Combiners for a-Si modules

EPV Solar EVP-54

The Isc is 1.49 A

The cut sheet does not list a series fuse rating for the module.

But it does say something about being able to use up to 8 in parallel
without external protection.

I am in the hunt for installation instructions.

- 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.parrish at calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kirpal
Khalsa
Sent: Tuesday, July 21, 2009 3:11 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] String Combiners for a-Si modules

Peter...depending on the series fuse rating you might be able to get away
with more strings in parallel before series fusing is required........what
panels are they and what is the series fuse rating of the modules?
Fronius has a white paper explaining when series fusing is required and when
you can get by without.......it all relates to series fuse rating and
Isc......the higher the series fuse rating and the lower the Isc the more
strings you can parallel with out adding series fusing........
-- 
Sunny Regards,
Kirpal Khalsa
NABCEP Certified Solar PV Installer
Renewable Energy Systems
www.oregonsolarworks.com
541-218-0201 m
541-592-3958 o

On Tue, Jul 21, 2009 at 2:44 PM, Peter Parrish
<peter.parrish at calsolareng.com> wrote:

We are doing an engineering design for a large scale PV ground mount system
based on a-Si modules. Since the Isc of the modules is 1.5 A, instead of 7-8
A of typical c-Si modules, are there special low-current combiners out
there? Does each string need an overcurrent protection device? Any help with
a-Si based system design would be greatly appreciated.

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.parrish at calsolareng.com
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

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