[RE-wrenches] Voltage Degradation with Uni-Solar laminate

[Luke Christy]

Thanks to everyone for your responses, both on and off-list. You guys rock.

Allan,
The system was originally installed in 2000 with an Ananda controller/disconnect box. The giant one with the mercury relays. It failed about 6 years ago and an MX-60 was installed to replace it. I agree that a modern controller is a no-brainer. I'd like to avoid having to replace the MX-60, but i don't see any way around it if I do a re-wire. 

To Ray's point, doing the string sizing exercise shows that a Classic 250 with 8 mods in series is probably the easiest solution, although there might be clipping in some circumstances.
The existing MX-60 is in trouble for anything over 5 in series. 
-Luke



On May 31, 2015, at 11:30 PM, Allan Sindelar <allan at sindelarsolar.com> wrote:

> Luke,
> I deleted your first message, but I thought you wrote that the system was pre-MPPT, with strings wired as 4 12 Vnom in series. IT seems to me that given insufficient Vmp, a modern controller is a no-brainer anyway, and it's only a matter to which one to use.
> 
> A Classic 250 is the easy route that lets you solve a major problem with a simple and sensible component upgrade. It'll cost the customer nearly as much for a winter return trip to estimate Voc.
> But I agree with Jay and Randy: first check the existing array for failures.
> Allan
> 
> Allan Sindelar
> allan at sindelarsolar.com
> NABCEP Certified PV Installation Professional
> NABCEP Certified Technical Sales Professional
> New Mexico EE98J Journeyman Electrician
> Founder (Retired), Positive Energy, Inc.
> 505 780-2738 cell
> 
>  
> On 5/31/2015 11:22 PM, Luke Christy wrote:
>> Allen, 
>> With 8 modules in series I think I'll be looking at a Classic 250 for sure to be comfortable with winter morning VOC. 
>> I don't really know what kind of combiner situation I'll find up in the attic. It may be easy enough to re-wire into strings of 6 instead of strings of 8, though that is still probably going to push me just over the 150 VOC hard limit of the MX-60. I may not be able to get around replacing the controller. 
>> 
>> -Luke
>> 
>> 
>> 
>> On May 31, 2015, at 10:59 PM, Allan Sindelar 
>> <allan at sindelarsolar.com>
>>  wrote:
>> 
>> 
>>> Jay,
>>> Whoa, I'd be careful there. Unless there's been a change while I was away on my bicycle, Outbacks are still 140V rated maximum voltage and 150V hard maximum. 142Voc in May suggests that doubling strings in series will easily exceed max Voc in winter. That's why I previously suggested Classic 200 or 250. Am I missing something?
>>> Allan
>>> 
>>> Allan Sindelar
>>> 
>>> allan at sindelarsolar.com
>>> 
>>> NABCEP Certified PV Installation Professional
>>> NABCEP Certified Technical Sales Professional
>>> New Mexico EE98J Journeyman Electrician
>>> Founder (Retired), Positive Energy, Inc.
>>> 505 780-2738 cell
>>> 
>>>  
>>> On 5/31/2015 2:23 PM, jay peltz wrote:
>>> 
>>>> HI Luke,
>>>> 
>>>> To add here.  I'm unclear if you have measured each string or the whole array at 71v.  
>>>> I would check each string for voc/isc.  
>>>> 
>>>> And then if they are consistent, I agree that putting 2 strings in series with a new controller might help out.  
>>>> You can try it with the MX-60 as you are at only 142v. If it works better then a new higher voltage CC would be required for winter higher voc.
>>>> 
>>>> Let us know what you find out.
>>>> 
>>>> jay
>>>> 
>>>> 
>>>> 
>> Luke Christy
>> 
>> NABCEP Certified PV Installation Professional™: Certification #031409-25 
>> NABCEP Certified Solar Heating Installer™: Certification #ST032611-03       
>> CoSEIA Certified PV Installer 
>> 
>> Solar Gain Services, LLC
>> PO Box 531
>> Monte Vista, CO. 81144
>> 
>> SGSRenewables at Gmail.com
>> 
>> 719.588.3044
>> 
>> www.sgsrenewables.com
>> 
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Luke Christy

NABCEP Certified PV Installation Professional™: Certification #031409-25 
NABCEP Certified Solar Heating Installer™: Certification #ST032611-03       
CoSEIA Certified PV Installer 

Solar Gain Services, LLC
PO Box 531
Monte Vista, CO. 81144
SGSRenewables at Gmail.com
719.588.3044
www.sgsrenewables.com