[RE-wrenches] Add-On to DGT, string inverter, w/Different Modules on 2nd string

[Ash Bowersock]

Thanks for the good info Brian. I had tried to explain the single MPPT issue to the client, but probably didn’t use the right words and just made him mad because “the system was designed to accomidate an addition”… ughhhh.

Ash Bowersock
Senior System Designer
[RGS Energy]<http://www.rgsenergy.com/>


833 W. South Boulder Road | Louisville, CO 80027
tel 303.222.8387

RGSEnergy.com<http://www.rgsenergy.com/>

Confidentiality Note: This e-mail message may contain confidential or legally privileged information and is intended only for the use of the intended recipient(s). Any unauthorized disclosure, dissemination, distribution, copying or the taking of any action in reliance on the information herein is prohibited. E-mails are not secure and cannot be guaranteed to be error free as they can be intercepted, amended, or contain viruses. Anyone who communicates with us by e-mail is deemed to have accepted these risks. RGS Energy is not responsible for errors or omissions in this message and denies any responsibility for any damage arising from the use of e-mail. Any opinion and other statement contained in this message and any attachment are solely those of the author and do not necessarily represent those of the company.



From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Brian Mehalic
Sent: Tuesday, June 21, 2016 2:00 PM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] Add-On to DGT, string inverter, w/Different Modules on 2nd string

An inverter with a single MPPT can only operate at a single DC voltage at any one time; with two different PV source circuits of different voltages, then the inverter will be unable to operate at the MPPT of the combined array (the operating voltage may be the actual Vmp of one string, but probably not both, and maybe not either!).

Try to match the voltages if possible - I believe the 175s are 72 cell modules (i.e. 864 cells in series for the 12 module source circuit) and the 280s are 60 cell, so 14 or 15 of them in series would best match the voltage of the old mods (maybe 14 assuming there has been some voltage degradation of the older mods).


Brian Mehalic
NABCEP Certified Solar PV Installation Professional™ R031508-59

Solar Energy International
http://www.solarenergy.org

SEI Professional Services
http://www.seisolarpros.com


On Tue, Jun 21, 2016 at 1:47 PM, Ash Bowersock <Ash.Bowersock at rgsenergy.com<mailto:Ash.Bowersock at rgsenergy.com>> wrote:
Good day RE Wrench crew,
I’ve got a client whom installed a 2kW array with a 3kW SunnyBoy inverter a number of years back. Due to the age of the system I assume it is single MPPT. The client oversized his inverter in the hopes of using it for this future expansion (and unfortunately his installer went along with it). The original modules were 12 SolarWorld 175’s I believe, and we would be looking at adding SolarWorld 280’s more than likely. To me it is clear that this is poor design practice and not something I am willing to do. My recommendation is a micro-inverter system that we tie in w/his existing using an AC Combiner. But the client wants to know exactly why we don’t want to just add a second string of 12 SolarWorld 280’s to his 6 year old SunnyBoy inverter.
Can someone please give me a technical reason why mixed modules on a string inverter is “poor design practice”?
The more technical and dry an explanation, the better ;)
If you can’t convince them, bore them to tears with the details.

Ash Bowersock
Senior System Designer
[Image removed by sender. RGS Energy]<http://www.rgsenergy.com/>


833 W. South Boulder Road | Louisville, CO 80027
tel 303.222.8387<tel:303.222.8387>

RGSEnergy.com<http://www.rgsenergy.com/>

Confidentiality Note: This e-mail message may contain confidential or legally privileged information and is intended only for the use of the intended recipient(s). Any unauthorized disclosure, dissemination, distribution, copying or the taking of any action in reliance on the information herein is prohibited. E-mails are not secure and cannot be guaranteed to be error free as they can be intercepted, amended, or contain viruses. Anyone who communicates with us by e-mail is deemed to have accepted these risks. RGS Energy is not responsible for errors or omissions in this message and denies any responsibility for any damage arising from the use of e-mail. Any opinion and other statement contained in this message and any attachment are solely those of the author and do not necessarily represent those of the company.




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