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

[Jerry Shafer]

I have 12 sharp 72 cell and that only 444 voc so that should not be an
issue, yes l know he has SW but they are very close
Jerry
On Jun 21, 2016 10:31 AM, "Brian Teitelbaum" <bteitelbaum at aeesolar.com>
wrote:

> Hi Ash,
>
>
>
> Are you sure that there are 12 of the SolarWorld 175’s on a single string?
>
>
>
> Those were 72-cell modules, and I would think that having 12 in series in
> CO would see open-circuit voltages over 600 VDC at least on some occasions.
> That’s 864 cells in series, with would be about equal to having 14.4
> typical 60-cell modules in series. That sounds too high to me for CO.
>
>
>
> One option would be to reduce the number of 175’s to 10 (720 cells in
> series) and match them with 12 of the 60-cell modules (also 720 cells in
> series). The older modules are 5” cells, so their amperage would be lower,
> but as long as you get the voltage as close as possible it should be fine.
> Of course, this doesn’t account for degradation, so you may want to do some
> actual voltage measurements on the old modules.
>
>
>
> One thing though – since twelve 280W modules is about 3360W, and you have
> a 3kW inverter, there really isn’t enough room to add. The older Sunny Boys
> had a much narrower MPPT voltage range, so I doubt that you could use
> strings shorter than nine 60-cell modules. I don’t see how you would be
> able to add much to the old inverter anyway. Adding a second inverter
> system may be your only option, unless you can find some used 175’s. 18 or
> 20 of the 175’s, in two strings, should work fine on the 3kW Sunny Boy.
>
>
>
> Brian Teitelbaum
>
> AEE Solar
>
>
>
>
>
> *From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
> Behalf Of *Ash Bowersock
> *Sent:* Tuesday, June 21, 2016 12:48 PM
> *To:* re-wrenches at lists.re-wrenches.org
> *Subject:* [RE-wrenches] Add-On to DGT, string inverter, w/Different
> Modules on 2nd string
>
>
>
> 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: RGS Energy] <http://www.rgsenergy.com/>
>
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> tel 303.222.8387
>
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