[RE-wrenches] AC wiring loss on micro-inverters

[David Brearley]

Maybe Marv can help out here. I¹ve talked with tech support at Enphase and
am under the impression that you can center tap their branch circuits to
reduce voltage drop. This technique was used on a project that we profiled
in SolarPro:

http://solarprofessional.com/article/?file=SP3_2_pg92_Projects_1&search=

David Brearley, Senior Technical Editor
SolarPro magazine 


On 6/11/10 2:50 PM, "Nick Soleil" <nicksoleilsolar at yahoo.com> wrote:

> Did you notice that in my calculation I divided the total amperage by 2 to get
> the average ampacity across the string.  This seems to be the best way to deal
> with that.  Otherwise the loss would have been over 2.8%
>  
> Nick Soleil
> Project Manager
> Advanced Alternative Energy Solutions, LLC
> PO Box 657
> Petaluma, CA 94953
> Cell:   707-321-2937
> Office: 707-789-9537
> Fax:    707-769-9037
> 
> 
> 
> From: "markf at berkeleysolar.com" <markf at berkeleysolar.com>
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
> Sent: Fri, June 11, 2010 7:02:00 AM
> Subject: Re: [RE-wrenches] AC wiring loss on micro-inverters
> 
> Nick,
> 
> Good to see other wrenches looking at this issue.  However, remember that
> in the interconnect cable between the last and the second to last Enphase,
> the current is small. If you really want to see how the loss is adding up
> you need a more detailed analysis that averages the voltage drop for the
> entire system of interconnect cables.
> 
> Mark Frye
> Berkeley solar Electric Systems
> 
>> > Hello wrenches and Marv:
>> >     How many Enphase inverters do you put on a single parallel string?
>> > The Enphase manual allows for up to 15, but I have found that a single
>> > string of 15 can have very high voltage rise on the AC wiring.  Up to
>> > 1.5% loss just on the Enphase cables, and that does not take into
>> > account resistance at the plug connectors or any home-run wiring.
>> >     15 inverters x 190 watts = 2850 watts
>> >     2850 watts / 240 Volts = 11.875 Amps (however at the beginning of the
>> > string it is 0 Amps)
>> >     Average Amps on the Enphase cables is 11.875 / 2 = 5.9375 Amps
>> >     length of contacts + internal wiring = ~6'
>> >     Total Enphase cabling length (6' x 15 inverters) = ~90'
>> >     5.9375 Amps @ 240 V running 90' on #14 AWG CU = 1.4% loss
>> > It is pretty hard to design for 1.5% voltage  drop if you have to size for
>> > 0% loss on your wiring!  I hope Enphase will increase the size of the wire
>> > in their cables soon.  Have you experienced issues with micro-inverters
>> > shutting off due to high AC voltages?
>> >
>> >  Nick Soleil
>> > Project Manager
>> > Advanced Alternative Energy Solutions, LLC
>> > PO Box 657
>> > Petaluma, CA 94953
>> > Cell:   707-321-2937
>> > Office: 707-789-9537
>> > Fax:    707-769-9037
>> >
>> >
>> >
>> >
>> > ________________________________
>> > From: i2p <i2p at aol.com>
>> > To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
>> > Sent: Thu, June 10, 2010 4:50:47 PM
>> > Subject: Re: [RE-wrenches] Real world PV production
>> >
>> >
>> >
>> > On Jun 10, 2010, at 7:57:53 AM, "Kelly Keilwitz, Whidbey Sun & Wind"
>> > <kelly at whidbeysunwind.com> wrote:
>> >
>> > PV Watts VASTLY underestimate PV production
>>> >>  in our area.
>> > PV Watts underestimates in Central Ca too.
>> >
>> > Don
>> >
>> >
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> 
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