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

[Nick Soleil]

Thanks David and Marv:
    I appreciate the feedback, and have considered the center tap option.  However, I have prefered to either divide the arrays into lower amp circuits (10-12 modules per circuit, depending on the wattage) or to run two AC homerun cables to two half length strings (2- 7 modules strings) per and then combine them at the Soladeck/Combiner Box.  Does Enphase offer the center tap cable on its price lists?

 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: David Brearley <david.brearley at solarprofessional.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Fri, June 11, 2010 1:04:13 PM
Subject: Re: [RE-wrenches] AC wiring loss on micro-inverters

 Re: [RE-wrenches] AC wiring loss on micro-inverters Maybe Marv can help out here. I’ve 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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