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

jay peltz jay at asis.com
Fri Jun 11 09:12:32 PDT 2010


Hi Nick,

You bring up a good point that Enphase should address more clearly.
However, I think the math should be done section by section to accurately account for the wire loss and not the total combined amps for the entire length.
If the loss's are too high then reducing the number in each string to an acceptable wire loss would be my recommendation.


On Jun 11, 2010, at 12:14 AM, Nick Soleil wrote:

> 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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