Mark, Enphase actually has a pretty good explanation of voltage drop calculations in their downloads- it's under application notes and details the drop through their cable so you can determine what voltage each of the micro-inverters will see. From that you can calculate additional losses and see how close you are getting to the high limit. You also need to know your starting point- the foothills in CA have a lot of areas where nominal line voltage is right up at the max allowable to start with, leaving very little headroom.
Gary Handelin, P.E. Solar Independence From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Nick Soleil Sent: Tuesday, February 15, 2011 10:01 AM To: RE-wrenches Subject: Re: [RE-wrenches] Can I handle the voltage drop? Hi Mark: I wouldn't feel comfortable with that scenario, either. Many inverters do shut off at 254V-255V, but most of them can be adjusted if you have the software and laptop for the job. Enphase generally shuts off when the AC voltage reaches 258V-259V. Keep in mind that just the Enphase cabling can add an additional 1.75% to the rise. I break my Enphase circuits into two sub-circuits of half length. Enphase is defintitely more tolerant of voltage issues than other inverters. Xantrex is the worst, but can be adjusted. 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: Mark Frye <ma...@berkeleysolar.com> To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Sent: Mon, February 14, 2011 7:42:11 PM Subject: [RE-wrenches] Can I handle the voltage drop? Folks, I am working on a proposal. It's a ground mount 300+ feet from the meter. There is an existing, near by run of #2 copper I can tap into. The desired system is relatively large, 64 amps AC max. I have modeled the yield using PV watts hourly data, applying a power loss based on the voltage drop at the varying current. This model shows a 3% loss in annual yield with the #2 copper. Because of the economics of the system, we can absorb this loss. My concern however is that I do not want the inverters to shut down when operating at higher currents. I do not want a high AC line voltage fault due to the voltage drop on the line. At the 64 amps max, the drop would be about 4%. Of course all the manufactures I talk with recommend keeping the drop on the AC below 1.5%. I am looking at using Enphase inverters which spec an AC voltage range up to 264V, or 10% above 240V nominal. What experience have folks had out there? How far can one realistically push the 1.5% limit and still avoid AC voltage faults when there is high voltage drop on the line? My guess is that everything would work out fine, but I stand to loss a huge amount of energy if the inverters are spending all their time faulting and resetting during daily peaks. Mark Frye Berkeley Solar Electric Systems 303 Redbud Way Nevada City, CA 95959 (530) 401-8024 <http://www.berkeleysolar.com> www.berkeleysolar.com
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