I've had the exact same problem except we also had high voltage at the transformer due to a utility substation being rebuilt. We had to open the voltage window of the inverter and that solved the issues.
On Wed, Aug 17, 2016 at 2:12 AM, <[email protected]> wrote: > Howard- > Any voltage drop at the house will be a function of current drawn by the > house load. Shut off most loads and there will be minimal voltage drop. If > there was a low voltage issue now before solar is installed, there would be > symptoms like florescent lights not working well. That's why they flicker > when a big motor kicks on nearby. > A transformer could be used to boost the voltage to the house, but that > assumes more or less constant load. When the house load is low there is > minimal voltage drop and the boosted voltage may become too high. The > utility service transformer may have different wire taps to adjust its > output voltage as well. But again, this assumes more or less constant load. > When there are long wire runs it is more common to use a pair of > transformers, one at the utility drop and one at the house, to boost (or > step up) the voltage at the service drop end to, say, 480 with a 2:1 > transformer. That is, the ratio of number of primary to secondary windings > is 2:1. Then at the house another matching transformer bucks (steps down) > the voltage back to 240. > The current in the long wire run is cut in half, and so is voltage drop. > This boosted voltage can be higher-- thousands of volts are not uncommon > on ranch properties with miles-long wire runs. > > A solar inverter senses the voltage at it's connection point, and raises > it's voltage a couple volts higher to push solar current into the wire. If > there is voltage drop in the wire, the solar inverter must raise it's > voltage even higher to overcome voltage drop and still be a couple volts > above the grid. If voltage drop is severe, the inverter will sense that > it's voltage is getting too high out of range and fault with a grid voltage > error. Grid voltage is not changing, inverter voltage is. > For example, we had an inverter sited at a 10 KW array connected to a > garage with 200' of existing 6 AWG AL buried wire. The attendant voltage > drop from nearly 40 amps solar current caused the inverter to raise it's > own voltage so much to overcome voltage drop that it faulted. It was > necessary to tweak the software settings to allow the voltage range to be > extended. > > When your client's 20 KW solar inverter is sited at the house, any solar > current will first be consumed by the house loads. This reduces current > through the long wire run and so reduces voltage drop. When the solar > current matches the house loads, no current flows through the long wire run > and there is no voltage drop. Everyone is happy, except the utility company > who now doesn't get to sell energy. > Excess solar current not consumed by house loads will run back through the > long wire to the utility grid, causing some voltage drop. This must be > overcome by the inverter raising it's voltage to still be a couple volts > over grid-voltage-plus-voltage-drop. > Without running the numbers I suspect that the less-than-40 solar amps you > may run into 4/0 AL wire will not be a problem. > > You will want to measure the voltage at the house under low and maximum > load conditions. > If the load is at max when the sun shines, a solar inverter will tend to > help alleviate any low voltage issue at the house, as Ray W. wrote. > > Don Barch > Energy Solar > > > Date: Tue, 16 Aug 2016 14:23:27 -0600 > From: Ray Walters <[email protected]> > To: RE-wrenches <[email protected]> > Subject: Re: [RE-wrenches] Buck-Boost transformer to mitigate high > voltage drop? > Message-ID: <[email protected]> > Content-Type: text/plain; charset="windows-1252"; Format="flowed" > > My guess is that in your case the GTPV will just help alleviate the volt > drop situation. I wouldn't start adding transformers, etc until you are > having a problem. Put in the contract that this extra cost may be > necessary for proper function, but I would keep it as a backup. Based > on the numbers you just mentioned, you would only be selling a surplus > of 30 amps, and the existing wire should be adequate for that. > > R.Ray Walters > CTO, Solarray, Inc > Nabcep Certified PV Installer, > Licensed Master Electrician > Solar Design Engineer > 303 505-8760 > > On 8/16/2016 1:16 PM, Howard Arey wrote: > > > > Answers to all: > > > > No ? I did not measure voltage at the house. Right now, only an > > assumption of voltage drop based on my perception of what ?typical? > > loads might be on this 150-amp service. I wasn?t expecting to see such > > small wires for such a long run from transformer to house when I > > showed up there without a voltmeter. He is a heavy user, using 6,000 > > kwh in some months > > > > We?re looking at a 20KW system (he has some other expansion > > requirements, he has the roof space, and the need.) I roughly estimate > > that he?ll use onsite 40-50 amps of the 82 amps at peak inverter power > > output. > > > > Interesting to hear of one transformer response and hope to learn more > > on that, too. > > > > *Howard ?Scot? Arey* > > > > Owner, Solar CenTex > > > > 254-300-1228 > > > > [email protected] > > > > www.solarcentex.com <http://www.solarcentex.com/> > > > > https://www.facebook.com/SolarCentex > > > > Rated #1 Solar Installer in Texas by Solar Reviews > > <http://www.solarreviews.com/solar-companies/top-100- > residential-solar-power-contractors-2016/texas/>__ > > > > Solar Centex Logo - No Back > > > > > On Tue, Aug 16, 2016 at 12:16 PM, Howard Arey <[email protected]> > wrote: > > Good day, > > > > I have a potential client that has an existing 1,000 foot run from the > meter and transformer at the street to the home. This is 4/0 Al and quick > calcs show the voltage drop at over 12%. He acknowledges that the wire is > undersized to keep voltage at/about 240 volts (I have not measured directly > at the street / transformer yet). > > > > I know the wire has the necessary ampacity to carry his current service > needs and to carry amps from the to-be-suggested solar system. > > > > My concern is that the voltage drop will change the 240 volts at the > street/transformer/meter to 211ish (or will I see a higher 268?sh voltage > at the far house end?) at the house. The inverter will try to synch to this > voltage but of course this is outside of typical inverter parameters. > > > > So, instead of re-running much large wire, does anybody have experience and > comments about potentially using a buck-boots transformer at the home to > get us back to 240 volts? This would need to be service entrance sized. > > > > *Howard ?Scot? Arey* > > Owner, Solar CenTex > > 254-300-1228 > > [email protected] > > > > > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: [email protected] > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: http://www.mail-archive.com/[email protected]. > org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > -- *Will White* Curriculum Developer e: [email protected] w: www.solarenergy.org p: 802-272-3092 PV Installation Professional # 093006-34
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