Then just as a follow up, I looked at the SMA-41 datasheet. This shows that it runs at it's highest efficiency when the output power / rated power is about 0.4 to 0.6, and the only real loss in efficiency comes when you are running at about 0.1 and below.
On Wed, Mar 3, 2021, 8:35 PM Dave Tedeyan <dtede...@taitem.com> wrote: > I've never really trusted PVWatts on this. I just did a quick test using > my location in the northeast, with all the standard values and then just > changing the DC to AC ratio. It's telling me that a ratio of 1.5 is almost > exactly the same as a ratio of 1, and that around 1.3 is best. You actually > lose about 2% at 0.5 and about 8% production at a ratio of 2. > > So I can only conclude that either PVWatts does not have a great > calculation, or the efficiency loss due to not running the inverter at > rated power is worse than I assumed. > > Cheers, > Dave > > On Wed, Mar 3, 2021, 6:14 PM Jason Szumlanski < > ja...@floridasolardesigngroup.com> wrote: > >> I've used that document many times when clients question the ratio. I >> wish I knew exactly how the PVWATTS ratio calculation worked. I know >> there's information on how this is all done, but I don't really have the >> time or inclination to study it. I'm wondering if someone knows how >> accurate It is. >> >> On Wed, Mar 3, 2021, 4:04 PM Jay <jay.pe...@gmail.com> wrote: >> >>> Emphase has a white paper showing production vs module size and >>> locations around the country. >>> >>> I don’t know if it’s more accurate than pv watts but you might check it >>> out. >>> >>> Jay >>> Peltz power. >>> >>> On Mar 3, 2021, at 12:13 PM, Jason Szumlanski < >>> ja...@floridasolardesigngroup.com> wrote: >>> >>> >>> I'm wondering how accurate the DC to AC ratio is when using PVWATTS. I >>> did a quick PVWATTS analysis at my local area using a typical commercial >>> roof tilt and found that using a 420W module on an IQ7A versus a 385W >>> module on an IQ7+ yields almost identical results. The 420W module has 1% >>> less annual production at to the 145% ratio compared to the 132% ratio with >>> the 385W module. >>> >>> Given that, I can't imagine why anyone would use the IQ7A versus the >>> IQ7+ on a 208V system. Why incur the additional cost if the AC output >>> current is identical for both inverters? >>> >>> If PVWATTS is right, I guess it's a non-issue in my local area, but it >>> may vary in other locations where clipping is more common. The heat here >>> results in little clipping at a 132% ratio here, and I guess at 145% the >>> morning and afternoon advantages largely outweigh the mid-day clipping >>> increase. >>> >>> Jason Szumlanski >>> >>> >>> >>> On Tue, Mar 2, 2021 at 10:00 AM Jason Szumlanski < >>> ja...@floridasolardesigngroup.com> wrote: >>> >>>> I was surprised to learn that the IQ7A is limited to 290 W continuous >>>> at 208 volts. That pretty much puts Enphase out of the running for light >>>> commercial jobs with new high-powered 72 cell panels. Any thoughts on this? >>>> >>>> Jason >>>> >>> _______________________________________________ >>> List sponsored by Redwood Alliance >>> >>> List Address: RE-wrenches@lists.re-wrenches.org >>> >>> Change listserver email address & settings: >>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>> >>> There are two list archives for searching. When one doesn't work, try >>> the other: >>> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ >>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >>> >>> List rules & etiquette: >>> http://www.re-wrenches.org/etiquette.htm >>> >>> Check out or update participant bios: >>> http://www.members.re-wrenches.org >>> >>> _______________________________________________ >>> List sponsored by Redwood Alliance >>> >>> List Address: RE-wrenches@lists.re-wrenches.org >>> >>> Change listserver email address & settings: >>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>> >>> There are two list archives for searching. When one doesn't work, try >>> the other: >>> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ >>> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >>> >>> List rules & etiquette: >>> http://www.re-wrenches.org/etiquette.htm >>> >>> Check out or update participant bios: >>> http://www.members.re-wrenches.org >>> >>> _______________________________________________ >> List sponsored by Redwood Alliance >> >> List Address: RE-wrenches@lists.re-wrenches.org >> >> Change listserver email address & settings: >> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >> >> There are two list archives for searching. When one doesn't work, try the >> other: >> https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ >> http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org >> >> List rules & etiquette: >> http://www.re-wrenches.org/etiquette.htm >> >> Check out or update participant bios: >> http://www.members.re-wrenches.org >> >>
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