In the same issue of SolarPro as the “Optimal PV-to-Inverter” Sizing Ratio” article (April/May 2010), the lead article is “Production Modeling for Grid-Tied PV Systems” by Tarn Yates and Bradley Hibberd at Borrego Solar:
http://solarprofessional.com/article/?file=SP3_3_pg30_Yates While your question below can’t be answered using PVWatts, it can be answered using the Solar Advisor Model (SAM), which was developed by NREL and Sandia w/ DOE funding. SAM is available for free download here: www.nrel.gov/analysis/sam/ David Brearley, Senior Technical Editor SolarPro magazine NABCEP Certified PV Installer ™ david.brear...@solarprofessional.com Direct: 541.261.6545 On 4/19/10 6:40 PM, "Jim MacDonald" <j...@solaresystems.com> wrote: > SB8000US only good for 480 Vac, we’re tying in at 208. > > 11 strings has been calc’d to be OK (<600vdc) for record low -4 fahrenheit > (-20 celsius). > > I think the big concern as mentioned is getting the Voc high early in the AM > to wake the inverter up, also maintaining the Vmp later in the day to keep it > running for as long as possible into the late afternoon/ evening. > Will those extra kWh gleaned in the early AM/ late PM over the course of 365 > days be more than the kWh clipped during peak production times with the 9.075 > kWdc? > NYC average summer highs between 79 and 84 fahrenheit early june-late august.? > Sunlink rack @ 10° on a silver-painted built-up roof. > > Time-of-use utility $ peak-shaving is not an issue here. > > Thank you > > > > > > From: re-wrenches-boun...@lists.re-wrenches.org > [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Darryl Thayer > Sent: Monday, April 19, 2010 5:58 PM > To: RE-wrenches > Subject: Re: [RE-wrenches] overfeed 7kW gridtie inverter or drop a mod per > string? > > > The temperature correction is the concern. I have heard lots of stories of > inverters dieing when it gets to cold. Look in the code book 690.7 at the > temperature correction table. Go to weather.com and find your record low > temperature. Find you Tc factor and will your senerios work? I have heard > from a sunny boy rep that it is OK to over power by 1.25% > darryl > > --- On Mon, 4/19/10, Dana <d...@solarwork.com> wrote: > >> >> From: Dana <d...@solarwork.com> >> Subject: Re: [RE-wrenches] overfeed 7kW gridtie inverter or drop a mod per >> string? >> To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org> >> Date: Monday, April 19, 2010, 4:31 PM Many times we switch to another >> module manufacturer as one will not fit or another inverter manufacturer. >> PVPowered has a more relaxed window and we have had fine success with them >> when SMA does not fit. >> Cold is the dictator and the 600 VDC threshold. > Thanks, Dana Orzel > Great Solar Works, Inc web - www.solarwork.com E - d...@solarwork.com V - > 970.626.5253 F - 970.626.4140 C - 970.209.4076 "We have been slow to give up > on the myth of the Earth's generosity. Rather grandly, we have overdrawn our > accounts." Barbara Kingsolver - Water is life. From: > re-wrenches-boun...@lists.re-wrenches.org > [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Jim MacDonald > Sent: Monday, April 19, 2010 2:37 PM > To: RE-wrenches@lists.re-wrenches.org > Subject: [RE-wrenches] overfeed 7kW gridtie inverter or drop a mod per > string? > > For a straight grid-tie system@ 10 degree tilt, 180 azimuth, zero/little > shade, NYC avg 4.29 kWh/m²/day. Feed an SMA7000 with (3) strings of 11 > Suntech STP275’s [9.075 kWdc] Or Do strings of 10, so itd be 8.250 kWdc into > the 7 kWac inverter. Strings of 11= 491.7 Voc; 386 Vmp Strings of 10= 447 > Voc; 351 Vmp The tradeoff would be power clipping at/around noon in the > sunny months in the 9.075 kW scenario; Inverter sleeping late every morning > and retiring early in the evenings in the lowered voltage scenario. Trying > to figure out which would yield more kWh at the end of the year. Any ideas > appreciated, thanks Jim MacDonald Solar Energy Systems, LLC Brooklyn, > NY 11222 www.solarEsystems.com <http://www.solaresystems.com/> No virus > found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.801 / Virus Database: 271.1.1/2819 - Release Date: 04/19/10 > 00:31:00 >
_______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org