August makes a good point. There really isn't much solid info on the topic of dissimilar orientations.
In the experiments I've conducted using different orientations and tilts on the same strings the production almost exactly matches the average projected production across the orientations and tilt. In regard to using mix matched modules in parallel strings I haven't seen any noticeable difference in performance either. Of course this is an advanced technique and requires an awareness of string voltages and amperages in order to avoid excessive power clipping. The biggest problem with using different manufacturers panels with each other appears to be more bureaucratically driven rather than performance based. What I mean to say is that because the manufacturers are unlikely to provide a written endorsement allowing you to use their panels in the same string with someone else's, you may have trouble with a bureaucrat requiring that endorsement. There is a lot of rumor floating around about how important it is to use the same panels and the same orientations and tilts. And I agree it is important, but there may be circumstances that over ride those rules. I've had many systems where for esthetic or available space reasons a panel or 2 in a string of modules was put at an entirely different tilt and orientation. I've played quite a bit with it and haven't noticed any reduction in performance that would warrant the elimination of what might be 10 to 30% of the string or perhaps even the entire string. However with inverters like enphase coming to market it becomes easier to ensure that every panel in a string is at the same orientation and tilt. I always recommend the best tilt and orientation possible but sites and circumstances coupled with other details specific to the site sometimes force us to go with less than optimal string placement practices. A healthy well rounded understanding is important and I don't feel that the industry has done enough to create that understanding yet. Best practices have certainly been promulgated but the context has not been fully explained or explored yet. Inverter reps and installation reps and panel reps have made many many representations based on their best guesses and in some cases what they have seen first hand. We the implementers are the guinea pigs, get used to it. Thankfully the kinks are getting worked out. Perhaps in another couple decades when things settle down we'll have properly documented studies of mix matched panels, orientations and tilts. Of course by then things will be so completely different that it wont matter any way. My 2 cents, Sky Sims Ecological Systems http://www.ecologicalsystems.biz 220 County Road 522 Manalapan, NJ 07726 732-462-3858 toll free)866-759-7652 fax)732-462-3962 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Darryl Thayer Sent: Friday, September 12, 2008 12:16 PM To: RE-wrenches Subject: Re: [RE-wrenches] Actual losses from dissimilar orientations onsingle inverter Hi all There are a couple of principals here 1) NEVER NEVER PUT TWO STRINGS OF DIFFERENT ORIENTATION IN SERIES!! 2)The currents are dependent upon irradiance, which varies greatly. 3) The voltage and the Vmp is rather close for varying irradiance, and therefore if forced non coincident orientation in parallel is not so great. In that the currents will add and both strings will be near MPP. 4) of course the caveats that parallel strings must always be of the same modules and same count. Darryl --- On Fri, 9/12/08, August Goers <[EMAIL PROTECTED]> wrote: > From: August Goers <[EMAIL PROTECTED]> > Subject: [RE-wrenches] Actual losses from dissimilar orientations on single inverter > To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org> > Date: Friday, September 12, 2008, 9:38 AM > Wrenches - > > The correspondence below brings up a question I've been > pondering... What > are the actual losses due to differing string orientations > on a single > inverter? Are there significant differences between the > major inverter > manufacturers? What if we have a very steep roof facing > East - West, would > we be better off with two inverters? > > The well known Fronius white paper > (http://www.fronius-usa.com/worldwide/usa.solarelectronics/downloads/fro nius > _ig_reaction_to_non_optimal_conditions.pdf) seems to > indicate that losses > will be in the ~1% range. I took a SMA class a couple years > back and they > indicated that the losses were probably closer to the 3% > range, maybe even > more. Maybe things have changed by now, it would be great > if some > manufacturer reps would chime in. > > Does anyone have any data or solid info on this issue? > > Looking forward to hearing the latest. > > Best, > > August > > August Goers > > Luminalt Energy Corporation > O: 415.564.7652 > M: 415.559.1525 > F: 650.244.9167 > www.luminalt.com > [EMAIL PROTECTED] > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On > Behalf Of William > Miller > Sent: Thursday, September 11, 2008 4:34 PM > To: RE-wrenches > Subject: Re: [RE-wrenches] trouble shooting system with Sun > Tie > > Dana: > > The failure mode of the original ST inverters were a > failure in the MPPT > algorithm. The inverter would sweep the impedance too high > until the > voltage would collapse. The inverter would then take > several minutes until > it allowed the PV voltage to rise again. This would repeat > throughout the > day resulting in a significant decrease in overall output. > You could > witness this over any given half hour period. > > Regarding arrays in dissimilar orientation: The loss due > to differing > orientations should be about 1%, IF all modules in each > string are facing > the same direction. This is because the different IV > curves are of a > similar shape when superimposed on each other. The ST > inverter might be > less able to average these curves and more susceptible to > collapse. > > Did you check the array fuses? > > William Miller > > > At 03:23 PM 9/11/2008, you wrote: > >Hi all, > > > >I was called out this week to trouble shoot a system I > didn't install. > >It's a five year old 1.44kW system with the > following: Sun Tie ST 1500 > >inverter and 12 Astro Power modules. It only produced > 634kWh last > >year. With our sun here, the shading, orientation, > equipment, etc. it > >should have produced around 1123kWh. > > > >I've heard a lot about Sun Tie failures, but > don't know the details. > >What are the common failure modes? Is it likely that a > failure of the > >Sun Tie would leave it operating, but only producing > half what it > >should? > > > >When I showed up the system was producing 950W on a > relatively sunny > >day - seemed pretty reasonable. After restarting the > inverter it only > >produced around 150W. Is the MPPT very, very slow to > find that sweet > >spot, or what was going on there? > > > >The system is comprised of three strings of 4 modules > each. When I was > >there all three strings were producing about the same > current, so that > >leads me to believe it's not a module failure. > > > >To make things more fun, the modules were installed at > two different > >orientations. One string is at 38d slope, 30d east of > true south, > >while the other two are at 36d slope, 75k east of true > south. This > >certainly has a detrimental impact on the performance, > but it doesn't > >seem to me that it could account for all of that energy > loss. > > > >Thoughts? > > > >Thanks a lot! > > > >Dana > > > _______________________________________________ > 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 > > _______________________________________________ > 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 _______________________________________________ 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 No virus found in this incoming message. 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