jfish Posted July 30, 2013 Share Posted July 30, 2013 I understand that in the 6.10 revision new shading losses for diffuse irradiation have been added for tracking systems. According to the FAQ http://forum.pvsyst.com/viewtopic.php?f=30&t=694post on this topic, it seams that this is the first time in any PVsyst version that tracking systems have included a system loss for the diffuse component. Since I have upgraded to the 6.10 version, I have the opportunity to compare the results from simulations run prior to 6.10 to those run with 6.10 and I have some questions and concerns.I have found that in two example single axis horizontal tracking systems with backtracking, one in north-central US and one in southwest US, the "Near shadings: irradiance loss" that is now included in the loss diagram is -2.4% for the southwest site and -2.7% for the north-central site (all system details and losses were unchanged from 6.08 to 6.10). This is much higher than I expected from the explanation provided in the FAQ post. Both sites coincidentally have a 31% diffuse ratio (diffuse/GHI). Why is this loss so high? For another example system I ran in 6.10 for a 25 degree fixed tilt system in the northeast US I only get a "Near shadings: irradiance loss" of -2.4% for a system with a higher GCR (46% vs. 33%) and a higher diffuse/GHI ratio (45%).I am concerned that this new loss is a very significant change to prior versions of PVsyst and thus should be considered carefully. As someone who reviews many PVsyst reports from dozens of users on a regular basis I can say that this change presents a very significant challenge to the multitude of users of the PVsyst tool. There are hundreds of MW of tracking systems out there that were modeled in PVsyst prior to version 6.10 and hundreds more will continue to be modeled by users who have not upgraded. This presents a real challenge to people who analyze PVsyst reports and system performance issues. Is the suggestion that the industry no longer consider any tracking system production modeled prior to version 6.10 because they are erroneous?Applying an additional >2% loss to our systems is not something that is good for the industry. We need to have full confidence in this change. We need to better understand how to apply this issue to systems modeled prior to 6.10. Millions of dollars are at stake with changes like this. How much confidence do we have in the new modeling method? Are there studies to support this change? Are there papers we can reference? Have third party firms reviewed this change?PVsyst is an excellent tool and one I value very highly. I really appreciate all the work that goes into the creation and maintenance of this powerful tool. With the success of this tool comes a significant responsibility however so I would ask that major changes like this be supported with more transparency and support.Thank you.Jason FisherCharlottesville, Virginia, USA Link to comment Share on other sites More sharing options...
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