tecnun

Hello Bruno, and thanks for you analysis, In my opinion, we are overprotecting our system at the expense of a superconservative design. Just a few thoughts: - We are assuming that in the event of a really cold cold day, assuming that the cells have not heated yet, during a daytime and under an irradiation over 500 W/m2 an event of electrical shutdown and reconnection (only at those events there exist open circuit conditions) - We are assuming that at abovementioned event, there exist no quality, mismatch, soiling, DC ohmic etc losses - We are assuming that the inverter does not protect itself from avobe 1500 V events. We have being chatting about this issue with the main inverter suppliers - We are also assuming that this "fatal" event is befalling at the very beginning of the PV Plant COD. We must take into account in my opinion LID and natural degradation PVsyst is, so far, accounting in Design Conditions (Project Settings) CELL temperature at this worst case event. Our proposal is to limit string sizes, but taking into account the "real" worst case. Is it too difficult to program this algorithm? Changing module parameters in my opinion is too risky and complicated to bring to a measure. Looking forward to your feedback BR Tecnun

Thank you very much Lazare

Thanks Lazare, Just as an example (SANDIA): It´s common to find the Voc peak in the range of 600-1000 W/m2 of POA, so in cold days the lowest daytime temperature does NOT determine the highest Voc. Let´s bring this scenario to a warm equatorial site like Colombia: There exists the real possibility of designing with 34 modules per string, and the maximum Voc (1.464 V < 1.500) happens at 650 W/m2 and a cell temperature of 43ºC. If we are limited to cell temperature of 30ºC, this would lead us to set the ambient temperature in this simulation to 17ºC, and the peak Voc now would rise to 1.512 V, so we would have to limit to 33 units per string. This is only an example. The main problem is that in PVsyst you fix the cell temperature, but it must be a combination of temperature. wind and radiation, so my suggestion is to build internally what i have made in an excel, taking into account METEO yearly data not just a cell temperature, dont know if i ve explained... BR Tecnun

Thank you Michele, it's now quite clear BR Tecnun

Perfect, thanks Dtarin for your huge knowledge of this software, I ended up thinking you worked for PVsyst Team because of that knowledge and generous help haha. Yes, it may be a challenge to optimize other more sofisticated tracking algorithms like the one you propose, hope this could be eventually implemented Kind regards Jose

Thank you and sorry for so many post replies. I understand now (hopefully!!), factors like FshdAlb are then divided by ALBEDO irradiation ONLY thats why they are in my example so high (1-factor so low) but they add few ABSOLUTE (global) shadings, is that correct? The question about why there is no beam losses is bcs we are analysing tracking modes without objects like trees or buildings etc, so they reflect the inner algorythm that the movement of the tracker and its backtracking is forced to avoid ANY beam loss, correct also? If we were simulating fixed structures there should exist beam losses that would be aggregated to the global loss as if there were linear, and they would add another extra loss called "electrical losses" depending on 1P/1H configuration and depending on the number and effect of bypass diodes (or if it is half cell...), right? These things are being set in equation i supposed. What there is not being computed i guess is to consider another backtracking algorythm depending on these last paragraph factors (1P/1H, half cell, diodes...) right? is it being in your software development for futures versions? Again so thankful for your help BR

Thanks Dtarin, Sorry but I still have not understood these exported figures: What do they stand for? I ve highlighted one specific hour where FShdGl, FShdDif and FShAlb are not zero, FShdGl = Global ?? Global = Direct + Diffuse, there is no direct shading so it should be equal to FShdDif as far as I know... Anyway i still dont understand why there is no direct shadings, they should be the most important ones, shouldnt they?? Please need some help :idea:

Edit: I think the attenuation factor is something separate from the diffuse shading factor, which is "..independent of the sun's position, and therefore constant over the year...". From how the manual reads, the attenuation factor is something the software calculates when there are shading objects in the shade scene. So if you have trees or buildings (or basically a non-zero beam loss), you will get a non-zero attenuation factor. If you do not have objects, this factor remains zero. "The diffuse attenuation factor should be calculated, by integrating simultaneously the shading factor due to horizon, the near shadings factor according to the table, and the IAM attenuation factors over the visible part of the sky hemisphere. " - We dont know the integrals being performed, but perhaps if near shading (beam) is zero, the result is zero. In the case of backtracking mode there is no attenuation factor, all the shadings come from diffuse+albedo, this is absolutely clear thanks for last response. But, looking deeper to the hourly shading factors, we observe that, apart from diffuse and albedo, there exists global factors below 1, which to my understanding they should be equal to diffuse (global = direct + diffuse). Am I right? Could it be a bug? BR

Edit: I think the attenuation factor is something separate from the diffuse shading factor, which is "..independent of the sun's position, and therefore constant over the year...". From how the manual reads, the attenuation factor is something the software calculates when there are shading objects in the shade scene. So if you have trees or buildings (or basically a non-zero beam loss), you will get a non-zero attenuation factor. If you do not have objects, this factor remains zero. "The diffuse attenuation factor should be calculated, by integrating simultaneously the shading factor due to horizon, the near shadings factor according to the table, and the IAM attenuation factors over the visible part of the sky hemisphere. " - We dont know the integrals being performed, but perhaps if near shading (beam) is zero, the result is zero. In the case of backtracking mode there is no attenuation factor, all the shadings come from diffuse+albedo, this is absolutely clear thanks for last response. But, looking deeper to the hourly shading factors, we observe that, apart from diffuse and albedo, there exists global factors below 1, which to my understanding they should be equal to diffuse (global = direct + diffuse). Am I right? Could it be a bug? BR

Ok that's really clear. I guess this plot of angles in fixed structures considers the same pitch, bcs if we decrease it the albedo shading would remain... Thanxs again Dtarin

Sorry, what is the role of ALBEDO in this case? I forgot to mention before... BR

Thank you Dtarin, Just for double checking: The shading losses are composed by these items: 1) NEAR SHADINGS: I) Irradiance losses a) Mutual due to adyacent structures - Direct irradiation (zero in the case of actual PVsyst backtracking) - Diffuse irradiation (coming from vaulted ceiling) b) Other near objects (trees or buildings for example) II) Electrical losses (due to string configuration) 2) FAR SHADINGS (for example mountains, horizon shadings in general) 1-I, 1-II and 2 are accounted separately on the final losses "tree", in the report. Attenuation is zero just when direct irradiation + other near objects are equal to zero BR Jose

Ok now haha, thanks! viewtopic.php?f=30&t=2522 With this topic we are seeing they vary with the angle. Anyway this attenuation = 0 should be accounted non equal to zero right? BR and thanks for the agile response

Yes, but it sais "attenuation for diffuse / albedo = 0.00000", what do you guys mean with "attenuation"? Diffuse or albedo are not considered isotropic? BR

Sorry for the insistance, this issue is quite important for us for sharing it with our Clients and Technological Colleagues, in order to be comfortable with the results. Given that backtracking algorithm is set to avoid every shadow, we cannot understand why in the report, there is a percentage of shadowing identified. Let me explain with this example: As we can see it exists 1,57% of irradiance losses due to near shadings. But...let see now these table & graphs: It seems like backtracking has cancelled any shadow during the entire year of simulation. Where are these 1,57% irradiance losses imputed? Gain? it should not i think, as gain is already attributed hereinabove (30,4%). Also when we simulte shading animations in the shading scene, no shadow is spotted. Is there any explanation? Only reason i see is that 1,57% is the gaining loss due to backtracking movement, and 30,4% is "plain" gain without considering any backtracking. Is it that? BR