Auriane Canesse

By default we recommend Uv=0 as this coefficient is trickier to measure and varies even more from one PV installation to the next. There can be a large difference between the wind speed from a data provider (measured at 10m above ground, not always close by) and local conditions at the module level. But yes to be more accurate you simply need to measure this coefficients on your installation. https://www.pvsyst.com/help/project-design/array-and-system-losses/array-thermal-losses

Hi Zahra, PVsyst has only one temperature model as described here: https://www.pvsyst.com/help/project-design/array-and-system-losses/array-thermal-losses/index.html?h=temperature#thermal-model Our recommendation is using Uc = 15 W/m²·k for modules with a fully insulated backside (eg. PV roof tiles). But BIPV has a very wide range of PV designs so no we do not have recommendations for BIPV in general. If you import cell temperature measurements they will be used directly in the simulation insteand of using the temperature model. For the long tem losses, the degradation factor is applied to Imp/Vmp. The one diode model is fitted again to compute the IV curve of the modules and these are used in the simulation. The mismatch factor on the other hand is an effective correction. Individual modules are expected to degrade at slightly different rates, hence increasing the mismatch losses over time. For each module, a degradation loss is drawn from a gaussian distribution (defined in the ageing tool). The modules are assumed to degrade at that rate over the years an the mismatch factor is computed from that. The mismatch factor is added to the array losses. Unfortunately, we do not have white papers describing these 2 points, only the help pages.

Dear Zaki We do not cap negative values in the Perrez model when computing the circumsolar brightness. They arise when implementing the model and we keep them to avoid biasing the result towards positive values. This term is added to the isotropic component and the irradiance itself is never negative. The horizon is not implemented as a band. The horizon component is calculated using the Perez/Ineichen's 1990 model, but it is directly added to the diffuse irradiance. Horizion shadings are applied as a fraction on the diffuse irradiance but not to the horizon irradiance component separately. For the air mass, we use the the Kasten model described in Ineichen's thesis "Mesures d'ensoleillement à Genève", which is corrected for altitude as well (exp(-0.00013*altitude)) https://unige.swisscovery.slsp.ch/discovery/fulldisplay?vid=41SLSP_UGE%3AVU1&search_scope=MyInst_and_CI&tab=41SLSP_UGE_MyInst_CI&docid=alma991006463789705502&lang=fr&context=L&adaptor=Local Search Engine&query=sub%2Cexact%2CKANTON GENF (SCHWEIZ)%2CAND&mode=advanced&offset=0 I hope this helps you in your study

Currently, the only way to import sub-hourly data in PVsyst is to use the "custom file" import format. https://www.pvsyst.com/help/meteo-database/import-meteo-data/custom-meteo-files/index.html

The formula you have been applying is for a 2-sided test (~chances that the result is different, larger or smaller) whereas in this case a 1-sided test is appropriate (~chances the result is larger only) https://en.wikipedia.org/wiki/One-_and_two-tailed_tests

The bifacial performance ratio is only displayed on the report when the bifacial simulation is turned on (in System -> bifacial system -> use unlimited shed or tracker) The standard PR is not valid for bifacial systems because it does not include the incident irradiance on the panel back side. Since the production of the panel is the same in both computations, the PR is always higher than the BPR. https://www.pvsyst.com/help/project-design/results/performance-ratio-pr.html?#bifacial-performance-ratio

The temperature is generated from the monthly values saved in your site file, using the Meteonorm algorithm https://www.pvsyst.com/help/physical-models-used/synthetic-data-generation/index.html

-99 is an invalid value for all parameters. The extrapolation feature has been removed and any missing value will be treated as missing (0 irradiance). The help will be corrected in the next release. I apologies for the confusion.

Unfortunately, it is impossible to extrapolate irradiance, missing data or invalid data (-99) will be set to 0. This is due to the intrinsic variability of the irradiance. I will clarify our help page on this point.

Yes you can import either GHI or POA irradiance measurements into PVsyst via the custom import. https://www.pvsyst.com/help/meteo-database/import-meteo-data/custom-meteo-files/formats/general-format.html We advise the minimal data to be irradiance and ambiant temperature. If you do not have temperature measurements, Tamb will be generated synthetically.

I cannot reproduce your error, I get an altitude of 24m for your coordinates. What PVsyst version are you using? The steps you are following are correct, I would suggest updating to the latest PVsyst version. Please contact us again if the problem persists

I'll post the answer here for other users as well: this is not a bug, horizon profiles below 2° are not considered in PVsyst: https://www.pvsyst.com/help/project-design/shadings/far-shadings-horizon/index.html

Dear Rob, I cannot reproduce your error in version 8.13 (current latest version). Could you please send an email to support@pvsyst.com with the concerned project so I can investigate this issue? And could you confirm which version you are using?

Dear Chen, Thank you for forwarding this article, it is an interesting study. However, most of the conclusion is misleading: PVsyst doesn't use the Module temperature in the simulation but rather the cell temperature. The cell temperature is not measured directly in this study (it would require placing temperature sensor inside a module during fabrication). The difference between module temperature and cell temperature is corrected for in section 3.4 and the coefficients Uc and Uv are recomputed there. These values (table 6) correspond physically to what should be used in PVsyst. The range found is ~[29-32] which is reasonably close to our default recommendation. Note that the authors also mention that the model used to compute cell temperature has not been validated for their specific technology, so the results should be taken with a grain of salt.

Hello Chen, We did not carry out dedicated studies on how array pitch affects the heat dissipation. However, the thermal losses are indeed influenced by the PV module support structure and it affects the convective cooling on the back plane. The advised U coefficients corresponding to each structure type are described here: https://www.pvsyst.com/help/project-design/array-and-system-losses/array-thermal-losses/index.html#u-value-determination It is also possible to measure the U coefficient values for your installation as explained here: https://www.pvsyst.com/help/project-design/array-and-system-losses/array-thermal-losses/u-value-measurement.html

Hello James, If the dip in irradiance is not due to missing data, I would need your files to look into this issue in more detail. Could you send your project at support@pvsyst.com ? Auriane