André Mermoud

Nothing has been changed in the model at this level (except perhaps for amorphous modules with very high Voc). But probably the parameters of the module you are using have been updated (on request of the manufacturer).

Taking the flash-test uncertainty into account in this parameter would be equivalent to a "Worst case" choice. By respect to the factory flash-tests, you can also take the eventual LID losses into account. Please see my comments on How to define the "Module Quality loss" parameter in the FAQ

This arises sometimes and we don't understand exactly why. This is related to the font size you are using in your Windows installation. Choosing "Small fonts" should in principle solve the problem. But not in any case. If so, please contact us.

This is not possible in PVsyst. The Horizontal global and diffuse components are computed by a retro-transposition, in order that the recalculation of the POA value will be the same as specified. Now I don't have an explicit model for performing the retro-transposition from a diffuse component measured in the collector plane. This is a non-standard problem, which would require some modelling work. I can't envisage such a development until several months, but I pout it on my to-do list.

Thank you for pointing this problem out. I will correct it in the next version 5.60.

You have probably a time shift of more than 30 minutes (one hour or more). Please observe your data by respect to the "Clear Day" model, using "Meteo tables and Graphs" / "Graphs" in hourly values". The different ways of correctin this are listed in My transposed POA data don't match the imported values.

When you open PVsyst, the first item of the menu (at the left) is named "Files" (or "Fichier" or "Dateien" or "archivos" in other languages).

You manage the favorites in the database lists: "Tools" / "PVModules" (or "Inverters", or ...). For selecting a favorite, you right-click it (and the line becomes green). For suppressing a favorite you also right-click it (from the "All components" list). It is not possible to suppress it from the favorite list, I have to think about this for a next version.

I don't know what is exactly a swiging door algorithm. But the meteo data imported in PVsyst (*.MET files) are in hourly values and extremely compact. Usual files have less that 75 kB.

This depends on which version of PVsyst you are using. The angle definitions of Helios3D for southern hemisphere are a little bit strange and not usual. I have updated the program PVsyst for the version 5.58, using specific file samples provided by Helios3D. Please send me your files if they don't work well with the latest version of PVsyst.

This is a safety condition: the inverter maximum input voltage should never be overcome: this could damage the input electronics. Now Voc voltage of a PV array depends on the temperature: the practice is to take here the lower ambient temperature ever observed on the site. In middle regions of Europe the usual practice is to take -10°C (except in mountains where it should be lower). In the USA, people uses to takes the minimum observed during last 30 years. You can define this temperature in the Project dialog: - in the version 5: button "Site and Meteo > Next". - in the version 6: button "Albedo and settings" If you really want to overcome this limit (at your own risk), you have to change the VmaxAbs value in the inverter's definition (and sometimes also the limit for the PV module).

In PVsyst the orientation conventions are (contrary to Architect's conventions): - For Northern hemisphere, the Azimuth = 0° corresponds to the South. The azimuth is positive towards west (clockwise angles). Therefore: East = -90°, West = +90°, North = + or -180° - For Southern hemisphere, the Azimuth = 0° corresponds to the North. The azimuth is positive towards west (anti-clockwise angles). Therefore: East = -90°, West = +90°, South = + or -180° These configurations are explicit on the little graphs when defining the plane orientation. Note about red dots: The red dots have no "physical" meaning (it is not the same point on both diagrams) ! By convention in PVsyst the red dot is always a dot that you can drag with the mouse. For example in the Orientation graphs, on the left diagram it commands the tilt, and on the right diagram it commands the orientation.

In the 3D tool, the sheds should not be defined for each module. These are generic surfaces ("tables") for receiving sets of modules, and should be defined as big as possible for avoiding too high calculation time. Please see With my big power plant, the calculation time is prohibitive in the FAQ.

The Meteonorm program (V7.1, fully included in PVsyst V6) holds measured meteo data for about 1'500 sites in the world, named "Stations" (10-30 years monthly averages, in the range 1980-2010). But it allows also to get meteo data for any location on the earth, either by interpolation (between the 3 nearest stations), or on the basis of satellite data when no sufficiently near site is available. The "native" database present in PVsyst is based on these 1'500 Meteonorm measuring "stations". However in the PVsyst "Databases > Geographical sites" option, you can choose any location on a google map (or simply by specifying the coordinates), and get meteo data for this location either from Meteonorm or from the NASA-SSE database. Please see the post below for the procedure. Therefore even if you don't see your country in the database list, it will be present after you will have defined a site for your location. Now you have tools in the software for easily importing data from many well-known irradiation databases: Meteonorm (whole earth), Satellight (Europe), PVGIS (Europe and Africa), Nasa-SSE (whole earth), Soda-Helioclim, Retscreen, NREL TMY3 or SolarAnywhere(SUNY) in the US, EPW in Canada, NREL(TMY3) for India, etc. For this, please open "Databases" / "Import Meteo Data", choose the source, and press F1 for more details in the Help, a description of each source and the procedure for importing them. If you can obtain climate data from your Meteorological Service, of if you have your own measured data, you have also a general tool for importing data from almost any ASCII (text) file. Now there are several companies which distribute Satellite recent data for anywhere on the earth: e.g. SolarGIS, Helioclim-SoDa, 3Tiers, Vortex . They avail of recent data in hourly values, but this is for pay. You can also import these data readily into PVsyst using "Databases" / "Import Meteo data". NB: when you have Meteo data in Monthly values, you have to generate a synthetic hourly file for using them in the simulation.

You have tools in the software for easily importing data from many irradiation databases: - 3TIER-Vaisala (recent satellite data for the whole world, for pay), - ASHRAE IWEC2 (hourly TMY, whole world), - Canada EPW (Hourly TMY) for Canada, - Explorador Solar (Chile), - Meteonorm (whole world), - NASA-SSE: monthly data for the whole world, by cells of 1°x 1° lat/longitude (110 km), - NREL TMY for the USA and for India, - PVGIS (Europe, with also a new database of recent data, and Africa), - Retscreen (canadian program, montly values), - ReuniWatt (recent satellite data for the whole world, for pay), - Satellight (Hourly values for any pixel of 5 x 7 km2 in Europe), - Soda-Helioclim (monthly and Hourly values for Europe), - SolarAnywhere : recent satellite hourly data for the USA and Hawaïï - SolarGIS: recent satellite data for the whole world, for pay. - VortexSolar: recent satellite data for the whole world, for pay. For this, please open "Databases" / "Import Meteo Data", and press F1 for more details, a description of each source and the procedure for importing them. If you can obtain climate data from your Meteorological Service, of your own measurements, you have also a general tool for importing data from almost any ASCII file.

In PVsyst, we have taken the convention to label all data which don't correspond to measured data at a given time as 1990. This is the case, namely, of all Synthetic hourly data, or TMY/DRY datafiles (assemblies of periods of different years). In most results (tables/graphs) the references labels will appear without year reference (generic year). The meteonorm data present in the software for any location on the earth are averaged value (over 10 years or more). When using them the software will tell you the years range of these particular data, depending on the region, usually between 1990 and 2010. The NASA-SSE data of PVsyst are averages of 1983 to 2005 years. Now if you want to perform simulations for one or several "real" years, you have to get the data of each of these years of course (from another source). NB: PVsyst is only able to treat data of one year at a time. Several years will give rise to several *.MET files, and several simulation runs.

No. PVsyst is only able to treat data of at most one year at a time. Several years will give rise to several meteo files (*.MET files), and therefore several Simulation runs. After performing these simulations you can average the results if you want. Please note that the TMY2/3 databases don't provide 30 years of data, as often believed.

The simulation is based on an hourly data file (*.MET). When only monthly values are available, PVsyst generates hourly values according to a model in a stochastic (random) process. For irradiances, PVsyst uses the "Collares-Pereira" model, which generates a series of daily irradiations, and then hourly irradiances within each day, using fully stochastic process (Markov matrices). This model tries to reproduce irradiance time series, with a statistical behaviour analogous to measured values in several sites in the world. The result will be a synthetic hourly year, which is completely different from one execution to another one. During simulation of a grid-connected system, the differences on the yearly yield may be usually up to 0.5 to sometimes 1%. The effect will be higher when simulating systems with non-linear beghaviour like stand-alone. For temperatures, as the temperatures are mainly governed by atmospheric circulations rather than irradiation, we don't have any model relying the daily temperature to the irradiations. Nevertheless the temperature within a given day is rather well correlated to the irradiance. It takes a rather sinusoidal shape, with an amplitude about proportional to the daily irradiation, and a phase-shift of about 3 hours. In absence of a day-to-day model, the passage to the next day is randomly modified in order to obtain the required monthly average and a reasonable amplitude. Therefore, the model waits for the "meteo" monthly average temperature (24h)" (not the Daytime average !), and irradiance data. For constructing a Synthetic Meteo file, please use "Tools" / "Synthetic Hourly Data Generation". When choosing a site within a project, PVsyst will automatically create the corresponding Synthetic file if there is no corresponding file in the \Meteo\ database elaborated by Meteonorm. NB: The Collares-Pereira model has been established in the 1980's, when the irradiance was not so well understood as nowadays. To my knowing nobody has published about this model since these early researches. The version 5.xx of PVsyst uses this original version of the model. However the Meteonorm team has significanntly improved the model, and implemented it in the new Meteonorm program. The version 6 of PVsyst makes use of this new version of the synthetic generation model.

You can import hourly or daily meteo data from almost any Text (ASCII) file, provided that there are data of one recording time step on one line. For this please use "Databases" / "Import ASCII meteo file" and press F1 for getting the detailed procedure. After importing, please carefully check the quality of your imported values, especially their time definition, with the tool "Meteo tables and Graphs" / "Check data quality". You have information about data quality in the help (typing F1): "Geographical and Meteorological data > Hourly meteorological data > Hourly meteo data quality check".

PVsyst is only able to perform simulations starting from the Horizontal irradiance GlobHor. This is motivated by the fact that we only avail of models for estimating the Diffuse irradiance in the horizontal plane (the diffuse irradiance is used namely for transposition model and shading or IAM calculations). Therefore starting from Plane irradiance (POA) requires first to perform a retro-transposition for getting the horizontal global and diffuse irradiances, which will lead to the specified POA after transposition. This uses the Liu-Jordan (or Erbs) model for the evaluation of diffuse. When using these data, the simulation should retrieve the exact input POA value. If this is not the case, it indicates that there was a problem during the import process. The usual problem is a time shift between the measurement time and the PVsyst time. If the measurements are not accumulated at the exact time (for example between 9:00 and 10:00 for the PVsyst 9:00 step), the solar geometry is not computed at the right time (middle of the interval) and the transposition my lead to very high errors in the morning or the evening, i.e. when the sun is low on the horizon (as the POA irradiance is divided by sin Hsol). This may lead to very high erroneous horizontal Global, which will be limited to the clear day model. In these cases a Time shift correction should be applied, already during the import process.

In PVsyst I have taken the convention of always labelling the beginning of a time step (8:00 corresponds 8:00 to 9:00 average). This allows to label the hours, days or months in the same way. Now if your own data are referred to the end of the hour (or other time step, you have an option in the importing format for taking this into account). See My transposed POA values don't match the imported values in this forum.

I have done a comparison between the different sources of data imported in PVsyst, and available for Europe: we can observe a discrepancy of the order of +/- 10 % (yearly sums) between all these sources, and this is of course the first uncertainty of the PV production forecast. This comparison is available in the PVsyst help "Geographical and Meteorological data > Import from Meteorological data sources > Meteorological data comparisons", or summarized on our site http://www.pvsyst.com. The differences may be attributed to the different years or periods concerned (climatic variations), the accuracy of the mesurements (sensor calibration, or models for satellite data), the quality of the data recording, etc. For example, the European climate has significantly evolved: we observe an increase of the order of 5% on an average since the beginning of this century in all measurements. This is namely apparent with the PVGIS database: the new SAF irradiation measurements (based on recent satellite data) are about 5% over the "classic" data from terrestrial measurements of the ESRA project (1981-1990). I don't have such a study for other regions of the world. For the USA, the TMY3 are probably reliable data, based on 1961-1990 measurements, and used as reference by everybody. A new database managed by the NREL (SolarAnywhere - SUNY model) provides recent satellite data for the whole territory. The direct import from this database will be available in the version 6, but you can already import these data as ASCII files in the present version. Please also refer to the works of Pierre Ineichen, available on our site http://www.pvsyst.com: "Global irradiation: average and typical year, and year to year annual variability", Ineichen, P., 2011, Research report of the Institut of the Environnemental Sciences, University of Geneva. and "Five satellite products deriving beam and global irradiance validation on data from 23 ground stations (IEA)", Ineichen, P., 2011, Research report of the Institut of the Environnemental Sciences, University of Geneva. Now please observe: we can have some quality criteria. But probably nobody knows which source is the most reliable, and which one will represent at best the future climate of a given site !

It is often believed that the TMY2/3 databases provide 30 years of real data. This is not true. The definition of "TMY - Typical Meteorological Year" (or "DRY - Design reference Year") is a one-year data construction, which gathers pieces of measurements (2-4 weeks) picked up from usually 30 years of real measurements, in order to construct a representative year for systems sizing or building thermal behaviour analysis. This construction obeys precise rules, and aims to provide an average year, but including some extreme values. The TMY3 are constructed using more recent data than the TMY2 (1991-2005 against 1961-1990 respectively). Please refer to the NREL site for TMY3 data. Now if you can get some real years of recent measurements (for example from SolarAnywhere of NREL), you can do the simulation for each available year, and then average the results (on a monthly or yearly basis).

The global irradiance is always a sum of the Beam, Diffuse, and Albedo components. With meteo data (on horizontal plane) there is no albedo of course, as the horizontal plane doesn't "see" the surrounding ground; therefore GlobH = BeamH + DiffH. If the global and DNI are available in the data, but not the diffuse, PVsyst calculates the corresponding Diffuse component from these data, and at execution the specified DNI will be restituted. Now if Diffuse and Beam (horizontal or DNI) are both specified in a dataset, there is a redundancy. The DNI can be deduced from the GlobH and DiffH (it is a definition, using the solar geometry, and doesn't imply any physical model). If there is a discrepancy with the DNI given in the file, it is an inconsitancy in the data, and PVsyst has no mean for managing this of course.

The format of the data structure obtained by "Copy" has indeed been changed with Firefeox V 13 (mid-June 2012). I have adapted the importing tool in the version 5.58 of PVsyst. Therefore please update PVsyst, or use another browser !