André Mermoud

Please see our FAQ I don't find Li-ion batteries in the database of PVsyst

OK, I have corrected this problem for the next version 6.13.

All the PV modules are specified for a 1000 V voltage limit in the array, by respect to ground (IEC norm). Therefore if you want to do that you should use very special modules, not available on the market. However this inverter is probably specified for using 2 symmetrical arrays (by respect to the ground voltage). In this case you should define the inverter as a "Bipolar" inverter, in the "Sizes" page, "Technology specificities". See the Advanced Energy inverters as an example.

This question is indeed very important. Therefore I have answered it in the FAQ for more visibility (For meteo measurements, should we use a pyranometer or a reference cell ?)

The pyranometer measures the temperature elevation of a blackbody when absorbing the light energy, under a double cupola of glas or quartz (greenhouse effect). Its response is well linear, covers a very large spectrum (flat response until up to 3 micrometers), and has a very good angular acceptance. The accuracy may attain 1-2% with very well calibrated instruments. The reference cell has a short-circuit current well proportionnal to the irradiance (with a little temperature dependence of +0.05%/°C), but it only measures the irradiance in the spectra according to the sensitivity of the PV cell (for crystalline silicon, limited to 1.12 eV, i.e. less than about 1.1 micrometer). Moreover the usual devices are covered by a flat glas, therefore the angular sensitivity is affected by the IAM (incidence angle modifier) reflexion losses. The accuracy is limited by these two phenomena, and cannot be better than, say, 5%. The answer to the question now depends on the use of the results. For measuring the performance ratio (PR) and its stability, the plane-of-array (POA) irradiance is required. The fact that the reference cell behaves in the same way as the array itself (sames biases, spectral and IAM) will provide a good reference for this measurement: the fluctuations of the PR discrepancies will be low. Moreover some reference cells also provide a measurement of the array temperature (by measuring the Voc). However the simulation process is waiting for an "absolute" irradiance input, i.e. without these biases ("meteo" measurement quality). It will include a correction for the IAM (PVsyst neglects the spectral effect for crystalline modules), and the PV module's specified behaviour (on which is based the model) is related to the full spectra (STC are for AM 1.5). Therefore, if you are only interested in the stability of the PV system along the time, the reference cell is well suited. But if you want to provide prognosis, or analyse and quantify the data in more details using the simulation process, you should use a Pyranormeter as reference. Precautions about irradiance measurements The irradiance measurement are rather difficult, and require a great care. - We strongly advise to perform them in the horizontal plane, not the POA (Plane of Array). - The horizontality of the instrument should be carefully adjusted. - The calibration given by the manufacturers is not always reliable. Moreover it may vary along the time (especially during the first years): please carefully check it, if possible periodically, against a reference instrument. - The instrument should be kept clean, without dust. - Usually the datalogger will perform a measurement every some few seconds, and average over a predefined time step. It is very important that this time step is well defined, and namely its stability along the life of the measurement. Otherwise this may induce time shifts when importing in PVsyst. - Check that there are no shades on the instrument at any time of the year (even the diffuse may be affected by shading objects).

Thank you for the suggestion. I note this on our ToDo list, which is already very long ...

Yes of course you can simulate tracking systems without backtracking. However there is no "generic" shading calculation like the "Unlimited sheds" option. You have to define the detailed geometry of your system in the 3D construction tool. NB: for the backtracking, you have also to define the 3D representation: there are no mutual shadows for the beam component, but the diffuse and albedo components are affected by the shading effect.

You are right: the "fast" calculation is done by interpolations in the shading factor table, and I introduced for the version 6 a "slow" simulation where the shading factor is computed explicitely at each step of the simulation. This is a good news that both results are compatible of course... With some very "structured" shadow shemes like row-to-row shadings, there may be little biases with the table interpolation; this new calculation allows to evaluate the effect of this bias. Now the objective of the "Module Layout" definition is to evaluate the electrical mismatch loss. This has to be compared to the calculation "according to module strings", for which as soon as a module is hit by a shadow, it becomes electrically inactive. Both calculation modes give rise to a second "electrical" shading loss contribution, which is mentioned in the array losses. Comparing these losses for both calculation modes should allow to determine the "Fraction for electrical loss" involved in the calculation "according to modules strings", in order to get the same contribution. But the calculation of the "linear" loss contribution - which corresponds to the irradiance deficit on the array - should be about the same.

PVsyst is quite able to model the CIGS modules: you should choose the technology CIS (equivalent to CIGS). Now with these PHOTON data, the specified Number of cells is 88, which leads to a Vmpp value of 0.23 V/cell. This is far below the usual values for CIS technology, the module organization is probably 2 strings of 44 cells in series. When you change this in the "Size and technology" page, please also go to the "Model parameters", and click the default checkboxes for Rshunt and Rseries (=> resp. 80 and 0.373 ohm). Because when trying to adjust the model with the false number of cells in series, PVsyst has fixed erroneous default values for these parameters. NB: During my researchs about modelling, I measured a CIS module during 7 years (one measurement every 10 minutes), and it obeys "perfectly" to the one-diode model (the RMS difference between Measured and Modelled values was < 1%, for any irradiance and temperature conditions over several years).

Some answers, but you should also refer to the help. 1. In a row arrangement, when the bottom cell line is shaded, the concerned string doesn't produce any electricity anymore. The by-pass diodes don't help in this case. As soon as 1/3 of the sub-modules (modules parts protected by a diode) of a string are shaded, the string's voltage is not sufficient to participate to the array power. You can only have a little recovery if the string is alone on the MPPT input, but it may also be below the Vmpp threshold of the inverter. 2. For this reason the "Fraction for electrical effect" should indeed be set to 100% with shed arrangement. 3. The mismatch loss parameter has nothing to do with the shadings effects (see How to define the Mismatch Loss parameter?) 4. See our FAQ What is the "Shading loss according to module strings", and What is the "Fraction for electrical effect".

I can't understand that. When the simulation has been performed with success, you are directly led in the "Results" window, with several options. The main one being "Reports".

You should desable it in the option "Partition in module chains" (icon in the left of the 3D edition), button "Cancel Partition".

PVsyst puts limits to the monthly meteo data, for avoiding erroneous inputs. These limits are applied on the Clearness Index value (Kt) which is the ratio of the measured irradiation to the extraterrestrial one. Therefore Kt is a measure of the transmission of the atmosphere. The limits fixed in PVsyst are Kt = 0.12 (months with very covered conditions), and Kt = 0.82 (very sunny months) (0.8 in older versions). PVsyst also puts a limit to the monthly Diffuse/Global (D/G), established at 0.13 (very sunny days). Usually the values of "normal" meteo data - all over the world - never exceed these limits. However the meteo conditions for Chile are really exceptionnal, and sometimes overcome these limits. You can change them in the Hidden parameters, topic "Miscellaneous".

See our FAQ With my big power plant, the calculation time is prohibitive

The nuVco may either be the result of the one-diode model (and it depends itself on the temperature), or you can specify the value given by the manufacturer. See our FAQ How to adjust the Voc temperature coefficient ?

I will correct it for the next version 5.72

I don't know. I can't reproduce this problem. When puttin 1° for the azimuth, it appears correctly on the report.

This comes from nowhere: you can put its value to 0 if you want. The value given here is just a default for a usual value. This represents the cost of the capital in general. Even if you don't perform a loan, you perhaps would like that your inversted capital yields some annual profit. This is equivalent to an interest which would have been obtained if you had invested your capital on the market: perhaps you want to recover this and it should be included in the final price of the energy.

For the first table (null anywhere), you have defined a tracking system with backtracking strategy. By definition, this mode avoids any mutual shadings, so that the shading factor (on the beam component) is always zero. In this table the orientation of the trackers is adjusted for each position of the sun. However the shading effects on the diffuse will not be 0 (see our FAQ How is calculated the shading loss on diffuse with tracking ? The second table seems to be quite correct, corresponding to an obstacle at south of your system.

Your 2 fields are on the same orientation, therefore you don't need to define heterogeneous fields. In the "Orientation" part, you should simply choose "Fixed tilted plane". Then, choosing to define "PV planes in sheds" is quite correct in the 3D shading part. You can construct any number of "PV planes in sheds" objects in your system, provided that you have the same orientation and a sufficient area for putting all the modules you have defined. NB: When you choose "Heterogeneous fields", the 3D shading construction waits for 2 fields (or groups of fields) in 2 different orientations.

There is no limit, the calculating time will simply increase, perhaps becoming prohibitive. And this doesn't depend on the total Power of the system, but on the number of "tables" (elementary mecanical rectangles receiving PV modules). For a 5 MW plant and reasonable tables sizes, there should not be problems with the version 6, where the shading factor calculation has been optimized.

There are indeed several "new" performance reports about the IAM. However this measurement is rather difficult to perform with accuracy, and there are high discrepancies between the results of different laboratories. I can just propose my own theoretical calculations, according to the Fresnel's laws, for a standard flat glass without Anti Reflective dispositives. IAM Fresnel calculation taking 2 reflexions into account, compared to ASHRAE parametrization. I took 2 reflexions into account, i.e. the first Air-glass interface, the reflexion on the bottom of the glass side (against the PV cells), and the secondary refraction from glass to air. The next contributions are completely negligible.

For the first problem of disposition: Putting modules in several orientations on a same shading object is really not easy to do, and we decided not to allow this. This is a relatively rare case, and it doesn't justify the big amount of development. However you can always redefine your planes as independent rectangular areas, for portrait and for landscape modules dispositions. For the area calculation error: I will check in the program For the third problem of deformation: This is only a display problem, the filed area itself is not affected. We will also check this for a next version. By the way we are just elaborating a tool for the direct positioning of modules during the 3D shading development stage. It will become possible to redefine the polygonal field as the envilope of the real modules, positioned by mouse.

The far shading losses are indeed depending on plane tilt. When the modules are at low tilt, the losses arise with a higher incident angle, and the loss applies to a lower beam irradiance amount (due to cosine effect). With a high tilt, the shades apply with a lower incidence angle, when the sun's rays are more perpendicular. For understanding this intuitively, you can take the exrtreme cases of an horizontal plane (which "sees" the horizon line quite marginally) and a vertical plane, which will be affected by low sun's height, when it should be very well irradiated.

Thank you for the suggestion. This is indeed on our ToDo list since a long time. But not at the top, sorry ... In the present time you can - export (copy/paste) the Tables of monthly values in EXCEL, with your chosen output values, and compare them in EXCEL. - use the "Batch Mode", which allows to perform several simulations with different parameters in one operation, and directly compare the results in EXCEL.