André Mermoud

This is another question. Here Ext is for "external" indeed. The waited value is the ambient dry bulb temperature, averaged over the month. A realistic daily profile will be constructed by the Synthetic hourly data generator, taking the concomitent irradiance into account. This will construct a sinus-like profile, with amplitude about proportionnal to the daily irradiance, and a delay of 2-3 hours (i.e. by clear day, the peak temperature is around 15H (solar time)). This model waits for the real average over 24H, not the "Average Daytime Temperarture" proposed by some databases.

In the present time, the only way of defining properly the terrain shape is to import a full system from the Helios3D program. When importing a system from this tool (with tilted basis sheds following the terrain), there is indeed a distribution of several "true" orientations and PVsyst works with an averaged value. However this possibility is not yet developed for systems directly developed within PVsyst. We will indeed think about a way of easily defining the terrain and PV tables on it for a next version, but probably not before some months.

Sorry, this problem was introduced n the version 6.16 by accident, and will be corrected in the next version 6.17, which will be released hopefully on 10/01/14

You should define the degradation effect using the "Module quality loss" parameter. Please see our FAQ How to define the "Module Quality Loss" parameter ?

The temperature specifications during the sizing - which you specify in the "Project's parameters, button "Albedo-Settings" - is only used for sizing purposes. It should give indications about the number of PV modules in series. You have a full explanation in the help "Project design > Grid-connected system definition > Array voltage sizing" - The "Lower temperature for absolute values" concerns the safety of the system: it is an "absolute" limit value. - The "Winter, Normal and Summer operational temperatures" have a low importance during the design (see the graph in the help or on the sizing tool). You can slightly overcome the MPP voltage limits without significant losses. The final test of the validity of your choice for the number of modules in series will be the Inverter loss below the minimum and over the maximum voltage during the simulation (on the loss diagram). NB: During the simulation, the array temperature is determined from the hourly ambient temperature and the irradiance, using a little energy balance model.

In the "Module Layout" part, you can analyse the electrical effect of a shade by clear sky conditions (when the modulelayout configuration is well defined, using the "Shading 3D" sweep, => "I/V curve"). This is indeed not simple ! You will see that with several strings in parallel, when one string is shaded the voltage of the MPP usually doesn't drop. As a contrary, with one only string per MPPT, the voltage drop due to beam shading may be important according to the shaded cells. However with a high diffuse ratio the "best" MPP will usually stay on the curve representing the diffuse, i.e. without significant voltage drop.

You are right. There is a problem above 10 MW, the unit change doesn't work correctly. You should indeed specify the value in kW although the displayed unit is in MW. I have corrrected for the next version 6.17.

The NEDO web site referenced above is fully in Japanese language. As we don't have Japanese people here at PVsyst, you can understand that we cannot propose anything for importing these data. Are these data in Hourly or in Monthly values ? If they are in hourly values, please us send a sample file, and we will see what we can eventually do with it.

The possibility of defining "heterogeneous fields" (multi-orientations), also with inverters mixed between orientation #1 and #2, is available in PVsyst since the beginning of the version 4. However in the versioon 6.13, you can define up to 8 orientations (and a "mixed" inverter between orientations #1 and #2), without the previous limitations about the mutual orientation difference limit.

For adjusting the maximum output of an inverter, you can simply modify the "Nominal AC Power" parameter in the definition of the device, and save it with under another filename, therefore creating a new device in your database. In your case you will define 1 sub-array with 2 normal 500 kW inverters, and one sub-array with your new 400 kW. Now since the version 6.11, under the button "Miscellaneous tools", you can limit the power of the whole system to a specified value. However the simulation will limit all Inverters identically, to a Pnom = 1400/3 kWax value.

We don't know how to access the Nedo database. Is is public ? Which kind of data does it provide ?

We cannot say anything if you don't mention which kind of wrong data. Please explain.

It cannot be regardless of the irradiance of course. The Maximum power is given by the one-diode model according to Irradiance and temperature conditions. The Pmax is more or less proportionnal to the irradiance (the deviation is this statement is given by the low-ligh efficiency behaviour).

This will be fixed in the version 6.14, to be released on 15/12/13

This may be a limitation of the specifications, but not an operating limitation of the inverter (i.e. the inverter will not limit the current by itself). In this case PVsyst doesn't directly check the current at the inverter input during the simulation. If it is an operating limitation, this will be related to the parameter "Minimum voltage for PNom". This means that you cannot reach the nominal power if you have a voltage lower than this limit. I.e. with lower voltages the possible output power will be reduced, just in order to match this maximum input current: If we define Pnom(dc) = Pnom(ac) / Effic, then Imax = Pnom(dc) / Vmpp For your example, Pnom(dc) = 900 kWac / 0.96 = 937 kW => VmppMin for getting PNom = 937 kW / 1400 A = 669 V. This should be a specification of the manufacturer in the database. You can observe on your file that all your high current values correspond to low MPP voltage.

In the Project's design mode, you have the same pre-sizing tool, which gives an advice about the battery sizing and the required PV array power, based on your Load definition, the desired number of autonomy days (without sun) and the accepted Loss of load. This tool is based on very quick calculations of the system over the whole year, day-by-day (see the FAQ How to size a stand-alone system). However, even in the reality, the battery sizing doesn't depend on the distribution of the load along the day. If you have an autonomy of more than one day, the battery will restitute the same energy whatever the distribution over 24H.

I think you are not aware of the complexity of creating a PDF document within a programming environment. DELPHI doesn't propose tools for creating PDF documents. This would represent a very big programming task, and we have other priorities in the present time.

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.