André Mermoud

See our FAQ How to interprete the warranty curve of the manufacturers?

This is a question of definition. I don't know if there is an official answer, but due to the difficulty of evaluating the rear side irradiance, I really doubt that this is a good idea.

Yes, I just discovered two errors in the SolarEdge new treatment with ageing: - The Module parameters ageing dispersion cannot be null, as fixed as default for optimizers. Please fix a little value (0.1% sufficient). - With very high electrical shading losses, the long-term shading evaluation (ModuleLayout) is overestimated.

In some applications outside of the simulation, this is a "standard" value (in the hidden parameters). During the simulation, PVsyst estimates the efficiency of the module with an initial efficiency, and then uses it in this expression (one iteration). By the way this value has a very low impact in the U evaluation: a difference of 1% (in efficiency) will give a difference of 1% on the U-value or the Temperature difference, i.e. 0.35°C if you have a DT of 35°C. The U-value has a very high uncertainty (5 to 10% or more if not really measured).

There is a new very detailed tool in the version 6.64, which addresses these questions of Mismatch between strings ("Detailed Losses > Module Quality - LID - Mismatch", button "Detailed Study"). The main conclusion is that the mismatch between strings of different currents (but comparable voltages) is really very low.

No, this is not possible in PVsyst.

There will be a detailed tool for this determination in the next version 6.65.

Yes it is correct. As mentioned in the dialog, the connexions between Boxes and Inverters should be counted as twice the distance (i.e. the total wire length).

The limit for the lower temperature is defined in the Hidden parameters, topic "Miscellaneous: Meteo, Simulation, ... ", item "Lower limit for monthly temperatures".

This is quite normal. The produced energy at the output of the inverter is the Active energy. The treatment of the Power factor is explained in detail in the Help, or in the FAQ Can I define a Power Factor in PVsyst ?

The data files of PVsyst are now text files. But they are not meant for a "public" use: the structure is managed by PVsyst, and may change according to conditions and data availability.

The required temperature (for the one-diode model) is indeed the Tcelll. However this is highly dependent on how you are defining (measuring) this back temperature. You will have a difference between TCell and Tback only if you have a heat flux. If you just glue a temperature sensor to the back side, you will indeed have a heat flux towards the outside medium (convection, radiation). In this case the difference will not be "3°C", as many people think, but a difference which is proportional to the (Tcell - Tair) difference (i.e. the irradiance), according to the heat resistivity of the back side (may be different with a plastic or a glass back coverage). If you cover your sensor with an insulation, you will limit (suppress) this heat flux, and you will effectively measure the cell temperature. Now if you put too much insulation, you will modify the effective equilibrium temperature of the cell at this point. At the University of Geneva, we did a comparison with a special module equipped with a thermocouple within the encapsulation, and several ways of measurement. We found that the best compromise was to cover the sensor with a polystyrene piece of about 7 x 7 x 1 cm. Please see the FAQ How is evaluated the module temperature during simulation ?

No, the SHD files connot be exported to Helios3D (nor any other graphic software).

Yes sorry, this is an known bug in the version 6.64. This will be corrected for the next version. In the meantime, you should use an older version for seing this graph.

For the backtracking calculation, this is not only a lack of PVsyst, but a real problem. The first thing is to think about how to define the backtracking with uneven PV trackers. The backtracking limit will be different for each tracker, and the exact calculation implies an interdependence between the trackers.

These curves show irradiance on the rear side, with respect to GlobInc. These are the result of a full year simulation for your meteo data. NB: We estimate that the Bi-facial model is suited for tilts up to, say, 35 to 40°. We don't know to which extent it remains valid for higher values.

The tracking is not developed in the "Preliminary Design" tool. However please never use this "Preliminary Design" tool for a detailed study of a PV system ! This is a very rough tool, only suited for an architect who wants to evaluate the PV potential during the pre-study of a building.

Are you using backtracking ? There were indeed several issues in the version 6.52, for tracking systems in some special configurations (pairs of 2 trackers, axis orientation). I should have a look on your project to identify the exact reason. But to my knowing the result of the V 6.63 should be correct.

The number of sheds is the number of rows (one behind the other) in your installation. This number is necessary for taking into account that the first row is not shaded. The collector band width is the width of your sensitive area: if you have one row of modules 1 x 1.5 m2, if in landscape this will be 1 m, and in partrait thsi will be 1.5m.

If you have only one row of modules in your shed (whatever portrait or landscape), this will be one. If you have two rows belonging to different strings, this will be 2. If you have two rows belonging to one the same strings, this will be 1.

I can't explain this, and I can't reproduce such a behavior. - Which version of PVsyst are you using ? - Please try to change the PV module (it is a customized one, perhaps with a bad parameter?) - Please try to change the Inverter model (same remark). If the problem persists, please send us your project, using "Files > Export project" in the main menu, to support@pvsyst.com. Please join the PAN and OND files used in this example.

When dealing with differences, the celsius degrees are identical to Kelvin degrees.

Please explain what you mean by "using the MPPT feature". All inverters use indeed the MPPT feature in a "native" way.

Definition We name "Albedo" the reflexion coefficient on a ground. When a ground receives some irradiance, it will re-emit a part of this irradiance and absorb the remaining. The albedo coefficient is the ratio of the re-emitted with respect to the received irradiance, This re-emission is supposed "Lambertian", this means that each point of the ground re-emits the irradiance in all directions. The specular reflexions (like on a mirror) are not considered in the albedo. PVsyst defines 2 kinds of Albedo parameters: - The albedo of the project, which is the albedo of the far terrain in front of the PV installation. It contributes to the irradiance in the transposition model. This is defined in the Project's settings dialog. - The albedo for the bifacial evaluation: this is the albedo of the ground, just below the installation, which is "seen" by the rear side of the collectors. It is defined in the bifacial dialog. Both may be defined in yearly or monthly values. The help provides usual values of the albedo coefficient, normally valid either for the far albedo and for the bifacial ground albedo. Albedo of the project When evaluating the irradiance on a tilted plane, the albedo contribution is the light "reflected" from the far terrain in front of the installation. In all transposition models, the albedo irradiance contribution is evaluated in the same way: AlbInc [W/m²] = ρ * GlobHor * (1 - cos (tilt) ) / 2 where GlobHor = irradiance on horizontal plane, tilt = tilt angle of the receiving plane and ρ = albedo coefficient. The expression (1 - cos i) / 2 indicates that the albedo contribution is maximal on a vertical plane (expression value (1-0) / 2) = 50%), and diminishes when the tilt diminishes (14% at 45°, 6.7% at 30°, 3% at 20% and only 0.8% at 10° tilt). The horizontal plane doesn't see any albedo of course. Shading factor In a sheds (rows) arrangement, only the first row "sees" the albedo (ground level). Therefore for the whole system, we have a shading factor on this contribution equal to (n-1)/n, where n is the number of rows. As an example, if you have 100 rows the shading factor will be 0.99 ! This is also valid for tracker arrays, where to albedo shading loss is a significant contribution to the irradiance diffuse loss, even with backtracking. If you have near obstacles in front of your system (buildings, etc) the far albedo contribution is not seen. The shading factor is an integral of the albedo contributions in all directions in front of the plane. In fact by analogy with the diffuse calculation, we integrate the contributions of the virtual portion of the sphere under the horizon, included between the horizontal plane and the plane of the collectors. This contribution is only accounted for the azimuths without near obstacle. As for the diffuse, this shading factor on albedo is independent of the sun's position, and therefore constant over the year. With a far horizon, you can choose the fraction of albedo (in front of the far horizon) that you will take into account. Albedo and PR As the albedo contribution is rather low in the global incident irradiance, the exact determination of the albedo coefficient is not very important. However in sheds or tracker systems, there is a perverse effect: the albedo is part of the GlobInc evaluation, which is the basis for the Performance Ratio determination. Therefore if you have a high albedo, you will have a higher GlobInc value. But as the albedo contribution is almost completely lost, the Yield will be the same. Therefore the PR will diminish !!! In other words, as the albedo loss is included in the PR, the yield will be the same whatever the albedo coefficient, but the PR will change ! As a conclusion The albedo contribution may become significant with little systems (BIPV) without shades on the ground level, and large plane tilts. But its contribution is low or negligible with big PV systems, so that its determination is not crucial. Albedo for bifacial systems This characterizes the reflexions of the ground, just below your PV system (for example your roof). I.e. this albedo coefficient concerns the surfaces which are directly "seen" by the rear side of your bi-facial PV modules. The bifacial irradiance contribution (and bifacial gain) will be directly proportional to this albedo value. Albedo coefficient measurement The albedo is measured with an albedometer, which is basically made of 2 solarimeters: one measuring the horizontal irradiance (GlobHor), and one reversed measuring any irradiance coming from below the horizontal plane. The albedo coefficient is the ratio between both measurements. The albedo measurements on-site should be long-term measurements. The instantaneous albedo value may depend on the height of the sun, the state of the ground (wet or dry), the ageing of the ground, etc. NB: Solarimeters in the plane of array, used for a reference incident irradiance in existing systems, should be positioned in a way that they "see" the albedo (on the first shed).. Otherwise the albedo coefficient has to be adapted (about null) when this POA irradiance is used in the simulation. This is particularly true for solarimeters measuring POA irradiance in tracking systems: They should be placed on a prolongation of the axis, without neighbor trackers. :

For the variant saving conditions, we have thought a lot. We give the possibility of saving when a minimum of parameter's coherency is met. For the components, the "Save as" is available when exiting the component by "0K", as soon as you have modified something in the component. You can of course open an existing component, modify the parameters as function of a "new" datasheet, and save your component when clicking OK. This is the recommeded procedure.