André Mermoud

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.

To my knowing this works quite well since a long time (probably more than one year). Previously there were slight over-powers in some very special conditions (some very few hours in a year). We have to analyze this. Please send us your full project, using "Files > Export project", to support@pvsyst.com.

No, it is not possible. In the present time PVsyst doesn't provide an API. The only way of performing several simulations with different parameters is the Batch mode (managed by an EXCEL file)

No. The Module Quality Loss is a constant factor, applied as constant derate factor at each step of the simulation. If you define a negative loss factor (for accounting for the positive sorting), this will give a gain. The tolerance is mentioned in the PAN file. This doesn't mean that it is accounted for in the simulation. Its only use in the software is indeed for the default of this parameter.

We have completely reviewed the management of SolarEdge products. This includes these new optimizers. This is now in version 6.64.

I am really aestonished about the Satellite data of 1957... This was just the year of the launching of the first satellite Sputnik (which was just able to send bip-bip-bip to the earth) !!! Are you sure you have read this in Meteonorm data ? For which site ??? Now the DLL presently imbedded in PVsyst (V6.62) is Meteonorm V 7.1. You can have slight differences with the nes Meteonorm V 7.2, as the models and database have been improved. Please have a look on the documentation on www.meteonorm.com.

When I developed the Histogram (a long time after the mismatch tool) I probably did not remember this option of cells mismatch, and I have not programmed it. In this case of cells within a module, the I/V characteristics plot is interesting, but the histogram is not really useful. By the way, I really didn't aware of the existence of this option of cells mismatch in PVsyst ...

When you tilt the base of the table, the angles change indeed. Please see our FAQ With sheds on a Tiklted roof, PVsyst changes my orientation

You are right, the default value of this parameter is not well managed in PVsyst. However this parameter is not known accurately (only measured by myself on a very old module, 20 years ago), but it doesn't have any significant impact in the PV module modelling. The only effect in the simulation would be an imperceptible difference in the electrical losses, only when one only cell is shaded in a sub-array. As soon as several cells are shaded, the resulting difference is null.

This problem has been fixed in the version 6.62.

You can change it in the Hidden parameters, topic "System design parameters", item "Soiling loss, default yearly average".

Why "should not have" PR and DiffHor ? This is a new presentation, that we thougt more informative than the Efficiencies. Now in a next version, we will give the opportunity of customizing some columns in the report. But I don't know when we will have time for that.

In PVsyst this is evaluated by applying the one-diode model. You have some formulas for computing the Pmpp with linear derates from the STC as function of temperature and irradiance, but to my knowledge not each point of the full I/V curve (or described in very specific papers). However these are approximations.

This means that your data are not correct. It could be a problem of units, or more probably the calibration of the solarimeter.

The development of a floating system is very similar to a normal terrestrial systems. We can identify two topics for which the treatment of floating systems may be slightly different: Temperature of the modules Unfortunately we don't have any information nor measurements about the temperature on the water. Due to the evaporation, the ambient temperature could eventually be slightly lower than the temperature measured on the ground area using the "Meteo standard" measurement (i.e. measure in a sheltered box, at 2m above a ground of grass of at least 100 m2). Or the U-value could be slightly different. The module temperature may be strongly dependent on the technology of the supports: are the modules directly "seeing" the water, or on a platform? etc... The only reliable way to determine these conditions would be to measure them on-site: see How is evaluated the Module temperature during simulation? NB: If you get such measured data, we (and the PV community) would be very interested to get the results ! Now in the simulation, if you want to decrease the operating array temperature you have to increase the Uc value in "Detailed Losses > Thermal Parameter". There is a limit to this parameter (50 W/m²K). If really necessary, you can increase it in the "Hidden Parameters", topic "System design parameters", item "Heat loss factor Maximum value". If necessary, we could indeed modify the thermal model for this specific situation, where the backside is "seeing" the water: perhaps develop a model involving the water temperature. We think about such a model, but we don't have any experimental data for establishing or assessing it in the present time. Remember that for crystalline modules, a decrease of 10 °C of the array temperature will increase the yield by about 3.5% to 4%. Albedo of a water surface The water absorbs a big part of the incident light. As amazing as it sounds, the albedo of the water is very low, some people propose about 0.06. Only when the sun is very low on the horizon, there is an important reflection, but this is specular and its duration is rather short. By the way for a big installation in rows, the albedo is not significant as it is only "seen" by the first row. The shading factor on the albedo for the whole plant is (n-1)/n, where n is the number of rows. As an example a system of 100 rows will have a shading factor of 99%, i.e. it will "see" only 1% of the albedo contribution. Therefore the definition of the albedo parameter has no real importance. Tracking systems If your system is a floating disc following the azimuth of the sun during the day, you should use the option "Tracking with Vertical axis". In the 3D scene you can then choose to have a common turning axis for groups of tracker tables.

These values are a result of the Clear day model. This model only depends on the geographic coordinates and the air mass, i.e. the solar geometry. Therefore you can calculate the values for any time.

The exposition to the sun is sufficient for enabling the LID degradation. However ths doesn't have any importance, as this concern the very beginning of the PV plant production, and therefoer a completely negligible amount of energy.

This is quite different: - the albedo mentioned in the project concerns the full "far" area in front of your installation. It is used in the transposition model. - The albedo of the Bifacial model describes the reflexion of the ground just under your PVsystem (roof, grass, rocks, painting, etc)

Since the version 6.60, we have implemented a model for the simulation of bi-facial systems. This model is for the moment restricted to shed-like systems, with the hypothesis of "unlimited sheds". We will develop models for other configurations later on. This tool becomes available in the software as soon as you choose a bi-facial PV module. In PVsyst, Bi-facial PV modules are characterized by one only parameter, the bifaciality factor, which is the ratio of the STC efficiency of the rear side with respect to the front side. For such a model, we have to evaluate the irradiance available on the ground, a reflexion parameter named "albedo", and the reemission to the back side of the PV array. This evaluation is done numerically, based on 2 basic hypothesis: the diffuse irradiance is isotropic, and the re-emission from a ground point is also isotropic. From V 6.64, the diffuse irradiance from sky on the rear side will also be taken into account. However this is a little contribution with reasonable tilts (less than 20°). Irradiance on the ground The irradiance available on the ground is calculated taking the shading of the PV system into account: - the beam component between the rows is obviously dependent on the sun's position, - for each point of the ground, the diffuse effectively reaching this point is calculated using the isotropy hypothesis of the diffuse (view factor of the sky). The diffuse distribution on the ground is independent on the sun's position. It is only related to the geometry of the system. Irradiance on the rear side The irradiance on each ground point is reemitted in all directions according to the Albedo factor. Again, using the isotropy hypothesis of the re-emission , we can calculate the fraction which is re-emitted to the PV array, and the quantity lost to the sky (view factor). The luminous energy available for each ground point is the sum of the diffuse component, only dependent on the geometry, and the beam component when this point is illuminated by the beam (depending on the sun position). We should emphasize here that the ground irradiance and reemission is dependent on the position below the array. NB: We have recently found a conceptual error in the Bi-facial model. Up to the V 6.63, we had considered the exchange between the ground and the rear side of the PV modules as an energy, when it is indeed an irradiance. This means that the reemitted energy to the rear side of the collectors should be renormalized by the involved surfaces. That is, the rear side irradiance should be multiplied by Pitch/Coll. width (1/GCR), which gives a factor of 2 or more! This has been corrected in the version 6.64. We have indeed: Energy(rear) = Albedo * ViewFactor * Energy(Ground) i.e. Irrad(Rear) * Coll area = Albedo * ViewFactor * Irrad(Ground) * GroundArea => Irrad(Rear) = Albedo * ViewFactor * Irrad(Ground) * GroundArea / CollArea Therefore Please use the version 6.64 and forget the results of the previous versions 6.60 .. 6.63 ! Other perturbations We should take several perturbations of this simple model into account: - a shading loss, which is characterized by a simple factor (could be the structures, the eventual junction box if on the rear side, etc ) - the rear side irradiance is not uniform, there is therefore a mismatch between sub-modules, leading to electrical losses. PVsyst doesn't have any reliable value to propose for this parameter in the present time, - The PV module may eventuially have some transparency (spacing between the cells - or even the modules): this will contribute to the ground irradiance. Now PVsyst provides a calculation framework - established with simple and well-defined hypothesis - which may be applied all over the year. This is a reasonable physical model, but we don't have any validation. Comparison with other studies However comparisons with existing experimental systems and publications is very difficult as: - Most of the experimental setups are made of one or two modules, above an "illimited" ground area. Therefore receving light from a big illuminated environment. The model in PVsyst supposes a realistic installation with Unlimited sheds, i.e. usual rows spacing and no additional albedo contribution from the edges of the system. - The results are often available for some specific conditions, not over a full year measurement. - The albedo conditions may be not realistic with respect to real systems (specific surfaces, variability when wet, ageing, etc).