André Mermoud

Yes indeed, the battery model of PVsyst uses information which is not always present on the datasheets. Some datasheets are really very brief. When you have to define a battery by yourself, you are advised to start from an existing battery, and adjust the relevant variables (mainly technology, kind of battery, number of cells in series and parallel, internal resistance (check dafault), self-discharge (check default), lifetime (numbe of cycles), sizes and weight

You can find some data about the current and voltage degradation in the works, namely, of the TISO in Switzerland. For example in this publication: https://www.researchgate.net/publication/256080133_TISO_10_kW_30_years_experience_with_a_PV_plant

We obviously don't avail of detailed ageing data for a specified PV module. The average degradation rate itself is really not well defined. In the literature you can find a wide panel of values (0.3% to 1%/year). The PVsyst proposition of 0.4% seems a reasonable choice for usual modules. The specific mismatch effect due to ageing has been developed "theoretically" as a tool in PVsyst, without any experimental basis. We don't know any publication studying this problem in the literature. The hypotheses under this evaluation (Monte Carlo evaluation of the dispersion progress) are purely speculative. Therefore this model is obviously not able to take your particularity into account in a reliable way. You can probably take a lower value for the Isc/Vos RMS.

The PVsyst proposition doesn't take the maximum current into account. It is your job to check it in your final design. However the maximum current of a PV array is not well defined: the value corresponds to the STC (1000 W/m2), but if the inverter is specified for a given maximum current, it will limit the array current during operation, by displacing the operating point on the I/V curve. By the I don't see where you find that maximum current of 180 A. The manufacturer specifies 325 A in the PVsyst database: Your configuration of 15 strings of 25 modules of 650 Wp represents a PV power = 243 kW, i.e. a current of 238 A under 1020 V at STC.

Please remember that we are working in hourly values. And the thresholds according to the battery SOC may arise during the hour, so that the transition from an operating state to another one may arise during the hour. Therefore you can have a "Battery full" state at the beginning of the hour, and a discharge during the rest of the hour. However there is also a visual artefact because you are showing lines from the middle of hour to the middle of the next hour. In your first plot, at 13:30 you have unused energy, but no BESS discharge. At 14:30, you have BESS discharge, but no Unused energy. The intermediate lines don't have any meaning.

First of all, the inverter's behaviour with grid voltage deviations is very rarely described in the datasheets, and probably different for each inverter. By the way, PVsyst doesn't treat possible Grid voltage variations along the time. This is not part of the input variables, and we really don't see from which source we could evaluate it in prevision simulations.

I don't see what you mean by "some modules are overlapping". For filling your field, you can do that manually by the mouse. But you can possibly use the option "Attribution automatique" (you have many options for doing this), and than correct what seems not suited for you, by exchanging/dragging the string attributions with the mouse.

PVsyst doesn't provide a plot for this variation, because the Voc is not of big interest for the simulation. You can get the results of the model for any Irradiance and temperature conditions, in the PV module definition dialog, main page, "Internal model result tool":

The answers to your questions are fully explained in the help: https://www.pvsyst.com/help/project-design/array-and-system-losses/ageing-pv-modules-degradation/index.html?h=ageing https://www.pvsyst.com/help/project-design/array-and-system-losses/ageing-pv-modules-degradation/module-performance-degradation.html 1. - ISC dispersion has nothing to do with the datasheets information. Its nature is explained in the help. 2. - You can evaluate the effect of the Current and Voltage degradation weighting by yourself, by excuting several simulations. You will see that this is not very significant. 3. - When you have one only module, it is quite obvious that you don't have any mismatch loss. 4. - In the ageing process, the mismatch between "degraded" modules increases along the time. 5. - This is an input parameter. The global degradation is the sum of the individual PV modules degradation and the increasing mismatch.

Sorry, I really don't understand your strategy. It is not the battery (or the Ecoflow) which decides when it starts charging or discharging, but the external conditions (user's needs or PV availability). Starting discharging at a given SOC doesn't make sense without a clear definition of the energy demand. PVsyst controls the the charging or discharging "autorizations" as a function of the SOC evolution. If you are discharging (drawing energy), the battery will stop delivering power when the SOC reaches the specified threshold "Minimum discharging". When you are charging, PVsyst will disconnect the PV production when the SOC attains the specified "Maximum charging". This may arise within hours, You have a part of the hour in one state, and another part in the other state.

Thank you for sending your project. However it doesn't show the same output as you have shown here: The message tells you that the maximum discharging power is highly undersized. Your load definition has many hours with a load demand of around 21.3 MW, including during night, and you limit the discharging power to 10 MW. When I specify 22 MW as a discharging power, as you did in your previous message, I don't see any error nor warning anymore.

The voltage drop of a PV array doesn't make much sense, as when the R*I² loss increases, the Pmpp will move on the I/V curve, and therefore the current will also be modified. PVsyst doesn't provide any guidelines for this difference between Power loss and Voltage drop, which depends on the I/V curve. We consider that the voltage drop is not defined, and of no interest in the case of I/V curves.

The EcoFlow is a grid-tied inverter, which can only be used (in PVsyst) in a grid-connected system. Now if you want to use it in a stand-alone system - which is probably more suited for your very special use - you should define it as a "Controller for Stand-alone" in the database. But the problem of the user's needs definition remains the same: you have to define it, whatever the way you are using the produced energy. The battery needs to "know" when it has to be charged or discharged.

Sorry, I can't understand that. Please send us your full project, using "Files => Export project" in the main menu. Send it by e-mail to support@pvsyst.com, and tell us in which variant you have this problem.

This concerns the inverter at the output of the battery pack. On the next page "Self consumption", please define the "Max. discharging power". As a first step, you can ask the default value proposed by PVsyst according to your consumption profile (checkbox on the right).