7 Key Checkpoints When Selecting Panels in PVSyst

Selecting panels in PVSyst is not simply a matter of picking products with higher rated output. In practice, whether the basic module data you input is correct, how voltage and output change with temperature, and how losses and shading are handled as part of your assumptions all significantly affect the accuracy of generation forecasts. PVSyst itself is designed around treating modules, strings, inverters, and grid connection together within a project design, progressing detailed simulations while checking consistency. PVSyst +1

Especially for practitioners who want to “select panels in PVSyst,” it is necessary to understand not only catalog value comparisons but also which items affect profitability and design conditions. In PVSyst, a module’s basic electrical characteristics, temperature coefficients, additional data, quality loss, mismatch, IAM, temperature parameters, and shading conditions are interrelated; treating any one superficially can change the overall results. This article narrows down and explains seven practical checkpoints that are hard to skip when selecting panels. PVSyst +2 PVSyst +2

Table of Contents

• First check the consistency between rated output and basic electrical characteristics

• Check temperature coefficients to understand behavior in high and low temperatures

• Always verify the consistency between series count and voltage conditions

• Don’t take PAN files and additional data at face value

• Align assumptions for module quality loss and mismatch

• Review models under temperatures and irradiance conditions close to actual operation

• Complete the selection including shading, layout, and maintenance

First check the consistency between rated output and basic electrical characteristics

When selecting panels in PVSyst, the first thing to confirm is not only the rated output but whether the basic electrical characteristics that make up that rated output tie together naturally. In PVSyst’s module basic data, the inputs that form the foundation are rated output, technology class, reference irradiance, reference temperature, Isc, Voc, Impp, Vmpp, and so on. PVSyst’s documentation further explains that the rated output is the manufacturer’s nominal value at STC and should be close to the product of Imp and Vmp. In other words, instead of comparing only surface-level wattages, start by checking whether the I-V fundamental values are free from inconsistencies. PVSyst +1

If you leave this vague while increasing the list of candidates, later you may not understand “why this module alone looks good in the results.” In practice, even candidates in the same capacity range will differ in how you combine series counts and how they match with inverters depending on whether Vmpp is relatively high, Impp is relatively high, or Voc has margin. PVSyst ultimately checks the consistency of the entire system, but it is important as a preliminary step that the module-side basic values are straightforward. The more a candidate’s rated output number stands out, the more carefully you should check its consistency with the basic electrical characteristics to stabilize later design decisions. PVSyst +1

Another easy-to-overlook point is the treatment of tolerances. In PVSyst, module tolerance information relates to the initial value of “Module Quality Loss.” The official documentation also explains that rated tolerance is used to initialize the default module quality loss, and PVSyst’s logic initializes the default quality loss based on manufacturer tolerances. Thus, even for candidates with similar rated outputs, different tolerance settings will change the initial loss assumptions. At the selection stage, you should include tolerances as a comparison axis, not just output values. PVSyst +1

Check temperature coefficients to understand behavior in high and low temperatures

The next important factor when selecting panels is the temperature coefficients. In actual projects, how much output drops in high summer temperatures and how high voltage rises in cold winter conditions affect both generation forecasts and electrical design. PVSyst handles temperature coefficients for Isc, Voc, and Pmpp; in particular, muPmpp relates to the temperature dependence of output, and muVoc is important for voltage-side safety at low temperatures. Official guidance summarizes that muIsc has a relatively weak impact, muVoc is important for sizing, and muPmpp should preferably be close to manufacturer-specified values. PVSyst +1

It is important to understand that PVSyst’s internal model values do not necessarily match data sheet values perfectly. PVSyst states that muVoc is treated as a result value of the single-diode model, and the model’s muVoc may not coincide with the specification value. However, that difference matters more for sizing that uses low-temperature Voc than for routine generation simulation. Therefore, PVSyst provides the option to use the datasheet muVoc in project settings for sizing. Checking temperature coefficients when selecting panels means not only looking at the numbers but also understanding “where PVSyst uses these values.” PVSyst +2 PVSyst +2

On the other hand, muPmpp is a parameter that directly ties to operational output differences. PVSyst introduces a muGamma correction to match the manufacturer-specified muPmpp, and recent versions improve accuracy by fitting a linear measured value between 25℃ and 45℃ to the model. Underestimating output decline at high temperatures can lead to overly optimistic summer generation forecasts, so verifying temperature coefficients is higher priority for projects in hot regions or rooftop projects where module temperature tends to rise. When candidate panels show only small differences, annual generation differences driven by temperature coefficients can flip the ranking. PVSyst +1

Always verify the consistency between series count and voltage conditions

One of the most accident-prone practical oversights when selecting panels in PVSyst is missing voltage conditions. Even if a module looks attractive on its own, the moment you form a series string it may not fit within an inverter’s MPPT range, maximum input voltage, or the module’s allowable system voltage, making the candidate difficult to use in design. PVSyst’s official documentation lists the conditions for valid series count: Vmpp at high temperature must be above the inverter’s minimum MPPT voltage, Vmpp at low temperature must be below the maximum MPPT voltage, and Voc at low temperature must not exceed the inverter’s absolute maximum input voltage nor the module’s allowable system voltage. PVSyst +1

Applied to practice, this means that even among modules with the same rated output range, usability can vary greatly with the balance of Vmpp and Voc. For example, a candidate with a relatively low Vmpp tends to approach the MPPT lower limit in high temperatures, whereas a candidate with relatively high Voc tends to approach the upper limit in cold winters. PVSyst automatically proposes series counts, but you should not accept that proposal uncritically; compare the voltage margins for each candidate. A candidate with small design margin can easily become disadvantaged by different weather assumptions or a revision of design temperature. PVSyst +1

PVSyst also shows pass/fail indications for compliance with allowable conditions as colored warnings in the system definition screen and size display. This is not merely an operational aid but an effective filter during panel selection. Rather than comparing spec sheets on a desk, inserting candidates into the tool and observing how warnings appear and how large the margins are yields a selection that withstands operation. Panel selection is not only choosing components but also choosing ease of string design. PVSyst +1

Don’t take PAN files and additional data at face value

When selecting panels in PVSyst, don’t rely too much on the presence of a PAN file as reassurance. PVSyst module definitions can include not only basic data but also additional data such as IAM, low-light characteristics, and measured I-V curves. The official tutorial notes that additional data can include IAM, low-light data, and measured I/V curves and that, unless there are special requirements, you don’t need to dig deeply into all items. Thus, while having more additional information for a candidate panel is not inherently bad, it does not guarantee that the data’s accuracy or basis is solid. PVSyst +1

Be particularly cautious about cases where IAM or low-light data are overestimated. PVSyst’s release notes mention strengthening information display when IAM or low-light performance in PAN files appears overestimated. Regarding IAM, it is also stated that even using the detailed loss comparison function, annual production should not differ greatly from a standard model; users are advised to compare carefully before using user-defined IAM. At the selection stage, instead of being swayed by attractive numbers, it is more prudent to question additional data with weak justification. PVSyst +1

Furthermore, additional data may include items related to shading calculations and electrical behavior, such as the number of bypass diodes and reverse-direction characteristics. PVSyst explains that the number of bypass diodes is useful for electrical shading calculations in Module Layout, while reverse-direction characteristics usually have little large impact. Therefore, for projects that analyze shading in detail, these items cannot be ignored, but increasing custom values without basis is not advisable. When using PAN files, remember that “more information does not necessarily mean more correct.” PVSyst +1

Align assumptions for module quality loss and mismatch

When selecting panels, it is essential to align comparison conditions among candidates. One easy-to-overlook aspect is the assumptions for module quality loss and mismatch loss. In PVSyst, Module Quality Loss is defined as a parameter representing “how reliable the actual module performance is compared to the specification,” and its initial value is set based on manufacturer tolerances. Moreover, that value applies as a constant proportion to Array Pmpp across all operating conditions, so it subtly affects selection comparisons. If candidate A’s quality loss is lenient while candidate B’s is strict, the comparison will not be fair. PVSyst +1

The same applies to mismatch. PVSyst’s Array Mismatch Losses explains that within a single string, current mismatch has a large influence, while voltage mismatch between strings has a relatively small effect. Using Detailed computation and String Mismatch tools, you can check how module variance, string length differences, and temperature differences translate into losses. In practice, it is important not only to compare the modules themselves but also to estimate the variance arising from layout conditions and construction conditions. Rather than tweaking loss assumptions differently for each candidate, comparing under the same rules increases the credibility of the selection. PVSyst

In particular, when comparing multiple proposals internally, mixing differences in panels with differences in assumptions tends to make discussion unproductive. For example, if one candidate uses the tolerance-derived quality loss as-is while another candidate’s value is manually adjusted, you cannot tell whether the apparent difference is due to real performance or to settings. If you perform panel selection in PVSyst, first align comparison rules such as quality loss, mismatch, soiling, temperature, and IAM, and then compare candidates under those unified assumptions to reduce decision variability. PVSyst +2 PVSyst +2

Review models under temperatures and irradiance conditions close to actual operation

To avoid ending panel selection at STC, it is important to check PVSyst’s internal model under conditions close to actual operation. PVSyst includes the Internal Model Result Tool, which displays the main electrical characteristics of the module for arbitrary irradiance and temperature conditions. This is not an input field for defining the model but a verification tool to see how the module behaves under current settings. When comparing multiple candidates, it is useful to look not only at STC but also at high summer temperatures and low-irradiance conditions, as the appearances can change significantly. PVSyst +1

This check is effective because PVSyst’s internal model results can slightly differ from specification values. The official documentation also explains that the maximum output at STC can vary slightly between different definitions and that muPmpp displayed by the Internal Model Result Tool is a tangent value and may differ from the specification’s expression. Therefore, during selection you should not stop at “because it was input,” but view the response under assumed conditions and verify that behavior is not unnatural. This is useful for interpreting output decline at high temperatures and calmly assessing differences in low-irradiance bands. PVSyst +1

In PVSyst project design you can also adjust module temperature parameters, wiring losses, IAM, mismatch, and other detailed losses. Thus, panel selection only makes sense once you progress to comparisons within the system including temperature and loss conditions rather than mere standalone module comparison. In practice, the most reproducible approach is to swap candidate panel data while keeping the same meteorological conditions, layout conditions, and loss rules and observe the differences. Accumulating comparisons with fixed conditions rather than impressions from numbers alone is where PVSyst delivers value. PVSyst +1

Complete the selection including shading, layout, and maintenance

Finally, do not confine panel selection to the module alone. PVSyst project design progresses by filling in losses, far-field shading, near-field shading, and Module Layout, based on detailed time simulations. Module Layout is an important step to treat electrical shading losses more precisely. In short, even the same panel’s effective advantage or disadvantage changes with site row spacing conditions, obstacles, string separation, and the way shading occurs. When choosing candidate panels, you need to consider whether “this module is easy to handle even at sites with shading or peculiar layout characteristics.” PVSyst +1

Also, PVSyst simulation results are only valuable when the assumptions used for the site are correct. If you cannot tie which panel was chosen, which temperature and loss conditions were used, or which shading conditions were assumed to on-site information, later verification becomes difficult. For practitioners, it is important not to finish selection with a single generation table but to leave the design rationale in a recordable form. The more PVSyst parameters connect with on-site measurements and records, the stronger the selection becomes. PVSyst +1

In that sense, if you want to carry panel selection accuracy through to site operation, tools that make iterative design and measurement easier are important. Considering site condition checks, layout records, and position information management for future verification, using means that facilitate handling position and records on-site—such as LRTK (iPhone-mounted GNSS high-precision positioning device)—helps link PVSyst assumptions with field reality. Do not end panel selection as a desktop comparison; raising design decisions to a level reproducible on site is what ultimately makes the difference in practice.