How to Configure PCS in PVSyst｜5 Basic Items for Capacity Design

Table of Contents

• Why PCS settings are important in PVSyst

• Basic power plant conditions to clarify before configuring PCS

• Basic Item 1: Check the relationship between DC capacity and AC capacity

• Basic Item 2: Align the input voltage range and the number of strings

• Basic Item 3: Set the PCS rated capacity and number of units

• Basic Item 4: Check the oversizing ratio and clipping losses

• Basic Item 5: Interpret loss conditions and simulation results

• Step-by-step process for configuring PCS in PVSyst

• Common mistakes and checkpoints in PCS settings

• Importance of capacity design reflecting site conditions

• Summary

Why PCS settings are important in PVSyst

When performing a power generation simulation in PVSyst, the items that tend to attract initial attention are the photovoltaic module capacity, installation azimuth, tilt angle, and meteorological data. However, in an actual power plant, the DC power generated by the modules is not used as-is. The generated DC power is converted to AC by the PCS and delivered to match the grid and equipment. Therefore, if the PCS capacity and input conditions are not set appropriately, the simulated generation, losses, and peak output limits will deviate from reality.

The PCS is the central device for power conversion in photovoltaic (PV) systems. In PVSyst, you need to configure not only the nominal capacity but also the DC-side connection conditions, the AC-side rated output, the allowable input voltage range, the operable power range, and other parameters. In particular, when module capacity is designed larger than the PCS capacity, the PCS may reach its output limit under sunny or low-temperature conditions, and part of the potentially producible power may be curtailed. This phenomenon is not necessarily undesirable from a design standpoint aimed at increasing energy yield, but in simulations it must be clearly identified as a loss.

When using PVSyst, it is important not to treat PCS settings as a standalone data-entry task, but to verify them in conjunction with the plant’s overall capacity design. If the number of modules in series is not appropriate, the array may fall outside the PCS input voltage range. If the number of parallel strings is excessive, the required input current and the circuit configuration may become impractical. Changing the number of PCS units will also alter the AC capacity and the oversizing ratio. In other words, PCS settings are central to energy yield calculations and are an important step in verifying the validity of the design conditions.

In PVSyst, you can review simulation results such as conversion losses, output limitations, array-side losses, and overall system performance indicators. By interpreting these results, it becomes easier to determine whether the configured PCS capacity is undersized, oversized, or within a practically acceptable range. Many beginners stumble over PCS settings not because the input-screen field names are difficult, but because they proceed without clarifying the relationship between DC capacity and AC capacity.

Basic power plant conditions to clarify before PCS configuration

Before configuring the PCS in PVSyst, it is important to first organize the power plant’s basic conditions. PCS settings are not completed simply by entering capacity and the number of units on the screen; they are linked to the modules, strings, installation conditions, and grid interconnection conditions. If you organize the information up front, it will be easier to identify the cause if inconsistencies occur during the configuration.

The first thing to check is the specifications of the solar module. Rated output, open-circuit voltage, maximum power operating voltage, short-circuit current, maximum power operating current, temperature coefficients, and so on are closely related to the PCS input conditions. In particular, because the open-circuit voltage rises at low temperatures, you need to confirm that it will not exceed the PCS’s maximum input voltage under cold conditions. Conversely, because the operating voltage falls at high temperatures, confirm that the PCS is within the voltage range in which it can stably perform maximum power point tracking.

Next, we will organize the plant's overall DC capacity. DC capacity generally refers to the capacity obtained by multiplying a module's rated output by the number of modules. For example, when many modules with a certain output are installed, their total becomes the array capacity. This capacity, compared with the PCS's AC rated capacity, serves as the basis for determining the oversizing ratio and the DC/AC ratio. In PVSyst, the relationship between this DC capacity and the PCS capacity is reflected in the simulation results, so it is important to enter it with design intent.

Furthermore, the meteorological conditions at the installation site also affect PCS settings. In colder regions, module voltage tends to be higher, so checking the upper limit of input voltage is important. In areas with strong solar irradiance or cool climates with high generation efficiency, the time spent at the PCS’s rated output may increase. Conversely, in high-temperature regions module output tends to decrease, and there may be fewer output limitations even with overloading. Thus, the suitability of PCS capacity varies not only with simple ratios but also with regional conditions.

Also, it is necessary to clarify the plant’s objectives. The approach to PCS capacity will vary depending on whether you want to maximize annual energy generation, suppress peak output to optimize the overall installation, or increase the DC side within a limited interconnection capacity. When using PVSyst, it is practical not to enter the design conditions once and be done, but to compare multiple capacity scenarios while examining the balance among energy generation, losses, and equipment conditions.

Basic Item 1: Confirm the relationship between DC capacity and AC capacity

The most fundamental aspect of PCS settings is the relationship between DC capacity and AC capacity. DC capacity is the total capacity on the photovoltaic module side, and AC capacity is the rated capacity that the PCS can output as alternating current. In PVSyst, this relationship is central to system design. If DC capacity is larger than AC capacity, the PCS may reach its output limit during periods of strong solar irradiance and the excess may not be output. Conversely, if DC capacity is too small, the PCS’s capability cannot be fully utilized, which can decrease efficiency in terms of equipment utilization.

In practice, designs often make the DC capacity larger than the PCS capacity. This is because solar modules do not always produce their rated output. Actual generation is affected by solar irradiance, temperature, soiling, shading, wiring losses, degradation with age, and so on. Therefore, even if module capacity and PCS capacity are the same, the PCS will only operate at its rated full power for a limited time. For this reason, there is an approach of slightly increasing the DC-side capacity to boost output in the mornings, evenings, and overcast conditions, thereby increasing annual energy production.

However, increasing DC capacity does not necessarily lead to better results. If DC capacity is increased excessively, output curtailment on sunny days increases and simulated clipping losses become larger. When configuring the PCS in PVSyst, you need to check the DC/AC ratio and assess the balance between the increase in annual energy yield and losses due to output limitations. Even if the simulation results show a certain degree of output limitation, the design may still be acceptable if it is reasonable from the standpoint of annual generation and equipment conditions.

On the PVSyst screen, in the system settings you enter a combination of the number of modules, the string configuration, the specifications corresponding to the PCS model, and the number of units. At this stage, rather than looking only at the total capacity, you should also check the DC capacity connected to each PCS unit. When multiple PCS units are used, if the connected capacities per PCS are unbalanced, certain PCS units may be more likely to experience output limiting. Even if the simulation shows the overall capacity, in the actual detailed design it is important to ensure consistency on a per‑PCS basis.

Also, the rated AC-side capacity is related to grid interconnection conditions and the capacity of the power receiving equipment. If the capacity available for interconnection is limited, it may not be possible to increase PCS capacity; instead, designs that increase DC-side capacity to secure annual energy production are considered. In such cases, multiple DC/AC ratios are compared using PVSyst to determine to what extent oversizing is reasonable. The first step in PCS configuration is to understand numerically the relationship between DC capacity and AC capacity and to clarify the design intent.

Basic Item 2: Align the Input Voltage Range with the Number of Strings

In PCS capacity design, it is essential to check not only the total capacity but also the input voltage range. PV modules connected in series add their voltages. When configuring strings in PVSyst, verify that the voltage determined by the number of modules in series falls within the PCS’s allowable input range. If this is mistaken, the simulation may produce warnings or the configuration may be invalid as an actual design.

What you should pay particular attention to regarding input voltage is the open-circuit voltage at low temperatures. Module voltage rises as temperature falls. Even if there is no problem under normal rated conditions, there is a possibility of exceeding the PCS maximum input voltage in low-temperature conditions such as winter early mornings. PVSyst performs voltage-range checks taking into account the ambient temperature conditions of the installation site, so if the number of modules connected in series per string is excessive, it needs to be reviewed. To design on the safe side, confirming the maximum voltage should be the top priority.

On the other hand, module voltage drops at high temperatures. If the number of modules in series is too small, the voltage may fall below the range required for the PCS to operate efficiently. Especially during daytime in summer, module temperatures rise and the operating voltage tends to decrease. If the input voltage falls outside the proper range, maximum power point tracking (MPPT) efficiency may decrease, or the operable range may narrow. Therefore, string design needs to verify both the upper limit at low temperatures and the lower limit at high temperatures.

When using PVSyst, after entering the number of modules in series you check the displayed voltage conditions and any warnings. If there are issues, you increase or decrease the series module count to bring them into the appropriate range. What is important here is that changing the series count also affects the number of parallel strings and the total number of modules. If you reduce the series count, the number of parallel strings increases to secure the same capacity, which affects the number of input circuits and wiring conditions. If you increase the series count, you approach the voltage limit and the risk during low temperatures increases.

The number of strings must also be aligned with the number of input circuits per PCS and the allowable input current. In PVSyst, a configuration that is theoretically connectable may not match the actual number of PCS inputs or the configuration of combiner boxes. Practitioners must be careful not to confuse the simplified inputs used for simulation with the circuit configurations required for detailed design. PVSyst is a powerful tool to support design studies, but whether a configuration can be constructed on site should be verified separately against equipment drawings and specification conditions.

Basic Item 3: Set the rated capacity and number of PCS units

The rated capacity and number of PCS units are important input parameters in PVSyst for determining the system’s overall AC capacity. By setting the rated output per PCS and entering the required number of units, the plant’s total AC capacity is determined. The capacity entered here directly affects the output limit, conversion losses, and the oversizing ratio in the simulation results.

In practice, the number of PCS units is determined according to the plant’s size and interconnection conditions. Small installations are often composed of a few units, while large installations configure the total capacity by combining multiple PCS units. In PVSyst, you select or create PCS specifications and configure how many of each PCS to use for the module array. During the preliminary capacity assessment stage, a PCS with a similar rated capacity is often provisionally set and later adjusted to match the actual specifications.

When setting the number of PCS units, what you need to pay attention to is not only the total capacity but also the distribution. For example, even with the same total AC capacity, a configuration that uses a small number of large PCS units and one that uses multiple medium-sized PCS units will differ in circuit design, maintainability, the scope of impact in case of failure, and required installation space. Even if the difference in energy yield in PVSyst is small, there can be significant differences in the practical equipment configuration. Therefore, when configuring PCS in PVSyst, it is desirable to consider not only energy production but also operational aspects.

Also, the conversion efficiency of the PCS also affects simulation results. The PCS exhibits specific efficiency characteristics not only when input power is close to its rated value but also at low output levels. During periods of low output, such as mornings, evenings, or cloudy conditions, the conversion efficiency can decrease. Because PVSyst takes the PCS efficiency curve into account, the selection of rated capacity can affect the annual energy yield. Choosing a PCS with excessive capacity can increase the time spent operating at low load, which is disadvantageous from an efficiency standpoint.

On the other hand, if the PCS capacity is too small, output clipping increases on sunny days. In particular, when the site's irradiance conditions are good and the module capacity is large, the PV system reaches the PCS's rated output for longer periods. As a result, simulation results show increased losses due to PCS output limitations. The important point is that while increasing PCS capacity reduces these losses, a balance with the equipment configuration and grid-interconnection conditions is necessary. A practical approach is to compare multiple scenarios in PVSyst and evaluate combinations of rated capacity and number of units.

Basic Item 4: Confirm the overloading rate and clipping losses

When configuring the PCS, practitioners should pay particular attention to the oversizing ratio and clipping losses. The oversizing ratio is a concept that indicates how much larger the DC-side module capacity is compared to the PCS's AC capacity. In photovoltaic power generation, modules do not always produce their rated output, so the DC side is made somewhat larger to increase annual energy production. However, if the oversizing ratio is too high, there will be more periods when the PCS's maximum output is exceeded, and that excess appears as clipping losses.

Clipping losses occur when the PCS reaches the maximum AC output it can convert. For example, even if the modules generate sufficient DC power, any portion that exceeds the PCS’s rated output cannot be delivered to the AC side. In this case, part of the energy that could have been produced in the simulation is clipped. In PVSyst, such PCS-induced output limitations can be viewed on the results screen. When designing with oversizing, always check how much clipping loss is occurring.

However, the presence of clipping losses does not necessarily mean the design is immediately bad. Increasing DC capacity can raise generation during mornings, evenings, and low-irradiance periods, and may be advantageous on an annual basis. What is important is the balance between the generation that is lost and the generation that is gained. As a way to use PVSyst, run simulations while changing DC capacity stepwise and compare changes in annual energy production, output limitation losses, and performance indicators. This will allow you to identify at what point increasing the oversizing ratio begins to yield diminishing returns.

Also, the tendency for clipping losses to occur varies depending on the region and installation conditions. In areas with strong solar irradiance and relatively low temperatures, module output tends to be higher, and PCS output limits are more likely to occur. Conversely, in hot regions where module output tends to decrease, clipping losses can be lower even at the same overloading ratio. Installation tilt and orientation also affect this. A south-facing configuration that concentrates the peak and a configuration that distributes it east–west place different demands on the PCS’s peak output.

When designing capacity in PVSyst, it is important not to treat the oversizing ratio as a mere numeric target. Although guideline ranges exist, the optimal value depends on equipment conditions, the region, grid interconnection conditions, and the power plant's objectives. Comparing the benefit of increased energy yield with the increase in output curtailment—while checking how much clipping loss appears in the simulation results—leads to practical decision-making for PCS settings.

Basic Item 5: Interpreting Loss Conditions and Simulation Results

Once the PCS settings are finished, review the simulation results to determine whether the settings are appropriate. In PVSyst, you can check not only the total energy generation but also a breakdown of various losses. The main items related to the PCS include conversion losses, output limitations, constraints due to input conditions, and efficiency degradation at low output. By interpreting these, you can determine whether there are any issues with the PCS capacity or string configuration.

The first thing to check is the conversion losses of the PCS. The PCS incurs certain losses when converting direct current (DC) to alternating current (AC). The higher the conversion efficiency, the smaller the losses, but in practice the efficiency changes depending on the magnitude of the input power. Even if efficiency is high near the rated point, it can drop at low output. In PVSyst, the efficiency characteristics of the PCS are reflected, so the annual conversion losses vary depending on the choice of rated capacity and the distribution of operating time periods.

Next, check the losses caused by PCS output limits. In designs with a high overloading ratio, these losses tend to increase. If the simulation results show significant output limiting, possible measures include increasing PCS capacity, reviewing DC capacity, and considering peak dispersion through azimuth and tilt. However, increasing PCS capacity is not always optimal. It must be aligned with grid interconnection conditions, equipment capacities, installation space, and operational policies.

Also, check the overall system performance indicators. In PVSyst, you can assess how much electrical energy is actually obtained compared with the theoretically available solar energy. If there is an issue with the PCS settings, the performance indicators may be lower than expected. However, performance indicators are not determined by the PCS alone; they include many factors such as shading, temperature, wiring, mismatch, and soiling. Therefore, when assessing the validity of PCS settings, it is important to break down the loss components and examine them.

One thing to avoid when reading simulation results is judging solely by the annual energy yield. Even if the annual yield looks large, design risks remain if clipping losses are excessively high or if there is little margin in the input voltage range. Conversely, even if output limiting is minimal, the PCS capacity may be oversized and cause poor efficiency at low loads. When using PVSyst, do not treat the results as standalone numbers; evaluate them comprehensively against the design conditions.

Detailed procedure for configuring PCS in PVSyst

The workflow for setting up a PCS in PVSyst is to create the power plant's project conditions, input meteorological data and installation conditions, and then combine the modules and the PCS on the system settings screen.

What is important for beginners is not just entering data in the order of the screens, but proceeding while understanding what each input item means.

First, set the meteorological and installation conditions for the target site. Because PCS capacity design is related to module output, if the meteorological data or installation angles are significantly off, an appropriate capacity assessment cannot be carried out. If you proceed with PCS settings while the installation orientation, tilt angle, terrain conditions, and shading conditions are not yet fully defined, it will later be difficult, when reviewing simulation results, to determine whether losses are caused by the PCS or by the installation conditions.

Next, set the specifications of the photovoltaic modules. If the module's rated output, voltage, current, and temperature characteristics are not correctly reflected, verification of the string configuration and the PCS input range cannot be performed correctly. In PVSyst, because the system is configured by combining module specifications and PCS specifications, it is important to first establish the DC-side conditions. Even if similar-spec data is used provisionally, it must be evaluated on the premise that it will be replaced with the official specifications later.

After that, set the PCS specifications and enter the number of units. This determines the overall AC capacity and makes the relationship with the DC capacity visible. After inputting, check the capacity ratio and any warnings displayed by PVSyst. If there are capacity mismatches, voltage range issues, or string configuration problems, adjust the number of modules in series, the number in parallel, and the number of PCS units. A common mistake beginners make is proceeding without thoroughly checking the warnings. Because warnings can indicate significant design inconsistencies, always review their details.

Furthermore, we run the simulation and review the results. We look at annual energy production, monthly energy production, PCS-related losses, and whether there are any output limitations. If necessary, we compare scenarios with different PCS capacities, different DC capacities, and different string configurations. The strength of PVSyst is that it can be used for design decisions by comparing multiple conditions. Rather than drawing conclusions from a single setup, checking several patterns makes it easier to justify the validity of the capacity design.

Finally, record the simulation conditions. Organizing which module capacity and which PCS capacity were set, the oversizing ratio used, and the amount of losses incurred will help with internal approvals, explanations to the client, and comparisons when making design changes. When you are not yet familiar with using PVSyst, you may tend to judge based only on the input screens, but in practice it is very important to document the rationale for the settings.

Common Mistakes and Checkpoints in PCS Configuration

One common mistake when configuring the PCS in PVSyst is looking only at the relationship between DC capacity and AC capacity and not sufficiently checking the input voltage range. Even if the capacity ratio appears appropriate, if the number of modules in series per string is too high, the maximum input voltage can be exceeded at low temperatures. Conversely, if the number of modules in series is too low, the operating voltage can become too low at high temperatures, potentially taking the PCS out of its proper operating range. Capacity and voltage need to be treated as separate items to check.

A common mistake is to judge the oversizing ratio by a fixed guideline alone. The oversizing ratio is a useful indicator, but the optimal value varies with the installation site, weather conditions, orientation, tilt, and grid-connection conditions. Even with the same oversizing ratio, areas with strong solar irradiation can experience larger clipping losses, while locations with considerable shading may see peak output suppressed. The purpose of sizing capacity in PVSyst is not simply to match a standard ratio, but to check what kind of energy production and losses will occur under actual conditions.

Also, care must be taken to avoid input errors when entering the number of PCS units. For example, if you intend to enter the capacity of a single PCS but it is treated as the capacity for the entire system, or conversely if you enter the total capacity as the per-unit capacity, the results will change significantly. In PVSyst, the overall AC capacity is calculated from the entered PCS capacity and the number of units. After configuration, always verify that the total AC capacity matches the design intent.

Misreading simulation results is also a common pitfall. An increase in annual energy production does not necessarily mean the design is good. If output limits increase significantly, you need to consider whether the increase in energy production is commensurate with the added equipment. Also, if you compare only total energy production without looking at the breakdown of losses, you will not know where improvements can be made. After configuring the PCS, check conversion losses, clipping losses, temperature losses, wiring losses, and so on separately.

Furthermore, simulations are sometimes run using an ideal configuration without reflecting on-site construction conditions. Even if the string arrangement looks neat in PVSyst, the same layout may not be feasible on the actual site due to parcel shape, walkways, slopes, shading, and wiring routes. If the conditions of the strings connected to each PCS input circuit differ significantly, mismatches may occur during actual operation. It is important to adjust simulation conditions while cross-checking them against the on-site design.

The Importance of Capacity Design That Reflects On-Site Conditions

PCS capacity design cannot be completed using desk-based figures alone. To perform high-precision simulations in PVSyst, site conditions must be reflected as accurately as possible. In particular, terrain, orientation, tilt, shading, surrounding obstructions, and the available installation area affect energy generation and peak output. If these conditions remain ambiguous, considerations of PCS capacity are likely to drift away from reality.

For example, even with the same module capacity and PCS capacity, whether modules are arranged uniformly on a flat site or distributed across a sloped or terraced site will change the generation peaks and the occurrence of shading. If shading occurs in part of the array, differences may appear in the generation conditions for each PCS input circuit. PVSyst allows you to set shading effects, but if you do not correctly grasp the site's topography and the positions of obstacles, you cannot reflect them in the simulation conditions.

Variations in azimuth and tilt also affect PCS settings. If all modules face the same azimuth, generation peaks tend to concentrate in specific time periods. On the other hand, if modules are distributed across different azimuths, generation peaks are dispersed, which can reduce PCS output constraints. With such designs, clipping losses can differ even with the same DC/AC ratio. By comparing multiple layout scenarios in PVSyst, the appropriateness of PCS capacity can be assessed more practically.

When incorporating on-site conditions, the accuracy of surveying and location information is also important. If the installation area, slopes, existing structures, and surrounding elevation differences can be accurately determined, the reliability of the conditions entered into PVSyst is improved. Conversely, if on-site information remains coarse, even if simulations show no issues, layout changes may occur during construction, requiring a review of PCS capacity and string configuration.

In designing solar power generation systems, it is important not to separate simulation from on-site verification. PVSyst is an effective tool for quantitatively assessing energy production and losses, but the reliability of its results depends on the quality of the on-site conditions entered. In particular, for PCS settings, module layout, string configuration, shading, and terrain interact, so it is essential to carefully collect on-site information and reflect it in the simulation.

Summary

To understand how to set the PCS in PVSyst, merely memorizing how to operate the input screens is not sufficient. The PCS is the central equipment that converts the DC power generated by the solar modules into AC, and the approach to capacity design greatly influences the simulation results. In particular, the relationship between DC capacity and AC capacity, the input voltage range, string configuration, PCS rated capacity and number of units, the overloading ratio, and checking for clipping losses are indispensable items in practical work.

First, by clarifying the relationship between DC capacity and AC capacity, the basics of the oversizing ratio and output limits become clear. Increasing the DC side can potentially increase generation in the mornings, evenings, and during low-irradiance periods, but if the time during which the PCS's rated output is exceeded increases, clipping losses will occur. In PVSyst, you can confirm this balance from the simulation results, so it is important to carry out capacity design while comparing multiple options.

Next, check the consistency between the input voltage range and the number of strings. Module voltage rises at low temperatures and operating voltage falls at high temperatures. Therefore, the number of modules connected in series per string must be set so that it does not exceed the maximum input voltage and still meets the voltage range required for operation. Checking voltage conditions as well as capacity ratios is fundamental when configuring the PCS in PVSyst.

In addition, appropriately set the PCS rated capacity and the number of units, and check conversion losses and output limits. Not only the annual generation but also examining the breakdown of losses allows you to determine whether the configured capacity is reasonable. If the oversizing ratio is high, check how much clipping loss is occurring and evaluate the balance with the increase in generation. In practice, it is sensible to compare multiple options, such as increasing PCS capacity, adjusting DC capacity, or reviewing layout/installation conditions.

When you are not yet familiar with how to use PVSyst, it is easy to overlook on-screen warnings and the meaning of numerical values. However, PCS settings are an important process that affects the overall design quality of a power plant. By organizing module specifications, meteorological conditions, local terrain, shading, azimuth, tilt, and grid-connection conditions and reflecting them in the simulation settings, you can achieve a more reliable capacity design.

In addition, obtaining on-site information is also important for improving the accuracy of PCS settings. If the installation area, topography, and locations of surrounding obstacles can be accurately identified, you can improve the shading settings, layout planning, and the appropriateness of string configurations in PVSyst. If you want to efficiently obtain on-site positional and topographic information, using an iPhone-mounted GNSS high-precision positioning device such as LRTK makes it easier to apply the high-precision coordinate data collected on site to preparing assumptions for design and simulation. By combining capacity design using PVSyst with high-precision on-site positioning, you can reduce discrepancies between desk studies and field conditions and achieve more practice-oriented photovoltaic system planning.