7 Key Inverter Settings to Note in the PVSyst Manual

Table of Contents

• The purpose of reading inverter settings in the PVSyst manual

• Point 1: Correctly assess inverter capacity and the DC/AC ratio

• Point 2 Confirm overload losses using a power generation simulation

• Point 3: Align the input voltage range and string configuration

• Point 4: Align the number of MPPTs and the input allocation with the site design

• Point 5: Examine the impact of inverter efficiency and low-load operation

• Point 6: Consider output limitations due to power factor and reactive power conditions

• Point 7: Key loss items to check in the report

• Summary

What it means to read inverter settings in the PVSyst manual

One of the factors that can significantly change the estimated energy yield in photovoltaic simulations is the inverter settings. While attention tends to focus on PV module capacity, orientation, tilt angle, and meteorological data, if the inverter’s rated capacity, input voltage range, MPPT inputs, overload restrictions, and power factor conditions are left ambiguous during analysis, even designs that appear valid on the surface can easily lead to discrepancies in actual energy yield estimates and loss evaluations.

When reading the PVSyst manual, it is important not to select an inverter merely as a device name, but to view the relationship between the PV array and the inverter as a single system. In PVSyst, the ratio of the nominal output of the PV array to the nominal output of the inverter is treated as the PNom ratio, commonly referred to as the DC/AC ratio. This ratio is defined as the nominal capacity of the PV array divided by the nominal AC capacity of the inverter.

One frequent pitfall in inverter settings is judging solely by whether the capacities match. In practice, even with the same solar cell capacity, making the inverter capacity smaller can sometimes reduce initial costs and simplify equipment configuration. However, when the DC-side output increases during sunny or low-temperature conditions, clipping occurs on the inverter side that limits output, and this is reflected in the generated power as overload losses. Conversely, if the inverter capacity is made too large, the inverter may spend more time operating in a low-output range, which can be disadvantageous in terms of efficiency.

Therefore, the purpose of checking the inverter settings in the PVSyst manual is not simply to memorize the meaning of the input fields. It is to verify, taking into account the design conditions, installed capacity, string configuration, solar irradiance conditions, temperature conditions, and loss conditions, whether the inverter configuration is reasonable for the expected energy yield. Here, we explain the seven key inverter-setting points that beginners tend to stumble over and that practitioners should check.

Point 1: Correctly assess inverter capacity and the DC/AC ratio

The first thing to grasp is the relationship between inverter capacity and the DC/AC ratio. When configuring an inverter in PVSyst, you check how the total capacity of the solar modules and the inverter’s nominal output are balanced. The DC/AC ratio here is the ratio of the PV array’s nominal capacity on the direct-current side to the inverter’s nominal capacity on the alternating-current side. In PVSyst’s documentation, the PNom ratio is defined as the ratio of the PV array PNom STC to the inverter PNom.

For example, if the solar array capacity is 1,250 kW and the inverter capacity is 1,000 kW, the DC/AC ratio is 1.25. Looking at this number alone, one might immediately conclude that losses will be large because the solar array capacity is greater than the inverter capacity. However, solar modules do not always produce output according to STC conditions. In real sites, the DC-side output varies over time due to irradiance, module temperature, azimuth, tilt angle, soiling, wiring losses, shading, and other factors. Therefore, making the inverter capacity equal to the PV array capacity is not always optimal.

What is important in the PVSyst manual is to view the DC/AC ratio not merely as a safety factor but in relation to the distribution of output throughout the year. PVSyst’s explanation presents the idea that, as a general design rule to avoid overload losses, the PNom ratio should be around 1.25 to 1.3. However, this is not a number to be applied mechanically to every project; it is a guideline that should be checked with detailed simulations.

In practice, in low‑latitude regions, high‑irradiance regions, regions where output tends to increase at low temperatures, and ground‑mounted projects with optimized orientation and tilt, peak output is more likely to approach inverter capacity. On the other hand, for roof‑mounted projects with distributed orientations, projects split east‑west, or projects with some degree of shading, even if the total PV array capacity is large, the time during which all strings produce their maximum output simultaneously may be limited.

Therefore, when setting inverter capacity in PVSyst, you should not stop at the DC/AC ratio number; you need to verify what generation pattern that ratio assumes. While a rough capacity ratio may be acceptable during the estimation phase, in the final energy-yield assessment it is important to reflect meteorological data, shading, temperature, and loss conditions, and to check whether overload losses and the annual energy yield are reasonable.

Point 2: Verify overload losses in the power generation simulation

One aspect of inverter settings that is particularly easy to overlook is overload loss. Overload loss occurs when the power input from the PV array exceeds the maximum the inverter can handle. Commonly called clipping, this refers to the condition where part of the DC power that could have been generated cannot be delivered as AC output.

PVSyst explains that the optimal sizing of an inverter should be determined based on the overload losses that can be tolerated during operation. In other words, when deciding inverter capacity, you should not simply match equipment capacity tables; you need to run annual simulations that account for actual weather conditions, installation conditions, and loss conditions to see how much overload loss will occur.

A small amount of overload loss does not necessarily mean the system is inappropriate. Increasing inverter capacity will reduce overload losses, but it can affect equipment costs, installation space, switchboard configuration, and maintenance conditions. Also, increasing inverter capacity to fully capture peaks that occur during only a very small portion of the year is not necessarily economically advantageous. Rather, designs that allow a certain degree of overloading and balance annual energy production with cost are sometimes adopted.

What’s important is to check the proportion of overload losses and the conditions under which they occur. For example, if overload losses are very small relative to annual energy production, that DC/AC ratio may be practically acceptable. On the other hand, if overload losses are large and the generation curve on sunny days is capped for long periods, it will be necessary to reconsider inverter capacity, change the string configuration, redistribute MPPT inputs, and consider azimuth diversification.

When reading the PVSyst manual, it is important not to treat overload losses as a single number, but to trace why that loss is occurring. The appropriate measures depend on whether the PV array capacity is oversized, the input voltage conditions are restrictive, MPPT allocation is unbalanced, or the active power limit is lowered by power factor conditions.

Also, although issues may appear minor in early-stage, coarse simulations, accounting for detailed shading settings, wiring losses, module quality, mismatch, temperature conditions, and so on can change how losses manifest. The PVSyst tutorial likewise states that the optimal inverter sizing is based on the allowable overload losses over the year, and explains a workflow in which the detailed loss conditions are defined afterwards.

Therefore, for inverter settings it is practical to follow a workflow of an initial capacity assessment, a recheck after reflecting detailed conditions, and loss verification in the final report. Rather than setting it once and leaving it, reviewing overload losses each time the design is refined will improve the accuracy of generation estimates.

Point 3 Align the input voltage range and string configuration

In inverter settings, not only capacity but also the input voltage range is important. If the voltage of the string formed by connecting solar photovoltaic modules in series does not fall within the inverter's allowable input voltage range and MPPT operating range, it will not generate power as expected. Even if the apparent capacity in PVSyst matches, inappropriate voltage conditions can cause losses or shutdowns due to voltage thresholds.

The voltage of a solar PV module changes with temperature. Generally, the open-circuit voltage is higher at low temperatures, and the operating voltage is lower at high temperatures. Therefore, when determining the number of strings, you need to check not only the voltage under standard test conditions but also the maximum voltage at the lowest ambient temperature, the MPPT voltage at high temperature, the inverter’s maximum input voltage, the minimum MPPT voltage, and the maximum MPPT voltage.

In PVSyst's explanation of inverter operating limits, loss items related not only to overload losses but also to minimum and maximum voltage thresholds, maximum input current, and other factors are organized. These are important for determining under which conditions the inverter can properly accept power.

A common stumbling block for beginners is the simplistic assumption that increasing the number of modules in series will make wiring more efficient, or that increasing the number of strings will increase capacity. In reality, increasing the series count too much carries the risk of exceeding the maximum input voltage at low temperatures, while reducing the series count too much carries the risk of falling below the MPPT lower limit at high temperatures. Either can lead to reduced energy production or to the design being infeasible.

Also, there are inverter models whose nominal output power changes depending on the input voltage. PVSyst's documentation also indicates that some inverters have a nominal power curve as a function of input voltage. For such models, it is not sufficient for the voltage merely to fall within the allowable range; you need to check how much output the inverter can handle in the voltage bands that are actually used.

In practice, you first check Voc, Vmpp, and the temperature coefficients from the module datasheet, then set the assumed minimum temperature and the assumed operating temperature for the design site. You then verify that the string configuration in PVSyst is within acceptable limits with regard to the maximum voltage at low temperatures, the MPPT voltage at high temperatures, and the normal operating voltage range. In particular, in snowy or cold regions you need to pay attention to voltage increases at low temperatures, while in hot regions or rooftop installations you need to pay attention to voltage decreases at high temperatures.

The input voltage range affects not only power generation but also safety and equipment warranties. By checking PVSyst for warnings, ensuring there are no abnormal voltage losses, and confirming that the inverter’s operating conditions in the report are appropriate, you can reduce design risks that capacity alone won’t reveal.

Point 4: Match MPPT count and input distribution to the site design

In recent years, inverters with multiple MPPT inputs have become common. MPPT is a maximum power point tracking mechanism that adjusts the operating point of strings or arrays to extract power as efficiently as possible. When checking inverter settings in the PVSyst manual, it is important to verify that the number of MPPTs and the allocation of strings to each input match the actual site design.

MPPT settings become important when orientation, tilt, shading, number of modules, and string length differ. For example, in designs like east-west roofs where output peaks are split between morning and afternoon, mixing strings with different orientations on the same MPPT can prevent optimal maximum power point tracking (MPPT), potentially leading to overestimation or underestimation of energy production. The same applies when dealing with south- and west-facing roof surfaces, roof surfaces with different tilt angles, or areas that experience different shading patterns.

PVSyst's documentation indicates that for inverters with multiple MPPT inputs, by default each MPPT input is treated like the same small inverter and is considered as the inverter's total PNom divided by the number of MPPTs. This is very important to understand when configuring, because if the number of strings per MPPT is unbalanced, certain MPPTs may end up with a higher DC/AC ratio and cause localized overload losses.

On the other hand, some real inverters have a power-sharing function that allows them to share output between MPPTs. The PVSyst documentation explains that actual inverters may be able to share total output among different MPPT inputs. If this function is not properly reflected, simulated losses can appear larger than the real-world behavior, or conversely the assessment can be more optimistic than the actual performance.

What should be checked in practice is whether the MPPT settings in PVSyst match the electrical drawings, single-line wiring diagrams, and the string schedule. You should verify which roof surface strings are assigned to which MPPT, whether the number of strings per MPPT is equal, whether strings with different orientations or shading conditions are mixed, and whether the actual equipment input specifications match the model in PVSyst.

Especially for rooftop installations, agrivoltaics, and ground-mounted systems with multiple orientations, MPPT allocation has a significant impact on energy production. Settings that are not a major issue in a simple single south-facing layout can become a source of losses in more complex layouts. When reading the PVSyst manual, it is important to understand MPPT not merely as a count of inputs but as a unit for separating and managing distinct on-site output characteristics.

Point 5: Assess inverter efficiency and the impact of low-load operation

The inverter converts the input DC power into AC power. This conversion incurs losses, which are reflected in simulations as inverter efficiency. In general, inverter efficiency is high near rated output and tends to decrease in low-output ranges. Therefore, if the inverter capacity is oversized, overload losses will decrease, but the time spent operating at low load will increase, which can be disadvantageous from a conversion-efficiency standpoint.

PVSyst’s explanation on inverter sizing also shows that if the inverter is oversized, the time spent operating in the low-output range increases and efficiency can drop. This is a very practical perspective when considering inverter settings. If the sole objective is to make overload losses nearly zero, there is a tendency to bias toward increasing inverter capacity. However, from the standpoint of annual energy production and economics, it is necessary to look at the balance between overload losses and conversion losses.

In PVSyst, what you want to check is whether the inverter efficiency curve is based on actual device data, whether the inverter model being used matches the planned model, and, for multiple-unit configurations, whether the number of units and their capacities have been entered correctly. If there is no model in the inverter database that closely matches, a similar model may be used as a substitute, but in that case you must carefully confirm that the capacity, efficiency, input voltage, number of MPPTs, and current limits are not significantly different.

The impact of low-load operation becomes apparent during mornings and evenings, on cloudy days, in winter, and during periods affected by shading. The share this represents of annual generation varies by project, but when comparing to the load curve—such as for self-consumption or rooftop installations—generation by time of day becomes important, so efficiency in the low-load range cannot be ignored. Rather than looking only at annual kWh, checking the shape of the generation curve and the output by time of day allows a more accurate judgment of the appropriateness of inverter settings.

Inverter efficiency is also affected by temperature and operating conditions. Looking only at the maximum efficiency listed in the equipment specifications does not allow you to determine the actual annual conversion efficiency. PVSyst can simulate based on annual weather conditions and output distribution, enabling evaluation of operational realities that are difficult to discern from catalog values.

During the design phase, comparing the option of downsizing the inverter and accepting overload losses, the option of a standard capacity ratio, and the option of increasing inverter capacity to reduce clipping makes decision-making easier. By comparing overload losses, inverter conversion losses, annual energy generation, and equipment configuration for each option, you can select an inverter setup that suits the power generation business or a self-consumption plan rather than simply choosing a capacity.

Point 6 Consider output limitations due to power factor and reactive power conditions

When configuring the inverter, you need to check not only active power but also power factor and reactive power conditions. In grid-connected projects, the utility, grid conditions, and equipment requirements may demand a certain power factor operation or reactive power control. If you evaluate energy production in PVSyst without taking these conditions into account, the available headroom for active power output during actual operation may be smaller than expected.

PVSyst's documentation states that when the inverter is required to generate reactive power, it can affect overload conditions depending on the inverter's rated power specifications. This means that power factor settings are not merely a grid-side configuration but also relate to energy yield simulations.

Inverters have an upper limit on apparent power. When active power and reactive power are handled simultaneously, the available range of active power may be constrained by the amount of reactive power. For example, if operated at a lagging or leading power factor rather than at unity (1.0), the maximum active power that can be extracted from the same inverter capacity may decrease. As a result, near the peak on sunny days output limiting can occur, producing effects similar to overload losses or output curtailment.

In practice, when a simulation is run the power factor conditions may not yet be confirmed. Even in such cases, preparing and comparing not only the standard case but also scenarios that reflect the expected power factor conditions can reduce the risk of later downward deviations in power generation. This is especially true for projects involving high voltage, extra-high voltage, mega-solar, or in regions with strict grid constraints, where it is best not to underestimate the handling of power factor and reactive power.

When reading the PVSyst manual, it's important not to stop at merely looking at the active power capacity on the inverter settings screen, but to adopt the attitude of verifying what kind of operation is required as a grid interconnection condition. Check the conditions decided by the electrical design side, the connection study responses, the interconnection negotiation documents, and the power factor range stated in the PCS specification, and align them with the simulation conditions.

Also, power factor conditions affect not only the amount of generation but also electricity sales plans and self-consumption plans. Even a slight change in annual generation can make a big difference in long-term financial results and capital investment decisions. By comparing multiple cases in PVSyst, it becomes easier to explain the impacts if design changes or grid condition changes occur.

Point 7 Cover the loss items that should be checked in the report

The final verification of inverter settings is performed using the PVSyst report and the loss diagram. You cannot assess the validity of the settings without confirming how the parameters entered on the input screen ultimately manifest as losses. For inverter-related items in particular, examine overload losses, losses due to the voltage range, losses due to current limits, conversion losses, and the impacts related to MPPT and input allocation.

In PVSyst's description of inverter operating limits, losses from exceeding the inverter's nominal power, losses due to voltage thresholds, losses due to maximum input current, and so on are shown. These items are not merely numerical results; they serve as clues indicating where problems lie in the design.

For example, if overload losses are large, possible causes include a DC/AC ratio that is too high, biased MPPT allocation, or the upper limit of active power being reduced by power factor conditions. If losses due to the lower voltage limit occur, possible reasons are that the string series count is too low, Vmpp at high temperatures falls below the MPPT range, or module specifications and temperature condition settings are not appropriate. If warnings or losses related to the upper voltage limit appear, the open-circuit voltage at low temperatures may be causing the problem.

Also, if losses related to maximum input current appear, you need to review the number of parallel strings, the current per MPPT input, and the inverter’s input specifications. Because high‑output modules in recent years tend to have larger current values, designing the number of strings with old assumptions can easily bring you close to the current limit. It is important not only to select device models in PVSyst but also to verify that the actual combination of module and inverter is valid according to the specifications.

When reviewing a report, you should avoid judging it solely by the total annual energy production. Even if the annual production is close to expectations, the breakdown of losses may show that certain items are unnaturally large. In that case, another configuration error may simply be coincidentally offsetting it. For example, if the shading settings are too lax and the generation appears higher while inverter overload losses are shown as large, it can be difficult to notice the problem from the total value alone.

In practice, before submitting the final report, we verify that inverter-related losses are consistent with the design intent. It is ideal to review the DC/AC ratio, string configuration, MPPT allocation, input voltage, input current, power factor conditions, inverter efficiency, and overload losses one by one, and ensure that no unexplained losses remain.

The value of using the PVSyst manual lies not only in understanding what the input fields mean, but also in connecting that understanding to how to interpret the results. By repeatedly checking settings against reports, you increase the reliability of the simulation and make it easier to accommodate design changes and explain them to clients.

Summary

When checking inverter settings in the PVSyst manual, simply selecting the model and entering the capacity is not sufficient. What matters is understanding the relationship between the PV array and the inverter, including annual generation behavior, site conditions, grid conditions, and the breakdown of losses.

First, check the inverter capacity and the DC/AC ratio to see how the inverter capacity is balanced against the PV array capacity. Next, confirm by simulation how much overload loss will occur and determine whether it is within an acceptable range. Finally, align the input voltage range and string configuration and verify that the maximum voltage at low temperatures and the MPPT voltage at high temperatures are within acceptable limits.

For inverters with multiple MPPTs, it is important that the input allocation matches the site’s orientation, tilt, and shading conditions. If there is an imbalance in the number of strings per MPPT or if strings under different conditions are mixed, it will affect losses and the assessment of energy generation. Also, the impacts of inverter efficiency and low-load operation should not be overlooked. Oversizing the inverter too much to reduce overload losses can increase other types of loss.

Additionally, in projects with power factor or reactive power conditions, the output limit for active power may be affected. If you run simulations without reflecting the grid interconnection conditions, the simulated generation may differ from the actual generation during operation. Finally, check PVSyst's report for overload losses, voltage thresholds, current limits, conversion losses, and so on, and review whether the settings and results are inconsistent.

Inverter settings are one of the areas in energy-yield simulation that require technical judgment. By reading the PVSyst manual and addressing seven points—DC/AC ratio, overload losses, input voltage, MPPT distribution, efficiency, power factor, and loss reports—even beginners can more easily understand the meaning of the settings, and practitioners can produce analysis results that are easier to explain. Checking not only the energy-yield figures but also the assumptions and settings from which those figures are derived is the shortcut to a reliable PVSyst analysis.