What does PVSyst do? Understand its role in photovoltaic design in 5 minutes

PVSyst is simulation software used to predict the energy production of photovoltaic installations and to check performance differences and loss factors under different design conditions. In solar PV design, it is necessary not simply to array panels but to comprehensively consider solar irradiance, azimuth, tilt angle, shading, temperature, electrical losses, system configuration, annual energy production, and so on, in order to assess the validity of a plan. PVSyst organizes the information required for that assessment and serves to help designers and project developers proceed with studies based on a sound basis.

Table of Contents

• PVSyst is software that supports design decision-making for solar power generation

• A 5-minute overview of what PVSyst can do

• Why PVSyst is used in photovoltaic system design

• Key input conditions that PVSyst checks

• Key points to check in energy yield predictions

• Design issues revealed by loss analysis

• PVSyst does not automatically provide the correct design solution

• Workflow for using PVSyst in practical projects

• Data to prepare before using PVSyst

• Points to watch when interpreting PVSyst results

• Approaches to improve accuracy in solar design

• Summary

PVSyst is software that supports design decision-making for solar power generation

PVSyst is a specialized simulation software used for the design of photovoltaic (PV) systems and for estimating their energy production. In solar power generation, it is necessary to consider many factors, such as how much solar irradiation the installation site receives, which direction and angle the panels should be installed, how much shading from surrounding buildings and terrain will affect the system, and whether the equipment configuration is appropriate. PVSyst is used to input these conditions and calculate the annual energy production and the breakdown of losses.

Many people who search for "What is PVSyst" are those who have just started working on photovoltaic system design or practitioners who have received a power generation forecast report but do not fully understand its contents. Even if they've heard the name, they often find it hard to understand what the software does, at which stage it is used, and what it means for designers.

In solar power system design, determining the installed capacity based solely on the available site area is insufficient. Even systems with the same installed capacity can yield different actual energy production depending on installation angle, orientation, solar irradiance conditions, shading, temperature, wiring, power conversion, and the combination of equipment. Judging profitability and performance only by installed capacity can lead to projects that looked promising during the planning stage producing less than expected during operation.

The role of PVSyst is to organize such uncertainties and quantify power generation based on a set of assumptions. Of course, it does not perfectly predict future generation. However, by clarifying the relationship between input conditions and calculation results, it makes it easier to compare design proposals, assess risks, and explain to stakeholders. In other words, PVSyst is a tool for evaluating solar power generation plans based on conditions and supporting rationale rather than intuition.

What You Can Do with PVSyst: A 5-Minute Overview

In one sentence, PVSyst predicts the energy production of solar power installations and visualizes the loss factors that affect those results. In professional practice, it is used to check the annual energy production, monthly generation trends, generation efficiency relative to installed capacity, losses due to shading, temperature-related losses, electrical losses, and the suitability of the equipment configuration.

The first step is to define the site conditions. Solar power generation experiences large differences in solar irradiance depending on the location. Regions with many sunny days and regions with many cloudy days will have different annual energy production even with the same installed capacity. Also, because the sun’s altitude and azimuth vary with latitude and longitude, the effects of tilt and orientation change as well. In PVSyst, these site conditions are used to set the solar radiation conditions that form the basis for the energy yield.

Next, set the layout, tilt, azimuth, installed capacity, and combinations with the power conversion equipment for the solar panels. In solar design, simply increasing the number of panels is not necessarily better. You need to take into account electrical connection conditions, converter capacity, the concept of overloading, and constraints at maximum output. PVSyst is used to reflect these equipment configuration conditions and calculate realistic energy production.

Furthermore, the effects of surrounding shading are also important. In solar power generation, even a small amount of shading can affect energy production. In particular, at low solar elevations in the morning and evening, shadows from buildings, trees, terrain, and nearby equipment are more likely to occur. In PVSyst, running simulations that take shading into account allows you to identify issues in the layout plan.

Finally, as part of the results report, review the power generation and the breakdown of losses. Rather than looking only at the final generation figure, it is important to see at which stages and in what ways losses occur. By tracing the flow from solar radiation to electrical power conversion, you can identify opportunities for design improvements and points of caution.

Why PVSyst Is Used in Solar PV Design

A major reason PVSyst is used in solar PV design is that it makes it easier to objectively explain the relationship between design conditions and energy production. In solar power project planning, multiple stakeholders are involved, including developers, designers, contractors, financial institutions, landowners, and project owners. Each emphasizes different considerations, but the information they all commonly need is how much power generation can be expected.

Power generation forecasts feed directly into decisions about project cash flow and capital investment. If annual generation is estimated to be large, profitability will also appear higher. However, if planning proceeds based on an overly optimistic forecast, discrepancies with actual performance after operation begins can become problematic. Conversely, if forecasts are overly conservative, projects that might actually be viable can be passed over. PVSyst calculates generation using a fixed procedure based on input conditions, making it easier to organize and clarify the rationale behind the forecast.

Also, in solar PV design, multiple scenario comparisons are often performed. When changing the tilt angle, the azimuth, the panel layout, the system capacity, or the inverter capacity, there are many combinations to consider. By using PVSyst, you can compare how each change in conditions affects energy production and losses.

In the early stages of design, it is important to estimate the expected energy yield. As the project progresses toward detailed design, more accurate terrain data, layout information, shading conditions, and equipment specifications need to be incorporated. PVSyst can be applied progressively from initial studies to detailed analyses, which is why it is widely used in practical photovoltaic design.

Furthermore, it is important that the design results can be easily compiled into explanatory materials. Not only can they present the predicted power generation, but they can also show the breakdown of losses and monthly trends, making it easier to explain to stakeholders why that level of generation is expected. Because solar power system design is highly specialized, the ability to explain the background behind the figures is of great value.

Main input conditions checked by PVSyst

To make accurate judgments with PVSyst, understanding the input conditions is indispensable. Simulation software produces results based on the assumptions entered. Therefore, if the input conditions are inaccurate, the resulting energy production estimates and loss analysis will deviate from reality.

First, the important thing is information about the installation site. The power output of a solar power system is strongly affected by solar irradiance conditions. If the installation site's latitude, longitude, elevation, or weather conditions change, the generation from the same equipment will vary. In particular, solar irradiance and temperature have a large impact on generation. While more solar irradiance increases the opportunities for generation, if temperatures become too high the panels' output decreases, so it cannot be said that hotter regions are always more advantageous.

Next are the panel installation conditions. Azimuth and tilt angle affect the amount of solar irradiance received. Generally, by choosing an appropriate orientation and angle relative to the sun’s movement, it is easier to increase annual energy production. However, the ideal angle or layout cannot always be adopted as-is due to site shape, land development conditions, racking/mounting constraints, maintenance access, surrounding environment, and so on. In PVSyst, you enter the design conditions that will actually be used and verify how much energy can be generated under those conditions.

System configuration is also important. If the capacity of the solar panels, their series and parallel configuration, the combination with power conversion equipment, or the input voltage and current ranges are not appropriate, power generation losses and equipment constraints can occur. It is necessary to check electrical compatibility as well as installed capacity.

Furthermore, shading conditions also have a significant impact on the input results. If there are buildings or trees nearby, if mountains or slopes are close, or if the row spacing between installations is narrow, shadows can occur depending on the time of day and season. Underestimating the effects of shading can result in actual power generation being lower than predicted. In particular, across projects from low-voltage systems to large-scale installations, packing the layout too tightly in an effort to make efficient use of the site can increase losses due to shading.

You should also verify the loss conditions related to wiring and power conversion. The power produced flows from the panels to the combiner box, the conversion device, and the grid interconnection point. In that process, losses occur due to wiring resistance and during conversion. PVSyst includes these electrical losses when checking the final generated energy.

Key Points to Consider in Power Generation Forecasts

When looking at PVSyst results, what many people first pay attention to is the annual energy production. Annual energy production is an important indicator that shows how much electrical energy a photovoltaic system is expected to generate in one year. In feasibility evaluations and investment decisions, this figure becomes the central focus.

However, it is dangerous to judge solely by the annual power generation. This is because, even with the same annual power generation, the stability and risks of a plan can vary depending on the conditions under which that figure was obtained. For example, a design with large shading losses and one with small shading losses may differ in their resilience to future operations and maintenance and to changes in the surrounding environment, even if they produce the same generation.

Monthly power generation is also an important point to check. Solar power generation fluctuates with the seasons. Factors such as solar irradiance, solar elevation, temperature, snowfall, and the frequency of rainy days influence monthly generation trends. Annual values alone do not reveal when generation is high and when it is low. Understanding monthly trends makes it easier to formulate revenue plans and forecast operational management.

Power generation per unit of installed capacity is also important. Although a larger installed capacity tends to produce a greater annual generation, that alone does not determine whether a design is efficient. Looking at how much generation can be produced per given capacity makes it easier to compare the quality of design conditions. For projects with significant site constraints, it may be better to prioritize generation efficiency and loss balance rather than cramming in more capacity.

The concept equivalent to the performance ratio is also indispensable when interpreting the results. It is an indicator that shows how much of the energy ideally obtainable remains as actually usable electrical energy. If the performance ratio is low, large losses may be occurring somewhere — from temperature, shading, wiring, conversion, or equipment constraints. You need to consider efficiency that accounts for losses, not just the absolute amount of power generated.

PVSyst's power generation forecasts do not guarantee future results. Actual power generation fluctuates depending on that year’s weather, equipment soiling, maintenance condition, equipment aging, and changes in the surrounding environment. Therefore, PVSyst results should be treated only as forecasts based on the assumptions at the design stage.

Design challenges revealed by loss analysis

PVSyst's great value lies not only in the final energy output but also in the ability to review the breakdown of losses. In photovoltaic power generation, the energy received from the sun cannot be used directly as electricity. Losses occur at various stages, and the final amount of electricity generated is determined by them.

The first loss to look at is the loss related to solar radiation. The amount of solar radiation received by the installation surface differs from the solar radiation on a horizontal surface. The tilt angle and orientation of the panels change the amount of solar radiation they receive. If the design conditions are not appropriate, the solar radiation that should be available may not be fully utilized.

Shading losses are also important. Shadows from surrounding obstacles and between pieces of equipment can reduce power generation. Because shading changes with the time of day and season, it can be difficult to judge from a single site visit. Checking the effects of shading in PVSyst can help you improve the layout and reconsider row spacing.

Temperature-related losses must not be overlooked. Solar panels generate more power the more sunlight they receive, but their output decreases as temperature rises. On rooftops or in poorly ventilated locations, losses due to temperature increases can be significant. You need to consider the temperature impact of the installation environment, not just selecting a location with a large amount of sunlight.

Electrical losses include wiring losses, conversion losses, and losses due to the operating ranges of equipment. A certain amount of loss occurs in the process of converting generated DC power into AC power. In addition, depending on the capacity balance between the panels and the conversion equipment, output may be limited during generation peaks. These losses are directly tied to considerations of system configuration.

When reviewing loss analysis, it is important not to regard the mere existence of losses as a problem, but to assess whether those losses are within a reasonable range. Losses will inevitably occur in any solar power installation. What matters is whether excessive losses are occurring, whether any losses remain that can be mitigated, and whether they can be explained by the design conditions.

PVSyst does not automatically produce the correct design

PVSyst is a convenient simulation software, but it does not automatically produce the correct design solution. If this is misunderstood, the results may be handled incorrectly. PVSyst is a tool that performs calculations based on the input conditions. If the input conditions do not accurately reflect reality, then no matter how detailed the report is, it will be insufficient for design decision-making.

For example, if obstacles present on site are not reflected, shading losses will be underestimated. If the terrain’s undulation or post-development heights differ, the actual layout and shading conditions will also change. If equipment capacity or configuration are entered incorrectly, the results for energy production and losses will change. In this way, the accuracy of PVSyst strongly depends on the accuracy of the input data.

Also, PVSyst results are reference material for comparing design conditions and do not constitute a final decision. In actual photovoltaic design, it is necessary to consider not only energy output but also constructability, maintainability, safety, ground conditions, drainage planning, the surrounding environment, legal regulations, and grid interconnection conditions. If you attempt to maximize only the energy output, construction and maintenance can become difficult, and issues such as shading and drainage problems may arise.

PVSyst is primarily a design-support tool focused on power generation simulation. Designers must interpret its results and make judgments in conjunction with other design conditions. Rather than assuming the numbers are correct simply because they are produced, it is important to verify why those numbers were obtained, whether the input conditions are reasonable, and whether they conflict with on-site conditions.

In practical work in particular, comparisons with past projects or similar cases are also effective. If PVSyst results deviate substantially from common expectations, there may be errors in the input conditions or settings. Rather than accepting the results as they are, verifying them against the designer’s experience and local information leads to more reliable energy-yield forecasts.

Workflow for Using PVSyst in Practice

When using PVSyst in practical work, the first step is to organize the planning conditions. Confirm the installation location, site boundaries, expected capacity, mounting configuration, connection conditions, surrounding environment, and so on, and clarify what kind of system will be considered. At this stage, detailed design is often not yet finalized, so multiple options may be compared using approximate conditions.

Next, set the meteorological and solar irradiance conditions. In solar power generation forecasting, the handling of solar irradiance data is extremely important. Confirm which region’s data will be used, how conservatively it will be treated, and whether it is reasonable as a long-term average. Because the selection of solar irradiance data can change generation forecasts, it is desirable to be able to explain the rationale.

Next, enter the equipment configuration. Set the number of panels, capacity, installation angle, orientation, connection configuration, capacity of the conversion equipment, and so on. Here, you need to proceed while checking whether the electrical conditions are satisfied. Even if you only match capacities on paper, if they do not fall within the actual operating ranges of the equipment, it will not be a realistic design.

The process of accounting for layout and shading conditions is also important. Set the on-site panel layout, surrounding obstacles, terrain effects, row spacing, and so on, and check losses caused by shading. In particular, when many panels are installed on a limited site, shading effects can increase. It is necessary to verify the balance between increasing installed capacity and maintaining power generation efficiency.

After running the simulation, we review the results. We look at annual energy production, monthly generation, loss breakdown, performance ratio, and whether there are any output limitations. If the results are lower than expected, we check whether the cause is shading, temperature, wiring, equipment configuration, installation angle, or similar factors. Conversely, if the results are higher than expected, we reassess whether the input assumptions are overly optimistic.

Finally, reflect the results in design decisions and in explanatory materials. The results from PVSyst serve as material to explain the validity of the plan to stakeholders. However, simply submitting the report is not sufficient. It is important to be able to explain what assumptions the results are based on, which losses are significant, and whether there is room for improvement.

Data to Prepare Before Using PVSyst

To use PVSyst effectively, it is important to organize the necessary data in advance. If you run simulations without adequate preparation, you will have to rely on many assumptions and the reliability of the results will decrease. Especially in practical work, you should organize and document the rationale for your inputs so you can explain them when the assumptions are reviewed later.

First, the basic information of the installation site is required. Confirm the address, latitude and longitude, elevation, surrounding environment, and site shape. If the installation location is not accurate, it will also affect the solar radiation conditions and the sun-path settings. For a large site or a site with elevation differences, you also need to consider which point within the site should serve as the representative point.

Next, information on the shape of the site or roof to be designed is required. For ground-mounted installations, site boundaries, land development plans, ground elevation, slopes, access paths, and setback/clearance conditions are relevant. For roof installations, roof area, pitch, orientation, obstructions, load conditions, and maintenance space are important. If this information is unclear, a realistic layout cannot be achieved, and power generation forecasts will also be uncertain.

Information about surrounding obstacles is also important. Buildings, trees, utility poles, fences, mountains, slopes, and existing equipment can all cause shading. The effects of shading can be difficult to assess accurately from site photographs alone. If possible, it is desirable to measure positions and heights and organize the information in a form that can be reflected in the design.

Equipment information is also required. Confirm the specifications, capacity, electrical characteristics, and connection conditions of panels and power conversion devices. However, the article does not need to depend on specific product names or brand names. In practice, correctly enter the specifications of the equipment planned for adoption and verify that the combinations of equipment are feasible.

We also verify wiring conditions and grid connection requirements. As wiring distances increase, voltage drop and losses may rise. In the early stages of design, rough estimates may be sufficient, but as the design progresses into detailed design you should reflect conditions that are increasingly close to reality.

Points to Note When Reading PVSyst Results

When reading PVSyst results, it is important not to judge solely by the final energy production. The results report displays many numerical values, but if you view them without understanding what each one means, you may overlook important issues.

The first thing to check is whether the input conditions are as intended. Verify that the installation location, system capacity, tilt angle, orientation, equipment configuration, shading conditions, and so on are correctly reflected. No matter how well the results are presented, they are meaningless if the underlying assumptions are wrong. In practice, it is important to make a habit of verifying the inputs before reviewing the results.

Next, check the breakdown of losses. When power generation is low, it is necessary to understand where the losses are largest. Whether the losses are primarily due to shading, temperature losses, conversion losses, or output limitations will call for different improvement measures. Increasing installed capacity alone without identifying the causes of the losses may not lead to a fundamental improvement.

It is also important to examine monthly power generation trends. Even if the annual generation is the same, differences in seasonal bias can alter the impact on business plans and operational plans. Results must be interpreted in light of regional characteristics such as periods of heavy snowfall, the rainy season, typhoons, or times with many cloudy days.

Be cautious even when the results look too good. If solar irradiance conditions are optimistic, shading is not adequately accounted for, or loss assumptions are set too low, the estimated power output can appear higher than it actually is. Because generation forecasts directly influence business decisions, the better the results look, the more carefully the assumptions should be checked.

On the other hand, even if the results are poor, you do not need to dismiss the plan immediately. If the cause of shading is limited to certain times of day or can be improved by changing the layout, there may be ways to address it. It is important to use PVSyst results as a basis for identifying problems and considering potential improvements.

Strategies for Improving Accuracy in Solar Design

To increase the accuracy of PVSyst in solar design, it is essential to understand on-site conditions as well as operate the software. The accuracy of energy yield predictions is affected not only by the calculation model itself but also by the quality of the site information entered. In particular, the site's shape, elevation differences, positions of obstacles, surrounding environment, and the orientation and tilt of the installation surface greatly influence the results.

In the early stages of design, public information, drawings, and preliminary survey data are often used for study. However, as the project moves closer to detailed design and construction, accurate location and elevation information acquired on site becomes increasingly important. Because solar power generation equipment is installed outdoors, it is necessary to confirm that the conditions on paper match the actual conditions at the site.

For example, even a slight difference in site elevation can affect the racking layout and how shadows fall. If the heights of nearby buildings or trees differ from those assumed, shading losses will also change. If the locations of boundaries or obstacles are off, the layout plan itself may need to change. Such discrepancies can lead not only to altered simulation results but also to rework during construction.

To master PVSyst, it is important not only to fine-tune the numbers within the software but also to correctly obtain site information and incorporate it into the design conditions. To give power generation forecast results credibility, you need to handle not only solar irradiance and equipment conditions but also the site's location information and three-dimensional conditions as accurately as possible.

Therefore, in solar PV design, the accuracy of positioning and on-site verification also becomes an important factor. In particular, for site boundaries, obstacle locations, confirmation of installation surfaces, and post-construction as-built inspections, having an environment where high-precision positional information can be easily obtained makes it easier to reduce discrepancies between the design and the actual site.

Summary

PVSyst is simulation software used to predict the power output of photovoltaic systems and to check losses and performance for each design condition. In solar design, many factors affect power output, such as installation location, solar irradiation conditions, azimuth, tilt angle, shading, temperature, equipment configuration, wiring, and power conversion. PVSyst is used to organize these conditions and to verify power output and the breakdown of losses numerically.

However, PVSyst does not automatically provide the correct design. If the input conditions do not match the actual site conditions, the results will also be difficult to trust. What is important is not to look only at the annual energy production, but to comprehensively verify the input conditions, monthly trends, loss breakdown, shading effects, and the validity of the equipment configuration.

Practitioners searching for "What is PVSyst" should first understand PVSyst as a tool for forecasting power generation and then use it as supporting documentation for design decisions. In photovoltaic design, both the ability to interpret simulation results and the ability to accurately assess site conditions are required.

If design proceeds while site location, elevation, and obstacle information are insufficient, plans that appear well-organized in PVSyst can still result in discrepancies during construction or operation. To improve the reliability of power generation forecasts, it is important to bring the desktop design and the actual site conditions as close as possible.

If you want to improve the accuracy of on-site checks and positioning, using an iPhone-mounted GNSS high-precision positioning device such as LRTK makes it easier to obtain the positional information needed for site boundaries, obstacle locations, and construction verification. By combining power generation simulations using PVSyst with high-precision positioning data obtained on site, you can clarify the basis for photovoltaic design and achieve consistent accuracy improvements from planning through construction and verification.