What is PVSyst? Five things you can learn from solar power generation simulations

In the planning and design of a solar power plant, how you estimate the expected power generation is crucial. The estimate of power generation affects project profitability, installed capacity, layout planning, construction planning, and operation and maintenance policies. Therefore, simply thinking “it should generate power because the area receives a lot of solar radiation” is not sufficient as a basis for practical decision-making.

PVSyst is simulation software used to study the power generation and losses of photovoltaic power systems. The official notation is PVsyst, but in Japanese practice it is sometimes written as PVSyst. It is used by setting conditions such as the plant location, meteorological conditions, module layout, tilt angle, azimuth, shadowing effects, and electrical losses, in order to check annual energy production, monthly trends, and the breakdown of losses. It can produce materials that are useful for designers, construction personnel, power plant operators, and technical reviewers to verify the validity of plans during the planning stage.

However, using PVSyst does not automatically produce correct results. If the input conditions are not aligned with the actual site conditions, the outputs will also deviate from reality. The important thing is not to accept the simulation results at face value, but to read them with an understanding of what they reveal and what they do not.

Table of Contents

• PVSyst is software for quantitatively assessing solar power generation plans

• What you can learn from PVSyst 1: an estimate of annual energy production

• What you can learn from PVSyst 2: monthly and seasonal generation trends

• What you can learn from PVSyst 3: generation losses due to shading and layout

• What you can learn from PVSyst 4: the impact of equipment configuration and electrical losses

• What you can learn from PVSyst 5: the validity of design conditions and comparative evaluation

• Points to be aware of when reviewing PVSyst results

• How to apply PVSyst to practical field work

• Summary: PVSyst is a tool for identifying not only estimated energy production but also weaknesses in a plan

PVSyst is software for numerically verifying solar power generation plans

PVSyst is a simulation software used to predict the energy production of photovoltaic systems and to verify differences between design conditions. In solar power generation, even with the same installed capacity, the generated energy varies depending on the installation site, solar irradiance conditions, panel orientation, tilt angle, surrounding shading, wiring, equipment configuration, temperature conditions, and so on. PVSyst is used to input these factors as conditions and to calculate the expected energy production and losses.

When planning a solar power plant, looking only at installed capacity is not sufficient. For example, even when installing solar panels with the same rated output, energy production will vary depending on whether they face south or east-west, whether the tilt angle is steep or shallow, and whether there are surrounding mountains or buildings. Also, in the overall plant design, various losses occur between the DC power generated by the panels and the AC power that is used or fed into the grid. In PVSyst, you can organize these factors as individual conditions and check how much they affect energy production.

When practitioners search "What is PVSyst", their intent is not merely to learn the name of the software but to understand what can be learned from energy-yield simulations, how those simulations can support design and construction, and to what extent the results can be relied upon. In particular, interpreting simulation results is important for solar power plant planning, layout verification after site development, validation of expected energy production, investment decision-making, and pre-construction design reviews.

One of PVSyst's features is that it allows you to check not only the total energy production but also the breakdown of losses. Looking only at the annual energy production figure can make it difficult to judge whether a plan is good or bad. However, by separating and examining shading effects, temperature-related losses, wiring losses, equipment conversion losses, and losses due to layout conditions, it becomes easier to identify the causes limiting energy production and the potential for improvement.

On the other hand, PVSyst does not automatically and accurately reproduce the site. If the local topography, surrounding obstacles, ground conditions after development, pile positions, racking layout, equipment specifications, and so on are not correctly reflected, the simulation results will diverge from reality. Therefore, it is easier to understand PVSyst as a tool for organizing conditions and checking the validity of a plan, rather than as software that provides a definitive answer.

What You Can Learn from PVSyst 1: Estimated Annual Energy Production

The most basic thing you can check with PVSyst is an estimate of a solar power plant’s annual energy production. Annual energy production is an important figure directly tied to the financial planning and equipment planning of a power generation business. In a solar power plant, the amount of electricity generated leads to revenue from electricity sales and benefits from self-consumption, so it is necessary to understand how much generation can be expected at the planning stage.

Annual energy production is not determined simply by panel capacity. It is determined by a combination of factors such as the solar irradiance at the installation site, ambient temperature, panel orientation, tilt angle, shading effects, system configuration, and electrical losses. In PVSyst, you set these conditions and calculate the expected annual energy production. This allows you to confirm, as conditional figures, how much generation performance the planned power plant is likely to have.

In practice, verifying annual energy production is important not only during the initial planning stage but also when design changes are made. For example, you can compare how much the annual energy output changes depending on differences in design conditions—such as changing the panel layout, altering the tilt angle, adjusting row spacing, or accounting for surrounding shading. If the difference in output is small, it may be reasonable to prioritize constructability and maintainability; if the impact on generation is large, the design should be reviewed.

Annual power generation is also used as material to explain the scale of a power plant. When sharing plans among stakeholders, explanations based only on intuition make judgment difficult. Having simulation results from tools like PVSyst provides an estimate of generation based on the set conditions, making it easier for designers, contractors, power producers, and operations managers to discuss on the same assumptions.

However, the annual energy production is only a projected value based on the specified conditions. Actual generation will vary depending on year-to-year weather, snowfall, soiling, equipment failures, curtailment, maintenance conditions, and other factors. Therefore, when reviewing PVSyst results, it is important not to judge based solely on the annual generation figure, but to check what meteorological data were used, what loss assumptions were set, and what layout conditions were used for the calculations.

What you should pay particular attention to is when the power generation numbers look large. If the input conditions are too optimistic, the generation will also be shown as high. If shadow settings are insufficient, loss assumptions are too small, the actual layout differs, or terrain conditions are not reflected, a simulation may produce good results while actual operation may fail to reach expectations. Annual generation is important, but only by checking the assumptions that support that figure does it become information usable in practice.

What PVSyst Can Reveal 2: Monthly and Seasonal Power Generation Trends

In PVSyst you can check not only annual energy production but also monthly and seasonal generation trends. Solar power generation is not constant because irradiance and solar elevation change with the seasons. While daylight hours are longer in summer, higher temperatures can cause efficiency losses. In winter temperatures may be advantageous, but daylight hours are shorter and solar elevation is lower, making systems more susceptible to shading.

By checking monthly power generation, you can identify imbalances in generation that are not apparent from the annual total alone. For example, even if the annual generation is similar, the operational perspective changes between a plan where generation is concentrated from spring to summer and a plan that experiences a large drop in generation during winter. When assuming self-consumption, it is also important whether the seasonal variation in demand aligns with the seasonal variation in generation. Even when assuming electricity sales, understanding seasonal generation trends helps with comparisons to actual values and early detection of anomalies.

Seasonal generation trends are also relevant when evaluating shading. During periods of low solar altitude, shadows from surrounding buildings, trees, terrain, and racking rows tend to extend further. Even if shading appears to have little effect in summer, it can cause significant losses in winter. Checking monthly generation and shading impacts in PVSyst makes it easier to investigate the causes of reduced generation in specific seasons.

Also, during the operational phase after construction, monthly simulation values are useful as a guideline. By comparing actual power generation with the simulation results, you can confirm whether the plant is operating close to expectations. Of course, actual weather varies from year to year, so they will not necessarily match exactly. However, if generation consistently falls significantly in the same season each year, if a particular month shows a much larger shortfall than expected, or if output does not increase despite many sunny days, these can prompt checks for soiling, shading, equipment malfunctions, wiring faults, vegetation overgrowth, and the like.

When examining monthly and seasonal power generation trends, it's important not simply to look at the peaks and valleys of the graph but to consider the underlying reasons. By separating and checking whether generation increases in a given month or decreases in a given season due to temperature effects, solar irradiance, or shading, you can deepen your understanding of the project. PVSyst results can be used not only to predict generation but also as material for understanding the characteristics of the power plant.

What PVSyst Reveals, Part 3: Power generation losses caused by shading and layout

A major problem at solar power plants is generation loss caused by shading. Because solar panels generate electricity from sunlight, shadows from surrounding buildings, mountains, trees, utility poles, fences, equipment, or adjacent rows of panels reduce power output. In particular, when part of a plant is shaded, the reduction in output is not always limited to the area actually in shadow. Depending on electrical connections and system configuration, the effects of shading can extend over a much wider area.

In PVSyst, by setting layout conditions and shading conditions you can evaluate generation losses caused by shading. This allows you to determine how much shading will affect the planned power plant and in which seasons or times of day shading is likely to be problematic. Shading assessment is particularly important for sites with terrain elevation differences or where there are obstacles nearby.

Generation losses due to panel layout are also important. At solar power plants, there is often a tendency to try to install as many panels as possible on a limited site. However, if row spacing is too tight, front rows can cast shadows on rear rows, potentially reducing energy output. This is especially true in winter and at sunrise and sunset, when the solar altitude is low and shadows are longer, so the choice of row spacing affects energy output.

On the other hand, widening the spacing between rows makes it easier to reduce the effects of shading, but it can decrease the number of panels that can be installed on the same site. In other words, in power plant design it is not enough to simply eliminate shading; you must comprehensively consider installed capacity, energy output, constructability, maintainability, site preparation conditions, aisle width, and so on. By using PVSyst, you can compare the differences in energy output when changing the layout and assess the balance in the plan.

What you need to watch for when assessing shading and layout is how well the simulation model reproduces the actual site. Even if the drawings look fine, on the real site factors such as ground elevation after earthworks, slope faces, drainage facilities, surrounding trees, temporary structures, and access/maintenance paths can affect shading and layout. In particular, if site surveying or as-built conditions after construction differ from the design drawings, the calculation settings in PVSyst may not match the actual power plant.

Therefore, shadow simulations should not be completed solely as a desk-based study; it is important to verify them against on-site conditions. By checking terrain data, layout plans, site photographs, survey results, and the status of surrounding obstacles, and reflecting them in the simulation where necessary, you can make decisions that are closer to practical reality. PVSyst is useful for visualizing the impact of shadows, but to increase the reliability of the results, the accuracy of site information is indispensable.

What You Can Learn from PVSyst 4: Effects of Equipment Configuration and Electrical Losses

PVSyst lets you examine the losses that occur from the power produced by solar panels until it becomes usable power. In solar power generation, the power generated by the panels is not all delivered as output. Multiple factors affect the generated energy, including wiring losses, conversion losses in equipment, output reduction due to temperature, and limitations imposed by system configuration.

In practice, the factors that reduce power generation are often collectively referred to as "losses", but they are not a single thing. Losses occur at each stage: the conditions affecting how solar irradiance reaches the panel surface, the conditions under which the panel produces electricity, the conditions for collecting the generated power, the conditions for converting DC to AC, and the conditions for exporting to the grid or loads. PVSyst organizes and displays these losses by item, making it easier to identify where generation is being lost.

When considering equipment configuration, the relationship between panel capacity and conversion equipment capacity is important. At a power plant, the characteristics of generation and output change depending on how the capacity on the panel side and the capacity on the conversion-equipment side are combined. If the panel capacity is increased, the conversion equipment may reach its upper limit during periods of strong solar irradiance. In that case, some of the generated power may not be output. Conversely, by adjusting the combination of capacities, it is possible to increase the utilization rate in the morning and evening and during cloudy conditions.

Wiring losses are another factor that must not be overlooked. As the size of a power plant increases, wiring distances and electrical design begin to influence energy production. If wiring is long, currents are large, or design conditions are not appropriate, losses can increase. By reviewing PVSyst results, you can see how much wiring and equipment configuration are affecting energy output.

Temperature-related losses are also important in photovoltaic power generation. Solar panels tend to generate more power when irradiance is stronger, but they have the characteristic that output decreases as temperature rises. Therefore, even if solar irradiance is high in summer, efficiency can decline due to increases in ambient temperature and panel temperature. PVSyst calculates energy production taking temperature effects into account based on meteorological and installation conditions.

When reviewing the results of electrical losses, it is important to check whether the values for each item are reasonable. If the losses are too small, the input conditions may be more optimistic than reality. Conversely, if the losses are large, there may be opportunities for design improvement. For example, this can lead to reviewing wiring routes, re-evaluating equipment layout, reconsidering combinations of capacity, or considering circuit configurations that are less susceptible to shading.

One of PVSyst's strengths is that it allows you to check not only the total energy production but also the breakdown of losses. Even if energy production is lower than expected, if you can determine which factors are most significant, it becomes easier to devise corrective measures. Conversely, judging only by the annual energy production without looking at the loss breakdown can lead to overlooking design weaknesses. In practice, it is important to examine the composition of losses alongside the energy production figures.

What You Can Learn from PVSyst 5: Validation of Design Conditions and Comparative Evaluation

One of the important things that can be understood with PVSyst is the validity of design conditions. In designing a solar power plant, multiple options arise. Depending on which conditions are adopted—panel orientation, tilt angle, layout spacing, system capacity, equipment configuration, wiring plan, installation area, etc.—the power generation, constructability, and maintainability will change. By using PVSyst, you can compare the differences in power output and losses when conditions are changed.

In comparative evaluations, simply choosing the option with the highest power generation is not necessarily the best approach. Even if power generation increases, it can be undesirable in practice if it makes construction more difficult, increases the amount of earthworks, worsens maintenance access routes, raises risks such as shading or drainage problems, or makes future inspections more difficult. Conversely, if power generation declines only slightly but constructability and maintainability are greatly improved, the overall plan can be better.

PVSyst can be used to support such decisions with numerical data. For example, you can check how much the annual energy production changes when the tilt angle is changed, how much shading losses are reduced when the row spacing is widened, and how the monthly generation trends change when the layout is modified. This allows you to compare design options not by intuition but as numerical values under defined conditions.

Also, PVSyst results help build consensus among stakeholders. Planning a solar power plant involves multiple parties, such as designers, contractors, power producers, land managers, and maintenance personnel. Because each party emphasizes different points, it is important to share the rationale behind design decisions. With simulation results, it becomes easier to explain why this layout was adopted, why this row spacing was chosen, and why this system capacity was selected.

However, when conducting comparative evaluations, you need to be careful about how you align the conditions. If meteorological data, loss settings, installation area, equipment conditions, etc. differ between options, you cannot make a valid comparison. Conditions other than the factor you want to compare should be kept as identical as possible, and you must check how the changes affected the results. For example, if you want to compare different tilt angles, it is fundamental to keep the other conditions the same.

Additionally, simulation results are intended as information to support design decision-making and do not replace all on-site considerations. In actual construction, ground conditions, delivery/access routes, accuracy of pile installation, errors in mounting structure installation, drainage planning, surrounding environment, and ease of operation and maintenance are also important. Proposals that appear advantageous from the standpoint of energy production in PVSyst may nevertheless be difficult to implement if they do not suit site conditions. Therefore, it is important to evaluate PVSyst results together with drawings, surveys, on-site inspections, and construction plans.

Points to note when reviewing PVSyst results

When using PVSyst results in practice, there are several points to be aware of. The most important is not to make judgments based solely on the output numbers. The simulation results are calculated based on the input conditions. If the input conditions are not accurate, no matter how polished the report may look, its reliability for practical use will be low.

First, what I want to check is the handling of meteorological data. Solar power generation is strongly influenced by solar irradiance. You need to confirm whether the meteorological data used appropriately represent the conditions at the planned site, whether regional differences are not being ignored, and whether the assumed period and average trends are reasonable. The choice of meteorological data can change the projected power output.

Next, it is necessary to verify the installation conditions. Confirm that the panel orientation, tilt angle, layout, installation height, row spacing, terrain conditions, and so on match the site plan. In particular, when simulations are performed based only on pre-development drawings or preliminary layouts, they can differ from the actual conditions after construction. If terrain elevation differences or surrounding obstacles are not reflected, there is a risk of underestimating the impact of shading.

Loss conditions are also important. In PVSyst you can set and review various loss items, but you must check that the settings are realistic. There are multiple factors that reduce energy production, such as soiling, temperature, wiring, equipment conversion, shading, and equipment variability. If these are underestimated, the predicted energy production tends to be overestimated compared with reality. Conversely, if set overly conservatively, the project evaluation may become unnecessarily strict.

When looking at the breakdown of losses, it is important not to judge by simply adding the loss rates together. In PVSyst’s loss diagram, each loss is shown as a proportion of the energy at the previous stage, so summing the individual loss rates will not give the overall loss rate. You need to check at which stage losses occur by following the flow.

Also, the results from PVSyst do not fully guarantee the future performance of the power plant. In actual operation, year-to-year weather variability, equipment ageing, vegetation growth, soiling accumulation, inspection frequency, fault response, output curtailment, and changes in the surrounding environment can all affect generation. Simulations are an important decision-making input at the planning stage, but continuous inspections and performance management are required during actual operation.

When reviewing a report, it is important to check the annual generation, monthly generation, breakdown of losses, shading effects, system configuration, and assumptions together. If you isolate and compare only the total generation, you cannot perform root-cause analysis. By understanding why the generation is at that level, which losses are significant, and which conditions affect the results, you can make PVSyst results useful in practice.

How to Leverage PVSyst in Field Operations

To make PVSyst useful in on-site practice, it is important to link simulation results with design drawings and actual site conditions. Power generation simulations are desk calculations, but solar power plants are constructed on real land and operated for long periods. Therefore, the layout on the drawings, site topography, pile locations, racking orientation, maintenance access paths, drainage, surrounding obstacles, and other factors affect the final power generation performance.

For example, even if the layout looks ideal in PVSyst, the actual site may have elevation differences that cause variations in the tilt angles of the mounting frames and the orientations of the panel surfaces. If the ground after development differs from the assumptions made during design, the pattern of shading and the effective inter-row spacing conditions may also change. Also, if pile locations are shifted, this can affect the arrangement of racks and panels, and as a result the generation conditions as designed may not be reproducible.

Therefore, to make effective use of PVSyst results, it is important to link information across the planning, construction, and post-construction phases. In the planning phase, compare the expected energy yields and losses of multiple options to determine the design policy. In the construction phase, verify that the actual layout and terrain do not deviate significantly from the design conditions. After completion, compare measured data and generation performance with simulation results to identify operational issues.

What is particularly effective in field operations is using simulation results as a "reference for identifying problems." When there is a discrepancy between PVSyst results and actual values, rather than simply judging that power generation is low, check which periods show the largest discrepancies, which times of day the output does not increase, and whether the cause is shading, soiling, or equipment issues. Having simulation results makes it easier to prioritize on-site inspections.

Also, when planning a power plant, it is important for all stakeholders to share a common understanding. When sharing PVSyst results, you need to explain not only the generation figures but also the assumptions and the breakdown of losses. If the construction team does not understand the conditions intended by the design team, on-site changes could affect power generation performance. Conversely, if the design team is not aware of construction constraints, the plan may end up not matching reality.

PVSyst should not be considered something used only by designers; its value increases when the operational staff involved in power plant planning use it as a common basis for decision-making. By considering not only how to predict energy production but also how to reflect site conditions, how to verify after construction, and how to compare during operation, the simulation results become more practical documentation.

Summary: PVSyst is a tool for identifying not only energy yield but also weaknesses in a plan

PVSyst is software that simulates the power generation and losses of solar power plants and is used to verify the validity of planning conditions. It lets you check many pieces of information needed for solar power planning, such as an estimate of annual energy production, monthly and seasonal generation trends, losses due to shading and layout, the impact of equipment configuration and electrical losses, and comparative evaluations of different design conditions.

In practice, it is important not to treat PVSyst results as mere generation numbers, but to clarify the planning assumptions and understand why energy production increases or decreases. Whether the annual energy production is high or low alone does not determine the quality of the design. By checking factors such as the impact of shading, layout conditions, temperature, wiring, equipment configuration, and loss settings, you can identify a plant’s weaknesses and opportunities for improvement.

Also, the accuracy of PVSyst depends on the input conditions. If the meteorological data, terrain, layout, surrounding obstacles, equipment specifications, or loss conditions differ from the actual site conditions, the simulation results will also deviate. For that reason, it is important to use the simulations in combination with drawings, on-site surveys, as-built conditions after construction, and actual power generation performance. Simulation is not a substitute for on-site verification, but a basis for making on-site verification more effective.

In planning a solar power plant, designs are required not only to increase power output but also to be easy to build, easy to operate and maintain, and capable of stable long-term operation. PVSyst serves as a tool to provide quantitative evidence for those requirements. In particular, it is a useful resource when you want to compare multiple design options, assess the impact of shading, or explain the basis for expected power generation to stakeholders.

On the other hand, in the practical work of solar power plants, there is a great deal of on-site information that cannot be fully captured by simulations alone. Pile locations, racking layout, post-development terrain, maintenance access paths, surrounding obstacles, and construction deviations directly affect power generation performance and operations and maintenance. After verifying the plan in PVSyst, it is important to accurately capture the site’s positional information and as-built conditions and to reconcile the design conditions with the actual state.

If you want to turn solar PV simulation results into on-site planning management and construction verification that can actually be used in the field, it is effective to also consider systems that support plant location information management and on-site verification. By linking the generation and loss issues identified in PVSyst to on-site layout checks and construction management, it becomes easier to reduce discrepancies between planning and the field. To more reliably advance a solar power plant from planning through construction and maintenance, a perspective that connects simulation results with on-site data is indispensable.