What is PVSyst? Basics of Power Generation Forecasting That Even Beginners Can Understand

Table of Contents

• What PVSyst is for

• Why energy yield forecasting is important in solar PV practice

• Basic input parameters used in PVSyst

• Fundamental concepts of energy yield forecasting

• Understanding losses changes how you interpret forecast results

• Key output items beginners should check first

• Common misunderstandings when using PVSyst

• Practical checkpoints to improve accuracy in real-world projects

• How to leverage energy yield forecasting in design, proposals, and operation & maintenance

• Summary

What is PVSyst used for?

PVSyst is simulation software used to predict the energy production of photovoltaic (PV) installations and to assess annual generation prospects while organizing design conditions and loss factors. In practical PV work, various conditions affect energy output, such as the solar irradiance at the installation site, panel orientation, tilt angle, system capacity, electrical configuration, the effects of shading, and output reductions due to temperature. Because it is difficult to accurately organize these factors using hand calculations alone, a dedicated simulation environment is used to predict energy production.

Many people who search for "What is PVSyst" have heard the name but are still at the stage of wanting to know exactly what the software checks, what kinds of tasks it is used for, and what to look for on the results screen. PVSyst is not simply a tool that outputs an annual energy production figure. Rather, the important point is that it allows you to verify the conditions under which the production was calculated and to see where and how much loss occurs.

In solar power planning, even systems with the same capacity can produce different amounts of electricity depending on the installation site, orientation, tilt, and surrounding environment. Moreover, before the generated DC power can be used or sold as AC power, losses such as temperature loss, wiring loss, conversion loss, mismatch loss, and losses due to shading occur. PVSyst is used to organize these multiple factors and present them in a visible form as a power generation forecast.

For beginners, it is important not to think of PVSyst as "software that automatically gives the correct numbers." If the input conditions do not match the actual site conditions, the resulting energy yield will also depart from reality. Conversely, if you carefully organize the on-site conditions and input assumptions that align with the design intent, it becomes easier to explain the validity of the energy yield prediction. In other words, PVSyst is both a tool for predicting energy production and a tool for checking the consistency of design assumptions.

Why Power Generation Forecasting Is Important in Solar Power Operations

When planning a photovoltaic power generation facility, forecasts of power generation affect all aspects of project viability, design, construction, and operation and maintenance. This is because the expected amount of generation changes the appropriateness of system size, installation methods, financial projections, electricity use plans, and maintenance policies. If planning proceeds while generation forecasts remain vague, problems are more likely to occur later, such as “it produces less power than expected,” “the impact of shading was underestimated,” or “the conditions of the power conversion equipment did not match the system capacity.”

Solar power generation does not produce the same amount of electricity at all times simply because equipment is installed. Solar irradiance varies with the seasons and time of day, and during periods of high ambient temperature panel temperatures rise, reducing output. On rainy or cloudy days the amount of sunlight is lower, and if there are shadows from surrounding buildings, trees, or terrain, generation drops during certain times of day. Taking these variations into account, it is necessary to estimate annual power generation.

Power generation forecasts are not just for knowing “how many kWh will be generated per year.” They provide the basis for judging which months have higher or lower generation, which losses are large, and how much improvement can be expected if design conditions are changed. For example, you can check how much annual generation changes if you slightly alter the tilt angle. If shading has a large impact, you can consider whether to review the layout or adjust the system capacity.

Power generation forecasts are important for practitioners because they relate to accountability. Solar power involves multiple stakeholders—such as the project owner, in-house design staff, construction staff, operations and maintenance staff, and those involved in finance and business planning. To explain calculation conditions and forecast results in a way that satisfies each of these parties, simulations with a solid basis are necessary. Using PVSyst makes it easier to explain generation forecasts, since it allows conditions, losses, and results to be organized into a single, coherent workflow.

Basic Input Conditions for PVSyst

To predict energy production with PVSyst, you first need information about the installation site. Typical items include latitude and longitude, elevation, meteorological data, irradiance, and ambient temperature. Because photovoltaic power generation is highly location-dependent, the weather conditions at the installation area greatly affect the accuracy of the prediction. Even with the same installed capacity, the annual energy yield can differ significantly between regions with good irradiance conditions and those without.

Next, the orientation and tilt angle of the solar panels are important. Orientation indicates which direction the panels face, and the tilt angle indicates how steeply they are inclined relative to the ground. In general, you consider the direction and angle that will maximize power generation efficiency according to the site's solar radiation conditions, but in actual projects they are constrained by roof shape, land shape, racking plans, constructability, surrounding environment, and so on. In PVSyst you set these conditions and check their impact on energy yield.

Equipment configuration is also an important input condition. Panel capacity, the number of panels, connection configuration, the capacity of conversion equipment, and how circuits are arranged all affect generation and losses. In solar power generation, the DC power generated by the panels is converted to AC power by conversion equipment. In that process conversion losses occur, and depending on the combination of equipment capacities there can be periods when some of the generated power cannot be fully converted. Therefore, it is important to check the balance between the generation side and the conversion side.

Surrounding shading conditions are also an important input factor. Shadows cast by buildings, trees, mountains, utility poles, and between pieces of equipment can reduce power generation. In particular, during mornings, evenings, and winter the sun’s altitude is lower, so shading effects tend to be greater. If shading effects are not properly reflected, predicted power generation may be overestimated, widening the gap with actual operational results.

Furthermore, assumptions such as wiring losses, soiling losses, degradation over time, temperature characteristics, mismatch, and downtime/unavailability are also subjects to be considered. For beginners, rather than trying to understand every item perfectly, it is important first to grasp the idea that "energy output is determined by the accumulation of input conditions." When looking at PVSyst results, you should not only look at the final energy output but also check which input conditions are influencing the results.

Basic Approach to Power Generation Forecasting

The basis of power generation forecasting is to start from the solar irradiance falling on the installation site, calculate the irradiance received by the solar panels, and from that estimate the amount that can be extracted as electrical energy. In solar power generation, light from the sun reaches the panel surface and that light energy is converted into direct current (DC) power. After that, the DC power is converted into alternating current (AC) power via conversion equipment, and is used within the facility or sent to the grid.

Not all of the energy in this flow becomes usable electrical power as-is. The solar irradiance reaching the panel surface differs from the irradiance on a horizontal plane, because the amount of sunlight received changes with the panel's orientation and tilt. Also, when panel temperature rises, output decreases. In addition, it is necessary to account for resistance in the wiring, conversion efficiency, and partial generation losses due to shading.

In PVSyst, these elements are calculated step by step to predict the final energy production. What beginners should first understand is that predicting energy production is not a single simple multiplication but rather the result of combining solar irradiance, temperature, system configuration, losses, and operational conditions. At first glance, the annual energy production figure may seem simple, but there are many assumptions behind it.

For example, even if you install equipment of the same capacity in the same area, different panel tilt angles can change the seasonal distribution of generation. Conditions that favor summer production, conditions that favor winter production, and conditions that are advantageous for the annual total are not necessarily the same. Also, increasing system capacity may seem to simply increase generation, but depending on the balance with the capacity of conversion equipment and grid conditions, output may be limited during some periods.

When reading power generation forecasts, it's important to check not only the annual total but also the monthly generation, the generation efficiency relative to solar irradiance, the breakdown of losses, and the reasonableness of the generation output relative to the installed capacity. PVSyst organizes the information needed for these checks, making it easier to explain why the power generation figures are what they are.

Understanding Loss Changes How You Interpret Prediction Results

An important aspect when using PVSyst is how you treat losses. In power generation forecasting, you estimate the actual usable amount of electricity by subtracting various losses from the energy that would be produced under ideal conditions. In other words, simply looking at the predicted generation without understanding the losses does not allow you to correctly evaluate the forecast results.

Typical losses include losses due to shading, temperature, soiling, variations between panels, wiring losses, losses in conversion equipment, and losses due to output limiting. Each of these occurs for different reasons and requires different countermeasures. For example, if shading losses are large, layout planning, installation height, and checking surrounding obstructions are important. If temperature-related losses are large, it is necessary to check the mounting method and ventilation conditions.

What beginners should be careful about is not judging a loss value as good or bad on its own. Even if a loss looks large, it may be unavoidable given the site conditions. Conversely, a loss that appears small may be due to input conditions being set more leniently than they are in reality. When evaluating losses, it is important to verify that the design conditions and the site conditions are consistent.

By checking the breakdown of losses, you can identify opportunities to improve energy production. For example, if annual energy production is lower than expected, rather than simply increasing installed capacity, you can consider reducing shading effects, revising orientation and tilt, improving the wiring layout, or rebalancing with the power conversion equipment. The value of PVSyst lies not only in the final result but in providing the material for these improvement considerations.

In practical power generation forecasting, losses are not uniformly treated as "bad" to be simply reduced; instead, judgments are made in balance with site conditions, design constraints, constructability, and maintainability. Equipment with no losses at all is not realistic. What is important is to understand which losses are dominant, which are within acceptable limits, and which conditions should be reviewed to improve generation and reliability.

Result items beginners should check first

When reviewing PVSyst results, beginners tend to focus first on the annual energy production. While annual energy production is certainly important, it is risky to judge based on that alone. The first things to check are the input conditions, the monthly energy production, the breakdown of losses, the reasonableness of the energy production relative to the system capacity, and the consistency with the design conditions.

Annual energy production indicates how much electrical energy can be expected from the entire system. However, whether that figure is reasonable cannot be judged without taking into account the site's solar irradiation conditions and the system's capacity. Even if the production appears high, if the entered solar irradiation conditions are overestimated it may not match reality. Conversely, if the production appears low, it may be a reasonable result for a site with significant shading or installation angle constraints.

Monthly power generation is also important. Because solar power generation experiences seasonal variations, the annual total alone does not reveal operational characteristics. By checking monthly trends—such as whether output is higher in summer, how much it declines in winter, and how to account for the effects of the rainy season or snowfall—you can make equipment use and financial planning more realistic.

The breakdown of losses is essential for understanding where power generation is being reduced. In particular, losses from shading, temperature, conversion, wiring, and output limitations directly inform design decisions. If a specific loss is larger than expected, you need to recheck the input conditions and review whether they match the site conditions.

Also, verify the plausibility of the energy production relative to the installed capacity. If the generated energy is unusually high or low for the capacity, there may be configuration errors or overlooked conditions. As a beginner, instead of judging the results as soon as you see them, it is important to trace the flow from the input conditions through to the results. PVSyst provides detailed numbers, but the order of checks is crucial to turn those numbers into information usable in practice.

Common misunderstandings when using PVSyst

One common misconception among beginners starting to use PVSyst is the belief that if they enter data into the software it will automatically produce the correct energy generation. In reality, the reliability of simulation results is largely determined by the quality of the input conditions. If meteorological data, system configuration, shading conditions, loss settings, and so on differ from the actual site conditions, the results will be off as well. The software assists with calculations, but it is the practitioner who must assess the validity of the assumptions.

Another misconception is to assume that a design is better simply because it yields a larger power generation. If the aim is only to make the generation appear large, one can set shading and losses to be small or choose conveniently favorable conditions. What matters in practice are explainable, reproducible forecasts. Overly optimistic forecasts widen the gap with actual performance after operations begin and can undermine stakeholders' trust.

Also, caution is needed with the idea that all losses should simply be minimized. Design changes made to reduce losses can worsen constructability or maintainability. For example, significantly changing the layout to avoid shading can decrease land-use efficiency. Changing equipment placement to reduce wiring losses can also affect construction and maintenance access routes. Decisions should be made based on the overall balance of the design, not just power output.

Furthermore, care must be taken not to reuse settings from past projects as-is. Solar power generation conditions vary from site to site. Even with similar capacities or in similar regions, if the terrain, shading, orientation, tilt, or equipment configuration differ, the appropriate settings will change. Past settings can be a useful reference, but reusing them without confirming the site conditions can lead to reduced prediction accuracy.

PVSyst is a useful piece of software, but it is not a cure-all. Only when it is used in conjunction with on-site surveys, design drawings, survey data, equipment specifications, and construction conditions does it produce results that are truly useful in practice. For beginners, it is just as important to learn to question the input conditions and to develop the ability to interpret the results as it is to learn how to operate the software.

Points to Check for Improving Accuracy in Practical Work

To improve the accuracy of power generation forecasts, it is important to first accurately understand the on-site conditions. Organize and reflect in the simulation the installation site's location information, surrounding shading factors, topography, orientation, tilt, available area, and the positions of existing structures. If calculations are performed without adequately grasping the on-site conditions, no matter how detailed the settings, the reliability of the results will not improve.

Shadow conditions in particular have a major impact on power generation forecasts. Shadows cast by surrounding buildings, trees, mountains, and adjacent equipment change their extent depending on the time of day and the season. A single site visit may not be sufficient to fully grasp the effects of shadows over the course of a year. Therefore, it is important to verify this by combining drawings, survey data, on-site photographs, and information about the surrounding environment.

Next, verify the consistency of the equipment configuration. You must confirm that panel capacity, connection configuration, the capacity of conversion equipment, and circuit conditions match the actual design. Even if they appear valid in the inputs, they may not conform to actual construction or operational conditions. Power generation forecasts are part of the design and assume a configuration that can actually be constructed.

Loss settings should also be handled carefully. Assumptions such as soiling, wiring, temperature, degradation, and downtime vary depending on the project's conditions. Even when using standard values, it is desirable to be able to explain why those values are appropriate. In particular, for losses that significantly affect power generation, do not simply use small values; instead, evaluate them in light of site conditions and operational policies.

It is also useful to compare multiple cases. By comparing results under different conditions—such as changing the orientation or tilt, changing the layout, changing equipment capacity, or revising shading conditions—you can clarify the basis for design decisions. Relying on a single result can make it difficult to determine whether a design is truly appropriate. Comparisons allow you to examine the balance between power generation, losses, constructability, and maintainability.

Finally, it is also important to check the simulation results from a practical on-site perspective. If the figures are extremely optimistic or pessimistic, verify whether there are input errors or overlooked conditions. PVSyst performs detailed calculations, but that does not remove the need for review by the responsible practitioners. Rather, assessing—based on the calculation results—whether "this result is reasonable given the site conditions" improves the quality of the energy yield forecast.

How to Use Power Generation Forecasts in Design, Proposals, and Operation and Maintenance

Energy yield predictions by PVSyst can be used not only during the design stage but also for proposals, construction, and maintenance. During design, they provide input for evaluating equipment layout, capacity, orientation, tilt, and the balance with power conversion equipment. By comparing multiple design options and considering not only the expected energy yield but also the breakdown of losses and operational risks, you can select a more appropriate plan.

At the proposal stage, power generation forecasts serve as useful explanatory materials for stakeholders. Rather than simply stating "it will generate this much," you can explain under what conditions the calculation was made, what losses are anticipated, and how design constraints have been reflected. In particular, when asked to justify the projected generation, it is important to be able to show the connection between the input conditions and the results.

During the construction phase, it is important to confirm whether the assumptions made during simulation diverge from the actual construction. There may be cases where obstacles remain in locations that were assumed to be shadow-free during design, the orientation or tilt of panels differs from the design, or wiring routes change and thus alter loss conditions. If power generation forecasts are also used for post-construction verification, differences between the design and the site can be identified early.

During the operation and maintenance stage, comparing predicted power generation with actual power generation allows you to check the condition of the equipment. If actual generation falls substantially below predictions, soiling, malfunctions, changes in shading, wiring faults, inverter outages, or changes in the surrounding environment may be suspected. However, because there are year-to-year variations in weather, you should not judge based solely on a single year’s results; evaluation must take into account solar irradiation conditions and operational status.

Thus, PVSyst is not software that you use once at the planning stage and then discard. By organizing the design rationale, explaining the proposal, and linking it to post-construction verification and maintenance, the value of the power generation forecast increases. Beginners tend to focus first on the operations that produce the energy yield, but in practice, "how you assess the forecast results and how you use them" is what matters.

Summary

PVSyst is simulation software for predicting the energy production of photovoltaic power systems and for organizing design conditions and loss factors. It may seem difficult for beginners, but the basic concept is to estimate the final energy production by starting from the site's solar irradiation conditions and then adding up the solar irradiation incident on the panels, the system configuration, and various losses.

The important thing is not to look only at the final annual generation figure. You need to check whether the input conditions are reasonable, whether the monthly trends are natural, whether there are any anomalies in the breakdown of losses, and whether the results are consistent with the system capacity and site conditions. PVSyst is a tool to assist calculations; organizing input conditions and interpreting the results are the responsibilities of the practitioner.

To improve the quality of power generation forecasts, understanding on-site conditions is essential. Accurately confirming orientation, tilt, shading, topography, equipment layout, wiring, and the surrounding environment, and reflecting them in simulations, increases the reliability of the forecast results. In projects particularly affected by shading or terrain, carefully handling site location information and shape directly impacts the accuracy of power generation forecasts.

In the design of solar power systems and in power generation forecasting, it is important to grasp accurate on-site location information as well as desk-based conditions. If you want to improve the accuracy of field verification and positioning, leveraging LRTK, an iPhone-mounted high-precision GNSS positioning device, can streamline the acquisition of site coordinates and location confirmation, and make it easier to organize the on-site information that serves as the basis for power generation simulations.