PVSyst How-To Manual | 6 Steps for Energy Production Calculation

When calculating power generation with PVSyst, it is important not only to fill in the on-screen fields in order but also to proceed while understanding the meaning of the input conditions. Note that the official website uses the notation "PVsyst", but in this article we use "PVSyst" to match a more searchable form.

Simulation results for photovoltaic (PV) power generation are determined by the combined effects of multiple factors, such as solar irradiance, tilt angle, orientation (azimuth), equipment configuration, loss conditions, and shading. In particular, if inputs for site information, meteorological data, system capacity, tilt angle, orientation, or loss conditions are inaccurate, the estimated annual and monthly generation and the appearance of the loss breakdown can change. Therefore, in practice it is important to be able to explain which conditions were used as the basis for the inputs.

In this article, aimed at practitioners who search for "PVSyst manual", we organize the basic workflow for performing power generation calculations into six steps. So that even first-time users can grasp the overall picture, we explain not just the sequence of operations but also the rationale to check at each step and points to prevent input errors.

Table of Contents

• Clarify the overall picture before performing energy yield calculations in PVSyst

• Step 1: Set project parameters and site information

• Step 2: Verify meteorological data and solar irradiation conditions

• Step 3: Input the basic configuration of the photovoltaic system

• Step 4: Set azimuth, tilt angle, and installation method

• Step 5: Check loss conditions and the effects of shading

• Step 6: Interpret simulation results and apply them to practical operations

• Prevent common input errors in PVSyst energy yield calculations

• Connect energy yield calculations to on-site management and inspection operations

• Summary

Clarify the overall picture before performing energy production calculations in PVSyst

PVSyst is software used for design studies, energy production simulation, performance evaluation, and other tasks related to solar power generation systems. During the planning stage of a power plant, it is used to estimate annual energy production based on the solar irradiation conditions at the planned installation site and the system configuration. For plants in operation, it also helps establish baselines for comparing expected and actual energy production and for assessing the presence of anomalies or opportunities for improvement.

However, the energy output reported by PVSyst is a simulation result based on the input conditions. It does not fully guarantee actual generation. Actual measured output can vary due to weather, equipment condition, soiling, shading, downtime, construction quality, maintenance status, and other factors. Therefore, in practice, it is important not to look only at "how many kWh the calculation produced" but to check "under which assumptions that result was obtained."

The basic workflow for calculating power generation can be organized in the following order: setting location information, checking meteorological data, entering the equipment configuration, setting installation conditions, confirming loss conditions, and reading the results. Being mindful of this sequence makes it easier to verify the consistency of values later. In particular, installation location, module capacity, tilt angle, azimuth, and loss conditions are items that tend to strongly affect the results.

When using PVSyst for the first time, it is easier to understand if you complete a simulation once under standard conditions rather than setting all the detailed parameters from the start. After that, review conditions such as shading, losses, wiring, temperature, and soiling step by step to grasp how much each input affects the results. Be careful: changing many conditions at once before you are familiar with the operation can make it difficult to determine why the energy production increased or decreased.

Step 1: Set project conditions and site information

The first step is to set the project conditions that form the foundation for the power generation calculation. Here you organize the basic information that affects the entire simulation—such as the plant name, installation location, coordinates, elevation, and time zone. Because location information relates to the handling of meteorological data and the solar position, input errors can shift the assumptions underlying the entire result.

Particularly important are the latitude and longitude of the installation site. In solar power generation, the movement of the sun and solar irradiance conditions are directly linked to power output. A change in latitude alters annual irradiance patterns and solar elevation, and if longitude or time-zone handling is incorrect it can affect time-specific calculations. Rather than judging by address or place name alone, it is advisable to confirm the planned installation site’s location information as accurately as possible before entering it.

Elevation is another item that’s easy to overlook. Since elevation affects the assessment of site and meteorological conditions, in mountainous areas or regions with large elevation differences, set conditions as close to the actual site as possible within feasible limits. You don’t need to assume that power generation will change greatly based on elevation alone, but it’s important to verify that it does not contradict meteorological data or local conditions.

Project names and version control are also important in practice. Simulations do not necessarily finish in a single run. Design changes, capacity changes, angle changes, additions of shading conditions, or revisions to loss rates may lead to creating multiple calculation patterns. In such cases, if file names or project names are ambiguous, it becomes unclear which result is the latest or which conditions were adopted.

In practice, it is easier to manage files if you establish naming rules that include the project name, creation date, types of conditions, revision number, and so on. For example, distinguishing files as for initial study, after design revision, after applying shading conditions, or for final verification will help prevent confusion later when using them for reports or internal reviews.

It's important to develop the habit of reviewing your inputs once you've set the location information. If results look odd in the latter part of the power generation calculation, the cause may lie in the initial location settings or the choice of meteorological data. Although the initial steps may seem simple, carrying them out carefully reduces the verification burden in later stages.

Step 2: Check meteorological data and solar radiation conditions

Next to check are the meteorological data and solar irradiance conditions. In PVSyst’s energy production calculations, meteorological conditions such as the site’s solar irradiance, ambient temperature, and wind speed are important inputs. The annual energy production of a photovoltaic system is greatly affected not only by the system capacity but also by how much solar irradiance is available.

When selecting meteorological data, verify that the data are from a location close to the target site and that they suit the calculation purpose. Using data from locations far from the installation can fail to reflect local solar radiation patterns and temperature conditions. Coastal areas, mountainous areas, basins, and urban areas can exhibit different meteorological conditions even within the same prefecture.

There are several ways to think about solar irradiance, such as horizontal irradiance, diffuse irradiance, and direct irradiance. In PVSyst, the irradiance incident on the installation surface is calculated based on the selected meteorological data. It is important for practitioners to check not only the final energy production but also whether the input solar irradiance conditions are within a reasonable range.

Examining monthly solar radiation trends is also useful. Solar radiation varies by season, and in regions affected by the rainy season, snowfall, prolonged rain, or typhoons, monthly variability can be large. Even if the annual value alone appears reasonable, checking by month may reveal that specific months are unusually high or low. In such cases, review the selection of meteorological data and the site conditions.

Air temperature also affects electricity generation. Photovoltaic modules tend to exhibit reduced output as temperature rises. Therefore, even with the same solar irradiance, generation efficiency can differ between regions with high and low temperatures. Because PVSyst's results also show temperature-related losses, checking at the meteorological data stage whether the temperature conditions look reasonable makes it easier to verify results later.

Meteorological data are an important premise that influences the reliability of calculation results. Although they may appear simple to select, because they form the basis for power generation calculations they must be handled with attention to the chosen data's regionality, period, and representativeness. When using them for reports or internal explanations, record which meteorological conditions were assumed so that verifying the conditions later is easier.

Step 3: Enter the basic configuration of the photovoltaic power generation system

Once you have set the site and meteorological conditions, the next step is to enter the basic configuration of the power generation equipment. Here you set the PV module capacity, number of modules, number of modules in series and in parallel, the capacity of the PCS or inverter, the connection configuration, and so on. This step is the core of the power generation calculation, and input errors here tend to be reflected directly in the results.

The first thing to check is the system capacity. The power generation of a solar power system is greatly influenced by the total capacity of the modules installed. Based on the rated output per module and the number of modules, verify that the total capacity matches the design documents. Be careful, because unit mix-ups or errors in the number of modules entered can cause the annual energy generation estimate to deviate significantly.

Next, check the settings for the number of series and parallel connections. In photovoltaic systems, connecting modules in series raises the voltage, and connecting them in parallel increases the current. In PVSyst, this connection configuration affects electrical compatibility and loss calculations. If you enter series or parallel counts that differ from the actual design, the calculations may appear valid but can result in outcomes that do not match the real system configuration.

The capacity of the PCS or inverter is also important. If the PCS or inverter capacity is smaller than the module capacity, output may be limited during periods of strong solar irradiance. Conversely, setting it without understanding the concept of capacity ratio can lead to overestimated or underestimated power generation assessments. In PVSyst you can check the effects of losses and limitations according to the system configuration, so it is important to verify the capacity balance after entering the data.

The equipment selection screen displays many detailed specification values. What beginners often stumble over is accepting the displayed numbers as-is and skipping verification against the design documentation. In practice, you must always confirm that the selection items in the simulation match the actual equipment specifications being planned. Avoid expressions that depend on model numbers or fine details of specifications, and as a basic practice at least check that capacity, voltage range, connection configuration, number of units, and number of systems do not conflict with the plan.

Also, when conducting comparative evaluations in the future, it is useful to save cases with modified system configurations separately. If you increase or decrease capacity, change the tilt angle, or revise loss conditions, organizing calculation patterns will make it easier to explain differences in power generation. Because the system configuration is the foundation of the calculations, be sure to review the total capacity and the connection configuration after entering the inputs.

Step 4: Configure azimuth, tilt angle, and mounting method

The energy yield of a solar PV system varies depending on the orientation and tilt angle at which the modules are installed. Therefore, setting the azimuth, tilt angle, and mounting configuration is an essential step when performing energy yield calculations in PVSyst.

Orientation refers to the condition that indicates which direction the module surface faces. Typically, the direction is chosen with the sun’s movement in mind to maximize power generation, but actual installations are constrained by factors such as site shape, roof shape, surrounding environment, and construction conditions. In simulations, it is important to input an orientation that closely matches the actual layout plan.

The tilt angle indicates how much the module surface is inclined relative to the horizontal plane. Changing the tilt angle alters the distribution of incident solar irradiance and energy production across seasons. Increasing the angle does not necessarily increase the annual energy yield; factors such as regional solar irradiation conditions, installation orientation, snow, wind loads, constructability, and maintainability must also be considered. In PVSyst, you can compare multiple patterns with different tilt angles to verify changes in energy production.

The mounting method also affects the results. Ground-mounted, roof-mounted, or rack-mounted installations change the ventilation and temperature conditions on the rear of the module. If rear ventilation is poor, the module temperature is more likely to rise and temperature-related losses can increase. In PVSyst you can review thermal conditions and temperature-related losses, so it is important to choose settings that closely match the actual installation.

A common mistake at this step is misinterpreting the sign of the azimuth or the angles. If you enter values without checking which direction the software’s azimuth setting uses as its reference, the conditions may end up opposite to what you intended. Likewise, when entering roof pitch or angles from drawings as-is, you need to verify the units and the reference plane.

In power generation calculations, examining not only the final annual energy production but also the month-by-month variation deepens understanding. Changing the tilt angle and orientation can shift conditions that favor summer, those that favor winter, or those that tend to be more stable on an annual average. How you evaluate the results also depends on whether the plant’s objective is to maximize total annual production or to prioritize seasonal output trends.

After setting the installation conditions, be sure to cross-check them against the equipment drawings and the layout plan. Even if the inputs in PVSyst are properly set, if they differ from the actual installation plan the simulation results will be difficult to use as practical justification. Azimuth, tilt angle, and mounting method are items that are often required to be explained in power generation calculations, so it is important to retain the basis for your inputs.

Step 5: Check loss conditions and the impact of shadows

After entering the system configuration and installation conditions, the next step is to check the loss conditions and the effects of shading. In photovoltaic systems, not all of the solar irradiance that reaches the modules can be converted into electrical power. Power generation is reduced by various factors such as temperature rise, wiring resistance, conversion losses, soiling, mismatch, shading, and downtime.

In PVSyst, these losses are set for each item and reflected in the final energy production. Beginners should be careful not to leave the loss items at their default values simply because they "don't understand them." Default values are not always inappropriate, but using them without checking whether they match the project's conditions will result in a simulation that is difficult to justify later.

Losses from soiling vary depending on the installation environment. Assumptions differ according to site conditions, such as areas with heavy sand and dust, locations prone to falling leaves or bird fouling, or places where dirt is easily washed away by rainfall. Because they also depend on cleaning frequency and maintenance practices, it is important not to assume overly optimistic conditions.

Wiring losses are related to cable length, thickness, current, voltage, and other factors. At the rough-estimate stage calculations may be made under standard conditions, but as the design approaches the detailed phase it is necessary to align them with the actual wiring plan. If wiring losses are underestimated, the estimated power generation may appear higher than the actual.

Temperature-related losses are also important. Because module temperature tends to increase and reduce output, this should be checked together with the mounting method and ventilation conditions. Installations close to the roof surface or layouts with limited ventilation may be particularly susceptible to the effects of temperature rise. Even in regions with high solar irradiance, temperature losses can become large during periods of high ambient temperature.

The impact of shading requires particular attention in energy yield calculations. Shadows cast on modules by surrounding buildings, trees, utility poles, fences, terrain, or adjacent racking rows can reduce power generation. Because shadows change with the time of day and season, their effects can be difficult to assess by simple visual inspection alone.

PVSyst has functions to handle distant shading and near shading. Distant shading deals with the effects of mountain ranges and other distant obstacles, while near shading deals with the effects of objects located close to the power generation equipment, such as buildings, trees, and rows of mounting structures. When entering near shading, the position, height, distance, and azimuth of surrounding obstacles should be made as close to reality as possible; omitting obstacles too much can lead to an overestimation of energy yield, whereas entering them excessively can result in overly conservative outcomes.

In shading calculations, it's important not only to look at the annual loss rate but also to see which months and times of day are most affected. Whether shading occurs at low sun angles in the mornings and evenings, whether long shadows extend during winter, or whether shading from adjacent rows occurs will change the appropriate mitigation measures. To inform practical decisions such as layout changes, spacing adjustments, tree management, and maintenance planning, thoroughly verify the impact of shading.

Step 6: Interpreting Simulation Results and Applying Them to Practice

Once all conditions are set, run the simulation and check the results. In PVSyst you can review indicators such as annual energy production, monthly energy production, generation efficiency, and the breakdown of losses. The important point here is not to stop at the final energy production figure. To determine whether the results are reasonable, you need to read the input conditions together with the loss breakdown.

First, what you should check is the annual energy production. This is a basic indicator showing how much electricity the entire power plant is expected to generate in one year. However, the annual figure alone does not reveal which seasons have higher or lower generation. It is important to review the monthly generation and confirm that it aligns with solar irradiation conditions, the installation tilt angle, and the effects of shading.

Next, review indicators that show power generation and performance per unit of installed capacity. This makes it easier to assess not only the simple total generation but also whether the results are reasonable relative to the system size. While larger-capacity systems produce greater total generation, if generation per unit of capacity is low, there may be room for improvement in the design parameters or loss conditions.

Checking the loss diagram is also essential. PVSyst’s results allow you to see where and how much loss occurs from the incidence of solar irradiance to the final electrical output. By examining losses from shading, temperature, conversion, wiring, and so on, you can more easily identify the main causes of reduced power generation.

If the results are lower than expected, do not immediately change the equipment configuration; first check the input conditions. Review, in order, whether there are input errors in the site information, meteorological data, capacity, azimuth, tilt angle, loss conditions, or shading conditions. In particular, the unit of capacity, number of panels, number of modules in series, azimuth sign, decimal place of the loss rate, and dimensions of the shading conditions are items prone to mistakes.

Be cautious even when the results are higher than expected. A high generation figure may look good at first glance, but it could mean that the loss assumptions are too lenient, shading hasn’t been considered, or soiling and downtime haven’t been allowed for. When using the figures for business planning or financial assessment, overly optimistic generation estimates can lead to erroneous decisions later.

The simulation results can be used for design studies, internal briefings, customer presentations, maintenance planning, and performance comparisons. After operation begins, comparing actual power generation with the simulation results makes it easier to assess the plant’s condition. However, when comparing with actual values, it is necessary to consider the effects of actual weather, downtime, output control, inspection work, equipment malfunctions, and similar factors.

The results from PVSyst are simply calculations based on specified conditions. For practical use, it is important to organize the input conditions, calculation results, adopted assumptions, and points of caution as a set. Instead of extracting only the numerical results, present them in a form that can explain why that amount of energy generation was obtained, so they can be more easily used for planning and operational decisions.

Prevent common input mistakes in PVSyst energy production calculations

When you are not yet familiar with operating PVSyst, you can easily become confused by the large number of input fields. Common mistakes in energy yield calculations often arise not from complex settings but from insufficient checking of basic items. Basic items such as site information, capacity, tilt angle, orientation, and loss conditions should always be reviewed after input.

When setting the location, it is easy to mix up latitude and longitude, select weather data from sites far from the installation location, or forget to enter elevation. Especially when using data from nearby areas, check that the meteorological conditions are not substantially different from those at the target site. Coastal and inland locations, and plains versus mountainous areas, can exhibit different patterns in solar radiation and temperature.

In equipment configurations, errors in the number of modules and the total capacity are noticeable. Simply checking that the total obtained by multiplying the per-module capacity by the number of modules matches the design documents can prevent major mistakes. Also, if the number of series or parallel connections does not match the actual configuration, the electrical conditions and the appearance of loss calculations will change.

For azimuth and tilt angles, it is important to understand the reference used for input. If the notation on the drawings and the input rules in PVSyst do not match, calculations may be performed using a different orientation than intended. In particular, when dealing with multiple roof surfaces or systems with multiple orientations, you should organize the conditions for each surface before entering the data.

In loss conditions, it is easy for explanations to be insufficient when initial values are used as-is. Even when using initial values, recording why you judged those conditions to be acceptable makes it easier to explain later. Dirt, wiring, temperature, shading, and downtime are factors that can vary depending on site conditions and operational policies, so they should be reviewed as necessary.

When entering shadow data, errors in an obstacle’s height, distance, or azimuth will affect the results. If you cannot judge from site photographs or drawings alone, clarify the positional relationships of the obstacles and check them with attention to the times of day and seasons when shadows are likely to occur. If the impact of shadows is significant, it will affect layout planning and maintenance planning, so it is important not to treat it as a mere calculation item.

Deciding the order of checks is effective for preventing input errors. If you review in the flow of first site information, then meteorological data, then equipment capacity, then installation conditions, and finally loss conditions and result verification, it becomes easier to trace the cause. If each person has a different way of checking, the interpretation of results can vary even for the same case, so it is reassuring to standardize the checklist items within the company.

Connecting power generation calculations to on-site management and inspection operations

PVSyst's energy yield calculations can be used not only in the planning stage but also for on-site operations management and inspection tasks during operation. The estimated energy yield obtained from simulations serves as the benchmark for evaluating actual energy production. If actual output falls significantly below the estimate, it becomes an opportunity to check whether the discrepancy can be explained by irradiance conditions alone or whether there is an issue on the equipment side.

However, simply comparing simulated values and actual results is insufficient. Actual energy output is affected by daily weather, equipment outages, output curtailment, soiling, shading, installation conditions, maintenance status, and so on. Therefore, when making comparisons, it is necessary to evaluate them while checking the solar irradiance conditions and outage history for the period in question.

In site management, comparing the expected monthly generation and the actual monthly generation side by side makes it easier to notice anomalies. For example, if actual generation falls significantly short in a particular month, in addition to the effects of prolonged rain or snowfall, you should also check for equipment outages, soiling, increased shading, and vegetation growth. Changes that are easy to miss when looking only at annual values are easier to detect when viewed monthly or daily.

In inspection work, it is important to link the causes of reduced power generation to on-site verification. If a simulation indicates locations with high shading losses, the on-site inspection should focus on nearby obstructions and tree growth. If soiling is suspected to be a factor, check the condition of module surfaces, drainage conditions, and cleaning history. If losses related to wiring or connections are suspected, electrical inspection and review of records will be necessary.

The results of power generation calculations can also be used to build consensus among stakeholders. If the design team, construction team, maintenance team, and project management team can share the same assumptions, misunderstandings about power generation can be reduced. Conversely, if the input conditions are not shared, the results may take on a life of their own, and later it can become unclear why this figure was obtained.

In practice, rather than treating PVSyst results and on-site data separately, it is important to use them as a shared reference that connects planning, construction, operation, and inspection. By comparing the conditions assumed in the simulation with what is actually occurring on site, it becomes easier to grasp the power plant’s condition more accurately.

Summary

The process for calculating energy production in PVSyst can be organized into six steps: setting site information, verifying meteorological data, entering system configuration, setting azimuth and tilt angles, checking loss conditions and shading, and interpreting simulation results. Because each step affects energy production, it is important not to simply advance through the screens but to proceed while confirming the meaning of the input conditions.

In particular, location information, solar radiation conditions, installed capacity, installation angle, loss assumptions, and how shading is handled determine the validity of the results. Instead of judging solely by whether the power generation is high or low, being able to explain under which assumptions the results were calculated leads to simulations that are useful in practice.

PVSyst's energy production calculations are useful not only for studies during the planning stage but also for comparing actual performance after commissioning and for inspection and maintenance planning. By checking the difference between expected and actual energy production and comparing it with site shading, soiling, outages, and maintenance conditions, you can more easily identify areas for improvement.

In managing solar power plants, it is important to link simulation results with on-site information when making decisions. If you want to avoid leaving generation calculations as desk-based figures and instead apply them to on-site inspection and maintenance, consider using field management tools such as LRTK Solar, which make it easier to reconcile the assumptions of simulations with actual site conditions.