How to Enter Design Conditions in PVSyst | 7 Key Items to Check First

The purpose of entering design conditions in PVSyst is not merely to fill in fields on the screen. The aim is to reproduce, as realistically as possible, where the actual power plant is located, what solar irradiance it receives, at what angle it receives sunlight, how the equipment configuration converts power, and what kinds of losses it experiences during operation. Therefore, when learning how to use PVSyst, it is important not only to learn the operational procedures but also to understand how each input field affects the simulation results.

Design conditions affect not only the energy yield results but also various evaluations such as performance ratio, loss breakdown, monthly energy production, peak-time output limitations, string configuration, the appropriateness of oversizing, and the effects of shading. For example, even with the same module capacity, annual energy production can vary greatly if the installation site's latitude, tilt angle, azimuth, temperature, surrounding shading, wiring losses, or soiling conditions change. In other words, the design-condition inputs in PVSyst are the very foundation of the energy production calculation.

In practice, it is not always possible to finalize design conditions from the outset. In the basic design phase it is common to evaluate using approximate conditions, and in the detailed design phase to review site surveys, equipment specifications, layout, electrical design, shading analysis, and loss settings. Therefore, in PVSyst it is important to adopt the mindset of updating conditions as the design progresses rather than entering them once and leaving them unchanged. By using reasonable assumptions in initial studies and replacing them with evidence-based values in detailed studies, the accuracy and explanatory power of simulations are enhanced.

Also, when entering design conditions into PVSyst, it is important not to make judgments based solely on the values displayed on the screen. Conditions that are not easily reflected in the software’s input fields—such as the site’s topography, site development status, surrounding buildings, trees, utility poles, slopes (embankments), snowfall, salt damage, wind effects, and future nearby developments—also influence design decisions. PVSyst is a very useful simulation tool, but if the input values diverge from the actual site conditions, the output results will likewise become detached from reality. Therefore, when entering design conditions, you should take an approach of verifying them by combining drawings, on-site photographs, survey data, equipment specifications, and construction conditions.

First Item to Check 1: Project Site and Coordinate Conditions

The design condition you should check first in PVSyst is the project site. In solar power generation simulations, the latitude, longitude, elevation, and time zone of the installation site are the basic parameters. Sun altitude and azimuth, solar irradiance, temperature, and seasonal variations differ by location, so if the site settings are incorrect, the reliability of the predicted power generation will decline no matter how detailed the later inputs are.

When inputting the project site, first clearly identify the location of the target area. Rather than relying only on the address, it is preferable to use a reference point near the center of the area where the panels will actually be installed. In large-scale power plants, elevation, solar irradiation conditions, and surrounding shading conditions can differ from one end of the site to the other. In mountainous areas, reclaimed land, or sloped terrain, conditions may vary for each actual installation surface even if the address is the same. Therefore, if the design target area is extensive, it is useful to record as part of the design documentation where the representative point is placed, since this makes it easier to review the conditions later.

One thing to watch for with coordinate inputs is mistakes in latitude and longitude. When entering numbers manually, north versus south, east versus west, the position of the decimal point, and the difference between degrees-minutes-seconds and decimal degrees can result in a completely different location. In particular, when transcribing coordinates from external sources, you need to check that the formats are consistent. After input, always verify that the location is as intended by checking the map display, place name, and the consistency of meteorological data.

Elevation also affects power generation. At higher elevations, temperature conditions change, which can influence module temperature and generation efficiency. However, overly refining elevation alone offers limited improvement in accuracy if the meteorological data and temperature conditions remain coarse. What matters is the consistency between the site, elevation, meteorological data, and local conditions. For example, if a mountain project uses meteorological conditions similar to those of lowland areas, the trends in temperature and solar irradiance may not match the actual situation.

In practice, project site input tends to be postponed, but it is actually a condition that should be fixed at the outset. If the site changes, weather data, the sun’s trajectory, shadow analysis, and the approach to the optimal tilt angle all change. When entering design conditions in PVSyst, start by determining the coordinates of the target site and confirming that those coordinates match the design drawings and on-site information, as this will reduce rework in later stages.

Initial Item to Check 2: Meteorological Data and Solar Radiation Conditions

The next important factor is meteorological data and solar irradiation conditions. When calculating annual energy production in PVSyst, meteorological information such as irradiance, ambient temperature, and wind speed forms the basis of the simulation. In particular, irradiance is directly linked to energy production, so the results will vary depending on which meteorological data you use. When learning how to use PVSyst, choosing the right meteorological data is a very important point.

When examining meteorological data, first check whether the data come from a location close to the target site. Consider not only distance but also terrain, elevation, whether the site is coastal or inland, and whether it is urban or mountainous. Even an observation point that is close to the installation site can show different patterns of solar radiation and air temperature if a mountain lies between them or there is a large elevation difference. Conversely, data that are somewhat farther away may better represent actual conditions if the terrain characteristics are similar.

Under solar irradiance conditions, it is necessary to understand the handling of irradiance on the horizontal plane, irradiance on tilted planes, direct irradiance, and diffuse irradiance. Because solar panels are typically installed with a fixed tilt rather than horizontally, horizontal-plane irradiance alone cannot directly represent the irradiance that actually reaches the panel surface. PVSyst calculates the irradiance received by the panel surface based on location, meteorological data, tilt angle, azimuth, and other factors. Therefore, the quality of the meteorological data combined with the input of installation conditions determines the resulting power generation.

Ambient temperature should not be overlooked. Because photovoltaic modules have the characteristic that output falls as temperature rises, generation efficiency differs between regions with higher and lower temperatures even under the same solar irradiance. In regions that tend to become very hot in summer, temperature losses can become significant. Conversely, in cool regions, if solar irradiance is sufficient, the temperature situation can be advantageous. When entering design conditions into PVSyst, checking not only the annual irradiance but also the monthly temperature trends makes interpreting the results easier.

Meteorological data do not necessarily provide an accurate prediction of local future conditions. In many cases, annual power generation is estimated based on historical average weather patterns. Therefore, simulation results should be treated not as "the amount of power that will definitely be produced in that year" but as "an expected value based on the specified meteorological conditions." In practical documents, organizing the type, period, location, and whether any adjustments were applied to the meteorological data used will make explanations of the power generation more convincing.

First Things to Check — Item 3: Installation Method and Tilt Angle/Azimuth

When entering design conditions in PVSyst, the mounting type and the tilt and azimuth angles are factors that greatly influence energy production. The direction the solar panels face and the angle at which they are installed change the amount of solar irradiance received throughout the year. In particular, fixed ground-mounted systems, roof-mounted systems, sloped-site installations, east-west layouts, and low-tilt configurations exhibit different generation patterns even with the same capacity.

The tilt angle indicates how much the panel surface is inclined relative to the horizontal plane. In general, it is determined by taking into account the region’s latitude, maximizing power generation, ease of installation, wind loads, snowfall, aesthetics, and maintenance. While one approach is to set it close to the optimal angle if only power generation is considered, in practice it is necessary to simultaneously consider racking cost, land use efficiency, shadow spacing, and construction conditions. A lower tilt angle makes it easier to reduce row spacing, but care must be taken regarding rain washing away dirt, snowfall, reflection, and drainage.

The azimuth indicates which direction the panels are facing. The closer they are to facing south, the greater the daytime power generation tends to be; however, depending on the site shape, roof shape, grid interconnection conditions, and demand patterns, they may be arranged split east–west. East-facing increases morning generation, while west-facing increases afternoon generation. In PVSyst, entering the azimuth correctly allows you to assess generation trends by time of day, by month, and over the year.

What you need to be careful about here is not to confuse the azimuth on the drawings with the azimuth settings in PVSyst. On architectural drawings and site plans, up does not necessarily mean north. If you enter data without checking the drawing rotation angle, the difference between true north and magnetic north, or the orientation of the coordinate system, you may end up simulating a different orientation than reality. Especially for roof-mounted installations or projects with multiple surfaces, you need to enter the tilt angle and azimuth angle separately for each surface.

For the mounting method, confirm whether it can be treated as a simple fixed type, whether there are multiple mounting surfaces, or whether it is arranged to follow the slope of the land. Even for ground-mounted systems, if the site has a gradient, shading and the effects of row spacing can differ from the case when the site is assumed flat. For roof-mounted systems, roof pitch, ridge orientation, roofing material, load conditions, and maintenance access also relate to the design conditions. Inputs in PVSyst mainly focus on items that directly affect power generation, but in practice it is important to organize design conditions while also considering construction and maintenance.

First Things to Check — Item 4: Module Conditions and DC Capacity

Module conditions are the central input parameters in PVSyst that determine the performance of a power generation system. The DC-side capacity and generation characteristics are determined by the module’s rated output, temperature characteristics, voltage, current, number of modules, number of series, number of parallels, and the allocation to each installation surface. When entering design conditions, it is important to accurately reflect the specifications of the modules being used.

First, what you should check is the modules' rated output and the number of modules. Multiplying the rated output by the number of modules determines the DC capacity, but in practice you look not only at simple capacity calculations but also at the string configuration and how it pairs with the PCS. For example, because a module's open-circuit voltage rises at low temperatures, having too many modules in series can cause the PCS input voltage range to be exceeded. Conversely, if the number of modules in series is too small, the operating voltage can become too low and efficiency may suffer.

Temperature characteristics are also important. Modules are rated under Standard Test Conditions, but in real outdoor environments the cell temperature varies. At high temperatures output tends to decrease, and at low temperatures voltage tends to increase. In PVSyst, because temperature losses are calculated in combination with meteorological data and installation conditions, incorrect input of module specifications will affect energy yield and voltage assessment.

Also, in configurations that account for rear-side reflected light, such as bifacial modules, ground surface reflectance, installation height, row spacing, and the surrounding environment are relevant. However, because reflected-light conditions vary greatly from site to site, it is important not to make input values overly optimistic. Reflection conditions differ for white ground surfaces, gravel, grass, paved surfaces, water surfaces, and so on. In practice, it is necessary to check the local ground-surface conditions and set reasonable values, including the state of maintenance.

A common failure in module conditions is misreading the values on the datasheet. Rated output, open-circuit voltage, short-circuit current, maximum power operating voltage, maximum power operating current, and temperature coefficients are terms that are similar and prone to incorrect entry. In particular, pay attention to differences in units and the placement of decimal points. After inputting the values, check in PVSyst whether any warnings are displayed, whether the string configuration is reasonable, and whether there are any problems with the operating range at low and high temperatures.

DC capacity is an important value that indicates the power generation potential of the entire installation. However, simply increasing DC capacity does not necessarily lead to a proportional increase in generated energy. The actual amount of energy that can be delivered to the AC side varies depending on PCS capacity, solar irradiation conditions, output limits, shading, temperature losses, wiring losses, and other factors. When entering module conditions in PVSyst, it is important to look at the balance of the entire system, not just the DC capacity.

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Item 5 to check first: PCS conditions and AC capacity

PCS conditions are important design parameters for converting the power generated on the DC side to the AC side. When entering design conditions into PVSyst, check the PCS rated capacity, input voltage range, maximum input current, conversion efficiency, number of circuits, overloading ratio, and so on. If PCS conditions are not appropriate, they will affect not only the evaluation of power generation but also output limiting and the validity of equipment operation.

The relationship between DC capacity and AC capacity is particularly important in solar PV system design. It is common to design the DC capacity larger than the PCS capacity, but if it is excessively large, the portion that exceeds the PCS rated output during periods of strong insolation may be curtailed. This curtailment appears in simulations as output limiting or clipping. Moderate oversizing can contribute to an increase in annual energy yield, but if the oversizing ratio is set too high, the increase in generation relative to the added module capacity may become small.

Always check the PCS input voltage range. If the number of modules in series does not match the PCS operating range, efficiency may drop under low irradiance or high temperatures, or the voltage may exceed the upper limit at low temperatures. In PVSyst, you can combine module conditions and PCS conditions to verify the validity of the string configuration. If a warning appears, check what it means and review the number of modules in series, the number of strings in parallel, the number of PCS units, and the circuit configuration.

Conversion efficiency also affects power generation. The PCS incurs losses when converting direct-current (DC) power to alternating-current (AC) power. Because efficiency varies with load ratio, you should not judge solely by the rated efficiency but consider what level of efficiency will be achieved in the actual operating range. PVSyst can simulate the PCS efficiency characteristics, allowing equipment selection and power generation assessment to be considered together.

When setting AC capacity, be mindful of the grid interconnection conditions. Grid-side receiving capacity, contracted capacity, output control, reverse power flow restrictions, and protection device settings all affect the overall plant design. If the design conditions in PVSyst do not match the electrical design conditions, the simulation may be valid on paper but become difficult to use as actual design documentation. When using generation simulations for business plans or proposals, it is important to clarify the approach to DC capacity, AC capacity, PCS configuration, and output limitations.

A common mistake with PCS conditions is deciding the module-side conditions first and then trying to force the PCS to match them afterward. In practice, it is necessary to design while simultaneously considering module capacity, PCS capacity, string configuration, mounting surface, wiring distance, and grid conditions. PVSyst is an effective tool for checking this balance. By carefully confirming the PCS conditions at the design-input stage, you can reduce downstream design changes and power generation recalculations.

Item 6 of the initial checklist: Shading conditions and nearby obstacles

Shading conditions are an item that is easily overlooked in the design condition inputs in PVSyst, yet they have a large impact on energy production. Even if only part of a solar panel is shaded, it can affect the output of the entire string. In particular, attention should be paid to shadows from the low sun angle in the morning and evening, winter solar irradiance, surrounding buildings, trees, utility poles, fences, slopes, equipment, and adjacent rows.

When evaluating shadows in PVSyst, first consider distant shadows and nearby shadows separately. Distant shadows are caused by remote obstacles such as mountains or terrain, and they can block solar irradiance when the sun is below a certain altitude. Nearby shadows are caused by obstacles close to the panels, such as buildings, trees, rows of mounting structures, or equipment. Nearby shadows change shape depending on the time of day and season, and they directly affect power generation.

For ground-mounted installations, shading from adjacent rows is important. If the spacing between rows is narrow, the shadows of the front rows fall on the rear rows in winter and in the mornings and evenings. Increasing row spacing reduces the impact of shading, but it can also reduce the capacity that can be installed on the same site. Therefore, optimization must consider not only maximizing power generation but also site utilization, constructability, maintenance access routes, and the extent of earthworks. In PVSyst, you can combine layout and shading conditions to check losses caused by shading.

In roof installation projects, pay attention to shading from parapets, rooftop penthouses, ventilation equipment, antennas, adjacent buildings, and the like. If a roof has multiple surfaces, shading conditions can differ for each surface. Not only south-facing roof surfaces, but east- and west-facing surfaces and roofs with complex shapes can be significantly affected by morning and evening shadows. In rooftop installation projects, design drawings alone may not be sufficient to fully grasp the height and position of obstructions, so site photographs and survey data are important.

A common mistake when dealing with shading conditions is calculating power generation under ideal conditions without entering the obstacles that actually exist on site. In initial assessments it may be acceptable to estimate with simplified models, but when using the results in proposals or business plans, the treatment of shading needs to be made clear. If you present power generation figures that do not account for shading, you must explain that assumption; otherwise, discrepancies with actual generation later could become a problem.

Three-dimensional on-site information is useful for correctly entering shading conditions. Accurately capturing the position, height, and distance of obstacles, ground elevation differences, the height of panel rows, and the tilt of the mounting structures increases the reliability of shading analysis. When creating a shadow model in PVSyst, the precision of on-site information is directly linked to the results. Therefore, shading conditions are not something that can be completed by screen operations alone; they should be treated as design parameters to be considered together with on-site verification.

First Item to Check 7: Loss Conditions and Practical Factor of Safety

The final important item when entering design conditions in PVSyst is the loss conditions. In photovoltaic power generation, not all of the irradiance that reaches the panel surface can be extracted as electricity. Generation is reduced by various factors such as temperature losses, reflection losses, wiring losses, mismatch losses, soiling losses, PCS conversion losses, shading losses, aging/degradation, and curtailment. In PVSyst you can set these losses and review them as annual energy production and a loss breakdown.

When entering loss conditions, first check whether the standard initial values are appropriate for each project instead of using them as-is. For example, at plants with long cable runs, wiring losses on the DC and AC sides may become larger. In coastal areas or regions with a lot of dust and sand, you may need to assume higher soiling losses. In snowy regions, you should consider winter reductions in power generation and the impacts of snow. In high-temperature regions, temperature-related losses tend to be greater.

Mismatch losses occur due to module-to-module variations, differences in degradation, and variations in irradiance conditions. Even when using modules of identical specifications, they will not produce exactly the same output. In addition, partial shading or soiling can cause output differences within a string. In PVSyst these losses can be set as fixed conditions, but in actual field sites they are also affected by installation quality and maintenance status.

Soiling loss is an aspect that is often overlooked. In regions with frequent rainfall natural cleaning may be expected, but panels with low tilt, areas with high dust levels, locations affected by bird fouling, and sites near agricultural land or unpaved roads are more prone to soiling accumulation. If soiling loss is set too low, actual power generation may fall below simulations. Conversely, setting it too high can make the project's viability appear harsher than necessary, so it is important to set a reasonable value based on site conditions and the maintenance plan.

A practical safety margin is also important. Power generation simulations are forecasts for design decisions and profitability assessments and do not fully guarantee future weather or operations. Therefore, proposals and business plans need to be aware not only of the expected power generation but also of the uncertainty of conditions. It is important, taking into account factors such as interannual weather variability, equipment degradation, maintenance status, output curtailment, snowfall, and changes in the surrounding environment, not to assume unduly optimistic conditions.

By looking at PVSyst's loss breakdown, you can identify which factors are affecting power generation. Whether temperature losses, shading losses, or PCS output limitations are large will change the direction of design improvements. For example, if shading losses are large, reviewing row spacing and layout may be effective. If PCS output limitations are significant, there may be room to reconsider the oversizing ratio and PCS capacity. If wiring losses are large, the wiring route and cable specifications need to be reviewed.

Common Mistakes When Entering Design Conditions in PVSyst

A common mistake when entering design conditions in PVSyst is looking at input items individually and failing to check overall consistency. Location, meteorological data, tilt angle, azimuth, modules, PCS, shading, and losses are interrelated. Even if one condition is correct, if it contradicts the others, the resulting energy production will be difficult to trust.

For example, there are cases where the site is correct but the meteorological data is from a distant region. Or the layout plan shows a south-facing orientation, yet on PVSyst the azimuth has been entered in the opposite direction. The ratio of module capacity to PCS capacity may remain unrealistic, or warnings about the string configuration may be overlooked. Such mistakes can be hard to notice if you only look at the generation figures.

Also, it is common to continue using the provisional conditions set for initial studies unchanged into the detailed design stage. In the early phase, estimated tilt angles, estimated row spacings, and standard loss rates may be used. However, as the design progresses, the actual equipment specifications, layout, wiring, site grading, and shading conditions become clear. Nevertheless, if you present power generation based on the initial conditions, the real design and the simulation conditions will become misaligned.

Overreliance on output results is also a form of failure. PVSyst can perform detailed simulations, but it cannot deliver accuracy beyond the input conditions. Even if you produce detailed numbers while site conditions remain unknown, that accuracy is limited. In practice, it is important not to treat simulation results as "the correct answer" but as "calculation results based on the specified conditions." In design documents, clearly stating which conditions were assumed, which items are assumptions, and which items need to be reviewed later will reduce misunderstandings among stakeholders.

Also, insufficient checking of units is a common mistake in practical work. PVSyst input values involve various units such as angles, capacity, voltage, current, distance, elevation, and loss rates. If you enter values without confirming whether they are percentages or coefficients, kilowatts or watts, meters (ft) or millimeters (in), the results can change significantly. After entering values, check for on-screen warnings, unusually large losses, or extreme energy production, and, if necessary, review the conditions.

The Importance of Connecting Design Conditions to On-site Information

To correctly input design conditions into PVSyst, it is essential to connect not only desk-based design information but also on-site information. Photovoltaic power plants are outdoor installations and are affected by many site conditions such as terrain, obstacles, ground elevation, site development plans, surrounding environment, maintenance access routes, drainage, snowfall, and vegetation. If this information is lacking, PVSyst may produce clean simulation results that do not match actual construction or operation.

Particularly important are the coordinates and elevation information. When considering panel layout, shading conditions, site development plans, and maintenance access routes, on-site location and elevation data form the foundation. Even sites that appear flat can have subtle elevation differences that affect drainage, racking heights, and how shadows form. On sloped terrain, the relative heights between rows play a major role in shadow analysis. When evaluating shading and layouts in PVSyst, how accurately you can capture the site's three-dimensional information is critical.

On-site photographs are also useful. They allow you to check trees, utility poles, adjacent buildings, fences, existing structures, ground conditions, and surrounding development that may not be apparent on drawings. However, because photos alone make it difficult to accurately grasp distances and heights, it is advisable to combine them with positioning or survey data as needed. If the information obtained from on-site verification is reflected in PVSyst’s design conditions, the explanatory power of the simulation results will be improved.

Also, having a system for sharing design conditions within the team is important. When the person responsible for power generation simulations, the person responsible for layout design, the person responsible for electrical design, the person responsible for on-site verification, and the person responsible for construction management are all different, miscommunication of conditions is likely to occur. For example, if an obstruction is confirmed on site but not shared with the person responsible for simulations, it will not be reflected in the shading conditions. Conversely, if the row spacing or tilt angle assumed in PVSyst is not reflected in the construction drawings, the assumptions for the expected power generation will be invalidated.

Design conditions are not mere input values but assumptions that should be shared among project stakeholders. To acquire practical-level proficiency in using PVSyst, it is necessary not only to learn the software operations but also to understand how to collect, organize, and convert field information into design conditions. With this perspective, power generation simulations become practical documentation that supports design decisions rather than just calculation results.

Summary: The Accuracy of Design Conditions Determines the Reliability of Power Generation Simulations

When entering design conditions in PVSyst, the first items to check are seven: the project location, meteorological data, mounting method, module conditions, PCS conditions, shading conditions, and loss conditions. They may appear to be independent input items, but in reality they interrelate and determine the results of the energy generation simulation. If the location changes, solar irradiance conditions change; if the tilt angle or azimuth changes, the irradiance on the panel surface changes; if the combination of modules and PCS changes, output limits and conversion losses change. Shading, soiling, wiring, and temperature conditions also certainly affect the annual energy generation.

What’s important when using PVSyst is not just filling in the fields on the screen in order. It is checking that the values you enter are consistent with site conditions, design drawings, equipment specifications, construction conditions, and maintenance plans. While initial studies may involve assumptions, you should not leave those assumptions unaddressed; updating them as the design progresses leads to reliable simulations.

Also, rather than looking only at the calculated annual power generation, it is important to check the breakdown of losses, monthly trends, output limits, and the effects of shading. Whether the results are higher or lower than expected, you should be able to explain the reasons based on the input conditions. Because power generation simulations are involved in business viability decisions, equipment design, construction planning, and maintenance planning, building up well-founded design assumptions affects the quality of practical work.

In particular, understanding on-site conditions is indispensable for improving the input accuracy of PVSyst. Accurately confirming coordinates, elevation, obstacles, terrain, installation area, and the surrounding environment strengthens the credibility of the design conditions. An effective approach is to obtain high-precision position information on site and use it as the basis for design and simulation. By using LRTK (iPhone-mounted GNSS high-precision positioning device), it becomes easier to record installation areas, checkpoints, obstacles, and terrain conditions based on position information acquired on site. If you want to bring the design condition input in PVSyst closer to actual field conditions, combining desktop simulation with high-precision on-site positioning using LRTK can improve the accuracy and efficiency from power generation assessment to pre-construction checks.

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