8 Evaluation Axes for Comparing Design Proposals in the PVSyst Manual

Table of Contents

• Prerequisites for starting design proposal comparisons in the PVSyst manual

• Evaluation Axis 1: Do not judge solely by annual power generation

• Evaluation Axis 2: Identify opportunities for improvement from the breakdown of losses

• Evaluation axis 3: Compare under matched solar radiation conditions and shadow effects

• Evaluation axis 4: Assess the validity of module placement and array configuration

• Evaluation Axis 5: Assess the balance between inverter capacity and the oversizing ratio

• Evaluation Axis 6: Check for differences caused by temperature conditions and installation environment

• Evaluation Axis 7: Select options that are easy to explain in report outputs

• Evaluation axis 8: Compare including constructability and operational risks

• Use the PVSyst manual to translate comparisons of design proposals into practical implementation.

Prerequisites for starting design proposal comparisons in the PVSyst manual

In designing photovoltaic systems, even when assuming the same site, the same installed capacity, and the same modules, simulation results can vary greatly depending on layout, orientation, tilt angle, string configuration, inverter selection, how shading is handled, and loss settings.

Therefore, when comparing design proposals, you should not simply choose the one with the highest energy yield; you need to confirm why that result occurred, which conditions are influencing it, and whether it will be feasible when actually constructed and operated.

The purpose of reading the PVSyst manual is not just to learn how to operate the interface. It is important to correctly read the input conditions and output results for each design proposal, align the assumptions for comparison, and organize them into materials that can be used for decision-making. In practice, stakeholders such as clients, designers, contractors, financial institutions, and O&M personnel place emphasis on different points. Some want to maximize energy generation, others want to reduce construction risk, some prioritize long-term maintainability, and others seek clarity for presentation materials.

A common mistake when comparing design proposals is to take the numbers shown on PVSyst's result screen at face value, line them up, and judge superiority based solely on annual energy production or performance ratio. At first glance, the proposal with higher numbers may seem optimal, but behind the scenes shading losses may have been underestimated, the temperature loss settings may not match the site environment, or the inverter's operating margin may be insufficient. The figures used for comparison only have meaning when the underlying assumptions are aligned.

Therefore, when using the PVSyst manual to compare design proposals, first clearly define which conditions are common across the proposals and which conditions are changed. Common conditions include meteorological data, installation site, module type, basic system capacity, grid interconnection conditions, and the approach to loss settings. Changed conditions include azimuth, tilt angle, array spacing, array configuration, inverter capacity, shading model, mounting structure type, and wiring routes. If this distinction remains unclear when making comparisons, you will not be able to explain the causes of differences in energy generation.

Also, PVSyst simulations do not automatically determine whether a design proposal is good or bad. They are, at best, a tool to calculate energy production, losses, operating conditions, and reports based on the input conditions. Final decisions require a comprehensive evaluation that includes site conditions, constructability, maintainability, regulatory requirements, contract terms, and future operational risks. In this article, with reference to the PVSyst manual, we organize and explain eight evaluation axes you should keep in mind when comparing design proposals, presented from a practical, user-friendly perspective.

Evaluation Axis 1: Do not judge solely by annual power generation

The first thing that tends to attract attention when comparing design proposals is the annual energy generation. PVSyst's results show the annual generated energy and the energy exported to the grid, making comparisons such as “Option A produces X percent more than Option B” straightforward. Generation is an important indicator directly linked to project profitability and is an evaluation metric that cannot be ignored. However, judging design proposals based solely on annual generation may lead to selecting an option that carries risks.

For example, the evaluation can change significantly depending on whether a proposal's high annual generation is due to optimizing orientation and tilt angle, raising the oversizing ratio, or not adequately reflecting the effects of shading. Even if the generation is high, if the configuration is prone to output curtailment in certain seasons or time periods, it may not translate into the expected revenue in actual operation. Also, proposals that increase generation by raising installed capacity also increase construction costs, maintenance costs, and equipment replacement risks, so simple comparisons of generation alone are insufficient.

When using the PVSyst manual to view annual energy production, it is important to confirm which stage of the simulation results the energy refers to. The theoretical generation based on the irradiance incident on the module surface and the grid output after subtracting various losses mean different things. When comparing design options, you need to look not only at the final output but also at how much each loss contributes along the way.

Also, because annual generation is the result averaged over a year, it can mask seasonal biases and time-of-day output characteristics. In self-consumption projects, a plan that tends to generate during periods of high demand may be more advantageous than one with a higher annual generation. Even in feed-in projects, depending on output control and contractual conditions, a plan that delivers stable output throughout the year may be preferable to one whose peak output is too concentrated.

Therefore, use annual energy generation as an entry point for comparison, and then delve into the reasons for any differences in generation. When interpreting PVSyst results, do not automatically make the option with higher generation a candidate for adoption; instead, confirm whether that generation is derived from reasonable conditions and whether it conflicts with other evaluation criteria. The magnitude of energy generation is important, but it is only one indicator for understanding the overall picture of a design proposal.

Evaluation Axis 2: Identifying Improvement Opportunities from the Breakdown of Losses

When comparing design proposals in PVSyst, the breakdown of losses is particularly important. Differences in energy yield are displayed as results, but to understand where those differences originate you need to examine the loss components carefully. In photovoltaic power generation, energy is lost due to various factors such as solar irradiance, shading, temperature, mismatch, wiring, inverter conversion, clipping, soiling, and degradation. The relative merit of a design proposal depends on how reasonably these losses are minimized.

When you examine the breakdown of losses, the points that need improvement become clear. For example, in designs with large shading losses, there is room to review module layout, array spacing, and distance to obstructions. In designs with large wiring losses, it is necessary to consider string configuration, junction box and power conditioner placement, and cable length. In designs with large temperature losses, check whether the installation is rooftop or ground-mounted, whether ventilation is sufficient, and whether there are issues with racking height.

When comparing losses, it is important to distinguish whether the differences in results merely reflect differences in the set values or differences in the design proposals themselves. For example, if Proposal A uses a conservative setting for soiling loss while Proposal B uses a standard value, Proposal B may appear to have higher power generation not because its design is superior but because its input conditions are more lenient. If the approaches to setting losses differ between the proposals being compared, the comparison of results is not fair.

When setting loss parameters while consulting the PVSyst manual, it is important not to use the default values as-is but to consider whether they match the project’s conditions. In coastal areas, snowy regions, areas with a lot of dust, factory roofs, agrivoltaic installations, and mountainous regions, the assumptions about soiling, temperature, shading, snow, and maintainability change significantly. When comparing design options, if you are comparing at the same site, align the loss settings so that only the impact of different design conditions on losses is visible.

Also, the breakdown of losses is useful when explaining to stakeholders. Rather than simply saying "Plan A generates more electricity," it's easier to convince them by explaining that "Plan A has lower shading losses and reduced wiring losses, so its annual energy production is higher." Conversely, it may be reasonable to choose a plan whose generation is slightly lower but whose loss breakdown is stable and that involves lower construction and maintenance risks. PVSyst's loss analysis is an important evaluation metric for clarifying where a design can be improved and the reasons for adopting it.

Evaluation Axis 3: Compare under consistent solar radiation conditions and shadow effects

In solar photovoltaic simulations, the treatment of solar irradiance conditions and shading has a major impact on the results. When comparing design proposals, if the handling of meteorological data, site location, terrain, and surrounding obstructions differs, it becomes unclear whether differences in energy production are due to the design proposals or to input conditions. When consulting the PVSyst manual, you should verify that the selection of solar irradiance data, the calculation of irradiance on tilted surfaces, and the settings for near and far shading are consistent as comparison conditions.

When comparing multiple proposals on the same site, you should, in principle, use the same meteorological data. If you use different data sources, differences in annual solar irradiance and temperature will appear as differences in power generation. If you want to see the differences between design proposals, it is fundamental to align the meteorological data, installation location, elevation, and horizon conditions. On that basis, compare differences in azimuth, tilt angle, array layout, and shading.

The impact of shading is an item that requires particular attention when comparing design proposals. When buildings, trees, utility poles, mountains, adjacent equipment, rooftop protrusions, etc., cast shadows, the results depend on how detailed the shading model is. Over-simplifying shadows can lead to overestimating power generation, while being overly conservative can cause a favorable design to be overlooked. If the accuracy of shading inputs differs between the proposals being compared, a correct judgment cannot be made.

For example, a south-facing design with a larger tilt angle can be advantageous for winter solar gain, but it may also increase shading on the front-row arrays. A design with a lower tilt angle is less prone to shading effects, but it can reduce the efficiency of annual solar energy capture. Which is more advantageous depends on site conditions, latitude, array spacing, feed-in tariff, and self-consumption patterns. For such decisions, it is essential to compare both solar irradiance and shading under the same assumptions.

Also, for rooftop installations, the azimuth and tilt can differ between roof planes. The relationship between installed capacity and generation efficiency changes depending on whether modules are placed across multiple planes or limited to some of the better-oriented planes. Even if increasing capacity to boost total generation appears advantageous, including many shaded or poorly oriented planes can reduce generation per kW of capacity. In PVSyst, it is important to check not only the total energy production but also the generation per kW and the breakdown of losses, and to be wary of apparent advantages from increasing capacity.

Solar radiation conditions and shading assessment are the foundation that supports the rationale for design proposals. If these are ambiguous, the reliability of any judgments will decrease no matter how carefully you examine other evaluation axes. When using the PVSyst manual to make comparisons, first align the solar data and shading conditions, and then adopt an approach that reads the differences between each design proposal.

Evaluation Axis 4: Assessing the Appropriateness of Module Layout and Array Configuration

When comparing design proposals, module layout and array configuration are critical evaluation axes that affect power generation, constructability, and maintainability. In PVSyst, you can set the number of modules, azimuth, tilt angle, array segmentation, and string configuration to check the generation characteristics. However, a configuration that appears feasible on the screen is not necessarily easy to construct on site or suitable for long-term operation.

In module layout, you first check the usable area and layout efficiency. Even on the same site, the actual number of modules that can be installed varies depending on aisle widths, maintenance clearances, evacuation routes, separation from rooftop equipment, racking foundation positions, and snow and drainage conditions. Even proposals that show high energy yield in PVSyst will be difficult to adopt if they create on-site problems such as inaccessible maintenance and inspection routes, impractical racking anchoring positions, or excessively long cable routes.

In the array configuration, check the number of modules per string and the uniformity of the connections. If modules that experience different shading patterns are grouped in the same string, partial shading can more easily affect the overall output. Also, when surfaces with different azimuths or tilts are connected to the same MPPT, losses may occur due to differences in operating points. In PVSyst settings, it is important to verify that the electrical configuration matches the actual design intent.

When comparing multiple proposals, the energy generation per unit of capacity should not be overlooked. Increasing the number of modules tends to raise total generation, but if you use areas with poor orientation or shading conditions, the overall system efficiency can decline. Whether pursuing maximum capacity on a limited site or concentrating only on locations with favorable conditions to improve efficiency is more advantageous depends on the project's objectives. The option you should choose varies depending on whether you aim to maximize revenue from power sales, increase the self‑consumption rate, or prioritize investment efficiency.

Also, module layout affects future maintenance. Layouts that are difficult to inspect, that leave no space for replacement work, or that tend to accumulate dirt or falling snow unevenly will increase operating costs and the risk of failure over the long term. These factors are not easily reflected in PVSyst’s energy yield results, but they are very important in practice. When comparing design proposals, it is necessary to consider simulation efficiency and on-site serviceability at the same time.

When checking array settings while consulting the PVSyst manual, do not mechanically fill in input fields; instead confirm that the configuration matches the site drawings, electrical design, and construction plan. Simulations are intended to verify the validity of the design proposal, and it is meaningless to rate highly a layout that cannot be realized on site. Module layout and array configuration should be treated as an evaluation axis that links energy output and practical feasibility.

Evaluation Axis 5: Looking at the Balance between Inverter Capacity and Oversizing Rate

The selection of inverter capacity is a major decision point when comparing design proposals in PVSyst. In solar power generation, how the inverter capacity is set relative to the module capacity affects energy yield, clipping losses, equipment costs, capacity factor, and grid interconnection conditions. Increasing the oversizing ratio makes it easier to take advantage of generation during low irradiance or in the morning and evening, while during periods of strong irradiance outputs exceeding the inverter capacity may be curtailed.

PVsyst results allow you to check losses caused by the inverter and the effects of clipping. When comparing design proposals, you should not only consider whether the oversizing ratio is high or low, but whether it falls within a reasonable range for the project. A proposal with a high oversizing ratio may increase annual energy yield, but it can also increase peak-time output curtailment, causing the additional modules to deliver diminishing returns.

When evaluating the oversizing ratio, it is important to check not only the total annual energy production but also the amount of energy lost and the times when those losses occur. If clipping losses are small, it can be more economical to install more modules while keeping the current inverter capacity rather than increasing the inverter size. On the other hand, if clipping losses are large and output frequently hits the limit during certain seasons, there may be room to reconsider the inverter capacity and string configuration.

Also, the inverter's operating range is important. You need to check that the string voltage properly falls within the inverter's MPPT range, that the open-circuit voltage at low temperatures does not exceed allowable limits, and that sufficient voltage can be ensured even at high temperatures. Even if PVSyst simulation results look good, configurations with little margin in equipment specifications pose practical risks. When comparing design proposals, you must consider both energy yield and electrical safety.

When comparing multiple inverter options, the number of units, installation space, maintainability, and the extent of impact in the event of a failure should also be evaluated. A proposal that deploys a small number of large-capacity inverters can simplify installation and wiring, but it may result in a larger impact if a failure occurs. A proposal that distributes smaller-capacity inverters makes it easier to flexibly accommodate arrays with different shading and orientations, but it can increase the number of units and the maintenance required.

When using the PVSyst manual to check inverter settings, verify that the equipment data you entered is correct, that the combination with the modules is appropriate, and that the loss results do not show any anomalous values. When comparing design proposals, it is important to treat inverter capacity not merely as an equipment cost issue but as a comprehensive evaluation criterion affecting energy generation efficiency, reliability, and maintainability.

Evaluation Axis 6: Verify differences caused by temperature conditions and installation environment

Solar PV modules see their output decrease as temperature rises. Therefore, when comparing design options in PVSyst, the handling of temperature conditions and the installation environment is extremely important. Even with the same module and the same irradiance conditions, a design that installs modules close to the roof and a design that uses ground-mounted racking with assured ventilation will result in different module temperatures and thus different energy yields. In hot regions and roof-mounted projects, this effect cannot be ignored.

PVSyst's temperature losses are affected not only by the ambient air temperature in the meteorological data but also by the mounting configuration and ventilation conditions. Installations close to the roof surface tend to trap heat, which can lead to larger output reductions in summer. Conversely, ground-mounted installations or designs with generous racking height can expect wind-driven cooling, which may suppress temperature losses. When comparing design options, it is necessary to confirm that the temperature loss values reflect the on-site environment.

When comparing temperature conditions, it is important to note that even if the apparent difference in power generation is small, it can still affect long-term equipment lifespan and operational risk. In installation environments prone to high temperatures, stress on modules and peripheral equipment increases, raising the risk of degradation and failure. Some of these aspects may not be directly reflected in PVSyst results, but they are important considerations when evaluating design proposals.

In addition, in snowy or cold regions, attention must be paid to voltage rise at low temperatures. At low temperatures, the modules’ open-circuit voltage increases, so it is necessary to check that it does not exceed the allowable voltage of the inverter and connected equipment. Because the risks to be considered differ between high and low temperatures, evaluations based on regional conditions are required. By checking temperature-related settings and results while referring to the PVSyst manual, you can improve the safety and validity of the design proposal.

Differences in the installation environment involve not only temperature but also soiling, wind, rain, snowfall, salt damage, leaf fall, bird damage, and other factors. These conditions cannot all be fully reflected in energy yield simulations, but they do affect loss settings and maintenance planning. For example, in dusty areas soiling losses should be treated conservatively, and in snowy regions you must consider not only winter solar irradiation gains but also snow slide-off, snow loads, and the ease of snow removal.

In comparing design proposals, we not only check the numerical values of temperature losses but also assess whether a proposal is suitable for the site environment. Even a proposal that yields slightly higher power generation can be disadvantageous in long-term operation if its configuration tends to trap heat and is difficult to maintain. PVSyst's temperature conditions are an important evaluation criterion that links simulation accuracy with on-site suitability.

Evaluation Axis 7: Choose the proposal that is easy to explain in report outputs

When comparing design proposals in PVSyst, the clarity of the report output is also important. In practice, it is not enough for only the person who ran the simulation to understand the results. It is necessary to explain the differences between design proposals to many stakeholders, such as the client/owner, internal approvers, design reviewers, contractors, financial institutions, and O&M personnel. Therefore, whether the reports output by PVSyst are easy to use as comparison materials is also a factor to evaluate.

A good design proposal should not only have high power generation but also be easy to explain why it is reasonable. For example, if the report can demonstrate evidence such as low shading losses, suppressed temperature losses, inverter losses within an appropriate range, and wiring losses that are not excessive, it will be easier to convince stakeholders. Conversely, a proposal that has high power generation but contains unnatural items in the loss breakdown is likely to be questioned during explanations.

When using the PVSyst manual, it is important to understand the meaning of each item displayed in the reports. The reports contain a lot of information, such as annual energy production, performance ratio, specific yield, loss diagram, input conditions, equipment information, and shading settings. Being able to interpret these will be useful not only for comparing design proposals but also for explaining to third parties and for internal reviews.

When comparing reports, pay attention to standardizing the output format. If the displayed items and setting conditions differ for each proposal, the material becomes difficult to use for comparison. When placing multiple proposals side by side, it is important to organize them with the same metrics, the same units, and the same assumptions. For example, arranging annual energy production, energy production per kW, major loss items, shading loss, temperature loss, inverter loss, and clipping loss so they can be compared from the same perspective will make decision-making easier.

Also, the ease of explanation affects the period after a design proposal has been adopted. When comparing a facility’s future actual power generation with simulated values, if the initial assumptions are clear, it becomes easier to analyze discrepancies between the actual results and the simulations. To determine whether the differences are due to weather conditions, soiling or shading, or equipment malfunctions, it is important that the design-stage reports are well organized.

PVSyst reports function not merely as submission documents but as evidence of design decisions. When comparing design proposals, check not only the energy production and losses but also whether the output can be generated in a way that makes the assumptions and rationale understandable later on. Proposals that are easy to explain make it easier to build consensus both inside and outside the company and to accommodate design changes and reviews.

Evaluation Axis 8: Compare considering constructability and operational risks

PVSyst simulations are powerful for evaluating energy yield and losses, but when ultimately selecting a design proposal you must compare options including constructability and operational risks. A proposal that shows high energy yield in simulation is not necessarily the best option on site. If there are issues such as difficult construction, hard maintenance, difficult equipment replacement, complex wiring, or a high risk of shading and soiling, the long-term value will be reduced.

From the standpoint of constructability, we check module layout, racking plan, foundation locations, cable routes, equipment installation locations, delivery/access routes, and working spaces. PVSyst displays results mainly in terms of energy production, but on actual sites whether the layout is easy to construct affects the construction schedule and quality. A proposal that increases the number of modules through an impractical layout may look advantageous in total energy output, but it can lead to installation errors and difficulties in maintenance.

From the viewpoint of operational risk, we assess ease of inspection, fault isolation, access to replacement parts, changes in shading, changes in the surrounding environment, long-term degradation, and ease of cleaning. In particular, for rooftop installations and constrained/narrow sites, it is important whether people can safely approach after installation and whether inspection walkways are provided. Proposals that are difficult to maintain carry the risk of overlooking future declines in power generation or experiencing delays in repair response.

It is also necessary to take changes in the surrounding environment into account. Even in locations that currently experience little shading, adjacent plots may be developed, trees may grow, or additional equipment may be installed in the future. PVSyst simulations produce results based on the conditions set and do not automatically predict future changes. When comparing design proposals, we evaluate not only optimization for the current situation but also the margin to accommodate future changes.

When constructability and operational risks are taken into account, the option that maximizes energy production is not always optimal; a solution that balances energy production, cost, constructability, and maintainability can be the best choice. For example, even if the annual energy production is slightly lower, an option where wiring is easier to organize, inspections are easier to carry out, and the risk of shading is lower may lead to more stable long-term operation. By combining PVSyst’s numerical results with on-site practical perspectives, you can make more pragmatic, actionable decisions.

When using the PVSyst manual to compare design proposals, it is important not to treat simulation results as absolute answers but to use them as material for verifying whether a design can be implemented on site. Constructability and operational risks are difficult to quantify yet have a major impact on the success of a project. As the final evaluation criterion, be sure to include verification from an on-site perspective.

Using the PVSyst Manual to Translate Design Proposal Comparisons into Practice

When comparing design proposals in the PVSyst manual, it is important to comprehensively consider annual energy production, loss breakdown, solar irradiation conditions, shading, module layout, inverter capacity, temperature conditions, report outputs, constructability, and operational risks. A proposal with higher energy production may be attractive, but unless you verify that the result was derived from reasonable assumptions, can be constructed on site without undue difficulty, and can be operated stably over the long term, it cannot be considered the optimal option in practice.

Especially when comparing design proposals, clarifying the common conditions and the changed conditions is the starting point. If weather data, installation location, equipment specifications, and basic loss settings are not aligned, you cannot make a correct judgment by comparing them. First align the premises for comparison, and then interpret which design changes affected which results. PVSyst is an effective tool for visualizing these causal relationships.

To create comparison materials that are practical for use in the field, it is important not just to line up PVSyst reports as-is but to organize the key points needed for design decisions. Comparing annual energy production, energy production per unit capacity, major losses, shading impacts, temperature losses, inverter losses, clipping, construction considerations, and maintenance concerns from the same perspective makes it easier for stakeholders to make decisions. Being able to explain not only the numbers but the reasons those numbers arose improves the quality of comparisons between design proposals.

Also, comparing design proposals is not something that can be completed in a single iteration. By creating an initial design, running simulations in PVSyst, checking losses and risks, reviewing the layout and equipment configuration, and repeating the process of running simulations, the accuracy of the design improves. Instead of creating a perfect design from the start, it is important to identify areas for improvement from the comparison results and move toward a more rational design.

When reading the PVSyst manual, be mindful not only of the steps for operating the interface but also of how each setting affects energy production and losses. If you understand the meaning of the input conditions, it will be easier to find the cause when results look odd. Conversely, if you look at numbers alone without understanding what the settings mean, you may end up evaluating a design proposal based on incorrect assumptions.

The design option that should be chosen in the end is not the one with the highest power output, but the one that is best balanced for the project’s objectives. The evaluation axes to prioritize change depending on the project type—feed-in (sell-to-grid), self-consumption, battery-integrated, rooftop, ground-mounted, agrivoltaic, etc. By using PVSyst results and jointly assessing the business objectives, site conditions, construction plan, and maintenance plan, you can compare design options that are viable in practice.

If you cover the eight evaluation axes for comparing design proposals in the PVSyst manual, you can make well-explained design decisions that go beyond merely comparing energy yields. Rather than just reading the numbers, understanding the context behind them, communicating them clearly to stakeholders, and choosing a proposal that can be implemented on site is the quickest way to improve the quality of photovoltaic system design. When comparing proposals, use PVSyst not only as a tool for checking results but as a practical tool to improve designs and to advance consensus-building.