Five Ways to Read PVSyst Report Comparisons｜Basics of Comparing Proposals

In designing and evaluating the feasibility of solar power plants, it is common to compare simulation results across multiple proposals. Changing tilt angle, orientation, panel capacity, racking layout, or loss assumptions will alter the report figures even for the same plant. However, if you judge plans solely by annual energy production without knowing where in the report to look, you will be unable to explain why differences occurred.

When comparing PVSyst reports, it is important not simply to pick the plan with the highest generation, but to check input assumptions, irradiance, system capacity, loss structure, monthly trends, and performance ratio in that order. This article organizes and explains five basics that practitioners searching for “how to read PVSyst” should keep in mind when comparing multiple proposals.

Table of Contents

• Do not judge PVSyst report comparisons by annual energy alone

• How to read comparisons 1: Check whether the assumptions are aligned

• How to read comparisons 2: Look at annual energy and energy per unit capacity

• How to read comparisons 3: Look at loss breakdowns, not just PR

• How to read comparisons 4: Examine monthly generation trends and seasonal differences

• How to read comparisons 5: Organize differences between proposals so they can be explained

• Common misinterpretations in PVSyst report comparisons

• A practical, easy-to-use comparison procedure

• Summary: In PVSyst comparisons, read through to the reasons for the differences

Do not judge PVSyst report comparisons by annual energy alone

The first thing that tends to catch the eye in PVSyst report comparisons is annual energy. A plan with larger energy output may superficially appear superior. In business evaluations, where it is directly tied to electricity sales or self-consumption, annual energy is certainly an important metric. However, judging a plan solely on energy is risky.

This is because annual energy is the composite result of many factors: system capacity, irradiance conditions, loss assumptions, installation angle, azimuth, shading, temperature conditions, wiring conditions, and conversion equipment capacity limits. For example, one plan’s higher annual energy may simply be due to a larger panel capacity. Conversely, a plan with lower annual energy may be generating efficiently relative to its smaller installed capacity.

The metrics you should look at depend on the comparison purpose. If you want to evaluate overall project profitability, annual energy is important. If you want to assess design efficiency, energy per unit capacity and PR matter. To check loss factors, you need to read the Loss Diagram breakdown. To confirm the reasonableness of installation conditions, you must verify assumptions like azimuth, tilt, irradiance, shading, and temperature conditions.

Comparing PVSyst reports is not just about “which plan generates the most,” but about interpreting “why that plan yields that energy.” In practice, you must confirm not only the magnitude of energy differences but whether those differences are reasonable from a design perspective, whether input conditions are correct, whether losses are set too high or too low, and whether the results are explainable.

When comparing reports prepared by multiple analysts in particular, differences in modeling philosophy can greatly affect results. Even for the same site and apparent equipment capacity, discrepancies in chosen weather data, terrain conditions, shading settings, wiring losses, soiling losses, temperature losses, transformer losses, and auxiliary losses will change outcomes. Therefore, report comparisons should not only line up result numbers side by side but also compare underlying assumptions and loss conditions.

How to read comparisons 1: Check whether the assumptions are aligned

The first thing to verify in PVSyst report comparisons is whether the assumptions are aligned. Comparing energy or PR when assumptions differ makes it impossible to determine whether differences stem from design variations or input differences.

First, check the project location information. Latitude, longitude, elevation, time zone, and the reference point for weather data can significantly alter available irradiance and temperature conditions. In mountainous areas, snowy regions, coastal zones, or areas with elevation differences, small location differences can change the interpretation of weather conditions. When comparing proposals, confirm that the same site conditions are used.

Next, verify the weather data conditions. Annual global horizontal irradiance, diffuse irradiance, ambient temperature, and wind speed directly affect generation. When comparing reports that use different weather data, part of the generation difference arises from the weather data rather than design differences. Therefore, as a rule, use the same weather data when comparing design proposals. If different weather data are used, explicitly show irradiance and temperature differences when comparing.

Always confirm equipment capacity. PVSyst reports show DC capacity, AC capacity, DC/AC ratio, number of modules, string configuration, and the number and capacity of conversion equipment. A plan with larger annual energy may simply have a larger DC capacity. When comparing proposals with different capacities, you should look at generation per kW or per kWp, not just annual energy.

Module installation conditions are also important comparison items. Azimuth, tilt, racking pitch, installation height, relationship with terrain, array orientation, and the presence of inter-row shading greatly affect generation characteristics. For example, increasing tilt may improve winter irradiance capture but affect summer performance, morning/evening shading, wind load, and land-use efficiency. Shifting orientation away from due south not only affects annual energy but also changes the distribution of generation throughout the day.

Shading settings are often overlooked. Results change depending on how near-field shading, far-field shading, terrain shading, inter-row shading, and surrounding obstructions are modeled. If one plan models shading in detail while another simplifies it, loss differences reflect modeling choices rather than design. When comparing multiple reports prepared by third parties, ensure the shading modeling granularity is consistent.

Also check loss assumption premises up front. Soiling loss, IAM loss, mismatch loss, DC wiring loss, AC wiring loss, conversion loss, transformer loss, auxiliary losses, and treatment of degradation are areas where analysts’ settings often differ. If only one proposal uses strict loss assumptions, its energy will look lower. Conversely, optimistic loss assumptions make a plan appear better on paper but weaken its practical explainability.

Checking assumptions is a subtle but foundational step. Skipping it prevents correct interpretation of PR and losses later. The basic workflow for PVSyst report comparison is to first confirm whether the reports are comparable under the same conditions, and then read the results.

How to read comparisons 2: Look at annual energy and energy per unit capacity

After confirming assumptions, view the annual energy. Annual energy is a key indicator showing the expected total electricity the plant can produce. It plays a major role in project planning, profitability evaluation, power contracts, and equipment sizing.

However, when comparing multiple proposals, you should look not only at annual energy but also at energy per unit capacity. For example, even if Proposal 1 shows higher annual energy than Proposal 2, if Proposal 1 simply has a larger DC capacity, it is not necessarily the more efficient option. When capacities differ, converting to annual energy per 1 kWp removes capacity differences and makes comparison easier.

Looking at energy per unit capacity reveals utilization efficiency and the design’s appropriateness. For example, densely packing panels may increase total energy but also increase inter-row shading and clipping losses from overloading, which can reduce energy per unit capacity. In such cases, you must decide whether to prioritize total energy, efficiency, land use, or investment efficiency.

Also checking energy relative to AC capacity shows how conversion equipment is being used. For proposals with large DC capacity, output clipping may occur during strong irradiance periods. While annual energy may increase, clipping losses can make the marginal gain per added panel diminish. In such cases, balance DC/AC ratio and conversion equipment capacity rather than simply increasing capacity.

PVSyst reports present multiple generation-related metrics: energy sent to grid, array output, post-conversion output, and final usable energy, each with different meanings. When comparing, ensure you are looking at the same stage of energy. If one plan reports array output and another reports grid interconnection point output, the comparison is not like-for-like.

In practice, viewing annual energy, energy per DC capacity, and energy per AC capacity side by side clarifies matters. Annual energy indicates project scale, energy per DC capacity shows panel capacity efficiency, and energy per AC capacity shows how conversion equipment and interconnection capacity are used. Reading these three together makes design decisions easier than a simple energy-only comparison.

It is also important to look at differences between proposals in percentage terms. For example, a 50,000 kWh absolute difference means different things for a plant of 1,000,000 kWh versus 10,000,000 kWh. Converting differences to percentages as well as absolute values helps assess their impact. In PVSyst report comparisons, view both absolute and relative differences to accurately grasp magnitude.

How to read comparisons 3: Look at loss breakdowns, not just PR

PR is a commonly used indicator in PVSyst report comparisons. PR indicates how efficiently the PV system converts irradiance into energy. It normalizes for differences in capacity and irradiance to a degree, so it is often used for comparing proposals or checking third-party reports.

However, determining a plan’s quality solely by PR is risky. A high PR may look like high efficiency, but that can be due to how losses are modeled. For instance, setting soiling loss low, minimizing wiring losses, omitting shading, or not accounting for auxiliary losses will raise PR. In other words, high PR does not necessarily mean a design is reasonable.

When looking at PR, always check the loss breakdown in tandem. PVSyst reports show how irradiance is reduced at each stage, how array output falls due to specific losses, what losses occur after conversion, and how final output is reached. Reading this flow lets you decompose the causes of energy differences.

First, check irradiance-side losses. Incidence angle losses, near-field and far-field shading losses, soiling losses, and the effects of reflection or ground surface conditions influence energy before it reaches the array. Large differences here may point to installation angle, azimuth, inter-row shading, surrounding obstructions, soiling conditions, or ground reflectivity as causes.

Next, check module-side losses. Temperature losses, low-irradiance characteristics, module quality, mismatch, degradation, and losses from array configuration fall into this category. Large temperature losses may be influenced by mounting style, ventilation, racking structure, and ambient temperature. Mismatch or quality losses depend on initial settings or conservative assumptions.

Then examine electrical losses: DC wiring losses, conversion losses, AC wiring losses, transformer losses, auxiliary losses, and output clipping. These are closely linked to practical design. Longer wiring distances increase wiring losses; transformer and inverter placement and sizing affect losses. High DC/AC ratios can increase clipping. Different treatments of auxiliary losses affect annual energy and PR.

In proposal comparisons, look not only at total losses but at which losses increased or decreased. A plan may show higher annual energy because increased shading and clipping were offset by greater capacity—meaning the energy increase only reflects added capacity. Conversely, a plan may show little change in annual energy while improving wiring or shading losses, which could be considered higher-quality design.

Also be mindful of what the loss percentages are relative to. Percent values mean different things depending on the denominator—whether it’s relative to irradiance, array output, or post-conversion output. Misinterpreting percent values without checking the stage they refer to can lead to incorrect conclusions. When comparing Loss Diagram figures, read them as a flow.

Viewing PR as an entry point is useful, but PR is a summary metric. What practitioners must verify is why the PR is what it is. For high- or low-PR proposals alike, ensure you can explain which losses are driving the PR.

How to read comparisons 4: Examine monthly generation trends and seasonal differences

After checking annual energy and PR, it is important to examine monthly generation trends. Annual figures alone do not reveal which seasons drive differences. PVSyst reports allow you to review monthly irradiance, temperature, generation, PR, and losses. Comparing these items reveals each proposal’s specific characteristics.

For example, two proposals with similar annual energy may differ seasonally—one strong in winter and another in summer. A steeper tilt may favor winter irradiance capture but limit summer gains. An east-west biased azimuth may reduce midday peaks while increasing morning and evening generation.

When comparing monthly values, first look at differences in irradiance. If multiple proposals use the same weather data, horizontal plane irradiance and ambient temperature are generally identical. However, plane-of-array irradiance changes with tilt and azimuth. If plane-of-array irradiance differs, it likely stems from installation conditions. Before looking at generation differences, check how plane-of-array irradiance varies.

Next, check monthly PR. Even if annual PRs are similar, monthly PRs may vary widely. PR declines in summer may indicate temperature losses; winter PR declines may indicate shading, snow, low irradiance, soiling, or ground reflectivity issues. If a particular month’s PR is unusually low, recheck input conditions and loss settings.

Shading impacts are also clearer month by month. In seasons with low solar altitude, inter-row or surrounding-object shadows extend, so annual shading loss may look small while winter mornings and evenings suffer large losses. When shading affects selling price or self-consumption timing, seasonal and time-of-day impacts matter beyond annual totals.

Check clipping by month as well. Overloaded DC capacity can cause clipping during periods of strong irradiance and low temperature, such as spring and autumn. Even if annual clipping loss seems small, it may concentrate in specific months. To assess overloading effects, compare generation increases from added capacity against clipping losses on a monthly basis.

Monthly trend analysis is also important for future comparisons with measured data. Annual comparisons can be confounded by weather variation or outages. Viewing monthly behavior makes it easier to identify where actual performance diverges from design assumptions. For example, if measured summer output is low, suspect temperature, soiling, curtailment, or equipment downtime. If winter output is low, investigate shading, snow, or low-irradiance behavior.

When comparing proposals in PVSyst, do not first decide superiority by annual totals and only afterward look at months; instead, use monthly breakdowns to explain annual differences. Reading monthly generation, PR, and losses shows which seasons a proposal is strong or weak, which is useful for design explanations and client communications.

How to read comparisons 5: Organize differences between proposals so they can be explained

Ultimately, the important task in PVSyst report comparisons is to organize differences between proposals in a way that allows explanation. Simply listing numbers makes the materials less useful for decision-making. In practice you must be able to explain not only which plan is better but why the difference arose, whether it is reasonable, and which plan to adopt.

When creating a comparison table, separate input assumptions, capacity conditions, generation, PR, and major losses. Include weather data, site, tilt, azimuth, shading settings, and soiling in input assumptions. Put DC capacity, AC capacity, DC/AC ratio, number of modules, and conversion equipment capacity under capacity conditions. List annual energy, energy per unit capacity, PR, and monthly trends under results. Put shading, temperature, wiring, conversion, clipping, and auxiliary losses under losses.

This separation makes it easy to trace where generation differences come from. For example, if Proposals A and B differ by 3% in annual energy, determine whether that difference stems from irradiance capture, capacity, or losses. Decomposing the difference simplifies explanations to stakeholders.

Also present differences in both absolute and relative terms. Showing energy differences in kWh alone is insufficient; indicate percentage increase or decrease relative to a baseline so impact is clear. For PR differences, show not only point changes but which losses produced the difference.

Choosing a baseline proposal helps organize comparisons. Comparing every proposal pairwise can become convoluted. Use a reference such as the as-built plan, a standard design, an initial design, or the most reasonable option, and show how other proposals increase or decrease relative to it. A clear baseline makes it easier to explain the effects of design changes.

Separate large-impact and small-impact items. Trying to explain every small difference at the same level of detail complicates the material. In practice prioritize items that significantly affect energy or PR and treat minor items as supplementary. For example, if most of an annual energy difference is explained by plane-of-array irradiance, you do not need to center the explanation on minor wiring loss differences.

It is also effective to present conclusions first in explanatory materials. For example: “Proposal B increases annual energy compared to Proposal A, but the main cause is increased installed capacity and energy per unit capacity slightly decreases.” Or: “Proposal C shows high PR, but its soiling loss assumption is lower than other proposals, so direct comparison requires caution.” Such phrasing conveys meaning clearly.

PVSyst report comparison is not mere transcription of numbers. It is the work of translating design, analysis, construction, operation, and business perspectives into a form usable for decision-making. Ultimately, aim to explain differences in energy, losses, and design assumptions as a coherent story.

Common misinterpretations in PVSyst report comparisons

There are common misinterpretations in practical PVSyst report comparisons. Avoiding these improves comparison accuracy significantly.

One common error is to unconditionally regard the plan with higher annual energy as better. Annual energy is important, but larger capacity naturally yields higher energy. When capacities differ you must also check energy per unit capacity or PR to compare efficiency. Particularly, proposals that maximize panel count may increase total energy but also increase shading and clipping, reducing efficiency.

Another common mistake is evaluating plans only by PR. PR is useful but heavily influenced by input and loss assumptions. Optimistic loss settings raise PR; conservative settings lower it. Therefore, check whether loss assumptions are realistic, especially when a proposal exhibits high PR.

Be careful with summing loss percentages. PVSyst losses are calculated in stages, so simply summing displayed percent values does not always equal the total loss. Understand which energy stage each loss percentage refers to. When comparing Loss Diagram values, read them in the flow.

Overlooking differences in weather data is another pitfall. Reports using different weather data will have different irradiance and temperature, and thus different results. Comparing energy or PR across such reports mixes design and weather differences. When comparing third-party reports, first check how much irradiance, temperature, and site conditions differ.

Differences in shading settings also cause misinterpretation. A plan with detailed 3D shading modeling will differ from one with simplified shading. Before judging small shading loss values as good design, verify that shading was properly modeled. This is essential for sites with terrain undulation, surrounding structures, or inter-row shading.

Electrical losses like wiring and transformer losses vary with settings, so they can diverge between reports. If actual wiring distances, conductor types, voltages, current, and equipment layout are not reflected, loss estimates may deviate from reality. When comparing, do not assume the plan with lower wiring losses is better without checking whether those values are based on realistic equipment layout and wiring conditions.

Also avoid judging by annual values without checking monthly values. Two plans with similar annual energy may have very different seasonal generation profiles. For projects where self-consumption or specific time-of-day value matters, annual energy alone is insufficient. Checking monthly—and sometimes hourly—trends yields decisions closer to operational reality.

A practical, easy-to-use comparison procedure

To perform stable PVSyst report comparisons in practice, follow the same procedure each time. Without a fixed order of checks you may cherry-pick numbers and miss important assumption differences.

First clarify the purpose of the comparison. Are you comparing for maximum energy, evaluating the effect of a design change, checking differences with a third-party report, or assessing project economics? The metrics to prioritize change with purpose. If the purpose is unclear, you will find it hard to decide whether to prioritize annual energy, PR, loss rate, or equipment capacity.

Next, align and verify assumptions. List site, weather data, DC capacity, AC capacity, azimuth, tilt, shading, and loss settings, and check whether the reports are comparable. If differences exist, state them as part of the comparison premise. Do not force noncomparable reports into the same table; instead, note that “this difference includes assumption differences.” This approach clarifies interpretation.

Then check annual energy and energy per unit capacity. After looking at absolute energy, check metrics that normalize capacity. This separates overall project effect from efficiency relative to equipment capacity.

Next, review PR and the Loss Diagram. After seeing PR differences, always return to the loss breakdown. Identify which losses—shading, temperature, soiling, wiring, conversion, clipping, or auxiliary—affect the difference. If you cannot explain a difference, review input conditions and model settings.

Also check monthly values. Identifying which months cause annual differences helps understand the effects of tilt, azimuth, shading, temperature, and clipping. Explaining seasonal trends improves persuasiveness in client discussions.

Finally, translate comparison results into explanatory text. Beyond tables, describe “which plan excels at what,” “which differences result from capacity,” “which stem from loss assumptions,” and “what to watch at adoption.” This narrative step is crucial in practice. It allows nontechnical decision-makers and clients to understand the comparison.

Additionally, manage source data carefully. Record report version, analysis conditions, creation date, and changes to trace differences later. As proposals increase, identifying the latest report or what was changed becomes difficult. Including version control information in file names or comparison tables reduces verification errors.

PVSyst comparison may feel complex at first. However, fixing the order of checks stabilizes judgment. Following the flow of assumptions, energy, energy per unit capacity, PR, loss breakdown, monthly trends, and explanatory text produces comparison materials suited to practical use.

Summary: In PVSyst comparisons, read through to the reasons for the differences

When comparing PVSyst reports, do not judge solely by annual energy or PR; read which assumptions and which losses produce the differences. A plan with larger energy may simply have larger capacity. A plan with a higher PR may be using optimistic loss assumptions. Conversely, a plan with slightly lower energy or PR may be more conservative in assumptions and thus easier to justify in practice.

The basics of comparison are: first verify assumptions. If site, weather data, equipment capacity, azimuth, tilt, shading, and loss settings are not aligned, you cannot simply compare results. Then read annual energy, energy per unit capacity, PR, loss breakdown, and monthly trends in that order. Finally, organize differences between proposals so they can be explained for design decisions and client communication.

What matters in reading PVSyst is not memorizing numbers but understanding the flow by which generation is produced: irradiance arrives, is reduced by incidence angle and shading, converted by modules and reduced by temperature and mismatch, further reduced by wiring and conversion, resulting in final energy. If you keep this flow in mind, report figures become information that explains the plant’s design condition rather than mere lists.

For proposal comparisons of solar plants, field verification in addition to desk analysis is important. If layout drawings, actual terrain, surrounding obstructions, racking positions, cable routes, and as-built conditions differ from modeling assumptions, simulated and actual generation behavior will diverge. If site verification and construction management are poor, assumptions about shading, azimuth, tilt, spacing, and wiring distance become ambiguous and you cannot fully utilize PVSyst comparisons.

To improve efficiency of site verification, using an LRTK, a GNSS high-precision positioning device that attaches to an iPhone, is useful. Obtaining high-precision position data on site and recording equipment positions and measurement points makes it easier to reconcile analysis conditions with actual conditions. Linking PVSyst-derived design hypotheses with on-site positioning data and construction records enhances accuracy across design, construction, and verification. Reading PVSyst correctly and combining it with field information leads to practical and usable proposal comparisons for solar power plants.