Six ways to interpret PVSyst results for explaining them to clients

In the design and business planning of solar power plants, how to interpret PVSyst analysis results is critically important. PVSyst is a representative tool for simulating annual energy production and performance ratio based on irradiance, ambient temperature, panel capacity, PCS capacity, tilt angle, azimuth, shading, and various loss conditions. However, when explaining to a client, simply presenting technical numbers as they are will not get the message across.

What the client wants to know is not the detailed calculation formulas themselves, but how much this power plant is expected to generate, whether that result is reasonable, whether there are major risks to the revenue plan, and what to pay attention to in the design. In other words, when explaining PVSyst results, it is necessary to distinguish between the interpretation intended for engineers and the way the results are presented to the client.

PVSyst reports contain a lot of information. There are several items to look at, such as annual energy production, monthly generation, Specific Yield, Performance Ratio, solar irradiance, Array Loss, System Loss, Grid Injection, and the Loss Diagram. However, when explaining to the client/owner, rather than treating everything with equal weight, organizing the explanation in the order of conclusion, basis, losses, seasonal variations, design conditions, and follow-up items makes it easier to understand.

In this article, we explain six key ways to interpret PVSyst results when communicating them to clients. This approach is also useful for explaining the design of a solar power plant, sharing expected generation, providing preliminary explanations for financial institutions, coordinating with EPC and O&M, and conducting internal reviews.

First, state the annual power generation as the conclusion

When presenting PVSyst results to the client, the first item to check is the annual energy production. The PVSyst report shows, as outcomes, the amount of electricity ultimately sent to the grid and the available generation. What the client is most concerned with is how much electricity the solar power plant is expected to produce over the course of a year.

If you start by explaining the details of solar irradiance and losses right away, it becomes hard to see the big picture. It is more natural to first present the expected annual power generation as the conclusion, and then explain the assumptions from which that generation estimate is derived.

For example, when explaining to a client, describe in order: how many kWh per year the entire power plant is expected to generate, how much generation there will be per 1 kW of installed capacity, and, on a monthly basis, which seasons have higher output and which have lower. This makes it easier for them to understand the plant’s performance as an image rather than just as numbers.

When looking at PVSyst's annual energy production, you need to pay attention to which point's energy is being considered. The meaning changes depending on whether it is the output of the PV array, the AC output after the PCS, or the energy injected at the grid interconnection point. When explaining to the client/owner, it is important to focus on the energy that ultimately affects the project's financial performance.

One thing to be especially careful about is that PVSyst contains multiple indicators of generated energy. The energy theoretically obtainable from the irradiance received by the solar cells, the DC energy produced by the modules, the AC energy after passing through the PCS, and the energy sent to the grid are each different stages. When explaining to the client, focus mainly on the values that ultimately relate to electricity sales or self-consumption, and supplement by describing what kinds of losses occur along the way; this will make the explanation more convincing.

When explaining annual power generation, it is necessary to carefully convey that simulation results do not fully guarantee future performance. PVSyst provides predictions based on meteorological data and system conditions, and actual power generation will vary due to weather, snowfall, soiling, power curtailment, equipment outages, maintenance status, and other factors. Therefore, it is important to explain to the client that the results should be presented not as guaranteed values but as expected values under certain conditions.

However, if you emphasize uncertainty too much, the client will become anxious. The important point is to communicate that, although projected values are subject to variability, by clarifying the assumptions and checking the loss factors you can assess the validity of the projected energy yield. The results from PVSyst serve as a reference value for considering the plant plan and as a foundation for comparing design and operational conditions.

Communicating Power Plant Efficiency with Specific Yield

When explaining PVSyst results to a client, judging a PV plant solely by its annual energy production can be difficult. Since a larger installed capacity will naturally yield a higher annual generation, raw generation figures alone cannot be used to compare a plant's efficiency or the appropriateness of its design. This is why Specific Yield becomes important.

Specific Yield is an indicator that shows the annual electricity generation per 1 kW of installed capacity. It is commonly expressed in units of kWh/kWp. By looking at this value, you can check how much electricity is being generated per unit of capacity, regardless of the size of the power plant.

When explaining to the owner, it helps to say that annual generation is the total output of the entire power plant, whereas Specific Yield is a metric that measures performance per unit of installed capacity. For example, even when comparing plants with different capacities, using Specific Yield makes it easier to compare which plant is generating more efficiently.

When looking at PVSyst's Specific Yield, it is necessary to take into account the solar radiation conditions of the target area. In regions with high insolation, Specific Yield tends to be higher, while in regions with low insolation or heavy snowfall it tends to be lower. Therefore, rather than judging good or bad based only on the numbers, it is important to interpret them together with the area's solar radiation, temperature conditions, snowfall conditions, tilt angle, azimuth, shading effects, and so on.

When explaining to the owner, Specific Yield can be used to describe the basic power generation efficiency of a plant. For example, even for plants with the same 1 MW capacity, the annual energy output can vary greatly. Those differences arise from solar irradiance conditions, design conditions, loss conditions, PCS capacity, shading, wiring losses, temperature losses, and so on. Specific Yield is a convenient metric to use as an entry point for explaining these differences to the owner.

Also, Specific Yield is a metric that is convenient for comparing with other projects. If there are past projects in similar regions or with similar installed capacity, comparing those values with the current PVSyst results allows you to check whether the expected generation this time is excessively high or low. However, when making such comparisons, be cautious: meteorological data, module specifications, PCS specifications, tilt and azimuth angles, shading conditions, and how output control is handled may differ, so simple comparisons can be misleading.

When conveying this to the owner, describing Specific Yield as "the power-generation performance per unit of capacity of this plant" makes it easier to understand. Instead of only presenting the technical term kWh/kWp, adding that it is a value showing how much electricity is generated per 1 kW of installed capacity in a year helps non-specialist owners understand.

Explain the validity of design and losses using the Performance Ratio

When communicating PVSyst results to the client, the Performance Ratio is a critically important metric. The Performance Ratio, abbreviated as PR, indicates how efficiently a solar power plant converts the solar irradiation it receives into final generated energy.

For the project owner, PR is a somewhat abstract metric, but it is useful when explaining a power plant’s design and the plausibility of its losses. While annual generation and Specific Yield tend to be higher in regions with greater insolation, PR can, to some extent, decouple differences in solar irradiance conditions and be used as a metric for assessing the system’s efficiency.

When explaining to the owner, it’s easier to say that PR is "an indicator that shows how efficiently the entire system converts solar irradiance into electricity after receiving sunlight." If PR is extremely low, temperature losses, shading, wiring losses, mismatch losses, PCS losses, output curtailment, soiling, snow accumulation, and similar factors may be having a large impact.

However, PR is not a simple metric where higher is always better. For example, in cold climates temperature losses are smaller, so PR can appear higher. On the other hand, in regions with low solar irradiance the annual energy production itself may not be large. Conversely, in regions with high irradiance and high temperatures, generation may be high but temperature losses can make the PR appear somewhat lower.

Therefore, when explaining to the project owner, it is appropriate to treat PR not as a substitute for generation output but as an auxiliary indicator for checking the power plant’s loss structure. A clear sequence is to present the overall business picture with annual generation, show generation performance per unit capacity with Specific Yield, and use PR to explain the system-wide efficiency and the reasonableness of losses.

When reviewing PR in PVSyst, it's also important to check which losses are affecting the PR. Module temperature losses, low-irradiance losses, IAM losses, shading losses, soiling losses, mismatch losses, DC wiring losses, PCS losses, and AC wiring losses accumulate to determine the final PR.

When communicating with the client, it’s important not just to provide the PR figure but also to briefly explain why that PR is what it is. For example, explaining that the design has minimal shading impact, that wiring losses fall within typical ranges, that PCS losses are based on equipment specifications, and how snow and soiling are being accounted for will increase confidence in the PVSyst results.

PR is often used to compare against other companies' reports or different cases. However, when making comparisons, you need to confirm that they were calculated under the same assumptions. If meteorological data, albedo, Soiling Loss, wiring losses, auxiliary losses, transformer losses, output control, or the treatment of PCS capacity differ, a difference in PR may be due to differences in input conditions rather than differences in design performance.

Explain where power generation is reduced in the Loss Diagram

In PVSyst reports, the Loss Diagram is useful for explaining things to clients. The Loss Diagram shows, step by step, where and to what extent losses occur as solar irradiance enters the PV array, becomes DC power, is converted to AC by the PCS, and is ultimately delivered to the grid.

For an owner, looking only at the power generation results makes it difficult to understand why the numbers are what they are. Using a Loss Diagram enables a visual explanation of the reasons for reduced power generation. Even with sufficient solar irradiance, small losses occur from temperature, shading, soiling, wiring, PCS, transformers, auxiliary equipment, and so on, making it easier to convey the flow that leads to the final generated power.

When explaining to the client, you don't need to read the entire Loss Diagram in detail. What's important is to clarify where the major loss items are, whether there are any unexpectedly large losses, and which losses can be controlled by design.

For example, temperature loss refers to the reduction in power generation efficiency caused by an increase in module temperature. This is influenced by the local ambient temperature, the mounting method, ventilation conditions, and module characteristics. It cannot be reduced to zero, but its impact can be mitigated to some extent by installation conditions and module selection.

Shadow losses are caused by surrounding terrain, trees, buildings, and shadows between mounting structures. It is necessary to explain to the client how the impact of shading on energy production is estimated in PVSyst. In particular, for projects on developed sites, in mountainous areas, on former golf-course sites, in snow-prone regions, or on sites with complex topography, the effects of shading and terrain are important.

Wiring losses occur on both the DC side and the AC side. They vary depending on cable length, current, voltage, cable size, PCS arrangement, and so on. When explaining to the owner, it is advisable to confirm and communicate that the wiring losses fall within the typical range and are not excessive in the design. If PCS are distributed, DC wiring tends to be shorter; if they are centralized, verifying wiring conditions becomes more important.

PCS losses are the losses that occur when converting direct current (DC) to alternating current (AC). A PCS has a conversion efficiency, and not all of the power is converted to AC as-is. In PVSyst, losses are calculated based on the PCS efficiency curve and the capacity settings. For the client, it is easiest to explain them as the normal losses due to PCS conversion.

What is important in a Loss Diagram is not to portray losses as something inherently bad. In a solar power plant, temperature losses, wiring losses, PCS losses, and the like will inevitably occur. The question is whether the losses are within a reasonable range, whether anything has been overlooked, and whether the assumptions are overly optimistic. When communicating with the client, explaining that you have organized the losses not to hide them but as the basis for the projected power generation will make for a more credible explanation.

Convey seasonal variations with monthly results

When reporting PVSyst results to the project owner, you need to check not only the annual generation but also the monthly results. Solar power generation undergoes seasonal variations in solar irradiance, which can cause large changes in output. Even if the annual generation appears sufficient, a month-by-month view may reveal a significant drop in winter or reduced output during the rainy season.

For the client, monthly results are important for getting an operational sense of the power plant. Annual generation figures alone can make it appear that generation is evenly distributed throughout the year.

However, in reality, some projects produce more from spring through summer and less in winter, and in snowy regions winter generation can drop significantly.

When reviewing PVSyst's monthly results, check the monthly irradiation, monthly energy production, monthly PR, and monthly temperature conditions together. It is natural for months with low irradiation to have low energy production, but if there are months where production is extremely low relative to irradiation, you need to check for the effects of snow, shading, output limitation (curtailment), assumed equipment outages, temperature conditions, soiling, and other influences.

When explaining to the client, it is easier to understand if you convey, in addition to the annual total energy production, which months produce more and which produce less. For example, explain that production tends to increase from spring to early summer, that in summer there can be temperature-related losses despite high solar irradiance, and that in winter production is lower due to reduced solar irradiance and the effects of snowfall.

In snowy regions, explaining the monthly results is especially important. If snow remains on the panels for periods of time, electricity generation will drop significantly. How PVSyst treats snow varies depending on settings and input conditions, so you should organize and communicate to the client how much snow impact you expect and whether it needs to be considered separately as a risk.

Monthly results also affect the outlook for revenue from electricity sales and the benefits of self-consumption. If the selling price of electricity is constant, annual generation becomes the primary factor, but for self-consumption projects the relationship with the demand curve is important. It is necessary to check whether the times of day and seasons with high generation align with the facility’s electricity demand.

In briefings for the project owner, monthly results can be used to communicate the power plant’s seasonal characteristics. By organizing which months have high generation, which have low generation, the reasons for those differences, and the seasons that require special attention, the owner can more easily form an image of conditions after operations begin. Because this information feeds directly into planning for O&M, inspection timing, grass cutting, snow removal, panel cleaning, and PCS inspections, monthly results are not merely a breakdown of generation but serve as reference information for operational planning.

Summarize the prerequisites and risks at the end

When conveying PVSyst results to the client, what you should always summarize at the end are the assumptions and risks. The energy production from PVSyst is a simulation result based on the input conditions. In other words, if the input conditions change, the results will change as well. When explaining to the client, you need to make clear not only the results but also which assumptions those results are based on.

The primary prerequisite to verify is the meteorological data. In PVSyst, energy production is calculated using meteorological data such as irradiance and temperature. Confirm which data source was used, whether the data is from near the site, and whether it is reasonable as a long-term average. Explain to the client that the expected energy production is based on meteorological data and will vary depending on actual year-to-year weather.

Next are the installation conditions. Module capacity, PCS capacity, tilt angle, azimuth, racking layout, string configuration, cable conditions, transformer conditions, and so on affect the PVSyst results. Inform the owner that these results are based on the current design conditions, and that if the design is changed the energy generation may also change.

Loss assumptions are also important. Soiling Loss, shading loss, wiring loss, PCS loss, transformer loss, auxiliary equipment loss, output limitations, etc., can significantly affect the results. When explaining to the project owner, you do not need to go into detail about every loss and the extent assumed for each, but you should make clear the items that have a major impact on power generation.

Clients are particularly concerned about whether the estimated power generation has been overestimated. Therefore, explaining how you handle risks such as soiling, shading, snow, output curtailment, and equipment downtime—not just optimistic conditions—will provide reassurance. Conversely, if you present only the estimated power generation while leaving the risks vague, it will be difficult to explain later when actual results differ.

When communicating PVSyst results to the client, transparency in the explanation is as important as numerical accuracy. Explaining the annual energy production, Specific Yield, PR, the Loss Diagram, monthly results, and assumptions in a single flow makes it easier for the client to understand what the results mean.

Also, PVSyst results do not complete the design review by themselves. In actual construction and operation, site topography, surveying accuracy, pile positions, racking layout, construction tolerances, land development conditions, and surrounding obstructions can also affect power generation performance. If the conditions assumed at the design stage differ from the actual site conditions, shadowing patterns, the scope of construction, and maintainability may be affected.

In such on-site checks, position verification using smartphone RTK or GNSS positioning is effective. By using a system like LRTK that combines an iPhone with a high-precision GNSS to verify on-site positions, it becomes easier to handle on site the layout shown on drawings, stake positions on site, the site development extent, point cloud data, and as-built verification. If you can link and verify the design conditions in PVSyst with the on-site situation, explanations to the client will become more concrete.

What matters to the owner is not just the PVSyst results themselves. It is that those results align with the site conditions, that the plant after construction matches what was assumed, and that it makes clear what points should be checked during operation. By conveying how to interpret PVSyst in combination with on-site verification and construction management, it becomes not merely an explanation of a simulation but an explanation of the overall quality of the power plant.

Summary

When presenting PVSyst results to a client, it is important not to simply list technical numbers but to organize them in an order that makes it easy for the client to make a decision. First present the annual energy production as the conclusion, then explain the generation performance per capacity using the Specific Yield, and check the overall system efficiency with the Performance Ratio. After that, use the Loss Diagram to explain where generation is being lost, present the monthly results to convey seasonal variations, and finally summarize the assumptions and risks.

The results of PVSyst do not fully guarantee the future performance of a power plant. However, if they are interpreted after clarifying the meteorological conditions, equipment conditions, loss assumptions, and design conditions, they provide the project owner with extremely useful information for decision-making. What matters is not emphasizing the power generation figures alone, but clearly communicating the basis from which those figures are derived.

When explaining to clients, it is important to strike a balance between avoiding difficult technical terms and not omitting necessary technical rationale. If you present the information in the order of annual energy production, Specific Yield, PR, losses, monthly variability, and assumptions, even clients who are not familiar with PVSyst will find it easier to understand the power plant’s performance and risks.

Furthermore, connecting PVSyst results with on-site verification and construction management increases the persuasiveness of your explanations. Confirming whether the design conditions are being reproduced in the field, whether there are discrepancies in shading or terrain conditions, and whether the as-built outcome after construction matches the plan also affects the reliability of the projected power generation. Thinking about how to interpret PVSyst not only as a desk analysis but including on-site verification leads to explanations that are easier for the client to understand and more practical for use in the field.