Five points to avoid hesitation when setting soiling losses in PVSyst

Table of Contents

• Why soiling loss settings in PVSyst become important

• Item 1: Do not treat soiling losses as a uniform fixed value

• Item 2: First organize how prone each site is to soiling

• Item 3: Consider slope, azimuth, and layout conditions together

• Item 4: Reflect cleaning and maintenance assumptions in the loss settings

• Item 5: Verify validity with comparative simulations and result screens

• How to turn PVSyst soiling loss settings into practical outcomes

Why soiling loss settings in PVSyst become important

For practitioners running energy production simulations in PVSyst, soiling loss settings are not merely a place to tweak a number at the end. Rather, they are highly practical assumptions used to bridge the gap between ideal generation conditions and actual on-site operation. Items like module capacity, azimuth, tilt angle, and PCS conditions are visually easy to compare and therefore tend to dominate design discussions. However, in real projects, no matter how well those conditions are arranged, an overly optimistic approach to soiling losses can quickly inflate annual energy projections. As a result, the numbers tend to lose persuasive power in internal comparisons or when explaining to clients.

Especially for those not yet familiar with PV simulation, there is a tendency to set soiling losses small at first to see higher energy production. That approach is understandable emotionally, but requires caution in practice. Soiling loss is not just a conservative number to reduce energy; it reflects site conditions including installation environment, ease of cleaning, surrounding conditions, and operational assumptions. In other words, how you set soiling losses indicates how closely you view the project under realistic assumptions.

Soiling losses may appear as a simple loss item, but in reality they are strongly linked to other design conditions. A different tilt angle alters impressions of how soiling remains, and whether the surroundings are mainly soil or gravel versus paved surfaces changes the thinking. A dense array layout that makes cleaning access difficult and a layout that ensures maintainability may not warrant the same soiling loss. If you use PVSyst in practice, treat soiling loss not as an isolated number but read it together with layout, maintenance, and environmental conditions.

Moreover, when soiling loss assumptions are well organized, it becomes easier to explain comparative proposals. Explaining why one proposal shows slightly lower annual energy, why the difference between proposals is not large, or why a given layout still has value becomes more coherent when soiling loss assumptions are included. Conversely, if this is vague, the resulting numbers tend to stand on their own without context. Understand that PVSyst soiling loss settings are an important task not simply for making conservative estimates, but for weaving real site conditions into the figures.

Item 1: Do not treat soiling losses as a uniform fixed value

The first point to keep in mind when setting soiling losses is to avoid treating them as a uniform fixed value. In practice, there is a temptation to reuse numbers from past projects or to adopt generally safe-seeming values unchanged. Of course, provisional values are necessary in initial studies. However, if you treat those as finalized assumptions, project-specific conditions become obscured. In PVSyst, differences in soiling loss matter less as absolute magnitudes and more as whether the numbers carry project-specific meaning.

For example, even within the same region, impressions of soiling change with surrounding environment and site conditions. A site dominated by paved surfaces with little dust feels different from one with many exposed soil areas during development, so using the same loss value may feel off. Further, thinking about soiling differs immediately after construction compared to once operations have stabilized. While PVSyst does not require entering all these conditions directly, you must decide how much of these differences to incorporate into the loss coefficient. In short, think of soiling loss not as a reused number but as a translation of condition differences.

Also, treating it as a uniform fixed value can mask differences between comparative proposals. One proposal may place arrays near buildings or roads and be more susceptible to dust or debris, while another may be farther from slopes or bare ground and thus somewhat gentler on soiling within the same site. If you evaluate all proposals with the same soiling loss, differences may appear to be determined only by configuration conditions. If you want meaningful practical comparisons, noticing such mismatches is important.

As a countermeasure, before deciding a soiling loss, quickly organize the conditions likely to influence soiling for that project and judge whether the project is suitable for a uniform assumption or requires more careful consideration. You don’t need to set fine coefficient differences for every project, but at least confirm whether a reused value naturally applies to the current site. To avoid hesitation in PVSyst, start by treating soiling loss as an assumption that carries project-specific meaning rather than a single fixed number.

Item 2: First organize how prone each site is to soiling

To set soiling losses practically, first organize how prone each site is to soiling. Although PVSyst only appears to require inputting a loss coefficient, behind that number are the site’s environmental conditions. Deciding a number without considering whether the surroundings are mainly soil or crushed stone, mostly paved, affected by traffic, near farmland or development, or influenced by sea breeze and blowing sand weakens the persuasiveness of the result.

In practice, people often focus only on the site itself and treat surrounding conditions lightly. However, soiling losses are not determined solely within the site. Factors including dust kicked up from adjacent roads, nearby construction or development progress, the condition of slopes and exposed land, and runoff patterns all matter. You don’t need to quantify all of these, but identifying which projects are likely sensitive to soiling is enough to change how you set losses. Even if PVSyst does not accept these differences directly, you should organize them as assumptions to reflect in the coefficients.

Also, within the same site, different areas may have different proneness to soiling. Areas near buildings, slopes, entrances, heavy equipment tracks, or low spots with poor drainage may not be suitable to assume the same conditions as other blocks. In practice, people often do not assign numerical differences this finely, but being aware these differences exist changes how you evaluate layout proposals and interpret comparison results. Soiling loss settings in PVSyst may look like uniform numerical inputs, but their quality depends on how well you read site condition differences.

As a measure, before simulation, review surrounding environment and site conditions to judge whether to take a conservative view on soiling losses or apply a general assumption. If you have multiple proposals, check which one is closer to a more soiling-prone environment to improve comparison accuracy. To avoid hesitation when setting soiling losses in PVSyst, first organize site-by-site soiling proneness in words, then proceed to quantify it.

Item 3: Consider slope, azimuth, and layout conditions together

To set soiling losses appropriately, do not separate them from tilt angle, azimuth, and array layout. In practice, soiling losses may seem to be determined only by environmental conditions, but impressions change depending on how equipment is arranged. A different tilt angle alters how soiling tends to remain, and differences in azimuth, row orientation, and array density affect cleaning ease and soiling distribution. Being aware of these relationships in PVSyst makes loss coefficient choices more practice-oriented.

For example, a proposal with a smaller tilt angle might look favorable for site utilization, but impressions of how soiling flows and remains may differ. Conversely, a proposal with larger tilt might restrict row spacing but change the soiling outlook. Regarding azimuth, the position relative to nearby roads or slopes can change which rows feel more soiled. When assessing soiling losses in PVSyst, do not treat the loss coefficient as an isolated number; read it together with array conditions.

Looking at layout relationships also makes it natural to evaluate cleaning and inspection ease. A proposal that secures ample access aisles versus one packed tightly to the limit will lead to different expectations for soiling accumulation. In practice, not just the number for soiling loss but also how much of that loss can be absorbed through operation is important. To connect PVSyst comparisons to practice, include maintenance conditions in your view.

As a countermeasure, when creating comparative proposals that vary tilt, azimuth, or row spacing, pause to consider whether it is acceptable to keep the same soiling loss value. You do not need to change the loss coefficient for every comparison, but check whether clearly different installation conditions are being assumed with the same premise. When setting soiling losses in PVSyst, it is important to consider not only the environment but also how equipment is placed.

Item 4: Reflect cleaning and maintenance assumptions in the loss settings

A commonly overlooked point when setting soiling losses is the cleaning and maintenance assumptions. Soiling losses are not determined by environment alone; their meaning changes depending on how the soiling will be handled operationally. Although PVSyst presents a single loss coefficient input, in practice this reflects cleaning frequency, inspection structure, accessibility, and availability of access aisles. In other words, soiling losses should be considered an assumption that includes operational conditions, not just natural conditions.

For example, a layout that secures good access and maintenance space may make inspections and remedial actions easier when soiling is noticed. Conversely, a layout that prioritizes site utilization and packs arrays tightly might increase nominal capacity but make soiling management harder in operations. In that case, applying the same soiling loss coefficient may not be appropriate. If you estimate losses in PVSyst, consider them together with layout maintainability.

Being aware of cleaning assumptions also makes it easier to explain proposals. You can explain why you took a slightly conservative view of soiling losses for one proposal and why you did not for another by referencing differences in layout and access. In practice, stakeholders will question not only the energy numbers but also whether those numbers are natural given the operational premises. If you want to make strong use of PVSyst results internally, include cleaning and maintenance assumptions when setting losses.

As a countermeasure, when setting soiling losses, confirm not only the site environment but also the ease of inspection and cleaning. When comparing layout proposals, if maintenance access differs, it is worth pausing to review the loss assumptions. To avoid hesitation in PVSyst, read soiling losses as a design assumption that includes operational conditions, not merely as a naturally occurring loss.

Item 5: Verify validity with comparative simulations and result screens

Finally, use comparative simulations and the result screens to verify the validity of soiling loss settings. Because PVSyst returns numbers once you input a loss coefficient, it is tempting to accept the assumption as-is. However, in practice you must reverse-engineer from the results to confirm that the number is truly appropriate. Whether a soiling loss is too large or too small is often hard to tell in isolation and becomes clearer through comparisons with other proposals or by checking consistency with final results.

For example, if two proposals that should not differ much based on layout or equipment conditions show a large annual energy gap, the way soiling losses were set may be over-influential. Conversely, if there are clear differences in surroundings or maintainability but results barely change, you may be treating soiling losses too uniformly. Use PVSyst comparisons not simply to choose the higher number but to check whether the loss coefficients are natural as design assumptions.

When reviewing results, check not only annual energy but also other losses and seasonal trends. Ensure that weighting soiling losses more heavily has not hidden other differences or produced inexplicable discrepancies. Because PVSyst returns your assumptions directly in the results, you can use unexpected result behavior to revisit your premises. In practice, this back-and-forth improves the quality of design decisions.

As a measure, after setting soiling losses, do not be satisfied with a single proposal; run at least one comparative scenario to view the differences. Then confirm whether annual values, monthly trends, and other losses are consistent. To avoid hesitation in setting soiling losses in PVSyst, it is more important to question and adjust the numbers based on results than merely to enter them.

How to turn PVSyst soiling loss settings into practical outcomes

What the five points above have in common is the principle of not treating soiling losses as a single loss number. Do not process them as a uniform fixed value; organize site-specific soiling proneness; consider tilt, azimuth, and layout together; include cleaning and maintenance assumptions; and finally verify validity with comparative simulations and result screens. When you follow this flow, soiling loss settings in PVSyst function as assumptions that bring design proposals closer to reality rather than corrections to lower numbers.

What matters for practitioners is not setting the soiling loss that yields the highest energy. What truly adds value is being able to explain why that loss is expected for the given project. If you organize site conditions, surroundings, tilt, array layout, and maintainability, simulation results become easier to use for internal comparisons and design discussions. Conversely, prioritizing appearance and setting losses small can later undermine design consistency.

Improving the accuracy of soiling loss settings also requires not relying solely on desk simulations. If site boundary, access routes, slopes, nearby roads, existing equipment, and ease of cleaning are vague, the assumptions about soiling loss become weak. To apply PVSyst figures to practice, repeatedly iterate between field understanding and simulation to confirm the meaning of the loss. Soiling losses are not only screen loss coefficients but also reflections of on-site operational conditions.

In that sense, when you want to progress on-site location checks or coordinate acquisition more reliably, utilizing iPhone-mounted high-precision GNSS positioning devices such as LRTK can be effective. If you can better organize on-site position information and site conditions, assumptions about layout and maintenance access when setting soiling losses in PVSyst become clearer. If you can form a flow where PVSyst raises desk comparison accuracy and LRTK supports field understanding accuracy, soiling loss settings evolve from simple coefficient inputs to grounded practical judgments. Carefully setting soiling losses not only improves the accuracy of energy yield forecasts but also strengthens the design capability that connects desk work and on-site realities.