Eight settings to review when PR looks low in PVSyst

Table of Contents

• First things to consider when PR looks low in PVSyst

• Setting 1 Review consistency between meteorological data and the installation site

• Setting 2 Confirm that azimuth and tilt angle assumptions match site conditions

• Setting 3 Review the 3D scene and shading settings

• Setting 4 Inspect module settings and the treatment of temperature losses

• Setting 5 Check string configuration and mismatch conditions

• Setting 6 Reexamine PCS settings and how the DC/AC ratio is set

• Setting 7 Organize various loss coefficients such as wiring loss and soiling loss

• Setting 8 Reframe availability losses and downtime assumptions realistically

• Perspectives for turning PVSyst PR improvements into practical decisions

First things to consider when PR looks low in PVSyst

When a simulation in PVSyst shows a PR that looks lower than expected, many practitioners feel uneasy. Especially when PR—rather than raw energy—is low, it’s easy to suspect a major flaw somewhere in the design. However, the important point is not to jump to conclusions based solely on the PR number. PR is an indicator that reflects a stack of assumptions, so there is rarely a single reason for a low value.

In practice, while attention often focuses on module and PCS selection, the causes that depress PR are frequently dispersed across multiple settings: meteorological data, shading, temperature, wiring, strings, loss coefficients, downtime assumptions, and so on. Therefore, changing only one item at random often won’t significantly improve the numbers unless the root cause is addressed. It’s important to first prioritize which settings are most likely to strongly affect PR and review them in order.

Also, a low PR does not necessarily mean the simulation is wrong. If site conditions are restrictive and shading or aisle conditions are properly considered, a modest-looking PR may be appropriate. Conversely, assumptions that are too idealized can produce an overly optimistic PR. In practice, what matters is not the absolute height of the number but being able to explain what assumptions produced it.

Here, I organize and explain eight settings that practitioners should prioritize when PR looks low in PVSyst. It is important to read them not as isolated items but as interrelated factors. Inspecting them in sequence makes it easier to narrow down the main contributors depressing PR and clarifies the direction for design adjustments.

Setting 1 Review consistency between meteorological data and the installation site

The first thing to check when PR looks low is the consistency between the meteorological data and the installation site. In PVSyst, not only the generation but also the apparent PR are heavily influenced by how meteorological conditions are represented. If the meteorological data assumptions are misaligned with the installation site, the modeled irradiance and temperature conditions can differ from reality, which will change the impression of PR. No matter how carefully equipment conditions are set, the overall comparison won’t be stable if this is off.

In practice, it’s common to use data from a representative station near the candidate site or to reuse data from a neighboring station used in a previous project. That approach is natural in preliminary studies, but it’s a separate question whether those assumptions are truly appropriate for the current site. Differences in elevation, surrounding topography, and whether the site is coastal or inland can alter not only irradiance but also apparent temperature conditions. If PR is lower than expected, you should first question whether this initial assumption is misaligned.

Also, review monthly patterns as well as annual values. Even if annual irradiance isn’t far off, a different monthly distribution can change how PR appears. Checking whether the low PR is concentrated in particular seasons or persistent year-round helps reveal meteorological data–related anomalies. When comparing options in PVSyst, mismatches between site conditions and meteorological data make it hard to interpret PR differences as design differences.

Therefore, when PR looks low, stop and confirm the relationship between the installation site and the meteorological data. Reorganizing which station was used as the basis and how well that station represents the site often clarifies the results. The first step to improving PR is not to doubt the equipment but to verify whether the meteorological assumptions are reasonable.

Setting 2 Confirm that azimuth and tilt angle assumptions match site conditions

Next, review the azimuth and tilt angle assumptions. In PVSyst, aligning azimuth and tilt toward ideal conditions generally improves apparent generation. However, if the chosen orientation or tilt is inconsistent with actual site or earthworks conditions, the PR figure can become artificially odd. In practice, what’s important is not the condition that produces the cleanest numbers but whether the assumptions reflect what can realistically be implemented on the site.

For example, if the tilt requires extensive earthworks or the azimuth is unnatural given the site shape, the consistency with other loss assumptions is likely to break down. If row spacing or shading settings don’t match that “ideal” orientation, the result won’t just be a low PR; the overall scenario becomes hard to justify. When interpreting PVSyst results, treat azimuth and tilt not as mere input values but as assumptions that underpin shading and array design.

Also, if annual generation looks reasonable but PR feels inconsistent, the angle assumptions may be responsible. If the azimuth or tilt is biased toward an ideal, the relative relationships among loss items can skew PR. Conversely, reverting to site-consistent assumptions may slightly change generation but increase confidence in the PR. In practice, consistency of assumptions is often more important than absolute numbers.

When PR looks low, check whether azimuth and tilt really reflect site conditions. Review slope direction, existing structures, aisle locations, and earthworks policy to judge whether the angles are natural. To use PVSyst results in practice, treat orientation and tilt as expressions of site conditions, not just numbers.

Setting 3 Review the 3D scene and shading settings

A very common cause of low-looking PR is the 3D scene and shading settings. In PVSyst, how you create Near Shading and the 3D scene changes how shading losses appear. If shading assumptions are too lax or too strict, the impression of PR will vary. Projects where self-shading within the site mixes with shading from nearby buildings or trees are especially sensitive; the precision and organization of the 3D scene greatly affect PR interpretation.

In practice, the workflow often ends up placing arrays close together first and checking shading last. However, if shading has a strong effect, that can change the meaning of the layout itself. If row spacing, aisles, edge clearances, slope positions, or obstacle heights and distances don’t match the site, the losses shown as depressing PR can appear misaligned with reality. When evaluating shading in PVSyst, it is more important that the scene reflects the main shading causes accurately than that the 3D view looks tidy.

Also, in shading evaluation, you want to check not only annual loss totals but which seasons, times of day, and which rows are most affected. A shadow concentrated in winter mornings has a different implication from a slowly accumulating year-round shadow. Being aware of which strings or sections see partial shading helps interpret the effect electrically rather than as mere shaded area. Don’t short-circuit to “shading is bad” just because PR is low—differentiate shading characteristics.

Therefore, when PR looks low, review the 3D scene assumptions, Near Shading settings, obstacle organization, and how row spacing interacts with tilt. If you have comparison cases, fixing the shading assumptions and then changing the layout to see how much difference arises clarifies shading contributions. To improve PR in PVSyst, trace shading losses back to how those shadows were generated, not just look at the loss rate.

Setting 4 Inspect module settings and the treatment of temperature losses

Module settings and how temperature losses are treated are easy to overlook as causes of PR decline. In practice, attention tends to focus on module capacity, dimensions, and compatibility with PCS, while temperature-related losses are treated as a single loss coefficient. However, in PVSyst temperature impacts significantly affect annual generation and PR. Moreover, this loss depends not only on ambient temperature but also on array density, ventilation, and the surrounding environment, so applying a blanket assumption can diverge from reality.

For example, even within the same region, modules on open flat land feel different thermal conditions than modules in dense installations with many structures nearby. Changing tilt or row spacing alters ventilation, which can change how temperature losses appear. When PR is low in PVSyst, don’t only suspect shading and wiring; check whether temperature losses are stronger than expected.

Also, separating module settings from temperature losses flattens the depth of comparisons. A module option that looks superior on paper may close the gap once temperature conditions are included. Conversely, options that seemed similar at first can show a clear practical difference when temperature is considered. PVSyst is not just a tool to compare equipment nameplate differences but to see how equipment behaves under site conditions.

When PR is low, break down module settings and temperature-loss assumptions. Organize whether the cause is equipment selection, temperature expectations, or differences in ventilation due to layout. Treat temperature losses in PVSyst as a central loss factor that can strongly influence PR rather than a minor adjustment; this changes how you interpret results.

Setting 5 Check string configuration and mismatch conditions

When PR is low, checking string configuration and mismatch conditions is essential. In practice, one may accept a module count and PCS capacity as satisfactory, but in PVSyst the way they are grouped affects generation and PR. If a single string contains columns that receive different shading, columns with slightly different orientation or tilt, or sections with different temperature conditions, mismatch losses can manifest in the numbers.

For example, forcing edge rows with different conditions into the same grouping or treating sections separated by an aisle as a single group can produce neat-looking configurations on paper but substantial internal variation. When PVSyst shows a low PR, the cause is not always simple shading or temperature; it can be mismatch from the configuration. This is especially true in complex site geometries or multi-block projects where ignoring this effect accumulates errors.

Also, layouts with poor string grouping are often disadvantageous for maintenance and fault response, which can affect availability losses and long-term outlooks. In practice, don’t just look at generation; reinterpret why the loss arises as a potential design-organization issue. PVSyst shows not only whether a configuration is feasible but also whether that configuration is natural.

Therefore, when PR looks low, check whether elements with large condition differences are mixed within the same string and whether the way array sections are grouped is forced. If you have comparison cases, changing how strings are cut and observing PR movement reveals mismatch-driven impacts. Remember that improving PR in PVSyst sometimes means revising circuit groupings rather than equipment specs.

Setting 6 Reexamine PCS settings and how the DC/AC ratio is set

PCS settings and how the DC/AC ratio is set are also critically important causes of an apparently low PR. In practice, module-side capacity is often decided first and PCS is then allocated, but whether that balance is natural affects how clipping and conversion losses appear. When PR looks low in PVSyst, don’t just inspect PCS conversion efficiency—review how the DC side is stacked against the AC side.

For example, a heavily overbuilt DC-heavy case may increase annual generation but also produce strong clipping effects that lower the perceived PR. Conversely, giving too much headroom on the PCS side might make the configuration simple but leave DC potential underutilized. PVSyst should be used to find where that balance is natural rather than to chase the highest number.

Also, PCS settings tie into string configuration and wiring losses. If the PCS feed arrangement is strained, the outcome can show up not just as clipping but as a general lack of coherence in the proposal. Reviewing PCS is therefore not only about changing equipment but about reassessing the proposal’s overall balance. Without this perspective, an option can look good numerically while being weak in justification.

If PR seems low, check not only PCS parameters but the DC/AC assumptions and the rationale behind the chosen ratio. As a comparison, slightly varying the ratio and observing how clipping and PR move helps narrow down the cause. Improving PR in PVSyst requires reinterpreting the entire DC–AC relationship in the design conditions, not only PCS efficiency.

Setting 7 Organize various loss coefficients such as wiring loss and soiling loss

When PR is low, be sure to revisit loss coefficients like wiring loss and soiling loss. Practitioners often reuse numbers from past projects or apply uniform values, but array layout, aisle conditions, site extent, and surrounding environment differ, so the same coefficients may not be appropriate. Because PVSyst ultimately aggregates to annual generation, these subtle losses can accumulate and strongly affect the impression of PR.

For example, in a wide, dispersed site wiring losses will present differently, and in a site with many bare-earth areas the approach to soiling losses will differ. A dense array that’s hard to clean and another layout that facilitates maintenance should not automatically share the same soiling loss. Ignoring these condition differences and applying one-size-fits-all coefficients blurs differences between options and hides root causes. When reading PR in PVSyst, confirm what each loss coefficient is intended to represent.

Also, don’t just inspect coefficients individually—identify which losses are dominant. What is the primary driver: shading, temperature, wiring, or soiling? That determines what to address next. When PR looks low, don’t simply adjust numbers downward uniformly; identify which losses are strong and restore assumptions that match the project.

Therefore, when reviewing PVSyst results, check the loss tree and each loss item to determine which coefficients look natural and which appear overstated or understated. Improving PR is not merely raising a number but aligning loss assumptions with site conditions. Items like wiring and soiling, which are easy to overlook, are worth careful review.

Setting 8 Reframe availability losses and downtime assumptions realistically

Finally, review availability losses and downtime assumptions. In practice, there’s a tendency to view generation under the assumption of ideal continuous operation, but in the field there are always factors that reduce uptime: inspections, cleaning, failures, communications issues, and delayed recovery. If availability losses are set too optimistically in PVSyst, generation may look high while PR interpretation diverges from field experience. Conversely, if they are set unreasonably high, even strong proposals can look weak in the long term.

What’s practically important about availability losses is not to compress stoppage causes into a single fixed value. Planned outages like scheduled maintenance carry different implications for design than unpredictable failures or delayed recoveries. Designs with poor maintenance access, complex equipment zoning that’s hard to isolate, or difficult site access will show different availability characteristics even with the same equipment. To evaluate PR correctly in PVSyst, read the numbers including these operational conditions.

Availability losses also connect with shading, soiling, and maintainability. An arrangement that’s easy to clean may allow lighter soiling and downtime assumptions, while a layout with few aisles may require accounting for longer recovery times. In short, availability losses are not a standalone loss but a reflection of both design and operation. Reviewing this area when PR looks low often unexpectedly clarifies the entire set of assumptions.

As a countermeasure, when setting availability losses, first verbally organize the project’s maintainability, monitoring setup, and ease of recovery. When creating comparison cases in PVSyst, confirm whether uniform availability assumptions are appropriate or whether maintenance conditions differ. Making PR usable in practice requires aligning assumptions not only with theoretical yield but also with how the plant will actually be operated.

Perspectives for turning PVSyst PR improvements into practical decisions

What the eight settings have in common is that PR should not be treated as a mere outcome metric. Meteorological data, azimuth, tilt, shading, temperature, strings, PCS, loss coefficients, and availability losses are not independent; they overlap and together determine the final PR. Therefore, when PR looks low, the focus should not be on suspecting a single setting but on sequentially organizing which assumptions are dominantly affecting the result. Thinking of PVSyst as a tool that facilitates comparison and decomposition makes it easier to use.

What really matters for practitioners is not creating the highest PR scenario. What’s valuable is being able to explain why that PR has that value. A high PR that doesn’t match site conditions is fragile and likely to break later. Conversely, a modest PR that is realistically organized—including shading, temperature, wiring, and downtime assumptions—constitutes a robust design. Use PVSyst comparisons not as a number contest but to check which option is built on the most credible assumptions.

Also, to truly improve the precision of PR, don’t confine yourself to desk simulation. Ambiguities in site boundaries, slopes, aisles, nearby buildings, existing equipment, and maintenance access make assumptions fuzzy. Using PVSyst in practice requires repeatedly reconciling site understanding and simulation so you can determine which settings are natural and which are overly optimistic. PR is not merely a calculation result; it’s a reflection of site conditions.

In that regard, when you want to secure position and coordinate information more reliably in the field, it can be effective to use an iPhone-mounted GNSS high-precision positioning device such as LRTK. If site position data and conditions captured in the field are easier to organize, the layout assumptions, obstacle conditions, aisle conditions, and maintenance assumptions used to improve PR in PVSyst become clearer. By increasing desk-comparison accuracy with PVSyst and supporting field data accuracy with LRTK, improving PR becomes less about mere numerical adjustment and more about grounded practical judgement. Careful interpretation and improvement of PR not only increase the accuracy of energy forecasts but also strengthen the design capability that connects desk work and the field.