In this document
This document explains how to find and read the PV system losses section in Solargis Evaluate, and how each loss value in the section is calculated.
Accessing PV system losses
The PV system losses page is available in Solargis Evaluate under the Analysis section of the left navigation panel. To open it, expand Analysis, and select PV system losses.
The page is divided into two tabs — Yearly and Monthly — allowing you to switch between an annual summary and a month-by-month breakdown of losses.
Yearly losses
The Yearly tab offers an easy-to-read summary of PV system performance and its inefficiencies. It is a good starting point for system performance investigation and optimization, allowing you to identify the largest sources of inefficiency at a glance.
The yearly view contains two components:
The Energy conversion and related losses table — a detailed numerical breakdown of all losses.
The Loss diagram — a visual summary of cumulative losses.
Energy conversion and related losses table
This table shows how incoming solar energy is reduced step by step throughout the system, from the initial solar resource to the final energy delivered to the grid. Losses are organized into three groups: input and optical losses, conversion losses, and electrical losses.
Each row in the table represents one step in the energy conversion chain. The following columns are present for each step:
Energy output / PVOUT specific [kWh/m² or kWh/kWp]: The energy output at this step as calculated by the Solargis Evaluate PV Simulator.
Energy loss [kWh/m² or kWh/kWp]: The energy output of the previous step minus the energy output of this step.
Energy loss partial [%]: The proportion of the energy output in this step to the energy output of the previous step.
Energy loss relative to previous [%]: The proportion of the energy loss in this step to the energy output of the previous step.
Energy loss relative to input [%]: The total energy loss from the first step of the section to the current step, expressed as a percentage of the energy output at the first step of the section.
Performance ratio cumulative [%]: Tracks overall system efficiency after each loss step. For optical losses, it is the proportion of the energy output at this step to the first step in the section. For electrical losses, it is the proportion of PVOUT specific at this step to the total GTI reference value. The final value represents the portion of initial solar energy delivered as usable electricity.
Note: All values shown in the table are rounded, so sums may not add up precisely. This is expected, as sums are calculated internally with higher accuracy.
The table is divided into three sections. Because each section uses a different reference, the baseline for the Energy loss relative to input column differs per section:
Input and optical losses: Reference is the global tilted irradiation (GTI) on the front side and rear side separately. Shows the initial irradiation values and stepwise reductions from shading, soiling, angular, and spectral effects on both module sides.
Conversion and electrical losses: Reference is the conversion of irradiation to DC in the modules. Lists losses from inverters, cables, transformers, and auxiliary systems.
Unavailability losses: Reference is the previous step — there is no shared common input value for this section. Includes internal unavailability, external unavailability, and snow losses.
Note: Optical and electrical losses are calculated within the simulation. Unavailability losses are calculated post-simulation. This is why the baseline differs between sections.
For the performance ratio calculation in the electrical losses section, Solargis Evaluate uses total GTI including rear side efficiency derating as the reference value. It is calculated as:
Where:
is the GTI on the front side of the module with horizon shading included. is the GTI on the rear side of the module with horizon shading included. is the bifaciality coefficient, specific to the PV module used in the system design. The coefficient expresses the efficiency of the rear side of the module in converting incoming solar radiation into electric current relative to the same efficiency of the front side. The value of this coefficient is typically 0.8 (80%).
This input GTI reflects real-world conditions, where the horizon-shaded solar radiation represents the ideal system input while accounting for the decreased efficiency of the rear side of the PV module.
Note: In some examples, global tilted irradiation on the front side and GTI effective may appear equal. This is coincidental and can naturally occur between other values as well.
At the bottom of the table, the capacity factor is shown. It is calculated as the ratio of the total system performance — considering technical availability and losses due to snow — to the theoretical maximum annual production. This theoretical maximum assumes that each installed kWp produces 1 kW continuously, 24 hours a day, year-round. The capacity factor is therefore obtained by dividing the total system performance by 8,760 kWh/kWp.
Loss diagram
Below the table, the Loss diagram presents a visual summary of the system's cumulative energy losses — both solar and electrical. It provides a view of where and how much energy is lost at each stage.
The calculation follows the values in the Energy loss relative to previous column (column 4) of the losses table. For bifacial systems, the optical losses (shown in grey) are calculated with respect to the sum of the front and rear side GTI, without consideration of the bifaciality factor.
Note: Shading losses (near) in the Loss diagram may appear high for bifacial systems. This is caused by the summing of optical losses for the front and rear sides of the PV module — rear side near shading losses can easily reach 50% of the rear GTI. The Loss diagram should always be read in conjunction with the energy conversion and related losses table.
Note: Each additional loss displayed is calculated from the previous cumulative loss value, not from the initial total power value. As losses accumulate, each subsequent loss is discounted from the remaining power output after all previous losses have already been accounted for.
Monthly losses
The Monthly tab provides a month-by-month breakdown of the same losses shown in the yearly view. Seasonal variations in environmental conditions throughout the year — primarily changes in the sun's path and ambient temperature — affect the performance of a PV power plant. The monthly breakdown enables the analysis of seasonal patterns, supports the identification of the underlying causes of underperformance, and helps optimize system design.
Monthly loss calculations follow the same rules as the yearly losses described above.
The monthly view contains three components:
The Breakdown of energy losses chart.
The Seasonality and interannual variability of monthly PV losses graph.
The Monthly energy conversion and related losses table.
Breakdown of energy losses chart
The Breakdown of energy losses chart depicts the percentage contribution of individual loss values and their total accumulation for each month.
You can toggle the visibility of each loss by clicking its name in the chart legend. Hovering over a value highlights it on the chart, showing its actual value per month along with the total for the year.
Important: The Breakdown of energy losses chart shows absolute loss values (non-cumulative).
Seasonality and interannual variability graph
The Seasonality and interannual variability of monthly PV losses graph shows cumulative monthly losses aggregated over all simulation years. It allows for the assessment of both seasonality and interannual variability in losses, supporting the establishment of realistic performance expectations for a PV plant under varying year-to-year conditions.
Monthly energy conversion and related losses table
This table details monthly energy losses throughout the PV system using the same structure as the yearly losses table. It starts from the initial solar input and tracks reductions at each stage across all months of the year.
The table rows cover the following loss groups:
Energy input: Shows monthly values for global horizontal irradiation and global tilted irradiation (front and rear sides), both before and after shading.
Optical losses: Lists monthly percentage losses from shading, soiling, angular, and spectral effects for both module sides.
Conversion losses: Displays the percentage loss when converting solar radiation to DC electricity in the modules each month.
Electrical losses: Breaks down monthly losses from inverters, DC/AC conversion, cables, transformers, and auxiliary systems.
Unavailability losses: Shows monthly internal, external, and snow-related downtime losses.
Display options
The dropdown menu in the top right of the table lets you choose how losses are displayed. The three options correspond to the following columns in the yearly losses table:
Losses in % of GTI without shading: Used to compare the magnitude of different losses. Corresponds to the "Energy loss relative to input" column.
Losses in % difference from the previous step: A standard way of presenting PV system losses; allows for the simple calculation of total loss as a sum of losses in individual conversion steps. Corresponds to the "Energy loss relative to previous" column.
Losses in kWh/m² or kWh/kWp difference from the previous step: Useful for understanding the total energy lost in each conversion step.
How losses are calculated
The following sections describe what each loss type represents and how it is calculated.
Optical losses
Optical losses affect solar radiation before it is converted to electricity. They are quantified per module side (front and rear).
Shading losses (horizon): Occur due to shading by the horizon line, reducing the solar radiation reaching the modules.
Shading losses (near): Occur due to partial or complete shading from nearby objects or structures blocking solar radiation from reaching the modules.
Soiling losses: Caused by the accumulation of dust and dirt on solar panel surfaces.
Angular losses: Result from the angle at which sunlight strikes the module surface — as the angle of incidence increases from perpendicular, a larger fraction of solar radiation is reflected away.
Spectral correction: Reflects changes in the solar spectrum as light travels through the atmosphere. This value can be positive or negative depending on the spectral composition of solar radiation at the site.
GTI effective is the resulting effective global tilted irradiation value after all optical losses have been applied to both the front and rear sides.
Conversion losses
Conversion of irradiation to DC in the modules: Arises during the conversion of sunlight into electrical energy within PV cells. More details are in the Argus electrical simulation overview.
Electrical losses
Electrical losses reduce the DC or AC energy output after conversion.
Inverter clipping losses: Occur when generated power exceeds the inverter capacity or operates under minimum capacity, causing the inverter to limit (clip) the output.
Grid power limitation losses: Occur when the grid constrains the power that can be fed in, limiting the system output.
DC losses (cable, combiner boxes): Arise due to resistance in DC cables and combiner boxes before inverter conversion.
Inverter (DC/AC conversion) losses: Result from inefficiencies during DC to AC conversion inside the inverter.
Auxiliary losses: Come from self-consumption by auxiliary equipment within the system.
AC cable losses (LV): Occur due to resistance in low-voltage AC cables as current flows from the inverter.
Transformer losses (LV/MV): Caused by transformation from low to medium voltages.
Additional AC and transformer losses:
AC cable losses (MV): Occur in medium-voltage cables during longer distance transmission.
Transformer losses (MV/HV): Losses caused by transformation from medium to high voltages, if a power transformer is used.
AC cable losses (HV): Occur in high-voltage cables connecting the power transformer, if used, to the grid.
Unavailability losses
Unavailability losses account for periods when the system is not producing energy due to operational issues.
Internal unavailability losses: Caused by maintenance activities or failures of internal components.
External unavailability losses: Caused by external factors such as grid outages or regulatory shutdowns.
Snow losses: Caused by snow covering the modules, preventing energy production.
Performance ratio
The cumulative performance ratio represents the portion of initial solar energy delivered as usable electricity. It is calculated differently for monofacial and bifacial systems.
For monofacial systems:
For bifacial systems:
The bifaciality factor is taken from the bifacial PV module specifications in the PV components catalog.