In this document
You'll learn how to read the PV long-term degradation page in the project's Analysis section: the lifetime PVOUT specific and performance ratio chart, the total photovoltaic energy output chart, and the PV electricity production over lifetime table, including the degradation rate applied to each year and the unavailability and snow loss toggle.
Long-term degradation of the modules is presented in the PV long-term degradation section. It depict the decline in your system's PVOUT over time — the drop in energy output caused by the ageing and performance degradation of the PV modules and other system components. They show how much production can be expected to decrease over the lifetime of the plant, which supports financial forecasting and operational planning.
The page is available in the project's Analysis section under PV long-term degradation, and the values are projected for the first 25 years of operation.
For the other chart groups and an introduction to the Analysis section, see How to read the charts. For the theoretical PVOUT values that do not include degradation, see PVOUT and performance ratio (PR), and for the methodology behind the degradation model, see System unavailability losses & long-term degradation.
Important: This page is available for PV energy systems only. It is not provided for GTI energy systems.
Notes:
The degradation rate applied to each year comes from your energy system configuration. The first year is typically higher than the following ones, as it also covers the initial degradation of new modules. You can review and change the rate in the Energy system designer.
The page contains the unavailability toggle in the top right corner, which includes or excludes internal and external unavailability and snow loss values in the charts and the table. They are included by default.
PVOUT specific and performance ratio
This chart plots the specific PVOUT projected for each year of the system's lifetime, from the start-up production in year 0 to the end of the modelled period. The performance ratio (PR) line is plotted against the secondary axis on the right and declines together with the output, as the system converts less of the same incoming irradiation into electricity as it ages.
The horizontal average line marks the mean specific PVOUT over the whole modelled lifetime, which is the value to use when a single long-term figure is needed rather than a year-by-year series.
Unit | |
|---|---|
X-axis | End of year (0–25) |
Y-axis (left) | PVOUT specific [kWh/kWp] |
Y-axis (right) | Performance ratio [%] |
How to use it
The chart shows how the yield per installed kWp develops over the lifetime of the plant, independently of its size. The steepest drop is between year 0 and year 1, where the initial degradation of new modules is applied; afterwards the decline follows the annual degradation rate and is close to linear.
Use it to judge how much of the initial performance remains at the end of the assessed period, and to check the production level around the years that matter for your business case — for example, the end of a PPA term, the point at which a performance guarantee is verified, or the year in which repowering is considered.
The PR line helps distinguish ageing from other effects: because it is expressed relative to the irradiation received, a declining PR shows that the loss comes from the system itself rather than from the solar resource.
Total photovoltaic energy output
This chart presents the same lifetime projection for the total output of the whole system, reflecting the actual modules and inverters used in the project. No performance ratio line is included, as PR is shown with the specific PVOUT.
The horizontal average line marks the mean annual production over the modelled lifetime.
Unit | |
|---|---|
X-axis | End of year (0–25) |
Y-axis | PVOUT total [MWh] |
How to use it
This is the chart to work with when you need absolute energy volumes: the energy the plant is expected to deliver to the grid in each year of its lifetime. Combined with an electricity price or tariff, the yearly values feed directly into revenue projections, cash-flow models, and the levelised cost of electricity.
The lifetime average is a convenient input for a simplified business case, but the early years produce above it and the later years below it. Where the timing of the revenue matters — debt service in the first years, or the residual value at the end of the term — use the year-by-year values from the table instead of the average.
PV electricity production over lifetime
The two charts above are complemented by the PV electricity production over lifetime table, which lists the exact values behind them. Each row represents one year of operation:
Column | Description |
|---|---|
End of year | The year of operation. Year 0 is the start-up production, before any degradation is applied. |
Degradation rate [%] | The performance loss applied in the given year relative to the previous one. The first year is typically higher, as it also covers the initial degradation of new modules. |
PVOUT specific [kWh/kWp] | The expected yield per installed kWp in the given year. |
PVOUT total [MWh] | The expected output of the whole system in the given year. |
PR [%] | The performance ratio reached in the given year. |
How to use it
The table is the source of the numbers you transfer into your own models: pick the year you need and read the production and PR directly, instead of estimating them from the curve.
Comparing year 0 with the last year shows the total performance loss accumulated over the lifetime, and the degradation rate column makes the assumption behind that loss explicit — useful when your yield assessment has to be reviewed by a lender or an independent engineer, or when you compare module types with different warranted degradation rates.
The values can also be used to verify a module warranty: manufacturers typically guarantee a minimum remaining output in a given year, and the table shows the production the simulation expects at that point.