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Hi PVsyst!

I hope to get help form PVsyst team since it is not easy to find the answers or guidelines for P50 and P90 in PVsyst 

  1. What value should be plugged in for climate change and Annual variability? Is there any research article to refer to or white paper that established what % to use with confidence level? 
  2. Are these values (climate change and annual variability) applicable for P50, P75, P90?   
  3. How can we get the energy yield of P50 for 25 years in PVsyst? 
  4. How can we extract P90 values for 25 years in PVsyst?  

Best Regards,


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  1. Usually the weather data provider will provide the variability. It is already included in most TMYs on the market. For the climate change it is a bit more complicated. If you have a specific year of a time-series, you can ask yourself whether this year is above or below average and by how much (in terms of irradiance). For predictions we actually do not really know how to do this, an idea would be to look at multi-year trends for the location.
  2. Both are indeed used for P75 and P90. The P50 is controlled by the climate change % only, to shift the simulation value.
  3. You can use the aging tool (advanced simulation > aging tool) which allows you to simulate several years in a row and present the result in a formatted table / report.
  4. a 25-year-P90 is a concept we haven't implemented in PVsyst yet. You should not concatenate 1-year P90s, this approach is incorrect. Indeed, when taking longer sampling periods, the weather variability should decrease, by a factor 1/sqrt(n years) approximately. But note that the uncertainty does not decrease over the years. In practice after 25 years, you may get more or less 1.5-2% of variability + uncertainty.



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