At HelioScope, we pride ourselves on the accuracy of our simulations. DNV GL (formerly BEW Engineering) previously led a study that showed HelioScope production modeling to be within 1% of other commonly used models. Read the report here.
Like our P50 values, our P90, P95, and P99 values are also within 1% of other commonly used models. In this article, we document how we validated this accuracy.
Our approach to calculating P90, P95, and P99 values
P90, P95, and P99 values are obtained by simulating a system’s production with a multi-year weather file and calculating the reduction needed for actual production to outperform the estimated value 90%, 95%, or 99% of the time. The reduction is estimated through variability, which is primarily driven by weather.
HelioScope calculates P90, P95, and P99 values through a Gaussian distribution with P50 values as the mean. For variability, we take into account weather and system variability.
There are three ways we obtain weather variability:
- If Meteonorm data is used, we use the weather variability provided in that weather dataset.
- If other multi-year weather datasets are used, we use the model from Pierre Ineichen’s 2011 paper Global irradiation: average and typical year, and year to year annual variability to estimate weather variability.
- Users can also provide their own weather variability values.
Note: Since P90 is obtained through simulating a system’s production over multiple years, if a custom or single-year weather file is used, we are not able to generate the P90, P95, and P99 values.
Verifying accuracy
HelioScope compared the result of our P50, P90, P95, and P99 values against that of PVsyst’s for a set of 8 projects. These 8 projects span 2 locations in the Northern and Southern hemispheres. They include a mix of Fixed Tilt and Single Axis Tracker designs, along with different tilt and GCR configurations.
In our testing, we found that HelioScope’s P90, P95, and P99 values were all within 1% of PVsyst’s, just like our P50 values. This confirms that the accuracy verified by DNV GL for P50 still holds for P90, P95, and P99 values.