By default, all HelioScope users can generate P50 reports. P90, P95, and P99 are also available for our Pro and Enterprise plan users. To upgrade to Pro, visit the Billing Page. To learn about our Enterprise plan package, please reach out to our sales team by clicking here
What are P50, P90, P95 and P99?
The "P" in P50 and P90 refers to probability (or sometimes percentile or probability of exceedance). A P50 value is a median value, which means we expect that 50% of the time, an outcome will fall above the P50 value, and 50% of the time, it will fall below the P50 value. P90 represents a more conservative slice of the same distribution; a P90 value is a value that will be met or exceeded 90% of the time. If P90 energy production is 1,000kWh, for example, there is a 90% chance in any year that the array will produce 1,000kWh or more. P95 and P99 represent values that will be met or exceeded 95% and 99% of the time, respectively.
Many institutions will request a P90 energy production estimate when providing financing for a solar project. While P90 is typically 2-4% lower than P50 production, a more significant difference between P50 and P90 values indicates more energy production variability, usually due to more weather variability (as shown below in the first graph, compared to the second graph).To learn more about P90 and P50, we suggest looking at this article at HeatSpring. Also, this article provides more details about the values accuracy study behind our P90, P95, and P99 values.
How can I generate a P50 and P90 in HelioScope?
P50 Generation
To generate a P50 report with HelioScope, select a typical meteorological year ("TMY") file for the weather. TMY weather files represent P50 weather conditions, so selecting a TMY file in your condition set will automatically generate a P50 energy production model.
P90, P95 and P99 Generation
To generate a P90, P95, and P99 report with HelioScope, select a typical meteorological year ("TMY") file for the weather. The Probability Distribution setting can be adjusted in the Condition Set of HelioScope New Experience. Toggle Enable Probability Distribution to begin using this feature.
Once Probability Distribution is Enabled, use the P90, P95 and P99 checkboxes to choose which Probability Values to calculate and display on the Production Report. Additionally, Weather Variability and System Variability can be adjusted. System Variability includes the option to adjust PV Module Modeling Parameters, Inverter Efficiency, Soiling Mismatch, Degradation Estimation, and Custom Variability. The Resulting Weather & System Variability is a sigma or sum of all the percentages entered for Weather Variability and System Variability. Click Save after changing any of these values to add them to the Condition Set.
P90 Simulation Results
To view the results of the P90, P95, and P99 generation, a Production Probability graph and Production Probability Variables table will be automatically added to the Production Report in HelioScope Classic and New Experience:
Additionally, for HelioScope New Experience, the Production Probability graph and Production Probability Variables can be added as widgets to a custom report:
My project location does not have a multi-year weather file. How can I get a P90 to generate?
Some of HelioScope's multi-year weather datasets are unavailable outside of the United States. To conduct P90 analysis in these locations, upload weather datasets with multiple years from a different source. NSRDB is a publicly available and free source of data, with coverage in India and the Americas. SolarGIS, SolarAnywhere, 3TIER, and Meteonorm all offer global coverage for a price, and Climate.OneBuilding offers free international weather datasets.
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.
An example of a weather file with a single year selected instead of multiple years:
Because only a single year was selected, the Probability Distribution will not generate a report: