GHI and DNI uncertainty data

GHI and DNI model uncertainty

Uncertainty quantifies the confidence in the accuracy of long-term solar resource parameters. The Uncertainty page in Solargis Evaluate offers insights into uncertainty values for key metrics such as GHI (Global Horizontal Irradiance) and DNI (Direct Normal Irradiance), enabling you to make well-informed decisions in solar energy planning and analysis.

Uncertainty estimates are available to Full evaluation projects only and are part of the Full evaluation project package at no additional cost. You can read more about the uncertainty estimates here.

Important: Uncertainty estimates in Solargis Evaluate are not displayed by default - you need to activate it in the Project data add-ons.

Note: The Uncertainty estimates may take up to several hours from the time of request to show in the Analysis section.

Uncertainty estimates in Evaluate

We provide uncertainty estimates separately for GHI and DNI on the dedicated pages. These pages present a comprehensive uncertainty framework for solar resource assessment. The pages offer the data in a structured format as follows:

• Model uncertainty: Shows the inherent uncertainty in the modeling methods used to calculate the GHI and DNI values. GHI models demonstrate lower uncertainty than DNI models, which is expected as GHI is typically more stable and easier to model than DNI.

• Uncertainty due to Interannual variability: Quantifies how much solar resource values naturally fluctuate year-to-year due to weather patterns. This variation decreases significantly as the averaging period extends from 1 to 30 years.

• Combined uncertainty of LTA at 90% probability of exceedance: This combines both uncertainty sources to provide overall confidence levels, critical for financial modeling.

• Minimum expected LTA values at different Pxx: This table presents the minimum irradiation values (kWh/m²) expected at different probability thresholds (Pxx - probability of exceedance) across various time periods (1, 20, 25, and 30 years), allowing stakeholders to select appropriate risk levels for project planning.

Note: We have highlighted widely-used industry standard values in the table for your convenience.

Expected yearly values for different Pxx

This chart details the minimum annual values of GHI or DNI at the combined uncertainty for any Pxx scenario from P99 to P01. The curve shows the probability distribution of annual Pxx values, with key Pxx points (e.g., P99, P90, P75, P50) highlighted to indicate the value that is exceeded with a specified probability percentage.

Pxx scenarios explained

Pxx stands for “exceedance probability.” For example, P90 is a statistical estimate expected to be exceeded in 90% of the years considered in the analysis (considered a conservative estimate), while P50 is the median value (expected to be exceeded in 50% of years).

Markers for Pxx points enable you to quickly see how the expected values change depending on the chosen confidence level.

Usage and interpretation

• Risk assessment: Use different Pxx values to understand combined uncertainty (comprising model uncertainty and interannual variability) for a given location or scenario. Higher Pxx (P90, P99) reflects more conservative estimates, applicable for risk-averse planning; Pxx (P50) represents average or typical expectations.

• Planning and communication: Select the Pxx metric that matches the risk appetite and reporting requirements of your project stakeholders.

  • P50: Average expectation, useful for performance estimates.

  • P90/P75: Conservative scenarios, common in financial and technical risk assessments.

  • P99: Very conservative, used for maximum confidence.

• Project development: Identify which values to use in proposals, reports, and technical documentation based on required certainty.

Further details about Pxx scenarios can be found in our methodolgy.