Typical Meteorological Year

TMY, or Typical Meteorological Year, data is a year-long synthetic historical time series that has realistic physical variation in irradiance and that matches expected long-term total solar irradiance. In solar applications, accurate, bankable TMY data representing typical irradiance years are used for modeling and simulating the performance of assets under typical weather conditions.

TMY data is calculated by analysing and combining real periods from a multi-year dataset based on statistical criteria to create a synthetic year that reflects typical weather conditions. Solcast’s TMY API selects representative periods to match the long-term average historical irradiance, and includes key weather parameters including multiple solar irradiance measures, temperature, overall climate conditions, and even albedo and aerosols. Check our irradiance methodology.

TMY data is preferred for project financing, and is useful for representing weather conditions that vary every single day. Historical time series data is best when analysing long term weather trends (like snow soiling), correlation of weather with other circumstances (like energy prices) or variation and risk over time. TMY data is ideal for designing and optimising assets, bankable energy assessments for project financing, and performing long-term energy yield projections.

While a viable solar project may be feasible and potentially profitable, a bankable solar project meets stricter criteria required by financiers, including extensive risk assessments and credible performance data. Being bankable means that a project is considered reliable and financially sound to secure funding from investors or lenders. So, it’s important to choose globally validated, bankable TMY and historical data when doing solar resource assessment. Check how the Solcast data compares with other historical irradiance data providers, or use DNV's Solar Resource Assessment tool to make the comparison.

P50 and P90 are probabilistic scenarios, used for managing and understanding the risk of variable weather conditions, where the number denotes the percentage of years that will exceed that value. For due diligence and solar resource assessment, having multiple probabilistic scenarios is beneficial for better decision making and risk management. TMY P50 represents the median or average conditions, reflecting typical long-term weather patterns while TMY P90 represents a more conservative “low end” scenario, indicating conditions that are exceeded 90% of the time, used to understand the downside risk of a “bad year”. Solcast offers probabilistic scenarios for TMY at any “Pxx” level.