Typical Meteorological Year

TMY, or Typical Meteorogical Year, data is a synthetic dataset that represents average weather conditions in a specific location. In solar applications, accurate, bankable TMY data representing typical irradiance years are used for modeling and simulating the performance of assets under average 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 average historical irradiance, and includes key weather parameters including multiple solar irradiance measures, temperature, overall climate conditions, and even albedo and aerosol. 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 the recent DNV bankability study of Solcast data, and see how it compares with other historical irradiance data providers.

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.