Vaisala Energy Support
What is the “TMY” Data Type in the Solar Time Series Download tool?
The “TMY” data type will create a data file that covers a single year at hourly resolution, sometimes called an 8760 for the number of data rows in the file. TMY stands for Typical Meteorological Year and this file is meant to represent “typical” conditions at a site. The TMY files from the Solar Time Series Tools are both "GHI-" and “DNI-conserving," meaning that the means of these variables are targeted to tightly match the long-term means.
Vaisala uses a proprietary method for TMY creation. Starting from the long-term time series, we determine the long-term annual and monthly means as well as monthly diurnal patterns. We then choose 4-day periods from across the dataset to create a month, for example Jan 1-4 may be from 1998, Jan 5-8 from 2005, and so on. Once we have a complete month, we verify that it matches the long-term monthly mean to within in 0.5% for GHI and 1% for DNI. Once we have 12 months created, we check to make sure GHI and DNI match their long-term annual means to within 0.3% and 0.5%, respectively.
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