GHI
The radiation reaching the earth’s surface can be represented in a number of different ways. Global Horizontal Irradiance (GHI) is the total amount of radiation received from the sun on a surface horizontal to the ground. This value is of particular interest to photovoltaic installations and includes both Direct Normal Irradiance (DNI) and Diffuse Horizontal Irradiance (DIF).
The following chart shows the total GHI calculated from 52 years of weather station data at the Cranbrook airport.
The average is 1,203 kWh/kW/m2/yr and the minimum /maximum are 1,056 and 1,311 respectively.
The dataset has 2 types of variances.
- The variance between GHI estimated and its actual value. According to Environment Canada and NRCan that provided the data, the root-mean-square error (RMSE) for hourly solar GHI amounts are typically around 30% . The long term average error however is 5% or lower.
- The second variance is related to the year-to-year variation of solar irradiation, depending on the weather and other climatic factors. The yearly Standard Deviation is 5.35 %.
As the 2 variances are independent, the combined SD is their norm or 7.32%.
Next: Statistics→
You must be logged in to post a comment.