Solmetric SunEye 210, Руководство пользователя

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4-5
Solar Access and Interpretation of Data
Numerical Calculations
Numerical Calculations
When using the NREL - TMY3 data, the hourly insolation data is taken directly from the data-
base for the weather station specified. When using the NASA data, the following numerical
assumptions are made by the SunEye software when calculating results:
• Solar constant (above-the-atmosphere solar irradiance): 1367 W/m
2
• Atmospheric pressure: 1013 mBars
• Atmospheric temperature: 15 °C
• Panel orientation: south with tilt equal to latitude
• Clearness index (K
T
): NASA historical monthly averages by latitude and longitude
For either weather model, the solar access numbers reported by the SunEye are percentages that
are calculated by first calculating insolation (Wh/m
2
) for every 15 minute time interval, every
four days, for the entire year. This insolation value includes either average historical weather
data for the latitude and longitude set in the session (NASA model), or hourly TMY3 weather
data for the closest NREL station (NREL – TMY3 model, US only). Next, the skyline data is
analyzed to determine which 15 minute intervals throughout the year are shaded. The sum of the
unshaded 15 minute insolation values for a given period (for example 1 month) divided by the
total insolation possible (assuming no shading) for the same period times 100 gives the solar
access percentage for that time period.