	Latitude	decimal degrees + northern hemisphere - southern hemisphere
	Longitude	decimal degrees + east of Greenwich - west of Greenwich
	Time Zone	local standard time TZ
	Year
	Month
	Day
	Hour	Standard time only!
	Minute
	Temperature	ambient temperature in °C
	Pressure	barometric pressure in mb
	AOD	aerosol optical depth at 500 nm in "base e" units
	Water Vapor	precipitable water vapor in cm
	Tilt	degrees of tilt of the surface from the horizontal (to have the surface automatically track the sun type the value 180)
	Azimuth	tilted surface's azimuth angle clockwise from North (if tilt=0, this value is ignored)

This interface is driven by the National Renewable Energy Laboratory's (NREL) Richard C. Bird's Simple Spectral (spectrl2) model.

A clarification of parameters

Aerosol optical depth:
Aerosol optical depth (also known as atmospheric turbidity) is a measure of sunlight attenuation by aerosols (particles suspended in a gas). It is wavelength dependent. For the above model, an AOD value at 500 nm (nm= nanometers) is required. Typical values of AOD at 500nm range from less than 0.2 for very clear skies to values greater than 1 for dusty, smoky areas.

(Precipitable) Water vapor:
The total amount of water in the atmosphere that, if precipitated out, would be measured as liquid water depth (in cm).

Tilt and azimuth:
The orientation of the surface whose irradiated surface is being modeled. For example, if you wish to model the irradiance on a photovoltaic panel, you will need to supply the tilt (angle between horizon and panel), and the azimuth (the direction where the face of the panel is facing).

Last Modified on Friday, March 13, 2009

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