To compute direct and diffuse irradiance over an arbitrarily oriented slope, fill in or modify the values below.
The model computes potential solar radiation for clear skies, it does not take into account terrain obstruction, shading or clouds. To incorporate those effects for specific studies, please contact us.
Location is the name of the site, can be real or imaginary, it is used only for reference. Must be only alphanumeric characters.
Latitude dec. deg: the geographical latitude in degrees and decimal degrees. To convert from degrees, minutes and seconds to decimal degrees use the conversion tool. Values must be in the range -90 to 90.
Longitude dec. deg: the geograpical longitude in degrees and decimal degrees. To convert from degrees, minutes and seconds to decimal degrees use the conversion tool. Values must be in the range -180 to 180.
Day: day of the month, from 1 to 31 (choosing the 31st of February will return the 3rd of March).
Month: choose from the drop-down menu.
Altitude (m): elevation over sea level in metres. To convert from feet use the conversion tool.
Visibility (km): it is the maximum distance in km where large objects can be distinguished in the horizon. The value given (50 km) is for a clean atmosphere. This is a proxy for atmospheric turbidity, it is choosen as many airports report visibility, while other parameters, such as Linke Turbidity, are more difficult to obtain. Airport reports (METAR) are given here (choose 'Decoded').
Temperature °C: temperature in degrees centigrade, use CT to convert from Farenheit.
RH (0-100): Relative Humidity in percentage, values from 0 to 100. Airport reports (METAR) normally include RH.
Ozone thickness: ozone layer thickness in cm. Divide Dobson Units by 1000 to get the equivalent in cm. Check the TOMS (Total Ozone Mapper Spectrometer) pages for current values.
Albedo ground (0-1): albedo of the surrounding terrain, e.g. 0.8 to 0.95 for fresh snow, 0.17 for deciduous forest, 0.35 for sand, etc.
Timezone (timezone map): the timezone, a good approximation is (-1)*longitude/15, longitude in degrees and west is negative.
Slope Orientation (0-360): orientation of the surface, solar panel, roof, etc. If looking north it will be 0°, if looking south will be 180°. Range 0 to 360 degrees
Slope Tilt (0-90): inclination of the surface or panel with respect to the horizontal, 0° is flat 90° is completely vertical. Range is from 0 to 90 degrees.