Delta-T SPN1 Technical Note

Also see for SPN1: User manual

Contents

Delta-T SPN1 Technical Note Manual pdf 3 page image

SPN1 DNI Firmware- Use of the DNI function3 of 8 5/4/2016www.delta-t.co.ukHow do I calculate DNI if my SPN1 is horizontal?DNI = (SPN1 Direct)/Cos ϴ……………………………..(1)Where:- ϴ = zenith angleSPN1 Direct = SPN1 Total(Global) – SPN1 Diffuse.Given the latitude, longitude and correct time relative to GMT the SPN1 firmware works out the sun’szenith angle and calculates DNI for a horizontally mounted SPN1 using equation 1.Note: Delta-T also can provide an Excel spreadsheet add-in to do this - see www.delta-t.co.uk.You may find this spreadsheet useful, for instance - to check you are sending the SPN1 the correctparameters.Location & TimeIt is important to use the correct sign conventions to use when specifying Latitude, Longitude and alsothe time zone offset from GMT.Time ZoneYou need to know the local time at the SPN1 and how many hours you are ahead or behind GMT(Greenwich Mean Time) or UTC (Universal Time). For our purposes GMT and UTC are equivalent.The time zone generally increases by 1 hour for every 15° East of Greenwich, with the internationaldate line separating GMT+12Hrs from GMT-12Hrs. There are however many exceptions, as the mapbelow demonstrates. The SPN1 time zone must be in the range -24:00 to +24:00 in hours and minutes.LocationYour site location is another key input to many of the functions.Latitude is entered in decimal degrees, with positive values for North, negative values for South.Latitude must be in the range -90° to +90°.Longitude is entered in decimal degrees, with positive values for East of the Greenwich meridian,negative values for West. Longitude must be in the range -180° to +180°Zenithangle ϴSPN1 Sensor tilted directly towardsthe sun measures the Direct NormalIrradiance (DNI)Horizontal SPN1receivesDNI x Cos ϴϴ1kW/m21xCos(ϴ) kW/m21kW/m2