There is a problem of availability of sufficient and functional instruments for measuring solar radiation in Nigeria due to the high importation costs and maintenance. In order to alleviate this problem, the design, construction and testing of a reliable model pyranometer (RMP001) was done in Mubi, Adamawa State of Nigeria. Detailed instructions were provided for assembly and calibration. Bearing cost, photodiode active-surface and signal-to-noise ratio in mind, the most suitable photodiode for this application was BPW21. The pyranometer was constructed around the photodiode held with a protective plastic case. The CMP3 pyranometer was used as a standard for calibration and comparison. A calibration constant of 5230 ± 0.02 Wm-2 was obtained. The stability of the RMP001 comparedfavourably with the CMP3 during a day open – sky test giving irradiances of 20.76 and 21.7 Wm-2 for RMP001 and CMP3, respectively, at 5:25 p.m. RMP001 will be used for the collection of authentic irradiance data for comparative evaluation with the theoretical predicted results given by researchers.