An hourly solar radiation model under actual weather and terrain conditions: A case study in Heihe river basin

This paper describes an hourly incident solar radiation model, which could be used to estimate long-term global radiation, direct radiation and diffuse radiation with high spatial and temporal resolution under its de facto weather and terrain in large regions. The model is based on parameterized radiation transfer theory, and has referred to some data from the NCEP/NCAR (National Centers Environmental Prediction/National Center for Atmospheric Research) and some information about topography. The model was successfully used to calculate hourly instantaneous solar irradiance by a spatial resolution of 1 km×1 km in Alberts projection, in the Heihe river basin with a drainage area of 130,000 km2 in 2002. Now that only observed global radiation data at three automatic stations is available in Heihe river basin, global radiation at the three stations is used to validate the model. The three automatic stations are deployed in the mountain (Xishui), in the oasis (Linze), and in the desert area (Erjinaqi), respectively. The measured hourly instantaneous global radiation data do not comply with the calculated series at Xishui, with a determination coefficient R2=0.71R2=0.71. While at Linze and Erjinaqi stations, the determination coefficients are 0.90 and 0.91, respectively. The main reason why large errors are observed at Xishui station is that total cloud percent data from the NCEP/NCAR do not have a high spatial and temporal resolution. Also the spatial resolution of the observed data is not consistent with the calculated values. According to the model numerical test, topography is an important factor affecting model results on uneven land surfaces. Besides, in arid desert regions with even land surfaces, the 6 hourly model results agree with NCEP/NCAR global radiation data and measured data well.