Radiation is measured by Met. bureau using radiometers on flat ground Therefore, interpolation surface contains no samples of radiation on an inclined surface Alternative is to model radiation using a deter- ministic, process-simulation model-"cloudy - requires user to provide estimates of about 10 parameters to calibrate model to prevailing atmospheric and terrain conditions calculates radiation on an inclined surface• Radiation is measured by Met. bureau using radiometers on flat ground Therefore, interpolation surface contains no samples of radiation on an inclined surface • Alternative is to model radiation using a deter￾ministic, process-simulation model - “cloudy” requires user to provide estimates of about 10 parameters to calibrate model to prevailing atmospheric and terrain conditions calculates radiation on an inclined surface