Simulation of daily solar irradiance

Solar irradiance is an important input parameter for many simulation models dealing with plant responses to the environment and is not measured in as many locations as temperature and precipitation. This situation has led to the development of algorithms to simulate solar irradiance with measured temperature and precipitation. The objectives of this research effort were two-fold: (1) to determine if a location-specific algorithm to simulate solar irradiance (based on temperature and precipitation) developed in the central Great Plains of the US could be used in other locations and (2) to determine if these results could then be used to develop a generalized algorithm. Data (temperature, precipitation, and solar irradiance) from a wide variety of locations (climates) were used to develop the location-specific and generalized algorithm. Simulated values of solar irradiance from both algorithms were evaluated with independent data from the same locations. A second independent data set was used to evaluate the generalized algorithm. For the first independent data set using the location-specific algorithm, root mean square errors (RMSE) varied from 2.6 to 5.5 MJ m(-2) per day. Using the generalized algorithm, RMSE varied from 3.2 to 5.5 MJ m(-2) per day, excluding Barrow, AK, which had an RMSE of 6.8 MJ m(-2) per day. For the second independent data set using the generalized algorithm. RMSE ranged from 4.0 to 5.8 MJ m(-2) per day. The RMSE for simulated solar irradiance was relatively large when the mean annual temperature term (DeltaT), which is used in the generalized algorithm, was relatively small and precipitation was relatively high. With this caveat, the generalized algorithm can be used to simulate solar irradiance at locations where only daily values of temperature and precipitation are measured. The RMSE values reported in this study compare favorably to results for other algorithms used to simulate solar irradiance. An advantage of this approach is its relative simplicity and ease of use. (C) 2003 Elsevier B.V. All rights reserved.