Estimating solar radiation on slopes of arbitrary aspect

Solar radiation is a major environmental factor, controlling for example, p lant growth, inactivation of fecal microbial contaminants, and soil propert y evolution. Modeling the magnitude and complexity of changes in solar radi ation under cloudy conditions is a challenge. In this paper, we present a s imple approach for estimating daily global solar radiation on any sloping s urface with arbitrary aspect given global radiation data for nearby flat te rrain. The system is a further development of existing models and consists of two parts. The first part estimates direct and diffuse components of sol ar radiation from measured global radiation for a horizontal surface. The s econd part uses separate estimates of direct and diffuse radiation to calcu late the daily global radiation throughout the year on slopes of different steepness and aspect. The performance of the system was verified with solar radiation data on various slopes and aspects at latitude 37.8 degreesC in New Zealand. (C) 2001 Elsevier Science B.V. All rights reserved.