2 - Resource assessment and site selection for solar heating and cooling systems

Abstract

This chapter focuses on solar resources: how solar resource information is obtained and how it is used to assess the energy available to flat plate and concentrating collectors commonly used in solar heating and cooling applications. Owing to the variability of the resource in both time and space, care must be taken to ensure that the characteristics and accuracy of the resource data are well understood for assessing solar system performance. The chapter first provides several key definitions of solar resources, including definitions for solar radiation, radiant energy (or radiance), irradiance, irradiation (or solar insolation), and solar energy. Characteristics of the spectral distribution of solar radiation at the top of the atmosphere and at the earth's surface are also described. The various key components of the solar resource (direct normal irradiance, global horizontal irradiance, and diffuse horizontal irradiance) are described. Procedures for converting these values into the solar resource available to various tilted surfaces for flat plate collectors are then discussed. The chapter then goes into how both measured and modeled solar resource data can be obtained. Various measurement strategies are described, and satellite-derived solar resource modeling concepts are also presented. Solar data can also be described when information on cloud cover is available, or from numerical weather prediction models. The chapter then concludes with discussions on the application of solar resource data to produce data sets, such as typical meteorological year data, and also data on exceedance probabilities (such as P90). Finally, there is a discussion as to how short-term high-quality measured data can be combined with long-term modeled data to reduce data uncertainty and improve data bankability.