Solar Engineering of Thermal Processes, 4th Edition

Chapter 2

Available Solar Radiation

In this chapter we describe instruments for solar radiation measurements, the solar radiation data that are available, and the calculation of needed information from the available data. It is generally not practical to base predictions or calculations of solar radiation on attenuation of the extraterrestrial radiation by the atmosphere, as adequate meteorological information is seldom available. Instead, to predict the performance of a solar process in the future, we use past measurements of solar radiation at the location in question or from a nearby similar location.

Solar radiation data are used in several forms and for a variety of purposes. The most detailed information available is beam and diffuse solar radiation on a horizontal surface, by hours, which is useful in simulations of solar processes. (A few measurements are available on inclined surfaces and for shorter time intervals.) Daily data are often available and hourly radiation can be estimated from daily data. Monthly total solar radiation on a horizontal surface can be used in some process design methods. However, as process performance is generally not linear with solar radiation, the use of averages may lead to serious errors if nonlinearities are not taken into account. It is also possible to reduce radiation data to more manageable forms by statistical methods.

2.1 Definitions

Figure 2.1.1 shows the primary radiation fluxes on a surface at or near the ground that are important ...