Solar Energy System Design
The largest solar electric generating plant in the world produces a maximum of 354 megawatts (MW) of electricity and is located at Kramer Junction, California. This solar energy generating facility, shown below, produces electricity for the Southern California Edison power grid supplying the greater Los Angeles area. The authors' goal is to provide the necessary information to design such systems. The solar collectors concentrate sunlight to heat a heat transfer fluid to a high temperature. The hot heat transfer fluid is then used to generate steam that drives the power conversion subsystem, producing electricity. Thermal energy storage provides heat for operation during periods without adequate sunshine. [pic]
Figure 1.1 One of nine solar electric energy generating systems at Kramer Junction, California, with a total output of 354 MWe. (photo courtesy Kramer Junction Operating Company) Another way to generate electricity from solar energy is to use photovoltaic cells; magic slivers of silicon that converts the solar energy falling on them directly into electricity. Large scale applications of photovoltaic for power generation, either on the rooftops of houses or in large fields connected to the utility grid are promising as well to provide clean, safe and strategically sound alternatives to current methods of electricity generation. [pic]
Figure 1.2 A 2-MW utility-scale photovoltaic power system co-located with a defunct nuclear power plant near Sacramento, California. (photo courtesy of DOE/NREL, Warren Gretz) The following chapters examine basic principles underlying the design and operation of solar energy conversion systems such as shown in Figure 1.1 and 1.2. This includes collection of solar energy, either by a thermal or photovoltaic process, and integration with energy storage and thermal-to-electric energy conversion to meet a predefined load. Study of the interaction of these subsystems yields the important guidelines for the design of optimal solar energy systems. System design tools are provided to produce optimal sizing of both collector field and storage so that optimum system designs can be produced. Since our emphasis is on the design of entire solar energy conversion systems rather than design of its individual components, both thermal and photovoltaic systems are included. This novel approach results from recognition of the commonality of most system design considerations for both types of solar energy systems. We will not dwell on the intricacies of individual component design, but instead encourage the designer to take experimental (or predicted) component input/output information and incorporate this into an overall system design. The system shown in Figure 1.1 employs parabolic trough line-focus collectors. We will cover this and other types of collectors for capturing the sun's energy including flat plate, parabolic dish, central receiver and photovoltaic collectors. The purpose of a solar collector is to intercept and convert a reasonably large fraction of the available solar radiation. For solar thermal systems this energy is converted into thermal energy at some desired temperature and then, maybe, into electricity. For photovoltaic systems as shown in Figure 1.2, intercepted solar energy is converted directly into low voltage direct current electricity. The engineering tradeoff between cost and performance of the components necessary to perform these processes has led to a wide variety of collector and system designs. Reviews of solar collector designs representative of the different concepts that have been built and tested are presented here. The following sections serve as an overview of the solar energy system design process. They follow in a general manner, the flow of logic leading from the basic solar resource to the definition of an operating solar energy conversion system that meets a specified demand...