To gain a deeper understanding of the anatomy of solar electric systems, we will begin with the grid-connected system, the simplest of all three. We begin with a basic schematic, shown in Figure 7-1. As you can see, this system consists of three main parts: a solar module, an inverter, and the main service panel. Let’s begin with the solar array.

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Image caption: Fig. 7-1

The anatomy of a grid-connected solar electric system.

Like all other solar systems, the grid-connected system consists of one or more solar electric modules also known as photovoltaic or PV modules (Figure 7-1). Each solar module consists of numerous smaller solar cells, usually round, square, or rectangular cells about 1/100th of an inch thick and made from silicon dioxide (Figure 7-2a). Silicon dioxide comes from a highly ubiquitous material, high-grade sand, and quartz rock. The solar cells most widely used today typically consist of two thin layers of silicon. As illustrated in Figure 7-1b, each cell in a module has numerous thin metal electrical connections (metal contacts) on the surface that gather up electricity generated by the cell.

A solar or photovoltaic cell is a solid state device that absorbs visible light and converts its energy to electricity. How that works is fascinating, but beyond the scope of this book. Suffice it to say that when sunlight strikes a PV cell it liberates electrons from silicon atoms. Thanks to some ingenious chemistry (boron and phosphorus are added to different layers of the PV cell), these electrons are forced to migrate from one side of the cell to the other, where they are drawn away by the metal contacts on the cell’s surface, as shown in Figure 7-2b. Flowing electrons form an electrical current.


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Image caption: Fig. 7-2

(a)Two solar cells.

(b)Note that solar cells consist of two layers. Light striking the layers liberates electrons from the silicon atoms. These atoms flow from the deeper layer to the more superficial layer and then are drawn off by the metal contacts on the surface, creating direct current electricity.

Because silicon reflects about 35 percent of the light striking it, the cells are coated with a thin, anti-reflective layer of silicon monoxide or titanium dioxide; it is applied after the metal contacts have been put in place. The back of the cell is made of a thin layer of metal that completes the electrical circuit, as shown in Figure 7-2.

Silicon cells are mounted in the metal-backed module casing and wired in series to boost the voltage. The unit is sealed by a clear layer of glass or, in some cases, durable sun-resistant plastic. Glass and plastic prevent moisture from reaching the cells and also resist the pounding force of hail stones. Typical modules produce between 40 and 200 watts of electrical power under peak sunlight conditions, although some manufacturers are producing larger modules that produce 300 watts. Numerous modules together form a solar array.

PV modules are typically mounted on a durable metal rack. The rack may be located on a roof of a home or on the ground in a sunny location with good access to the sun year round.  ....read more