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Chapter 1
Introduction
1.1 Photovoltaics – What's It All About?
Photovoltaics is a technology involving the direct conversion of solar radiation (insolation) into electricity using solar cells. Interest in photovoltaics has grown exponentially in many countries over the past decade, with worldwide photovoltaic sector growth since 1997 ranging from 30 to 85%.
A solar cell is essentially a specialized semiconductor diode with a large barrier layer which, when exposed to light, allows for direct conversion into DC electricity of a portion of the energy in the light quanta or photons arriving at the cell (Figure 1.1).
As individual solar cells generate very low voltage, a number of such cells are connected in series and are combined into a so-called solar module. Higher output can be obtained by wiring a number of modules together to create solar generators, which can be of any size.
The first usable solar cell was developed in 1954, and solar cells were first used for technical purposes in connection with space flight. Virtually all satellites that have been put into orbit around the Earth since 1958 are powered by solar cells, which were originally called solar batteries. The high cost of these early solar cells posed no obstacle to their use, since they were extremely reliable, lightweight and efficient. Following the 1973 oil crisis, interest in renewable energy increased, particularly in terms of solar power. Interest in photovoltaics has grown even further since the Chernobyl accident in 1986, which spurred the development of simpler and cheaper solar cells for terrestrial applications. This first generation of solar cells was initially used to supply electricity to remote locations (e.g. telecommunication facilities, holiday homes, irrigation systems, villages in developing countries and so on, as for instance shown in Figures 1.2–1.9). For such applications, photovoltaics has long since been an economically viable energy resource.Figures 1.2–1.9
The USA was in the vanguard of PV development and use in the 1980s, at which time various multi-megawatt PV power plants that had been built in desert regions were converting solar cell DC power into AC power that was being fed into the public grid. Many of these installations integrated single- or dual-axis solar trackers. The first such installation, which had 1 MW of power, was realized in 1982 in Hesperia, followed by a second, 6.5 MW, installation in Carrizo Plain. Both of these installations have since been dismantled. In the late 1980s, the Chernobyl disaster aroused interest in grid-connected systems in Europe as well. For many years Europe's largest PV installation (3.3 MWp) was the facility in Serre, Italy, which was connected to the grid in 1995. In recent years, PV power plants of 5 MWp and more have become increasingly prevalent in Germany and Spain. At the time this book went to press, the largest such plant was the 60 MWp PV power station in Olmedilla de Alarcon, Spain (around 150 km west of Valencia), which began operating in 2008. Various, even larger PV power stations are under construction or in the planning stages, including a 2000 MWp facility in China.
The largest PV power station in Switzerland (1342 kWp) is the BKW facility atop the new Stade de Suisse football stadium in Bern, where the first phase of the installation (855 kWp) began operating in 2005. Two years later the facility was expanded to full nominal capacity, and as at December 2009 was still the world's largest football stadium PV installation. Another large Swiss PV installation is the 555 kWp Mont Soleil power station, which is located at 1270 m above sea level and was connected to the grid in 1992. Information concerning other large-scale PV installations is available at www.pvresources.com. Various grid-connected systems around the world are shown in Figures 1.10–1.16.
