From the relatively basic idea of concentrating the Sun's rays to start fires or burn holes, to the much more sophisticated concepts embodied in today's systems for producing solar electricity, the concept of harnessing energy from sunlight has been translated into many forms over the years. In fact, tapping the Sun's potential as a virtually unlimited source of energy has been a tantalizing—but largely unrealized—vision that's now taking on increasing significance as the global consumption of energy stretches the long-term capacity of the Earth's nonrenewable natural resources. Although conventional photovoltaic cells have been around since the late 1950s, solar electricity still only contributes less than 1% to global electric power generation according to Strategies Unlimited, a PennWell company that has been tracking photovoltaic markets for 25 years. Hurdles to widespread commercial implementation of solar electricity generation include the lack of sunlight in certain regions and the relative inefficiency and cost of the photovoltaic cells, which have made it difficult for solar systems to compete economically with the entrenched infrastructure of existing alternatives.
It appears, though, that the balance is starting to tip more in favor of solar power. Driven by manufacturing process improvements, efficiency gains, and competition—and buoyed in part by government support for solar energy in Japan, Germany, and California—photovoltaic cell and module shipments have grown at a very respectable compound annual rate of 39% since 1998, according to Strategies Unlimited (see www.strategies-u.com). Last year's shipments increased by 49% compared to 2001 to reach a peak power capacity of almost 508 MW. In the future, additional growth will likely come from new applications for solar power beyond simply generating electricity for a national grid. Potential applications range from "blackout proof" solar-powered traffic signals to powering homes in remote locations (see p. 59). Additional advances include alternative materials systems for the photovoltaic cells and improvements in the efficiency with which electricity is used (such as solid-state lighting; see p. 99). These efforts will contribute to the future growth of economical solar energy production. Given the additional benefits of reduced pollution and lower greenhouse-gas emissions, perhaps we are seeing the dawn of a new era of solar power.