Early Solar Power Technology

In the centuries after the fall of the Roman Empire in the fifth century CE, the study of solar energy focused on so-called “burning glasses.” As noted by various Greek philosophers, mirrors and convex lenses can be used to concentrate the Sun’s rays, generate significant heat, and potentially start fires. Researchers throughout the Middle Ages made an effort to refine and improve burning glasses, and to experiment with mirrors to amplify their effect. In this regard, the centre of research shifted to the Muslim world in the tenth and eleventh centuries. Persian scientist Ibn Sahl investigated the properties of light and mirrors, and, in his work On Burning Mirrors and Lenses (984 CE), was the first to detail and explain refraction—the bending of light as it passes through different materials. Perhaps the most prolific researcher on this topic was Alhazen, a Basra-born scientist and mathematician who lived most of his life in Cairo, Egypt. Alhazen made innumerable contributions to the study of optics, and further refined the understanding of how mirrors and lenses could focus sunlight and generate heat.

This research continued on into the seventeenth and eighteenth centuries, as scientists experimented with various ways to refine and improve the technology. In addition to using it to ignite fires, scientists began to explore wider applications of this process. In short, how could the power of the Sun’s energy be captured, concentrated, and then applied to some other practical purpose? French engineer Salomon de Caus was one of the first to do so, using a burning glass to power a small water pump and fountain in 1615. In 1747, the French King Louis XV was presented with a mirror that could concentrate light to such a degree that its heat could melt silver. And twenty years later, Swiss scientist Horace-Bénédict de Saussure developed the first solar oven (or ‘heat box,’ as he called it), which captured the heat from the Sun’s rays through several layers of glass. The heat was sufficient to generate a temperature inside the box of 110°C (230°F). By the end of the eighteenth century, however, the practical applications of solar energy were still very limited.

The possibility of an expanded role for solar power came with the Industrial Revolution of the late eighteenth and early nineteenth centuries. With the development of steam-powered factory machinery and transportation, coal became the most important fuel in the industrialized world. Some, however, believed that solar energy offered a viable alternative as a power source. French scientist Augustin Mouchot was an early advocate of alternative energy; he cautioned that the world’s supply of coal was finite and could run out with little notice. With the financial backing of the French government, Mouchot developed a series of solar concentrators that powered steam engines in the 1860s and 1870s. Other scientists were inspired by Mouchot’s work and found ways to apply solar power to other sorts of machines, including water pumps and the printing press.

The full potential of solar energy, however, went unrealized. Solar powered machinery was typically large, expensive, and not terribly efficient. Scientists like Mouchot had faith in the future of the technology, but long-term research and development of solar power required substantial time and investment. With the cost of coal declining by the early twentieth century, and few pausing to heed Mouchot’s warning about the dangers of overreliance on a non-renewable energy source, the perceived benefits of solar power did not outweigh the costs; conventional fuels were simply cheaper and much more efficient. By the turn of the twentieth century, the application of solar power as an energy source for modern technology was still in its infancy.