The following post summarizes the author’s Chapter 7 of Let It Shine: The 6,000-Year Story of Solar Energy.
Alarmed by the prodigious amount of coal consumed as the industrial revolution moved forward, a French mathematics professor, Augustine Mouchot, warned in 1860 that “Eventually industry will no longer find in Europe the resources to satisfy its prodigious expansion…Coal will undoubtedly be used up” He then asked, “What will industry do then?” It must “reap the rays of the sun,” the French professor concluded.
Mouchot first studied what had already been done in times past to put solar energy to use. Mouchot discovered many fascinating solar machines built over the millennia, beginning with a sun-run siphon developed by Hero of Alexandria in the first-century BCE. To produce steam, he found the best combination would be to build a concave mirror that focused on a glass-covered boiler. On its first trial run in 1866, it vaporized enough water to run the world’s first solar-powered steam engine. “It functioned marvelously after an hour exposed to the sun,” he wrote, full of enthusiasm. He went on to construct even larger sun machines.
A reporter described one of his new solar motors on display by the public library at Tours in these words: “The traveler who visits the library of Tours sees in the courtyard in front a strange-looking apparatus. Imagine an immense, truncated cone that looks like a mammoth lamp shade, with its concavity directed skyward.” The reactions was one of amazement – a motor that ran without fuel, on nothing more than sunbeams.
In a later device, Mouchot amazed crowds in Paris by making ice from solar energy. He had connected to the sun motor a heat-powered refrigeration device invented a few years earlier. As Mouchot wrote, “Under a slightly veiled but continually shining sun, I was able, in spite of the seeming paradox, to utilize the rays of the sun to make ice.” While Parisians viewed the experiment as some magic show, Mouchot saw it as something that promised a great opportunity for the future, where sun-generated ice in tropical climates would keep food from spoiling. He was also the first to generate electricity from sunlight.
The principle behind his success was simple: When heat, in this case solar heat, is applied to the junction where two metals are soldered together, an electrical current is generated. But he had bigger plans: To heat the junctions of a hundred such bi-metallic couplings and in this way generated enough electricity to separate hydrogen from water and to store the hydrogen for fuel when the sun did not shine. But for all his efforts, he could not compete with the more efficient methods of electrical generation rapidly being perfected at the same time.
Non-steam uses for Mouchot’s concentrating solar apparatuses proved to be the most practical and popular. He replaced the boiler with a glass-enclosed cylindrical metal pot in which he baked a pound of bread in forty-five minutes and a perfect roast in less than half an hour. In another demonstration, he passed brackish water through the boiler to make it potable. The French Foreign Legion cooked in the lands of North Africa their meals with Mouchot’s solar oven. In remote areas of Algeria, settlers and explorers used his solar stills to make the brine water heavily charged with magnesium salts drinkable.