Powering the Dream_ The History and Promise of Green Technology - Alexis Madrigal [132]
The principle is well known to any school kid who has used a magnifying glass to burn ants. It goes like this: The sun’s direct rays can be collected over a relatively large surface and focused onto a point. Make your lens or mirror bigger and the point gets increasingly hotter.
Variations on the burning mirror theme had captivated a certain kind of aristocratic mind for millenia. Passed down through a clan of dedicated polymaths from Archimedes, who purportedly used them to set fire to the Roman fleet besieging Syracuse, to DaVinci, to the seventeenth-century Jesuit brainiac Athanasius Kircher, the secret of how to focus the weak power of the sun into an intense heat capable of burning a wooden navy was just emerging from legend and myth into the more prosaic realms of a newly science-obsessed Europe.4
But how could one make a burning mirror of sufficient size to drive a steam engine or smite your enemies? Large amounts of shiny material in a concave shape were not easy to come by—and it was heavy. In the early 1800s a mirror smaller than the one over a bathroom sink weighed 110 pounds.5 Some enterprising nobles broke their materials into segments and attached them to concave wooden scaffolding. That yielded mirrors with diameters up to five feet. Etzler, however, had a different idea. He wanted to use whole arrays of flat mirrors focused on a large boiler. In his 1833 manifesto, The Paradise Within Reach of All Men, Without Labour, By Powers of Nature and Machinery, Etzler wrote,
It is immaterial, too, of what size, form, or colour the pieces of such a mirror be; they are all to be of a flat surface. There is no curvature of their surface required as in the usual burning mirrors. All that is required for producing a focus, or burning spot, where all the reflections are concentrated, is to give each flat piece of such mirrors its proper place and inclination towards the sun.6
The question of how, exactly, to keep those mirrors in their proper place was easy. It “requires no laborious computation or preparation,” he wrote. They could be kept aligned with “nothing more” than “moving the mirror to the sun’s motion for casting its concentrated reflection or focus always on the same spot.” Etzler was a great futurist, but he was never much of an engineer.
Tracking the sun is perhaps the toughest problem solar engineers face, which Etzler might have known if he had read about Léon Foucault’s Heliostat or one of the other devices that eighteenth-century thinkers built to track the sun in natural sciences experiments. It was not until the early 1840s that any type of device to point the sun’s light in a particular direction was available. And Johann Silbermann’s heliostat could move only a tiny mirror, suitable only for microscopic investigations. By 1862 Foucault’s was bigger and better, but it, too, was nowhere near the scale required to point a bunch of mirrors at a boiler to make it produce steam.7 When a Greek engineer tried to replicate Archimedes’s legendary mast-burning feat in 1973, it took seventy-three perfectly coordinated men holding flat mirrors to set a wooden ship aflame.8
How far Etzler got in his experiments is unknown, but we can almost be sure that he failed, leaving only the idea behind. It waited to be rediscovered for more than a century.
The good news is that sun tracking is a data and control problem in an era defined by new advances in data collection and precise control of large systems.9
And it was there that a successful Internet entrepreneur-turned-investor named Bill Gross began to reimagine solar power plants for the twenty-first century. How to keep the mirrors pointed in the right spot with the least effort led his company, eSolar, down a remarkable, datadriven path that led Google to make the Los Angeles startup one if its first two energy