Sunrise for solar heat power
Four technologies aim to use heat from the sun to make electricity. But which one has the edge?
Nearly a century ago, American engineer Frank Shuman erected five immense, trough-shaped mirrors in Meadi, Egypt. The parabolic reflectors directed sunlight onto a tube suspended above their 200-foot lengths. Water inside the tubes boiled and created steam. The steam powered a 65-horsepower engine, which pumped 6,000 gallons of water per minute from the Nile River to nearby cotton fields. It was the world’s first concentrated solar power (CSP) plant.Skip to next paragraph
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CSP entails focusing the sun’s rays with a reflective surface and putting that energy to work. These days, the heat usually goes to generating electricity. But the principle is quite old.
The ancient Chinese used concave mirrors to start fires, and, according to legend, the Greek mathematician and scientist Archimedes once used mirrors, perhaps of polished bronze, to ignite and burn an invading Roman fleet.
Shuman was addressing a concern of his time: Fossil fuels, particularly coal, powered the Industrial Revolution – the trains and mills, among other things, that radically changed human experience. But what happens when they ran out?
“One thing I feel sure of, and that is that the human race must finally utilize direct sun power or revert to barbarism,” Shuman told Scientific American magazine in 1911.
Fighting during World War I destroyed Shuman’s plant. But in the end it was cheap, abundant oil that obviated his ideas – or seemed to.
The oil crises of the 1970s again piqued interest in CSP, and, in the 1980s, plants resembling Shuman’s began cropping up in the Mojave Desert. Then natural-gas prices plummeted and the cycle repeated itself. No new commercial-scale CSP plants were built for nearly 20 years.
Now CSP is poised for a second – or third, depending on when the count begins – renaissance. And this time, say experts, it’s here to stay. World CSP capacity is forecast to increase nearly 18-fold in the next five years, from its current 588 megawatt potential to around 10.5 gigawatts. (Very roughly, 100 megawatts is enough energy to power 80,000 houses.) More than half of that new CSP capacity will be installed in the United States.
Several factors are driving the CSP boom. Although utility companies have long viewed CSP as an option for generating electricity from the sun, they’ve hesitated to commit to the technology. That’s partly because CSP becomes efficient and cost-effective only at the megawatt (MW) scale.
Photovoltaics, by contrast, can be installed piecemeal on the kilowatt scale – a panel here, another there. And that’s why photovoltaics have so far dominated the solar market.
Now, the specter of carbon regulation has shifted attention back toward CSP. The prospect of large-scale solar plants is again attractive. The “renewable portfolio” standard – which requires increased production of energy from renewable sources – has also encouraged investment in CSP. And the investment tax credit – a potential 30 percent credit on qualifying solar projects – has made investors more willing to risk capital in CSP ventures.
Solar is here to stay, now