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Beyond Photovoltaics: Rebirth of the Other Solar Power

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By the middle of this century we may be getting a quarter of our energy from concentrating solar power, according to a new study by Greenpeace and solar industry groups, but most of us have never even heard of this low tech cousin to photovoltaics.

Two years ago, neither had I, and then I stumbled across a young inventor somewhere north of the Oregon-California border who is obsessed with perfecting the technology to roast coffee. When I pulled off Highway 5 for a video interview I'd set up with the co-founder of Solar Roast coffee-- I'd discovered him randomly online while looking for stories to shoot on our roadtrip home from Seattle--, I was unprepared for the hands-on lesson I was about to receive in solar concentrating technology.

Beautiful solar

David Hartkop is no engineer, in fact, he's trained in special effects, but the machines he'd mounted in his parents' backyard were simply smaller versions of the international power stations being touted as the next great step in solar. The technology is basic: instead of converting the sun's energy directly into electricity via solar cells, concentrating solar power (CSP) uses mirrors to concentrate sunlight to either heat something directly (for cooking or in Hartkop's case, for roasting coffee) or to heat water into steam to drive a turbine to generate electricity.

No one had warned me that while solar concentrators may lack the tech appeal of solar cells, they trump photovoltaics with their beauty. Perhaps it was the early evening light, but when David uncovered his first concentrator experiment- an old satellite dish covered with hundreds of tiny mirrors-, I was dazzled. As I tried to focus on my shooting and not the warm glow around us, Hartkop explained, "the overall effect of having all these mirrors is that you can basically focus the sunlight to a target and the target was our coffee roaster and it would raise the temperature up to what we need to roast which is usually between 450 and 500 degrees Fahrenheit. The first test we did we were able to heat up aluminum hot enough to melt which is around 1200 degrees Fahrenheit so we knew we'd have more than enough power." (See here for the video of Hartkop's inventions).

Thousands of suns

It's so powerful because the mirrors magnify, or concentrate, the sunlight to create the effect of hundreds, or thousands, of suns focused on one spot. Since CSP technology isn't limited by the ability of solar cells to capture sunlight, it has proven to be up to five times more efficient than photovoltaics.

So why have so few of us heard of it? In 1990, 90% of the world's solar electricity was being produced by solar thermal (according to the ex-CEO of Luz International, the first company to use solar concentrators for commercial power plants), but then natural gas prices fell and U.S. solar tax incentives disappeared and the much smaller-scale, less capital-intensive, photovoltaic plants became the preferred option in solar.

Big solar: an easy transition from non-renewables

Today, solar thermal- due to it being more efficient and affordable than PV, as well as more practical on a large scale- is back in vogue. This week, German firms announced that they're planning to form a consortium, Desertec, to install concentrating solar thermal plants in the deserts of North Africa which could eventually supply 15% of Europe's energy needs.

CSP are seen by many as ideal for replacing conventional power plants, not only because it works better the hotter it gets- unlike photovoltaics which become inefficient at high temperatures-, but concentrators, like natural gas, work with turbines so their reliance on existing technology could facilitate the transition to renewable power plants on a massive scale.

The largest series of solar installations in history, is currently being planned for the Southern California desert, will rely on CSP technology. The deal between BrightSource (a reincarnation of Luz International) and Southern California Edison will, when completed, provide more than 1,300 megawatts of electricity, enough to power 845,000 homes.

Hartkop's first dish type design is now a part of his concentrator graveyard in his parents' backyard, but the same technology is being used by companies like Stirling Energy System for their 850MW Solar One project which will use 34,000 dishes to provide power for 600,000 Southern California homes.

The renewables triumvirate: wind, photovoltaics and CSP

With so many solar thermal power plants being planned, the Greenpeace-solar industry report estimates that by 2030, CSP could provide 7% of the world's electricity. "This technology is actually taking off", explained report co-author Sven Teske to the Guardian, "we wanted to highlight that we have a third big technology to fight climate change -- wind, photovoltaics and now CSP."

CSP comes in many designs- dish/trough/tower- and Hartkop has experimented with most of them. Another highlight of Hartkop's graveyard is his parabolic trough, a concentrator that looks like a very shiny skateboard halfpipe. It's the concentrator design with a proven track record: the first trough was developed in 1912 by an American inventor for the Egyptian desert and the design was used for the first modern commercial solar concentrators built in the the Mojave desert in the 1980s. While the majority of completed solar concentrators today still rely on this model, Hartkop's didn't get hot enough and is now nothing more than "a giant solar barbecue" sitting in his parents' front yard.

Solar power towers for coffee... and 240,000 homes

I didn't get to witness Hartkop's latest concentrator fully-built, but he did show me the parts under construction of his new design, which instead of roasting just 1-3 pounds of coffee like his previous models, this new "giant solar tower" can roast about 30 pounds. "With the new one we're focusing all of the light onto a receiver that gets very hot," explained Hartkop as he walked amongst the large metal pieces of his new structure, "we draw in air through the receiver and we'll be bringing super heated air down and into the coffee roaster."

This same technique is being used outside Seville, Spain with the world's largest solar power tower, except here Solucar's 20 megawatt plant uses 1255 mirrors (each about half the size of a tennis court) to focus energy at the top of a 165 meter tower to heat water and run a turbine.

It's powerful stuff, the PS20 plant will power 10,000 homes, but it's part of a much larger CSP complex that should begin providing electricity to 240,000 homes when completed in 2013. The Solucar solar thermal power station is a part of the reason that Spain, with more than 50 projects in the works, is leading the world in the concentrating solar field.

Behold the aura of a concentrator

There's something magical about concentrating solar power and I'm not the only one who has noticed. When BBC News science correspondent David Shukman first caught site of the world's first power tower (the PS10) back in 2007, he "couldn't believe the strange structure ahead of [him] was actually real". Shukman described the structure as "bizarre" and said the entire place had a "glow- even an aura", but he wasn't frightened by it. Hartkop wasn't so lucky.

A few months ago, I received an email from Hartkop's mother explaining that since my visit to their home, her son had packed up his power tower and installed it in Pueblo, Colorado (where they had headquartered Solar Roast Coffee several years ago after realizing that their California hometown didn't get enough sun). Apparently, initially, they'd had some trouble with zoning issues for their apparatus after "at least one neighbor saw the mirror assembly, and thought that it might shoot planes from the sky".

Though the story ends well, due to a bit of concentrating-solar-consciousness-raising by Hartkop. "Dave visited all the nearby homes and farms, and talked with everyone", continued his mother in the email, "so that by the time the zoning committee met in January, one of the original objectors was a vocal supporter."

Maybe it's time for mass consciousness raising. If we are truly in the midst of a concentrating solar revolution- something born out by the number of new gigawatts planned-, we may all need to brace ourselves for sitings of this solar with an aura.

More info

An article on the technology behind concentrating solar power, as well as the complete interview with Hartkop.

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