IT GETS hot in Eldorado Valley,so Gilbert Cohen wakes early. Midsummer temperatures here in the Nevada desert regularly top 45 掳C. Cohen needs to be out in the field by 5 am if he is to get a day鈥檚 work done before the heat becomes unbearable. It also means that Eldorado is the perfect place for Cohen鈥檚 company to construct a solar power plant that could mark the renaissance of a proven but little-used technology.
Concentrated solar power (CSP) is the forgotten energy system. For some 20 years, nine CSP plants in California鈥檚 Mojave desert have been providing electricity for 350,000 people. The design is simple: parabolic mirrors focus the sun鈥檚 rays onto a chamber full of oil, heating it to almost 400 掳C. The hot oil is then used to provide steam for a conventional turbine that generates the power.
鈥淐oncentrated solar power is the forgotten energy system: it鈥檚 only recently that the economics have started to make sense鈥�
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The technology works, but it is only recently that the economics have started to make sense. 鈥淔ive years ago the banks didn鈥檛 want to talk,鈥� says Cohen, a senior vice-president at Acciona Solar Power in Raleigh, North Carolina. 鈥淣ow they call us every day. They want to get in on this.鈥�
The interest is partly a reflection of CSP鈥檚 extraordinary potential. According to an analysis published in Science last September (vol 313, p 1243), 39,000 square kilometres of CSP plants in the south-western US could supply half of the country鈥檚 energy needs. The technology may also provoke less hostility than other large-scale sources of renewable power such as wind farms, which often hit the buffers when locals object. CSP works best where the sun is most reliable 鈥� desert areas in which there often are no locals.
Hikes in the cost of rival energy sources have played a bigger role. Prices for natural gas are three times what they were a decade ago. Many US states are also forcing power companies to use renewable sources or limit greenhouse gas emissions, which will also bump up the cost of using fossil fuels.
At around 15 cents per kilowatt-hour, compared with around 4 c/kWh and 7 c/kWh for gas and nuclear respectively, CSP is still pricey, but in states like Nevada electricity demand peaks when the sun shines and people turn on air-conditioning. As demand soars, so does the cost of electricity, right up into the price range in which Acciona鈥檚 CSP plant will operate.
Longer term, CSP will be able to compete at all levels of demand, says Robert Pitz-Paal, who studies CSP technology at the German Aerospace Centre in Cologne. He predicts that the cost of CSP will halve over the next 10 years as the firms involved gain more experience. A decade later, it could be down to 5 c/kWh.
Future plants will also add a significant new advantage to the solar equation. Many renewable technologies are at the mercy of the elements. If the day is still, so are wind turbines. CSP is different. Plants can be built so that the hot liquid they produce is stored and used to drive the turbines hours or even days later. That allows them to operate during the night or when it is cloudy, making them much more flexible 鈥� and financially valuable.
That outlook has persuaded at least four power companies in the south-western US to sign contracts for CSP plants. Acciona鈥檚 facility, known as Nevada Solar One, will generate 64 megawatts when it opens this month. Outside the US, things are moving even faster. Spain has several CSP projects under construction. Algeria, which hopes eventually to profit by supplying green energy to Europe, signed a contract for a new plant last year. Two CSP facilities of different design are also being tested in Australia.
Not everyone is buying into the CSP hype, however. Jay Apt, a former NASA astronaut who studies electricity markets at Carnegie Mellon University in Pittsburgh, Pennsylvania, says the technology will only expand if the cost falls quickly enough 鈥� and he sees no guarantee that it will. Alternative low-carbon technologies such as coal plants that capture carbon dioxide and store it deep underground may well prove cheaper. It鈥檚 worth taking a bet on CSP, Apt says, but perhaps only a small one at this stage.
