RETURN OF THE SOLAR CHIMNEY?

Solar chimneys: Light at the end of the tunnel?
Jason Deign, 27 May 2010 (CSP Today)

"The idea for solar updraft towers…[originated in 1903]…In 1982 a German engineer…[trapped hot air] under a wide expanse of heat-absorbing material and then forced [it] up a central ventilation shaft, powering a turbine in the process…[but] only two fully-functioning solar updraft towers have ever been built: a 22-metre-high chimney in Botswana in 2005, and the 1982 prototype constructed by Jörg Schlaich of Schlaich Bergermann and Partners in Manzanares, Spain…

"Schlaich admits his pilot tower—a small-scale construction which produced up to 50 kW, had a height of 195 metres and a heat-collecting canopy measuring 46,000 sq meters…[was not optimal but] impressed with the results… In the Manzanares pilot, daytime heating of the ground under the canopy meant air continued to be heated into the night, driving the turbine around the clock. Researchers were also surprised to find that condensation allowed plants to blossom in the erstwhile dry earth…"

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"…[A solar chimney] requires no water, has virtually no running costs and can be built from low-tech materials…Professor Christos Papageorgiou, whose company FSC Technologies aims to commercialise air-filled, fabric-based ‘floating solar chimneys’ in place of rigid solar updraft towers, estimates a 5 MW plant could be built for around €10 million, producing some 20 GWh per year….[FSC argues that 3% of Earth’s desert] and 1%-efficient solar aero-electric power plants…can produce 50% of [world electricity in 2050]…

"But first the concept will have to win over sceptics, including many in the investor and analyst communities…[They say solar updraft towers] are inefficient, take up a lot of land..[are] not cost-effective…[have investor-detering] long lead times…[and] might lose out to more conventional projects, such as photovoltaic arrays…"

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"Despite this, Schlaich, who acknowledges solar updraft towers are not a proven technology and only become economically viable when very large projects are involved, remains upbeat, citing growing interest in Nigeria, Saudi Arabia and Germany…[T]he recent history of solar updraft towers is littered with grand projects, from a 750-metre tower planned for Ciudad Real, Spain, to a 1.5km high chimney in Namibia, that have yet to see the light of day.

"So while there is something alluring about the image of towers soaring over a kilometre into the sky and creating clean energy and cropland from barren desert sand, whether we will ever witness them more than 100 years after the first sketches is clearly still anyone’s guess."