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In a patchwork of agricultural fields outside Seville, Spain, two otherworldly towers rise above the plain. Nearby arrays of mirrors reflect light onto the towers, illuminating the water vapor and dust suspended in the air and creating visible beams. Within the towers, the thermal energy from the concentrated light creates steam, and the steam powers turbines to generate electricity. Known as PS10 and PS20, the mirror-tower networks are part of a larger project intended to meet the energy needs of some 180,000 homes—roughly the energy needs of Seville—by 2013, without greenhouse gas emissions.

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite captured this false-color image of PS10 and PS20 on August 29, 2009. Red indicates vegetation, shades of brown indicate bare ground and/or fallow fields, and blue indicates water. Human-made structures appear in shades of blue-gray. PS10 and PS20 appear as approximate circles punctuated by towers on their southern ends. Although less conspicuous than the circular arrays, rectangular arrays of mirrors operate south of the towers.

The mirrored heliostats that make up the arrays track the Sun’s position throughout the day and send concentrated energy to the nearby towers. A BBC correspondent who ascended PS10 in the spring of 2007 recorded sauna-like temperatures and searing ladder rungs near the tower’s top, and a mirror-illuminated glow to the entire area. PS20 began operating two years later.

As this image shows, the network for PS20 is larger than that for PS10. The tower sizes and energy capacities differ as well. Reaching a height of 115 meters (approximately 380 feet), PS10 is powered by 624 heliostats. Reaching a height of 165 meters (approximately 540 feet), PS20 is powered by 1,255 mirrored heliostats. PS20 was designed to produce twice the energy of its smaller, 11-megawatt neighbor. The towers both produced more energy than expected during trial tests. Although not the world’s first power towers, PS10 and PS20 became the first project executed on such a large scale.

NASA image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Caption by Michon Scott.