Concentrating solar power plant. Array of heliostats (mirrors with sun-tracking motion) at a concentrating solar power (CSP) plant. CSP plants use heliostats to reflect sunlight and concentrate it on to a small area. The concentrated solar energy is then used to produce electrical power. Here each mirror is equipped with a Sterling engine driven by a hydrogen gas filled piston. The sun's rays are focused onto the piston, heating the gas and driving the engine to generate electricity. Photographed at the Suncatcher Solar Power Plant, Peoria, Arizona, USA.