The solar thermal power plant Andasol 3 in Andalusia for the first time produced solar generated steam during a test phase in which the rows of parabolic mirrors were aligned with the sun. This test is another successful step on the way to completing and commissioning the solar power plant which will generate 50 MW. Andasol 3 is due to begin commercial operation in October 2011 and, together with the neighbouring sister plants Andasol 1 and Andasol 2 which are almost identical in design. Andasol 3 has a thermal storage which enables the power plant to generate electricity reliably for up to eight hours even at night or in cloudy weather. The investors are the Stadtwerke München, Ferrostaal, RWE Innogy and RheinEnergie. The Spanish company Duro Felguera together with Ferrostaal, Solar Millennium and their joint subsidiary Flagsol were responsible for planning and constructing the solar power plant.