A part of a power block at the Andasol solar power station is pictured near Guadix, southern Spain June 29, 2015. The plant is the biggest solar farm in the world and provides electricity for up to about 500,000 people. The 620,000 curved mirrors harness the sun's power even after dark, and the glass alone would cover 1.5 square km (0.6 square miles) - the size of about 210 soccer pitches. REUTERS/Marcelo del PozoPICTURE 20 OF 25 FOR WIDER IMAGE STORY "EARTHPRINTS: ANDASOL SOLAR POWER STATION"SEARCH "MARCELO ANDASOL" FOR ALL IMAGES