The Olmedilla Photovoltaic Park in Olmedilla de Alarcón, Spain, is the world’s largest photovoltaic plant. The Olmedilla Photovoltaic (PV) Park uses 162,000 flat solar photovoltaic panels to deliver 60 megawatts of electricity on a sunny day. It produces enough electricity to power more than 40,000 homes. The entire plant was completed in 15 months at a cost of about $530 million at current exchange rates. Olmedilla was built with conventional solar panels, which are made with silicon and tend to be heavy and expensive. So-called "thin-film" solar panels, although less efficient per square meter, tend to be much cheaper to produce, and they are the technology being tapped to realize the world's largest proposed PV plant, the Rancho Cielo Solar Farm in Belen, N. Mex., which is expected to cost $840 million, cover an area of 700 acres (285 hectares), and produce 600 megawatts of power.