Reuters: The Milan trade fair said on Tuesday it is commissioning the world’s biggest rooftop photovoltaic power installation covering some 270,000 square meters. "We have had seven offers from general contractors to build the plant and we’ll very soon trim that down to five. The winning bid will be the one that offers us the highest rental," said Ferruccio Ferranti, CEO of Sviluppo Sistema Fiera, a unit of the Milan fair group. Under the deal, the winning bidder will build the plant at …