Among renewable energies wind power is number one. Wind energy facilities are cheaper to set up and maintain, require less infrastructure and generate greater returns in the long run. Wind power has become a booming global industry with new and ever larger wind farms springing up everywhere. Large scale facilities in particular are supposed to be crucial for a global switch to renewables. Over the last three years alone the number of wind turbines across the world has more than doubled. The GLOBAL IDEAS reporters have visited China, India, Morocco and Germany to investigate the promises ? and challenges ? of wind power.