The three industrial boilers at the state-owned Codelco mine high in the mountains here once consumed 67,000 barrels of diesel a year to turn out shiny copper sheets for export. Now, the job is powered by nearly 3,000 solar panels that take advantage of the Atacama Desert’s cloudless blue sky. As the cost of solar and wind power declines, renewable energy has become increasingly attractive to power-hungry mining companies. Nowhere, though, is it more prevalent…