What went wrong with CPV?

For decades, green-energy advocates and solar power researchers struggled with a simple problem: nearly endless energy, freely available from the sun, and no economical way to collect it. With solar cell costs higher by an order of magnitude than conventional energy generation at the turn of this century, a straightforward solution presented itself: get a single solar cell to generate a large amount of energy by using cheap optical devices to funnel light from a large area into a small cell. By circumventing the cost issue in this way, these “concentrator photovoltaics,” or CPV, were hailed as the most promising pathway to low-cost solar electricity.