Concentrator photovoltaics (CPV) is a photovoltaic technology that generates electricity from sunlight. CPV photovoltaic systems use lenses and curved mirrors to focus sunlight onto small, but highly efficient, multi-junction (MJ) solar cells. To keep the sun focused on the relatively small solar cells, CPV systems use solar trackers to keep the focus on the solar cells and sometimes use a cooling system to further increase efficiency.
Some good general references are:
Green Rhino Energy- Concentrating Photovoltaics (CPV)
An Arizona example: Agua Caliente PV Power Plant Among World’s Largest