Practical multi receiver concentrator photovoltaic systems operating at high solar concentration levels up to 2000 suns experience large radiation, thermal and electrical loads in addition to large power density transients under routine operation. These systems require efficient cooling to manage the associated incident power densities between 100 to 200 W/cm2. Photovoltaic cells and thermal interface materials experience considerable stress under these load conditions. Their assembly is sensitive to contamination and process optimization. Efficient optical coupling of light at high concentration requires precise component alignment and tracking. We will discuss high power testing of single and multi receiver, high concentration systems comprising commercial triple junction cells, Fresnel optics, electric actuators, and cooled through a metal thermal interface using active and passive cooling methods. © 2010 IEEE.