A major step forward has been made towards cost reduction of terrestrial PV. World-record multijunction III-V solar cells have been integrated into a commercial Concentrator Photovoltaic (CPV) system.. A dense array of high-efficiency solar cells in the receiver of a high-intensity (∼500x) concentrator system has been identified as a viable, cost-effective system. Concentrator Ultra Triple Junction (CUTJ) cells have been developed for use in the Solar Systems CS500 solar electric power generator. The cell is designed for efficient conversion of the specific solar spectrum delivered to the system receiver while minimizing cell cost. Cells are optimized for maximum active area in a Solar Systems dense-array cell module. Solar Systems modules using CUTJ dense-array cells have demonstrated module efficiencies of over 35%. Field testing of CUTJ dense-array cells in a CS500 CPV dish unit at the Hermannsburg solar power plant in Australia was initiated in December 2005. A full multi-junction receiver in a CS500 dish has delivered over 30kW with an efficiency of almost 30%. Following qualification, these systems are slated for entry into the terrestrial market in 2006.