In 2011, Amonix installed over 35 MW of concentration photovoltaic arrays across the U.S. Southwest. In order to meet the competitive price targets of these projects, improvements have been made across the power path, from optics to cell. Modules that were fielded in 2011 produced over 20% more power than those fielded in 2009. The recent deployments provide feedback that enables ongoing optimization for field conditions. The ratio of currents that are generated by each of the subcells in the III-V multijunction is monitored and compared to prediction. An understanding of the balance in subcell currents leads to retuning of the epitaxial structure for higher energy yield. Losses in the optical path, including the effect of gridline width, have been reduced substantially. High-production cell efficiencies, combined with significant improvements in the optical path, have led to peak dc module efficiencies that exceed 34% under operating conditions. A record module rating of 33.5% outdoor operating efficiency has been confirmed by the National Renewable Energy Laboratory.