Non-uniform illumination produces significant local heating in concentration solar cells. In addition, it produces ohmic drops higher than expected, mainly because the cell operates locally at higher irradiance. Thus, a slight reduction in the open-circuit voltage and a stronger one in the fill factor are produced. However, the darker and colder part of the cell, at the maximum power point, becomes almost inactive, and this is beneficial because it contains the poor-quality edge region. Therefore, the only cell region in operation is the active illuminated part of the device, and it has excellent performances, so the reduction of overall performance is less than it might have been expected.