For many applications it is desirable to deliver energy at temperature higher than those possible with flat-plate collectors. Decreasing the area from which heat losses occur can increase energy delivery temperatures. This is done by interposing an optical device between of source of radiation and the energy-absorbing surface. He small absorber will have smaller heat losses compared to a flat-plate collector at the same absorber temperature. This paper present a method to evaluate the thermal performance of parabolic concentrating collectors.