The use of a selective absorber in a solar air collector permits the lowering of the forward heat loss by radiation to the environment. This technique improves the thermal heat performance of the collector, but it raises the cost price of the installation. To increase performance, it is essential to reduce the absorber temperature and in consequence the forward heat loss. To this effect, using finned systems, a fully developed turbulent flow is created, that cools the absorber and raises the air temperature. That remedies the low thermophysical properties of the air and at the same time shows that the use of any black-painted plate, as a nonselective absorber, permits the attainment of high thermal efficiencies with low cost.