In this project the technological challenges related with very high concentration levels (1000 suns) have been undertaken and solved. More specifically, the main goals achieved have been: - Concentrator GaAs solar cells with an efficiency of 25% at 935 suns and 21.9% at 2243 suns whose short-circuit current (25.77 mA/cm2) has been confirmed at Fraunhofer Institute. - Design and manufacturing of RXI-40 optical concentrators with a current gain of 1110 (geometrical concentration 1256), an acceptance angle of +/- 1.6 degrees for 90% of the maximum value and an aspect ratio of 0.27. - Temperature drop in operation from solar cell to ambient lower than 32º C. Several complete concentrator prototypes have been fabricated. Due to the low yield in this experimental phase, which is not a mass production one, no prototype has reached a high efficiency. However, the best experimental values obtained indicate that an efficiency of the whole prototype of 19.3% could be obtained. It is important to stress that this efficiency could be obtained with our present technology because there is no trade-off between the best values reached independently. The manufacture of the prototype has been done by incorporating several standard processes of Optoelectronics. As a consequence of this, together with the high efficiencies obtained as well as the high concentration level used (1000 suns) a PV plant nominal cost of 2.82 Euros/Wp and a cost of the electricity of 0.094 Euros/kWh could be obtained based on a 10 MWp production. If learning is applied, a PV plant nominal cost of 0.81 Euros/Wp and a cost of the electricity of 0.030 Euros/kWh could be obtained for the medium term based on a 1000 MWp production. The prototype is ready for further development oriented towards an industrialisation in order to build commercial flat concentrator modules.