We have fabricated a functional prototype of an ultralight power converter tile; a modular building block for a space-based solar power system. The tile is ~10 × 15 cm in area, and weighs 4.5 kg/m 2 . It comprises a photovoltaic (PV) solar energy collector, a radio-frequency (RF) power converter, and an array of transmission antennas. The PV collector subassembly utilizes ~15x, 1D parabolic trough reflective concentrators with triple-junction (3J) solar cells. It has areal mass of ~0.8 kg/m 2 , 74% optical efficiency, and a peak specific power of ~230 W/kg. We demonstrated wireless power transmission over a distance of ~50 cm in our lab. Analysis of the sources of mass and inefficiency suggest a path towards achieving dramatically higher performance with future designs.