And since the largest planar area you can cover given a square meter of PV cells is flat, a cylindrical collector is actually less efficient than a flat panel. In fact it's efficiency is a factor of 2/pi (0.6366), since it's just the ratio of semi-circumference (half cylinder) to the diameter (flat). When some of the Solyndra generation data leaked out, they were indeed about 40% less effective at generating power than a flat panel.
Could they have arranged their half-cylinders in something other than a plane? Yes, but non-planar arrangements run into the problem of shadows from one collector covering up another collector at certain times of the day. The net result is worse than a plane. So flat panels are always best. If you want to capture oblique sunlight more effectively, the mathematically best solution is to tilt the panels to follow the sun (shadows from panel to panel will still interfere at extremely oblique angles). Or to raise reflectors at certain times of the day to reflect the sunlight into your static collectors.