The problem solar panels have had to date is that they are more expensive than coal power ($3/W to $1/W). This is only really a problem of scale and funding though as is proven by the Nanosolar Powersheet which won the Popular Science Green Tech Grand Award for 2007. While they are no more efficient than the current solar cells, their manufacturing process makes them cheaper and quicker to produce while also making them more versatile.
By printing a layer of solar cells that use no silicon onto a wide range of materials as thin as a sheet of aluminium foil, these panels can be produced for a tenth the cost of traditional solar panels. And this is not just a pipe dream, funding from Larry Page and Sergey Brin have helped them build a plant that can produce 430 MegaWatts of panels a year and shipped their first batch of panels in December and have pre-orders for an entire years worth of production.