the inability of current technology to capture large amounts of the Sun's energy
the inability of current technology to store captured solar energy
inconsistencies in the availability of the resource
lack of demand for solar energy
Third choice: inconsistencies in the availability of the resource I think this is it. If we come to depend on solar energy, then we're expectedly out of luck at night, and we may unexpectedly be out of luck during long periods of overcast skies.
