There are a few but not many…
Some homeowners may not have suitable space. If you own an apartment or a condo you may not have rights to your roof space.
Solar relies on the sun, electricity can not be generated at night. Also clouds and storms restrict the amount of energy you can produce by blocking light rays that would have otherwise been absorbed by the solar panel.
Solar efficiency is also determined by the season. In the summer you can generate more electricity than you need because the sun is tilted closer to your location, while in the winter the sun is tilted farther from your location so you produce less energy.