Yes, solar power electricity is sustainable in my opinion. The panels are already built to a certain capacity of energy that they can store, the source of energy these panels tapped are in abundance though timely because very early in the morning and late evening the sun is not always available but if there is large in built panel that can tap energy for at least eight hours in a day, this will be enough for usage till the sun rise again, it is also advisable to have more panels if you rely solely on solar power, so that you can always replace them, if this is properly done electricity can be made available every 24 hours. The expenses of installation of the source is usually a one time commitment and the benefits last also forever.