The other day when driving all day in my car and thinking about a documentary I have seen about different scientific endeavors to find the new ultimate energy source, I was thinking what will happen when we'll run out of fossil fuels. Considering the way they were created, it is not possible to start producing more of them, and it is also undeniable that they WILL run out. What other source of energy can replace them? I mean solar, wind, hydro energy can power static sources like houses, but what about fuels that will power airplanes or boats for example?

I know solar powers space missions, but I am not sure it can power airplanes securely...also, what will happen once we do not have the fossil fuel backup anymore?