"In order for "alternate energy" to become feasible, it has to satisfy all of the following criteria:
1. It has to be huge (in terms of both energy and power)
2. It has to be reliable (not intermittent or unschedulable)
3. It has to be concentrated (not diffuse)
4. It has to be possible to utilize it efficiently
5. The capital investment and operating cost to utilize it has to be comparable to existing energy sources (per gigawatt, and per terajoule).
If it fails to satisfy any of those, then it can't scale enough to make any difference. Solar power fails #3, and currently it also fails #5. (It also partially fails #2, but there are ways to work around that.)
The only sources of energy available to us now that satisfy all five are petroleum, coal, hydro, and nuclear."
Like I said, read the whole thing.