Ultimately, the problem with solar, wind, and any other "periodic" or localized generation method is storage and distribution. I live in an area with incredibly cheap power due to hydro dams that generate well in excess of what we need. However, there's only so much we can do with that excess in terms of efficiency of generation because it costs so much to send that energy long distances.

In addition, you have the obvious periodic nature of solar and wind, which mean that not only do you have the distribution problems, but you also can't just flick it on and offset a bunch of peak load or burst demand (such as when hospitals "turn on" in the morning).

You could have 100% efficient solar technology, and it wouldn't change much the economics of green energy because of the physical nature of problem. Thus, you need to change how we deal with the physical nature, and thus the economics themselves by improving the technology in other places. I work for a startup which is building a combination of efficient storage infrastructure and a distributed software system to help manage the heuristics of controlling supply and demand with this storage system and generation technology (including solar and wind, but also traditional generation as well), helping to do things like smart "time shifting" of energy supply.

Since superconductors are still a ways off, and even with them it doesn't change the nature of periodic generation, I think storage technology is likely the most important area for investment in the immediate future (and not just because that's where my paycheck comes from :) )