What type of solar energy technology has the most future potential? In terms of dollars per watt, using theoretical efficiency limits, what technology holds the most promise to become the primary solar energy capture technology? 
My hunch is carbon-based modules, since materials are abundant and relatively easy to manufacture; however their efficiency currently is nowhere near silicon-based semiconductors. In the future, assuming that scientists will push very close to the theoretical limits, what will provide the most power for the lowest cost?
If this is relevant at all, I am trying to decide where to focus my graduate studies in physics, and I want to contribute in getting the most promising technology to its limit. If you can at least point me in the right direction to figure out the answer myself, I would greatly appreciate it.
 A: As an ex-physicist who now works as a quant in power markets I think it's safe to say the physics of the matter will be swamped by the economics in commodities and how power markets work.  Two things to note:


*

*power prices are set by markets and not by the viability of the technology (prime mover)

*solar is hard to make money with w/o a long term Power Purchase Agreement (PPA) and those are SUPER hard to come by.
There are many viable technologies available right now that from a physics perspective look very promising but from a market perspective are dead in the water.  
Consider flywheels from Beacon power:
http://www.beaconpower.com/
They approached my company a year or so ago looking to put together a deal with our origination group.  The technology is sound, proven, and is clearly efficient.  It's a really sweet idea that has tons of promise.  Did we do the deal?  No.  Unfotunately pricing out regulation is hard and the rules that are followed by ISOs for payouts on regulation services are unclear.  The ISOs are interested in the technology but they are making up the rules as they go and companies that try to make money off the flywheels are currently going back and forth with them to create a market structure that can allow someone who owns this technology to make a reasonable return.  By reasonable I mean one that beats out gas, coal, oil, etc.  
My point is that the market structure (or lack of one) is killing the deals for new tech like this.. Not the efficiency. Same goes for the solar (and the wind). The prime mover that will succeed is the one that's pushed by the companies that understand how best to work the power markets. Siting and development (meaning leaning how to best construct the installation) are huge factors as well. It's a bad scene when your dev guys don't know how to properly handle the solar modules or manage a solar installation project.  It is indeed true that the physics of the technology must create a low-cost solution but the final word on success for a particular tech will be more based on the market acumen of the policy groups involved and the marketing/origination function than anything else. 
Storage tech like flywheels from Beacon are a huge part of this puzzle too 'cause the sun never seems to be out exactly when you need it and the wind blows best during off peak hours. :)  You need a good way to store the power so you can release it during favorable times of the day.
All in all, figuring out what tech is 'most promising' is more than just making a choice based on physics.  It's a good question tho.  Ur best bet is to talk to someone in power-markets from a big company like Constellation, PG&E, or perhaps TVA and ask them about the hurdles those technologies face.  Then marry that up with a physics assessment on efficiency and you'll get a good hint on which tech to help push forward with your studies.
