In Ray Kurzweil's 2005 book "The Singularity Is Near: When Humans Transcend Biology", he covers a lot of ground. One very small section has to do with the possible benefits of nanotechnology on the energy sector. While he may be right about the future benefits, I don't think his facts are very accurate about the present.

On page 249 he has a number of figures about the efficiency of "commercially available" solar cells, stating among other things that today's solar cells are 34% efficient. I'm not sure where he got his figures, but the best I've been able to find is about 17.5% (which is for the individual solar cells, not the panels that are actually installed). In addition, the price that he quotes, $2.75 per watt is considerably less than the best I've found, which is $4.47 per watt. And those prices only include the solar panels themselves, not any of the supporting equipment (inverters, mounts, installation costs, etc).

Below are some of the solar panels I found for sale on the web.

Brand	Model	Type	Watts	Cost ($)	Cost/Watt ($)	Effic. (%)
Sharp		mono-crystal	185	$879.95	$4.76	17.5/14.21
BP	3125U	silicon nitride multi-crystalline	125	$598	$4.78
Kyocera	KC120	multi-crystal	120	$535.95	$4.47	14%
Kyocera	KC167G		167	$769	$4.60

1 17.5% cell efficiency, 14.2% panel efficiency.