Direct to Liquid Fuel
Experimental technology such as the Counter Rotating Ring Receiver Reactor Recuperator (CR5) at Sandia National Laboratories is demonstrating the conversion of solar energy directly into fuels like ethanol that are combustible in existing gas engines without modification. www.landartgenerator.org/blagi/archives/415
Another example is the work being done by Joule Biotechnologies Inc. in Massachusetts.
Although the process takes CO2 from the atmosphere, because the combustion of the fuel that comes from these technologies most likely produces CO2 again as a byproduct, the wide application of these systems could be seen as carbon neutral.