My research paper focused on determining how the cars of the future will be powered: electricity or ethanol from algae. Our economy has become so dependent on cheap transportation that increasing fuel prices are driving up the cost of every other good on the market. With that in mind, it's time we focus on transportation in a future in which oil is neither as available nor inexpensive as it is has been.
I found that PHEVs are not that far off, and that their progress depends greatly on improvements in battery technology. Once batteries have longer lives and are more dense in terms of energy storage, the PHEV age will soon begin. We are going to need more power plants, but aside from those capital costs, the infrastructure will not need dramatic changes to help usher in PHEV technology as our main means of transportation. The downfall is that essentially every car on the road would have to be replaced or adapted. However, as battery technology improves, the costs associated with PHEVs would be expected to drop considerably.
Ethanol has been much maligned recently as well all know. The current ethanol production industry in America relies greatly on government subsidies, but those subsidies won't last forever. Algae-based ethanol has a very promising future when evaluated on its environmental advantages. Right now, the technology is very expensive (~$20/gal), but those costs will come down as more research is done. Every car on the road today is capable of converting its fuel system to accept ethanol on a scale of $100s, but filling stations are not so flexible. It will cost about $34 trillion to convert existing stations to pump ethanol, and an infrastructure that large would be needed to support ethanol as the main transportation fuel. This bill would fall on the shoulders of private station owners as Big Oil has refused to even talk about the conversion costs on several occasions. Ethanol would still require the use of gasoline (the other 15% in E85) and emissions would only be improved slightly over gasoline usage.
When both technologies are compared, it seems that PHEVs are going to be the long-term (~50 years) winner. There will still be a need for an energy-dense liquid-fuel in the future, and algae-based ethanol could help fill that role. PHEVs scale much better than algae-based ethanol.