One of the most important issues of the first quarter of the 21st century will be clean, sustainable energy. I believe the key will be a panoply of sources: instead of using one process, one form of fuel (e.g., fossil fuels) to meet substantially alll of our energy needs, we will combine solar, geothermal, wind, waste biomass, and other sources as yet undiscovered so that no one thing has too big a burden.
One thing slowing progress is that, in part for reasons of infrastructure, petroleum is significantly cheaper than most other fuels. No one has any motivation to switch other than ecological altruism because it requires such a massive investment of time, money, and effort (to find a source for solar panels, or whatever it is).
In particular, using biodiesel in your car requires making it at home: there are no filling stations because so few people have appropriate vehicles, and no one wants a car that requires biodiesel because it’s so inconvenient to refuel.
One solution is to run your car on straight vegetable oil. This, however, makes it impossible to run the car on regular diesel fuel, which is available at filling stations, and it uses food crops (the U.S. grows so much corn that we feed it to cattle, whose bodies metabolize it far less efficiently and completely than grain, and make it into sweetener, which the government creates a market for by levying a tariff on sugarcane).
Another possibility is to use algae. Algae are easy to grow and not used for food, so there’s no chance of the fuel exacerbating food shortages. While the current method of extracting fuel from algae requires toxic solvents heavily regulated in this country, a company in Horseheads, N.Y., has developed a new solid catalyst that may alllow algae-based fuels to be produced at filling stations.