In short, there are none, except to agribusiness. Bioethanol is a failure, and always will be, just follow the math.
Premise 1: The vast majority of our imported fuel is used to power transportation. Cars, trains, ships, etc. The U.S. domestic oil supply can support trains, ships and planes. Cars are the only reason we import oil.
Premise 2: Very little oil is used to generate electricity. Most of that is generated by coal (49%), domestic natural gas (20%), nuclear (20%), hydro power (7%). All of these are domestic sources.
Premise 3: We don't really care how our cars get powered (ethanol, diesel, electric, gasoline, natural gas, etc) as long as they get the job done, i.e. transport us in safety and comfort from point A to point B. Therefore, all we really care about is the most efficient way to power cars that doesn't involve imported oil. Gasoline and diesel are out, so that leaves electricity, natural gas, and ethanol. Natural gas is another discussion. Let's focus on the easily comparable, and acre of corn versus an acre of solar cells. Which allows us to drive farther?
The average acre of corn produces 115 bushels. You get 2.5 gallons of ethanol per bushel. Let's get optimistic and round that up and say we get 300 gallons of ethanol per acre. The highest mileage cars get 40 miles per gallon. But ethanol is less energy dense, so the exact same car would get only about 28 miles per gallon of ethanol. Therefore in one year, and acre of corn will allow you to drive 8,400 miles. Sounds pretty good.
An acre-size solar panel can produce about 2,200 kilowatt hours (kwh) per 5 hour day, and in a year it can produce about 800,000 kwh. Now, there are line losses between the solar panel and the charging car, so figure a good 30% line loss. This means 560,000 kwh.
What does this mean for cars? The typical figures used is 0.25 kilowatt-hours (kWh) per mile traveled. So, one acre of solar cells should provide sufficient electricity for a electric car to travel...2.2 million miles. In other words, around 262 times what an acre of corn can achieve.
Now the comparison is not perfect. There are all sorts of losses and inefficiencies. But it is very hard to come up with any scenario where an acre of corn makes more fuel than an acre of solar cells. The bottom line is that plants are just really inefficient solar cells. Plants take solar energy and transform that energy into biomass, at an efficiency of just 1 to 2 %. Solar cells are typically > 10% efficiency. We take the biomass from corn and transform it into a more portable form, ethanol. A lot of the chemical energy is lost when we transition between corn and ethanol (those yeast need energy to grow - ethanol is their waste product). In additional, thermal engines are much lest efficient than electrical engines, and always will be. This is because much of the energy goes to heat, which is not used to move the car.
All in all, bioethanol is at best a transition technology to fully electric cars.
Now to get even dumber - we don't even need the acre of solar cells. If we charge the cars at night the current electrical capacity of the U.S. is sufficient to power most, if not all, the passenger vehicles on the road.
The only advantages to bio ethanol are the following:
1) Uses existing infrastructure and vehicles. Of course electricity uses existing infrastructure to deliver power right to the home.
2) Could potentially be made from non-food agricultural waste.
3) Could be used to power airplanes and boats.
4) Electrical cars are just coming on to the marketplace, and are likely to be expensive and inefficient in the short term, while chemical powered vehicles have been around for generations.