The major problem with using hemp as an alternative for energy creation is that it's illegal to grow hemp in America. Even though it's impossible to get high smoking hemp. There have already been successful experiments with hemp-oil powered cars in other countries. America's negative recent history with hemp is causing more trouble than makes sense, but it's not stopping innovators.
Every time you see a product made out of hemp, you can be sure that the hemp isn't coming from America. Other countries, Canada especially, have fast growing hemp industries. They are the one's making money selling hemp milk and hemp bracelets to stoners, vegans, and green minded people.
HempCar.org (top left picture) shows off their hemp-oil car all around the world as a way of promoting the hemp alternative. A group of Canadian companies in collaboration with an Alberta Crown corporation is building their own electric version of a hemp car, called a Kestrel (pictures on right). In this case the car is what is made out hemp materials. The fuel is electricity.
Hemp won't just power cars. We can use it to produce electricity and as a substitue for petroleum. That means we can stop looking for oil, and make our energy and plastics out of Hemp, which is a completely renewable energy source. The future of Hemp industry is going to big, just as soon as old prejudices in the American Government get out the way.