Most promising green technologies number ten: hydrogen

We are sure to catch some flack for choosing hydrogen as a promising green technology, but can't we all agree that there's some amount of potential in it? Consider the super clean emissions of a properly engineered hydrogen-burning vehicle. Even if a hydrogen-burning powerplant were not the main source of energy for a vehicle, either an engine running on hydrogen or a small fuel cell could provide additional range to an otherwise strictly electric vehicle. There are certainly many hurdles to overcome, but a huge amount of money is betting on the technology, and we've got to include it here. With an eye to the critics, we place hydrogen at spot number ten.

Let's move on to Number 9.