@GiraffeEars- A number of great resources exists for learning how to become an energy consultant, but most important will be education and experience. There is no prescribed curriculum for an energy consulting so you will need to research the field and find where your skill set will be most competitive.
There are generally two main aspects of energy consulting so you should have a background in either resource planning technology and engineering. Ideally, it would be good for you to have both. I would recommend taking courses on the basic sciences (i.e., physics, geology, and chemistry), mathematics, energy basics, energy conservation, energy efficiency, and communication. Some sort of business training will also be very helpful, especially if you are trying to start your own consulting firm.
Besides education, you should try to find a job at an energy consulting firm. This will give you real world consulting experience. If or when you venture off on your own, it might be a good idea to offer some work pro bono (to an NPO or similar) to build references and a network base.