The biggest problems I see with the alternatives to coal/gasoline/CNG is that there are no really viable storage solutions for them. Hydrocarbons store the energy locally and are available for use at any time.
Solar is great, while the sun is shining. Wind power is great (other than for birds and the people who live near them) while the wind is blowing. There is no convenient, low-loss way to store the energy created from these sources; all of them include pretty heavy conversion losses through converters/inverters or using the electricity generated to generate and store hydrogen. Batteries on a scale to provide storage for these to support a grid are clearly completely unattainable. Believe me, I'm not diametrically opposed to these technologies- I've done several projects with photovoltaics, solar space heating, and hydrogen fuel cells and think they are fascinating, but the realist in me says using these technologies large scale adds many more layers of complexity and opportunities for failure than coal/NG plants.
I also can see nuclear being a viable form of inexpensive generation- I was in the Navy and you can see when you run reactors on sound principles with extremely rigorous training and procedures, you too can have a 60+ year record of flawless operation. However, when you toss in lackadaisical maintenance procedures and cost-cutting to please bean counters, you can seriously run afoul in a horrible way.
Shannow, to (partially) answer your question, I think we have had some answers or at least good paths to chase for over 100 years which have either been suppressed or talked up enough as "crazy" or "impossible" as to discourage anyone from pursuing those technologies. Things like Tesla's bladeless turbine, wireless electrical transmission, and things like capturing radiant energy fascinate me to no end. I think Tesla had it right- we are awash in energy all around us; we simply need to let nature provide the work and harness it. Just think of what he may have achieved had his ideas not directly challenged the fortunes of the industrial tycoons of the day...