What is the best way for the US (or any other country) to generate 50% of its energy from renewable (or at least source that will last for 500 years) source in the next 20 years? My personal favorite is PV in the US Southwest with water->hydrogen as a storage medium for over night and for transportation. I am also a long time fan of solar power satellites but I think ground based is cheaper. I think the factor that is stopping the deployment is that both of the above are expensive. And for a country that can not even balance it's budget investing trillions of dollars in the future seems unlikely.