I see some interesting points raised here, though I also have some fundamental disagreements.
Putting those first: what we need isn't more time, or an energy miracle. It's to embrace limits, the fundamental limits of Earth's carrying capacity, and how many people, of a given material affluence, can be supported. This is a question I've been looking at for the past several years, or more accurately, I've spent much of that time trying to figure out what the fundamental question was, starting from "what are the big problems?" My answer:
How do we embrace limits to growth?
Gates raises a few really excellent points.
He dismisses the problem of not having a price on carbon. I'd return that not only is that a problem, but we've a much larger issue of not fully accounting for the creation or replacement price of the fossil fuels we've been consuming at a breakneck rate -- some 5 million years of petroleum accumulation are consumed every year. That itself is an accident and error of early economic theory (one which was very nearly corrected in the late 19th century), and of early theories, and derived law, of mineral rights law (look up the "rule of capture" for a few hours of entertainment).
His mini-biographies on Parsons and Deisel, collectively the two people who now power much of the world, was a telling rebuttal to the claim that capitalism rewards innovation. Neither man made much from their inventions, Deisel, as Gates says, committed suicide in the face of bankruptcy.
On the storage front, there is one possiblity that's open to us: liquid hydrocarbons. They're not a net energy gain, but if we're looking for a storage solution that's high-density, highly flexible, and has very long-term proven storage life (100 million years and counting), electrically-generated synfuels offer a plausible pathway. Specifically seawater-based Fischer-Tropsch fuel synthesis, studied for over 50 years by Brookhaven National Labs, M.I.T., and the US Naval Research Lab. There are undoubtedly complications, but it's an underconsidered option.
Also on the storage front, the Dr. Sadoway mentioned is one of the recent superstars in battery storage technology. His molten salt battery isn't something you'd want to put in a car, but with extremely abundant (cheap!) substrates, could form the basis of city-scale electrical storage. Not for hundreds of millions of years, but days to weeks, evening out supply inconsistancies for a grid dependent on intermittent renewables. The fact that this technology is facing obstacles is disheartening. It's also why I advocate both considering sustainable, carbon-neutral paths to liquid hydrocarbon fuels, and embracing limits.