The trick is holding onto that energy and moving it around, storing it and then delivering it where people need it. That's why carbon-based sources like oil are so great. They're transportable and shelf-stable.

So how will people store and transport energy from renewable sources? Batteries.

Last night, Elon Musk outlined his plan to bring a Tesla battery to homes and offices, generally as an adjunct to solar panels—green energy, on demand. The billionaire CEO unveiled the Powerwall, a battery in 7 or 10 kilowatt-hour sizes. For bigger operations, there's also a 100 kWh unit called the Powerpack. And the Powerwall doesn't just let you bank late afternoon solar for late night bingeing; you can also pull power from the grid during off-peak hours. All this for $3,500.