That would be hydro. After all, there's a reason the liberals are in a rush to tear out all of America's dams.
These days you don't need a huge dam to produce a lot of electricity. New generator technology makes the small dams far more viable. 10 or 15 feet of head is enough to produce something in the range of 1 half to 1 megawatt. Unlike wind, they produce every day all day. I can show you a report on two small dams in Ann Arbor Michigan that says those dams where the flow actually exceeds capacity around 28% of the time. When the wind exceeds the capacity of a windmill the generator stops. When the water exceeds the capacity of a dam, the excess is dumped over a spillway and the generators keep spinning.
There are a LOT of dams in the midwest. There are hundreds in Michigan alone. Granted, most wouldn't be viable but enough would be to help make us the world's leading oil and gas exporter.
Now imagine the number of dams east of the Mississippi and the one thing I actually like about the smart grid is the ability to feed electricity into it from multiple locations.