I suspect coal. The local power comes from a mix of contracts with plants using coal, a wind farm, nuclear plants and natural gas peaking. More wind farm proposals have been fought in court, "Not on my backyard!" I only know of one solar array & it's not very big. There had been a bigger one but a hail storm took it out. We just had a storm that started with freezing sleet, then 10" of drifting snow. The wind turbines, I can see from the road are offline, blades are covered with ice. Went by the solar array and it was covered in ice & snow. Neither has a battery storage system. There is a natural gas peaking plant near where I live. Went by it last night and could see condensate coming out of the building, so it was running. -12°F. There haven't been any major power interruptions for at least 20 years. Back then an ice storm took down a major transmission line. At home, last summer, we lost power for a few hours after a tornado dropped some trees on a power line. System is pretty reliable. I've got a gas fireplace @ home that I can operate w/o any electricity. There are two hydroelectric dams in the state connected into the grid. With all the interconnects it would be hard to tell where my power is coming from at any point in time.
I addition to Nebraska having a publically owned electrical system, we are the only state that does not have a two house state legislature. Putting up with one batch of politicians is considered more than enough here.