No need to think only within your own state borders. Germany has lots of wind farms and not much pump storage potential as well, they just send their surplus energy south to Austria for storage. Kansas could easily do the same with Colorado - ofc they would have to build more facilities first (afaik).

We export power all over the Southwest Power Pool actually! SPP even trades with ERCOT when we can and help them out if they're short. Kansas is quite green, with about 65% coming from renewables (Mainly wind, then nuclear), but we're too far north for Solar to be {wildly profitable|cost effective}, and wind doesn't blow all the time. Given our climate, with temps as low as -32f in the winter, and 105f in the summer, that unfortunately means we can't rely on renewables 100%. The only practical choice is coal and gas, which isn't my preference, but that's where we're at. I'd love to have a second nuclear plant somewhere in the state.

Ironically Colorado is a very hard partner to trade with. The major consumer (Denver) is in the center of the state. The entire eastern half is an empty plain and the western half of Kansas is a slightly less empty plain. From population center Kansas City to Denver is about 600miles, make energy trade a little impractical. They make a ton of their own wind energy on their open plain, and they were late adopters; they learned a lot from Kansas's expensive mistakes on wind power.

> but we're too far north for Solar to be {wildly profitable|cost effective}

If land is not overly expensive, then vertical bifacial solar can be quite viable. With snow or a light non-vegetated surface you should expect around 15% capacity factor in the worst month at 40 degrees and it will be skewed heavily towards morning/evening and slightly toward cloudy days compared to monofacial.

Doesn't get rid of the fossil fuels on its own, but should be cheap enough to displace most coal that remains after wind at a significant profit.

Can you create an underground reservoir, say from an expired oil field, that is of sufficient capacity to create a pumped hydro system in concert with a ground-level reservoir?

In theory, yes. But I do not believe an oil field would be suitable.

Hydro relies on a pressure difference. This means you want the turbine located at the lower reservoir, which is going to be tricky with an oil well. Oil fields are not a hole filled with oil but instead are just porous rock, which greatly limits the flow rate you can achieve from a single well. Oil fields are already pressurized, so you'd actually need to put in energy to get water in there.

And of course you'd be contaminating the water with oil and gas, which makes the upper reservoir a bit of an issue.

Sounds like oil fields are better suited to compressed gas storage. I wonder if salt caverns would work though? To solve the pump location issue, you could perhaps pump down air to get the water to come up.

We do have a ton of salt caverns actually, many centrally located (Hutchison, Ks if you’re interested. Great air and space museum there too oddly enough)

Unfortunately, water has the nasty habit of dissolving salt. As the Lake Peigneur Disaster taught us, mixing the two is generally a really bad idea.

That's how they create the salt caverns in fact: they pump hot water below impermeable limestone formations that were created when Kansas was an ocean 290 million years ago during the the Permian period. They use seismographs to watch the cavern formation and steerable drill bits to shape the formation.

Still need a place to keep all the water after you pump it out of the cave.

We call that a "pond".

Today I learned that the high point in Kansas is 4039 feet above sea level, and was marked by a plaque that states "ON THIS SITE IN 1897 NOTHING HAPPENED" until 2015 when the plaque was stolen.

You are spot on. Mt. Oread has 191 ft of prominence.

There's even a paper on it "Kansas Is Flatter Than a Pancake": https://www.usu.edu/geo/geomorph/kansas.html