A single generator has well over a hundred properties you would care about and although we're talking about 5 minute data, there are many many overlapping simulations being run around the clock and many of those simulations look into the future for many days. Then you have load data, topology data, equipment outages, load and wind forecast, thousands of pricing points that can be further decomposed into constituent prices, changing bids and offers, energy transactions...I could type for the next hour and only cover a small amount of what I know which is still a small percentage of what we actually store.
From a time-series perspective, a single generator can show well over a hundred line-charts and you can do that off of multiple study types...and you might have well over a thousand generators in your market, not to mention all the other logged objects such as transmission lines which also have lots of properties logged. You're right that time-series data can be compressed, but the SQL data is somewhat different I think.
In short, energy markets are hugely complex creatures. There is just so much going on that I have yet to get bored and have a non-busy day in nearly a decade of employment. It's an extremely exciting field for sure as there is just so much going on and so much change occurring. In the not so distant future, many experts think the lines between transmission and distribution will become blurred and we'll all need even more data to run the grid at peak efficiency and reliability.