Generation planning: making sure there is adequate generation of the right type at the right place to serve future demands.
I'm sure physicists will sneer at the idea, but a power engineer has to deal with physics and human behavior at the same time. We may approach quanta at the fast end of the time spectrum and demographics/politics at the slow end. The point is that it is a continuum. In some regions of the time domain behavioral and physical models overlap and interact. Engineers, but not scientists, are forced to deal with both.
For example, in the region of days-months, the dominant equations are the economics of the energy/capacity markets but everything bought or sold must conform to what the grid and the power plants are physically able to do. An operating plan must also be prepared for any weather nature might deliver, plus a spectrum of equipment failures and repairs.
These things can not be divided up and solved separately; they interact. We do however, break up the problem into different time domain regions. We partition by duration not by discipline.
Roughly speaking, anything less than 15 minutes is almost purely the comfortable domains of physics/chemistry/nuclear.