Create Documentation

[jd-lara]

I am opening an issue to track the fact that we need to make the documentation for PowerSimulations.

[jd-lara]

List of items that need explicit documentation

• [ ] Document the required interfaces for custom OperationModel types
• [ ] Review all docstrings

[claytonpbarrows]

Formulation docs TODOs:

• [ ] how to describe expressions? e.g. which variables are added to the power balance expressions
• [ ] services
• [ ] slacks
• [ ] PWL cost equations
• [ ] Missing categories
  • [x] Storage
  • [ ] Thermal
  • [ ] Hybrid
  • [ ] Branch
  • [ ] Network
  • [x] Renewable
  • [x] Hydro
  • [x] Load