Support Planning reserves

[staadecker]

Here's a summary of discussion on the planning reserves module for reference. We've decided to put work on this on hold for now.

Current state

• Currently storage technologies can't contribute to planning reserves.
• Currently all other technologies (incl. non-renewable) can contribute to planning reserves.

Issues

• Storage is expected to be an important source of reserves in zero-emission scenarios.
• In zero-emission scenarios, it doesn't make sense to have thermal plants as reserves.

Potential solutions

• Allow different scenarios to specify which types of energy sources are allowed (e.g. one scenario allows only renewable).
• Allow storage to contribute to planning reserves, this requires reformulating the model to consider state of charge of storage technologies. Pedro mentioned a 4-hour rule where storage technologies need to have enough storage for 4 hours to be considered as contributing to reserves (or something like that?).

[staadecker]

Update

Another thing I just noticed is that hydro is currently always credited its entire rated capacity for reserves (even if we can't dispatch nearly as much due to the average hydro flow constraint). @pesap @jszinai @PatyHidalgo

One solution is to rewrite the average hydro flow constraint to constrain a variable which is a maximum dispatch value and then to use that variable in the reserves module.