WIP: feedstock cost model and variable o&m

[elenya-grant]

Feedstock Cost Model

Note: this depends on work done in PR #219 and will require further additions to work done in PR #218 before this can be finalized

Added feedstock cost model that is flexible to handle different types of cost profiles. Costs can be provided as:

• a scalar, which means that costs are constant across timesteps and years
• a list that has a length equal to plant_life which means that costs are constant during a year but may change year-to-year
• a list that has a length equal to n_timesteps which means that costs change per timestep.

PR Checklist

• CHANGELOG.md has been updated to describe the changes made in this PR
• Documentation
  • Docstrings are up-to-date
  • Related docs/ files are up-to-date, or added when necessary
  • Documentation has been rebuilt successfully
  • Examples have been updated
• Tests pass (If not, and this is expected, please elaborate in the tests section)
• PR description thoroughly describes the new feature, bug fix, etc.

Related issues

Impacted areas of the software

• h2integrate/core/feedstocks.py
  • FeedstockCostConfig: configuration file for feedstock costs
  • FeedstockCostModel: cost model for some generic feedstock
• h2integrate/core/model_baseclasses.py: added VarOpEx output
• h2integrate/core/test/test_feedstock.py: new file for testing feedstock component.

Remaining to-dos

• add connection to feedstock cost component in h2integrate/core/h2integrate_model.py
• update both models in h2integrate/core/finances.py to include variable o&m (this is waiting on profast refactor pull-request to be merged in)
• Also requires PR on time information to be merged in

Additional supporting information

Test results, if applicable

[johnjasa]

Closing this as the changes have been included in #221 and #235