API changes
* The component `Transformer` is renamed to `Converter`.
When people hear "transformer", they think of electrical devices.
However, the Transformer is neither meant to be (only) electrical
nor bidirectional (as electrical transformers typically are).
Thus, the more generic term "converter" is now used.
(Note that we always had the argument "conversion_factor".)
* Unify API for constant sized objects and sizing of investment. For both, `Flow` and
`GenericStorage`, the argument `investment` is now deprecated. Instead,
`nominal_value` and `nominal_storage_capacity` accept an `Investment` object.
* Change investment for experimental :class:`oemof.solph.components.experimental._sink_dsm.SinkDSM`: Remove
obsolete parameters `flex_share_down` and `flex_share_up`.
* Mainline link component :class:`oemof.solph.components._link.Link` from experimental.
New features
* Add option to run multi-period (dynamic) investment models with oemof.solph as an experimental feature:
* You can change from standard model to multi-period model by defining the newly introduced `periods`
attribute of your energy system. Be aware that it is experimental as of now. `periods` is a dictionary
mapping the periods you want to model (usually years) to pandas.date_range objects.
* Add attributes `periods` to :class:`oemof.solph._energy_system.EnergySystem`.
* Introduce new Pyomo Sets `PERIODS` and `TIMEINDEX` in :class:`oemof.solph.models.Model`.
* Index all investment-related variables with `PERIODS` and flow variable with `TIMEINDEX`, which
is a tuple of periods and timesteps.
* Add lifetime tracking for investment options by introducing the attributes `lifetime` and `age`.
* Add new investment-related variables `total` holding the total capacity, `old` holding capacity
to be decommissioned, `old_exo` (for exogenous) holding existing capacity to be decommissioned and
`old_end` holding model-endogenously installed capacity to be decommissioned after its lifetime.
* Include discounting and calculating annuities in the objective function terms. Introduce attribute `discount_rate`
of :class:`oemof.solph.models.Model` and `interest_rate` for individual investment objects (options.Investment).
* Add `storage_level_constraint` that allows to set flows from/to storage (in)active based on storage content.
* `Model` now accepts a list of `EnergySystem` objects, which allows for modelling of cellular energysystems.
Documentation
* See extensive documentation in user guide and API reference for the new (experimental) multi-period feature.
* Be more strict about about oemof (meta package) oemof.solph (this package).
* Improved presentation of examples as part of the documentation.
Bug fixes
* Fixed error when calling `oemof_installation_test` as console script.
* Corrected several typos in the docs.
* Periods with multiple period lengths are now supported in multi-period investment.
* Add missing 'custom_attributes' for the link component
Testing
* Add tests for experimental SinkDSM component.
* Add tests for multi-period investment.
Contributors
* Johannes Kochems
* Patrik Schönfeldt
* Tobi Rohrer
* Julian Endres
* Jann Launer
* Lennart Schürmann