Merge pull request #1111 from oemof/revision/remove-discounting-funct…

…ionality

Remove internal discounting functionality

docs/usage.rst

@@ -1201,8 +1201,6 @@ but with a few minor additions and modifications in the investment object itself
   free to reinvest or choose another option to fill up the missing capacity.
 * You can define an initial `age` if you have `existing` capacity. If you do not specify anything, the default value 0 will be used,
   meaning your `existing` capacity has just been newly invested.
-* You can define an `interest_rate` that the investor you model has, i.e. the return he desires expressed as the weighted
-  average osts of capital (wacc) and used for calculating annuities in the model itself.
 * You also can define `fixed_costs`, i.e. costs that occur every period independent of the plants usage.
 
 Here is an example
@@ -1218,7 +1216,6 @@ Here is an example
                     maximum=1000,
                     ep_costs=1e6,
                     lifetime=30,
-                    interest_rate=0.06,
                     fixed_costs=100,
                 ),
                 variable_costs=3,
@@ -1252,7 +1249,6 @@ This would mean that for investments in the particular period, these values woul
                     maximum=1000,
                     ep_costs=[1e6, 1.1e6],
                     lifetime=30,
-                    interest_rate=0.06,
                     fixed_costs=[100, 110],
                 ),
                 variable_costs=3,
@@ -1327,13 +1323,6 @@ Besides the `invest` variable, new variables are introduced as well. These are:
 
 .. note::
 
-    * You can specify a `discount_rate` for the model. If you do not do so, 0.02 will be used as a default, corresponding
-      to sort of a social discount rate. If you work with costs in real terms, discounting is obsolete, so define
-      `discount_rate = 0` in that case.
-    * You can specify an `interest_rate` for every investment object. If you do not do so, it will be chosen the same
-      as the model's `discount_rate`. You could use this default to model a perfect competition administered by some sort of
-      social planner, but even in a social planner setting, you might want to deviate from the `discount_rate`
-      value and/or discriminate among technologies with different risk profiles and hence different interest requirements.
     * For storage units, the `initial_content` is not allowed combined with multi-period investments.
       The storage inflow and outflow are forced to zero until the storage unit is invested into.
     * You can specify periods of different lengths, but the frequency of your timeindex needs to be consistent. Also,

src/oemof/solph/_energy_system.py

@@ -182,6 +182,8 @@ def __init__(
             self._extract_periods_matrix()
             self._extract_end_year_of_optimization()
             self.use_remaining_value = use_remaining_value
+        else:
+            self.end_year_of_optimization = 1
 
     def _extract_periods_years(self):
         """Map years in optimization to respective period based on time indices

src/oemof/solph/_models.py

@@ -52,9 +52,6 @@ class Model(po.ConcreteModel):
         Solph looks for these groups in the given energy system and uses them
         to create the constraints of the optimization problem.
         Defaults to `Model.CONSTRAINT_GROUPS`
-    discount_rate : float or None
-        The rate used for discounting in a multi-period model.
-        A 2% discount rate needs to be defined as 0.02.
     objective_weighting : array like (optional)
         Weights used for temporal objective function
         expressions. If nothing is passed, `timeincrement` will be used which
@@ -84,17 +81,6 @@ class Model(po.ConcreteModel):
     rc : `pyomo.core.base.suffix.Suffix` or None
         Store the reduced costs of the model if pyomo suffix is set to IMPORT
 
-    Note
-    ----
-
-    * The discount rate is only applicable for a multi-period model.
-    * If you want to work with costs data in nominal terms,
-      you should specify a discount rate.
-    * By default, there is a discount rate of 2% in a multi-period model.
-    * If you want to provide your costs data in real terms,
-      just specify `discount_rate = 0`, i.e. effectively there will be
-      no discounting.
-
 
     **The following basic sets are created**:
 
@@ -134,7 +120,7 @@ class Model(po.ConcreteModel):
         InvestNonConvexFlowBlock,
     ]
 
-    def __init__(self, energysystem, discount_rate=None, **kwargs):
+    def __init__(self, energysystem, **kwargs):
         super().__init__()
 
         # Check root logger. Due to a problem with pyomo the building of the
@@ -190,9 +176,7 @@ def __init__(self, energysystem, discount_rate=None, **kwargs):
         self.dual = None
         self.rc = None
 
-        if discount_rate is not None:
-            self.discount_rate = discount_rate
-        elif energysystem.periods is not None:
+        if energysystem.periods is not None:
             self._set_discount_rate_with_warning()
         else:
             pass

src/oemof/solph/_options.py

@@ -63,11 +63,6 @@ class Investment:
     age : int, :math:`a`
         Units start age, given in years at the beginning of the optimization;
         only applicable for multi-period models
-    interest_rate : float, :math:`ir`
-        Interest rate for calculating annuities when investing in a particular
-        unit; only applicable for multi-period models.
-        If nothing else is specified, the interest rate is the same as the
-        model discount rate of the multi-period model.
     fixed_costs : float or list of float, :math:`c_{fixed}(p)`
         Fixed costs in each period (given in nominal terms);
         only applicable for multi-period models
@@ -95,7 +90,6 @@ def __init__(
         overall_minimum=None,
         lifetime=None,
         age=0,
-        interest_rate=0,
         fixed_costs=None,
         custom_attributes=None,
     ):
@@ -111,7 +105,6 @@ def __init__(
         self.overall_minimum = overall_minimum
         self.lifetime = lifetime
         self.age = age
-        self.interest_rate = interest_rate
         self.fixed_costs = sequence(fixed_costs)
 
         for attribute in custom_attributes.keys():

src/oemof/solph/components/_generic_storage.py

@@ -414,26 +414,18 @@ class GenericStorageBlock(ScalarBlock):
 
     **The following parts of the objective function are created:**
 
-    *Standard model*
-
     * :attr: `storage_costs` not 0
 
         .. math::
             \sum_{t \in \textrm{TIMEPOINTS} > 0} c_{storage}(t) \cdot E(t)
 
-
-    *Multi-period model*
-
-    * :attr:`fixed_costs` not None
+    * :attr:`fixed_costs` not 0
 
         .. math::
             \displaystyle \sum_{pp=0}^{year_{max}} E_{nom}
-            \cdot c_{fixed}(pp) \cdot DF^{-pp}
+            \cdot c_{fixed}(pp)
 
-    where:
-
-    * :math:`DF=(1+dr)` is the discount factor with discount rate :math:`dr`.
-    * :math:`year_{max}` denotes the last year of the optimization
+    where :math:`year_{max}` denotes the last year of the optimization
       horizon, i.e. at the end of the last period.
 
     """  # noqa: E501
@@ -585,26 +577,19 @@ def _objective_expression(self):
         r"""
         Objective expression for storages with no investment.
 
-        Note
-        ----
-        * For standard models, this adds nothing as variable costs are
-          already added in the Block :py:class:`~.SimpleFlowBlock`.
-        * For multi-period models, fixed costs may be introduced
-          and added here.
+        * Fixed costs (will not have an impact on the actual optimisation).
+        * Variable costs for storage content.
         """
         m = self.parent_block()
 
         fixed_costs = 0
 
-        if m.es.periods is not None:
-            for n in self.STORAGES:
-                if valid_sequence(n.fixed_costs, len(m.PERIODS)):
-                    fixed_costs += sum(
-                        n.nominal_storage_capacity
-                        * n.fixed_costs[pp]
-                        * (1 + m.discount_rate) ** (-pp)
-                        for pp in range(m.es.end_year_of_optimization)
-                    )
+        for n in self.STORAGES:
+            if valid_sequence(n.fixed_costs, len(m.PERIODS)):
+                fixed_costs += sum(
+                    n.nominal_storage_capacity * n.fixed_costs[pp]
+                    for pp in range(m.es.end_year_of_optimization)
+                )
         self.fixed_costs = Expression(expr=fixed_costs)
 
         storage_costs = 0
@@ -1096,8 +1081,6 @@ class GenericInvestmentStorageBlock(ScalarBlock):
         Lifetime for investments in storage capacity"
         ":math:`a`", "`flows[i, o].investment.age`", "
         Initial age of existing capacity / energy"
-        ":math:`ir`", "`flows[i, o].investment.interest_rate`", "
-        interest rate for investment"
         ":math:`\tau(t)`", "", "Duration of time step"
         ":math:`t_u`", "", "Time unit of losses :math:`\beta(t)`,
         :math:`\gamma(t)`, :math:`\delta(t)` and timeincrement :math:`\tau(t)`"
@@ -1785,7 +1768,7 @@ def _objective_expression(self):
             )
             for n in self.CONVEX_INVESTSTORAGES:
                 lifetime = n.investment.lifetime
-                interest = n.investment.interest_rate
+                interest = 0
                 if interest == 0:
                     warn(
                         msg.format(m.discount_rate),
@@ -1807,7 +1790,7 @@ def _objective_expression(self):
                     )
                     investment_costs_increment = (
                         self.invest[n, p] * annuity * present_value_factor
-                    ) * (1 + m.discount_rate) ** (-m.es.periods_years[p])
+                    )
                     remaining_value_difference = (
                         self._evaluate_remaining_value_difference(
                             m,
@@ -1825,7 +1808,7 @@ def _objective_expression(self):
 
             for n in self.NON_CONVEX_INVESTSTORAGES:
                 lifetime = n.investment.lifetime
-                interest = n.investment.interest_rate
+                interest = 0
                 if interest == 0:
                     warn(
                         msg.format(m.discount_rate),
@@ -1848,7 +1831,7 @@ def _objective_expression(self):
                     investment_costs_increment = (
                         self.invest[n, p] * annuity * present_value_factor
                         + self.invest_status[n, p] * n.investment.offset[p]
-                    ) * (1 + m.discount_rate) ** (-m.es.periods_years[p])
+                    )
                     remaining_value_difference = (
                         self._evaluate_remaining_value_difference(
                             m,
@@ -1874,9 +1857,7 @@ def _objective_expression(self):
                             m.es.periods_years[p] + lifetime,
                         )
                         fixed_costs += sum(
-                            self.invest[n, p]
-                            * n.investment.fixed_costs[pp]
-                            * (1 + m.discount_rate) ** (-pp)
+                            self.invest[n, p] * n.investment.fixed_costs[pp]
                             for pp in range(
                                 m.es.periods_years[p],
                                 range_limit,
@@ -1891,9 +1872,7 @@ def _objective_expression(self):
                         m.es.end_year_of_optimization, lifetime - age
                     )
                     fixed_costs += sum(
-                        n.investment.existing
-                        * n.investment.fixed_costs[pp]
-                        * (1 + m.discount_rate) ** (-pp)
+                        n.investment.existing * n.investment.fixed_costs[pp]
                         for pp in range(range_limit)
                     )
 
@@ -1965,15 +1944,11 @@ def _evaluate_remaining_value_difference(
                     self.invest[n, p]
                     * (remaining_annuity - original_annuity)
                     * present_value_factor_remaining
-                ) * (1 + m.discount_rate) ** (-end_year_of_optimization)
+                )
                 if nonconvex:
                     return convex_investment_costs + self.invest_status[
                         n, p
-                    ] * (n.investment.offset[-1] - n.investment.offset[p]) * (
-                        1 + m.discount_rate
-                    ) ** (
-                        -end_year_of_optimization
-                    )
+                    ] * (n.investment.offset[-1] - n.investment.offset[p])
                 else:
                     return convex_investment_costs
             else: