Add storage_costs to GenericStorage

examples/storage_costs/storage_costs.py

@@ -0,0 +1,143 @@
+# -*- coding: utf-8 -*-
+
+"""
+General description
+-------------------
+Example that shows the parameter `storage_costs` of `GenericStorage`.
+A battery is used to make profit from fluctuating electricity prices.
+For a battery without storage costs, it is beneficial to be empty
+the end of the time horizon of the optimisation. For a battery that
+assumes the average revenue, energy is kept at the end. 
+
+
+Installation requirements
+-------------------------
+This example requires oemof.solph (v0.5.x), install by:
+
+    pip install oemof.solph[examples]
+
+
+License
+-------
+`MIT license <https://github.com/oemof/oemof-solph/blob/dev/LICENSE>`_
+"""
+
+import numpy as np
+import pandas as pd
+from matplotlib import pyplot as plt
+
+from oemof import solph
+
+
+def storage_costs_example():
+    # create an energy system
+    idx = pd.date_range("1/1/2023", periods=13, freq="H")
+    es = solph.EnergySystem(timeindex=idx, infer_last_interval=False)
+
+    # power bus
+    bel = solph.Bus(label="bel")
+    es.add(bel)
+
+    es.add(
+        solph.components.Source(
+            label="source_el",
+            outputs={bel: solph.Flow()},
+        )
+    )
+
+    es.add(
+        solph.components.Sink(
+            label="sink_el",
+            inputs={bel: solph.Flow()},
+        )
+    )
+
+    electricity_price = np.array(
+        [
+            0.38,
+            0.31,
+            0.32,
+            0.33,
+            0.37,
+            0.32,
+            0.33,
+            0.34,
+            0.39,
+            0.38,
+            0.37,
+            0.35,
+            0.35,
+        ]
+    )
+
+    # Electric Storage 1
+    # Costs are designed in a way that storing energy is benificial until the
+    # last four time steps but emptying it is not a good option.
+    battery1 = solph.components.GenericStorage(
+        label="battery 1",
+        nominal_storage_capacity=10,
+        inputs={
+            bel: solph.Flow(
+                nominal_value=1,
+                variable_costs=electricity_price,
+            )
+        },
+        outputs={
+            bel: solph.Flow(
+                nominal_value=1,
+                variable_costs=-electricity_price,
+            )
+        },
+        initial_storage_level=0.5,
+        balanced=False,
+    )
+    es.add(battery1)
+
+    # storages that balance our fluctuating costs
+    # Electric Storage 2
+    battery2 = solph.components.GenericStorage(
+        label="battery 2",
+        nominal_storage_capacity=10,
+        inputs={
+            bel: solph.Flow(
+                nominal_value=1,
+                variable_costs=electricity_price,
+            )
+        },
+        outputs={
+            bel: solph.Flow(
+                nominal_value=1,
+                variable_costs=-electricity_price,
+            )
+        },
+        storage_costs=12 * [0] + [-np.mean(electricity_price)],
+        initial_storage_level=0.5,
+        balanced=False,
+    )
+    es.add(battery2)
+
+    # create an optimization problem and solve it
+    model = solph.Model(es)
+
+    # solve model
+    model.solve(solver="cbc")
+
+    # create result object
+    results = solph.processing.results(model)
+
+    plt.plot(
+        results[(battery1, None)]["sequences"],
+        label="content w/o storage costs",
+    )
+    plt.plot(
+        results[(battery2, None)]["sequences"],
+        label="content w/ storage revenue",
+    )
+    plt.legend()
+    plt.grid()
+
+    plt.show()
+
+
+if __name__ == "__main__":
+    storage_costs_example()

src/oemof/solph/components/_generic_storage.py

@@ -107,6 +107,8 @@ class GenericStorage(network.Component):
         investment variable instead of to the nominal_storage_capacity. The
         nominal_storage_capacity should not be set (or set to None) if an
         investment object is used.
+    storage_costs : numeric (iterable or scalar), :math:`c_{storage}(t)`
+        Cost (per energy) for having energy in the storage.
     lifetime_inflow : int, :math:`n_{in}`
         Determine the lifetime of an inflow; only applicable for multi-period
         models which can invest in storage capacity and have an
@@ -177,6 +179,7 @@ def __init__(
         inflow_conversion_factor=1,
         outflow_conversion_factor=1,
         fixed_costs=0,
+        storage_costs=None,
         lifetime_inflow=None,
         lifetime_outflow=None,
         custom_attributes=None,
@@ -230,6 +233,7 @@ def __init__(
         self.max_storage_level = solph_sequence(max_storage_level)
         self.min_storage_level = solph_sequence(min_storage_level)
         self.fixed_costs = solph_sequence(fixed_costs)
+        self.storage_costs = solph_sequence(storage_costs)
         self.investment = investment
         self.invest_relation_input_output = invest_relation_input_output
         self.invest_relation_input_capacity = invest_relation_input_capacity
@@ -415,13 +419,19 @@ class GenericStorageBlock(ScalarBlock):
                                 :math:`\delta(t)` and
                                 timeincrement
                                 :math:`\tau(t)`
+    :math:`c_{storage}(t)`      costs of having         `storage_costs`
+                                energy stored
     =========================== ======================= =========
 
     **The following parts of the objective function are created:**
 
     *Standard model*
 
-    Nothing added to the objective function.
+    * :attr: `storage_costs` not 0
+
+        ..math::
+            \sum_{t \in \textrm{TIMESTEPS}} c_{storage}(t) \cdot E(t)
+
 
     *Multi-period model*
 
@@ -596,7 +606,22 @@ def _objective_expression(self):
                             * ((1 + m.discount_rate) ** -p)
                         )
         self.fixed_costs = Expression(expr=fixed_costs)
-        return self.fixed_costs
+
+        storage_costs = 0
+
+        for n in self.STORAGES:
+            if n.storage_costs[0] is not None:
+                storage_costs += (
+                    self.storage_content[n, 0] * n.storage_costs[0]
+                )
+                for t in m.TIMESTEPS:
+                    storage_costs += (
+                        self.storage_content[n, t + 1] * n.storage_costs[t + 1]
+                    )
+
+        self.storage_costs = Expression(expr=storage_costs)
+
+        return self.fixed_costs + self.storage_costs
 
 
 class GenericInvestmentStorageBlock(ScalarBlock):

tests/constraint_tests.py

@@ -280,6 +280,7 @@ def test_storage(self):
             },
             nominal_storage_capacity=1e5,
             loss_rate=0.13,
+            storage_costs=0.1,
             inflow_conversion_factor=0.97,
             outflow_conversion_factor=0.86,
             initial_storage_level=0.4,

tests/lp_files/storage.lp

@@ -2,6 +2,10 @@
 
 min 
 objective:
++4000.0 ONE_VAR_CONSTANT
++0.1 GenericStorageBlock_storage_content(storage_no_invest_1)
++0.1 GenericStorageBlock_storage_content(storage_no_invest_2)
++0.1 GenericStorageBlock_storage_content(storage_no_invest_3)
 +56 flow(electricityBus_storage_no_invest_0_0)
 +56 flow(electricityBus_storage_no_invest_0_1)
 +56 flow(electricityBus_storage_no_invest_0_2)
@@ -51,6 +55,7 @@ c_e_GenericStorageBlock_balanced_cstr(storage_no_invest)_:
 = 40000.0
 
 bounds
+   +1 <= ONE_VAR_CONSTANT <= 1
    0 <= flow(electricityBus_storage_no_invest_0_0) <= 16667
    0 <= flow(electricityBus_storage_no_invest_0_1) <= 16667
    0 <= flow(electricityBus_storage_no_invest_0_2) <= 16667