Merge pull request #1094 from oemof/fix/storage_costs-for-initial-level

Fix/storage costs for initial level

docs/changelog.rst

@@ -9,6 +9,7 @@ These are new features and improvements of note in each release
     :backlinks: top
 
 
+.. include::  whatsnew/v0-6-0.rst
 .. include::  whatsnew/v0-5-4.rst
 .. include::  whatsnew/v0-5-3.rst
 .. include::  whatsnew/v0-5-2.rst

docs/whatsnew/v0-6-0.rst

@@ -0,0 +1,38 @@
+v0.6.0
+------
+
+API changes
+###########
+
+* Costs for energy storage are now defined for N-1 points in time
+  (initial time step is neglected). This is because with a balanced
+  storage, content of the initial and the first time step (which is
+  effectively the same) had double weight before. Also, if the
+  initial storage level is defined, the costs just offset the
+  objective value without changing anything else.
+
+New features
+############
+
+
+Documentation
+#############
+
+Bug fixes
+#########
+
+
+Other changes
+#############
+
+
+Known issues
+############
+
+* Incompatible to numpy >= 2.0.0. This is because of Pyomo, but we have to
+  enforce a lower version in our package.
+
+Contributors
+############
+
+* Patrik Schönfeldt

src/oemof/solph/components/_generic_storage.py

@@ -110,7 +110,8 @@ class GenericStorage(Node):
         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.
+        Cost (per energy) for having energy in the storage, starting from
+        time point :math:`t_{1}`.
     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
@@ -423,7 +424,7 @@ class GenericStorageBlock(ScalarBlock):
     * :attr: `storage_costs` not 0
 
         .. math::
-            \sum_{t \in \textrm{TIMESTEPS}} c_{storage}(t) \cdot E(t)
+            \sum_{t \in \textrm{TIMEPOINTS} > 0} c_{storage}(t) \cdot E(t)
 
 
     *Multi-period model*
@@ -616,12 +617,12 @@ def _objective_expression(self):
 
         for n in self.STORAGES:
             if n.storage_costs[0] is not None:
-                storage_costs += (
-                    self.storage_content[n, 0] * n.storage_costs[0]
-                )
+                # We actually want to iterate over all TIMEPOINTS except the
+                # 0th. As integers are used for the index, this is equicalent
+                # to iterating over the TIMESTEPS with one offset.
                 for t in m.TIMESTEPS:
                     storage_costs += (
-                        self.storage_content[n, t + 1] * n.storage_costs[t + 1]
+                        self.storage_content[n, t + 1] * n.storage_costs[t]
                     )
 
         self.storage_costs = Expression(expr=storage_costs)

tests/constraint_tests.py

@@ -283,7 +283,7 @@ def test_storage(self):
             },
             nominal_storage_capacity=1e5,
             loss_rate=0.13,
-            storage_costs=0.1,
+            storage_costs=[0.1, 0.2, 0.3, 0.4],
             inflow_conversion_factor=0.97,
             outflow_conversion_factor=0.86,
             initial_storage_level=0.4,

tests/lp_files/storage.lp

@@ -2,16 +2,15 @@
 
 min 
 objective:
-+4000.0 ONE_VAR_CONSTANT
 +56 flow(electricityBus_storage_no_invest_0)
 +56 flow(electricityBus_storage_no_invest_1)
 +56 flow(electricityBus_storage_no_invest_2)
 +24 flow(storage_no_invest_electricityBus_0)
 +24 flow(storage_no_invest_electricityBus_1)
 +24 flow(storage_no_invest_electricityBus_2)
 +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)
++0.2 GenericStorageBlock_storage_content(storage_no_invest_2)
++0.3 GenericStorageBlock_storage_content(storage_no_invest_3)
 
 s.t.
 
@@ -72,7 +71,6 @@ c_e_GenericStorageBlock_balanced_cstr(storage_no_invest)_:
 = 40000.0
 
 bounds
-   1 <= ONE_VAR_CONSTANT <= 1
    0 <= flow(electricityBus_storage_no_invest_0) <= 16667
    0 <= flow(electricityBus_storage_no_invest_1) <= 16667
    0 <= flow(electricityBus_storage_no_invest_2) <= 16667