Storage component minimum investment bug

[oakca]

I am using the solph.components.GenericStorage() with the following inputs:

# create storage
for st in self.storage.keys():
    storage['storage_'+st+'_'+self.name] = solph.components.GenericStorage(
                        label='storage_'+st+'_'+self.name,
                        inputs={bus['b_Elec'+'_'+self.name]: solph.Flow(
                            variable_costs=self.storage[st][4]*self.weight)},
                        outputs={bus['b_Elec'+'_'+self.name]: solph.Flow(
                            variable_costs=self.storage[st][4]*self.weight)},
                        investment=solph.Investment(
                            ep_costs=self.storage[st][0],
                            maximum=self.storage[st][1],
                            existing=self.storage[st][2],
                            minimum=self.storage[st][3]),
                        initial_capacity=self.storage[st][5],
                        inflow_conversion_factor=self.storage[st][6],
                        outflow_conversion_factor=self.storage[st][7],
                        capacity_loss=self.storage[st][8])

Here is an output of the self.storage[st][1] and self.storage[st][3]:

>self.storage[st][1]
1500000000000000
>self.storage[st][3]
1000

When I created the model, I checked the bounds of the storage variables, I was expecting to set the minimum invest level at 1000, but following is created:

   0 <= GenericInvestmentStorageBlock_invest(storage_Elec_Mid) <= 1500000000000000
   0 <= GenericInvestmentStorageBlock_invest(storage_Elec_North) <= 1500000000000000
   0 <= GenericInvestmentStorageBlock_invest(storage_Elec_South) <= 1500000000000000

I checked the source code and above mentioned bounds are created because of https://github.com/oemof/oemof/blob/dev/oemof/solph/components.py [ln. 497-502]:

def _storage_investvar_bound_rule(block, n):
    """Rule definition to bound the invested storage capacity `invest`.
    """
    return 0, n.investment.maximum
self.invest = Var(self.INVESTSTORAGES, within=NonNegativeReals,
                          bounds=_storage_investvar_bound_rule)

It looks like minimum bound is set to 0 for some purpose, but it makes the minimum investment option impossible. Is it a bug? or intentional?

[uvchik]

I have to say that it is a very strange attribute, but you are right it seems to be a bug.

I will have a look and let you know.

[uvchik]

It is not an urgent bug, so I will not make a hotfix release. But you can patch it yourself:

- return 0, n.investment.maximum
+ return n.investment.minimum, n.investment.maximum

You can also pick commit 498c408.