Hey there,

my interest is into reconstructing and understanding the value of the objective function after optimization when using the Investment.Storage module.

Since I got kind problems in understanding the API at the according topic I tried to reconstruct the output value

**om.InvestmentStorage.investment_costs()**

by using the output data from a csv-file after optimization. The according syntax to get the csv-file I used is: **results.bus_balance_to_csv**

The programmed storage-model is very simple:

```
solph.Storage(
label='Energiespeicher',
inputs={O_net: solph.Flow()},
outputs={O_net: solph.Flow()},
investment=solph.Investment(ep_costs=epc_storage))
```

I already got the value of **ep_costs(n)** and it is coherent to my expectations. But what I can’t figure out is the summed value of **invest(n)** see in the following equation documented in the API:

## How can I reconstruct this value with numerical data after optimization from the csv-file?

The storage capacity value of my timeseries (1 Day) multiplied with the value of **ep_costs** is not coherent with **om.InvestmentStorage.investment_costs()**

I would be very grateful to get an idea. I am using the OEMOF version 0.1.4.

cheers, Bastian