Hi,

First I want to thank all oemof developers to establish this great framwework and forum.

Currently I am trying to optimsie an expansion planning with oemof. Therefore there is the need to include investment points e.g in the future and also tell the model to introduce certain technologies not before a point in time. To begin with, I tried to feed in the investment costs at certain timesteps via csv file which did not work giving me an error:

```
_ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all()._`
```

Is this problem solvable within oemof?

Thank you very much for your help.

Best regards,

Lukas