I fixed some minor bugs and added some extensions, namely:
- added absolute pathes to use for input_file_excel
- avoid div by 0 error, in r_gnuUtilizationRate, if unit does not have a unit size
- changed parameter annuity to annuityfactor (as to my understanding, it is the annuityfactor and not the annuity and our students get quite confused)
- added output parameter r_investCapacity, which shows the invested capacity in MW (unitSize*r_invest)