is he there now ("...because I am in Sava's electric power station." ) or will he be there on Thursday? ("because I'll be in Sava's electric power station." )
Actually the slovenian sentence use present tense. I think that's like in French : "T'es là jeudi, parce que je suis à la centrale de..."
It's some kind (in French at the least) of colloquial utilisation of the present tense.
But I agree with you : "...because I'll be in Sava's electric power stationS" is better