generating electricity

The thermal power station needs one of 2 resources to generate electricity: lumber or oil. 

2.600 wood gets you 1.105 electricity in 39 min (depending on your building's level). or: 

5.200 wood gets you 1.820 electricity in 96 min (depending etc,)     

I have no level 10 power station yet, so I can't tell you the details of the 3rd wood option.

I would expect the 2nd one to generate more electricity per unit wood or at least the same, but not less!!  Therefore i do not use the other options. Is it really meant to be this way? https://imgur.com/a/cCqou

this is not different then how the petroglyph or museum works and is based on the same principal. If you are willing to use the short time and pay attention to the training you get more then if you just do the long ones and let it run.