Question

Where is the Power Plant in Platinum?

Answer 1

It's not in Platinum.

If you're looking for the Valley Windworks, that's by Floaroma Town.

Comments

actually, the power plant is the japanese translation of valley windworks. http://bulbapedia.bulbagarden.net/wiki/Valley_Windworks

Answer 2

If you mean the Fuego Ironworks then its located west of route 205. You have to have Surf to get there tho.
Source: http://bulbapedia.bulbagarden.net/wiki/Fuego_Ironworks