A power plant was a ground-based facility built to provide cheap and reliable energy to a city or even region.
In the late 2370s, the planet Quarra in the Delta Quadrant suffered from a labor shortage in its industrial power plants due to the low level of automation in Quarren technology. As a result, the Quarren military began a secret program of commandeering passing alien starships, erasing their crews' memories, and putting them to work. (VOY: "Workforce", "Workforce, Part II")
In 2375 there was an accident at the power plant servicing for Ferenginar's main city, causing a toxic cloud to hang over the city, rain from it disrupted communications. According to Grand Nagus Zek, the accident was caused by a greedy bastard contractor using substandard relays.