Steam just makes sense as a fluid for heat engines, thermal power plants are mostly steam, except when gas turbines are involved, but even then there's most of the time steam bottoming cycle. (gas turbine burns something, then exhaust is hot enough to power steam cycle) Unless thermal power plant is small, then it's more likely to be diesel engine (up to few MW). Only when it's photovoltaics, or hydropower, or wind farm (or tidal powerplant, or some other weird ones) there's no place for steam to be involved (solar thermal plants sometimes use steam cycle). Geothermal powerplants use steam if source is hot enough, otherwise it's something more volatile in organic Rankine cycle