Conventional sources and features of a station

Conventional sources of energy are the long-established sources that have been used on a large scale for electricity generation, mainly fossil fuels (coal, oil, natural gas), nuclear fuel and (in many textbooks) large hydropower. Fossil and nuclear fuels are finite and are being used up faster than nature can replace them.

Features of a steam (coal-fired) thermal power station

 Coal -> [Boiler] -> steam -> [Turbine]--[Alt]-> Grid
            ^                     |
            |                [Condenser]
       [Feed pump] <-- water -----+

1. Principle: Coal is burned in a boiler; heat converts water into high-pressure superheated steam, which drives a steam turbine coupled to an alternator (Rankine cycle).
2. Location: Near coal mines or a railway line and a large water source for the condenser and cooling.
3. Low initial cost per kW compared with hydro, and shorter construction time.
4. High running cost: Continuous purchase and transport of coal.
5. Low overall efficiency: About 30–40 %, because much heat is rejected in the condenser.
6. Pollution: Emits CO₂, SO₂, NOx, fly ash; needs ash handling, electrostatic precipitators and tall chimneys.
7. Large space for coal storage and ash disposal.
8. Slow start: Takes hours to start and load up; best used as a base-load plant.
9. Large unit sizes (200–1000 MW) possible; output is steady and independent of weather.
10. Water requirement is large for the condenser and boiler make-up.

Nepal has no such coal plants; its conventional backup is small diesel plants, while hydropower supplies the grid.