- Practice · 5 marks
Classification of hydroelectric plants
Short answer
Run-of-river plants use natural river flow with little storage, low cost, base load only in wet season. Storage plants store water behind a dam for controlled power generation year‑round. Pumped storage pumps water to an upper reservoir with off‑peak surplus, then generates peak power, improving system load factor with about 70–75% round‑trip efficiency.
Classify hydroelectric power plants. Explain run-of-river, storage and pumped storage plants with their merits.
Hydroelectric plants can be classified in several ways.
| Basis | Classes |
|---|---|
| Available head | Low head (below 15 m), medium head (15 to 70 m), high head (above 70 m) |
| Quantity of water | Run-of-river, storage (reservoir), pumped storage |
| Load served | Base load, peak load plants |
| Capacity | Micro (below 100 kW), mini, small, medium, large |
| Layout | Dam-toe, canal or diversion, tunnel type |
(The head and capacity limits differ slightly between textbooks.)
Run-of-river plant
Uses the natural flow of the river without significant storage; a small weir or barrage diverts water. Output varies with river flow, so it supplies base load in the wet season only and needs a standby in the dry season. Low cost and little submergence. Many hydro plants on Himalayan rivers are of this type.
Storage (reservoir) plant
A dam stores water in the wet season for use in the dry season. Output can be controlled according to demand, so the plant can supply base load or peak load. It also gives flood control and irrigation benefits, but the cost is high and a large area of land is submerged.
Pumped storage plant
Two reservoirs at different levels. During off-peak hours surplus power pumps water from the lower to the upper reservoir; at peak hours the water runs down through the turbines (often a reversible pump-turbine) to generate power.
Upper reservoir ~~~~
\ penstock
\
Pump/Turbine --- generator/motor
/
Lower reservoir ~~~~
Merits: improves the load factor of the whole system, gives quick start-up for peak load, and uses surplus off-peak energy. Overall cycle efficiency is about 70 to 75 %.
✓ Answer checked by Claude Sonnet 5.5
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