- 2070 Magh · 8 marks
ROR versus PROR hydropower plants
Short answer
ROR: no storage, base-load, output follows river flow, lower cost. PROR: daily pondage, peaking operation, higher installed capacity, better load following, extra pond and surge tank, but hydro-peaking and small submergence impacts. Both share weir, intake, desander, headrace, penstock, powerhouse, tailrace.
Compare the components, operation and characteristics of run of river (ROR) type hydropower plant with pondage run of river (PROR).
A run-of-river (ROR) plant uses the river flow as it comes, with no storage. A pondage run-of-river (PROR) plant adds a small pond that stores water for a few hours so the plant can follow the daily load and give more power at peak time.
| Aspect | ROR | PROR |
|---|---|---|
| Storage | None (only forebay) | Daily pondage, a few hours of storage |
| Headworks | Low weir | Weir or slightly higher dam to create pond |
| Extra component | — | Pondage with flushing arrangement |
| Operation | Base load; output follows river flow | Peaking; stores off-peak water, generates more at peak |
| Dry-season output | Low, nearly constant | Same energy, but concentrated into peak hours |
| Installed capacity | Based on design flow (e.g. ) | Can be higher than ROR for same river |
| Load following | Poor | Good, within the pond volume |
| Cost | Lowest | Higher (pond, larger dam, gates) |
| Environmental impact | Least; dewatered stretch only | Adds small submergence and hydro-peaking downstream |
| Sediment | Passes through after desander | Pond traps sediment, needs flushing |
| Value to grid | Energy only | Energy plus peaking capacity |
Components
Both have: weir/dam, intake, gravel trap, desander, headrace, forebay or surge tank, penstock, powerhouse, tailrace and switchyard. PROR adds the pondage (and its spillway and flushing gates) and usually has a pressure tunnel with surge tank.
Operation and characteristics
- ROR: turbine discharge equals river inflow minus riparian release; in the wet season it runs at full load and spills the excess, in the dry season it runs at part load.
- PROR: during the night the pond fills; in the 4–6 peak hours the plant runs at full load using inflow plus stored water. Total daily energy is about the same as ROR, but its value is higher because peak energy is scarce in Nepal.
- Examples: many small IPP plants in Nepal are ROR; Kaligandaki "A" and Middle Marsyangdi are PROR.
✓ Answer checked by Claude Opus 5.5 (high effort)
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