Reserve planning and utility interconnection

Reserve planning is deciding how much generating capacity, above the forecast peak demand, must be kept available (installed or running) so that supply continues reliably despite forced outages of units, planned maintenance, load forecast errors and low hydrology.

Reserve planning

Types of reserve

Reserve margin

$$\text{Reserve margin} = \frac{\text{Installed capacity} - \text{Peak demand}}{\text{Peak demand}} \times 100\%$$

Typical values are 15–25%.

Methods

1. Deterministic: Reserve ≥ largest unit, or a fixed percentage of peak.
2. Probabilistic: Using unit forced outage rates to compute LOLP/LOLE; reserve is chosen so that LOLE ≤ e.g. 1 day in 10 years (or 1 day/year).

Factors: Size of the largest unit, forced outage rates, maintenance schedule, load forecast uncertainty, hydrology (dry-year energy), and availability of interconnection.

Benefits of interconnection of utilities

1. Reduced reserve: Utilities share reserve; total installed reserve is less than the sum of separate reserves.
2. Improved reliability: Help from neighbours during outages; fewer blackouts.
3. Load diversity: Different peak times reduce combined peak and needed capacity.
4. Economic operation: Cheaper plants supply more load across the region; lower fuel cost.
5. Seasonal exchange: Nepal exports wet-season surplus and imports in the dry season through Nepal–India lines.
6. Larger, efficient units can be installed.
7. Frequency stability: More inertia; smaller frequency dips after disturbances.
8. Renewable integration: Variability of solar/wind is smoothed across a larger area.
9. Deferred investment: New plants can be postponed by importing power.

Drawbacks to manage: Faults can spread (cascading), higher fault levels, need for tie-line control, protection coordination and commercial agreements.