---
title: "Define reserve power"
subject: "Power Plant Design"
chapter: 2
key: "semester_8/power_plant_design:define-reserve-power"
source: https://www.bctengineer.com/q/semester_8/power_plant_design/define-reserve-power
site: BCT Engineering
---

# Define reserve power

Power Plant Design · Chapter 2: Integrated System Planning in Design Approach

- Asked in: 2079 Jestha, 2 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/power_plant_design/define-reserve-power
- Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-2

## Question

Define reserve power.

## Short answer

Reserve power is generating capacity above expected peak demand, kept for outages, maintenance and demand errors. It equals available capacity minus peak demand, includes spinning, non-spinning and cold reserve, and is usually 15-25% of peak.

## Answer

**Reserve power** is the generating capacity available in a power system over and above the expected peak demand, kept to supply load when units fail, are under maintenance, or when demand is higher than forecast.

$$
\text{Reserve} = \text{Available capacity} - \text{Peak demand}
$$

It includes **spinning reserve** (running units), **non-spinning reserve** (quick-start units) and **cold reserve** (units that need hours to start). It is usually expressed as a reserve margin of about 15–25% of peak demand. Example: a system with 1,150 MW capacity and 1,000 MW peak has 150 MW (15%) reserve.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Reserve power is best defined as:
   A. Capacity equal to the peak demand
   B. Generating capacity available above the expected peak demand
   C. Only the energy stored in reservoirs
   D. The power lost in transmission
   Answer: B. Reserve = available capacity - peak demand, kept for failures, maintenance and forecast error. (Key point: Definition)

2. Which set correctly lists the types of reserve?
   A. Spinning, non-spinning and cold
   B. Active, reactive and apparent
   C. Base, peak and intermediate
   D. Primary, secondary and tertiary load
   Answer: A. Reserve includes spinning (running), non-spinning (quick start) and cold (hours to start) reserve. (Key point: Components)

3. A system has 1,150 MW capacity and 1,000 MW peak demand. The reserve and margin are:
   A. 150 MW, 15%
   B. 150 MW, 13%
   C. 1,150 MW, 115%
   D. 15 MW, 1.5%
   Answer: A. Reserve = 1150 - 1000 = 150 MW, which is 150/1000 = 15% of peak. (Key point: Calculation)

## Related in Power Plant Design

- [Spinning reserve versus reserve power](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aspinning-reserve-vs-reserve) — Power Plant Design, chapter 2
- [Power system security and reserve requirement](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Asecurity-reserve-requirement) — Power Plant Design, chapter 2
- [Regional interconnection and reserve bottling](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aregional-interconnection-reserve) — Power Plant Design, chapter 2
- [Reserve planning and utility interconnection](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Areserve-planning-interconnection) — Power Plant Design, chapter 2
- [Define spinning reserve](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Adefine-spinning-reserve) — Power Plant Design, chapter 2