---
title: "Wind power pros/cons and output: 1.25 m blade"
subject: "Power Plant Design"
chapter: 1
key: "semester_8/power_plant_design:wind-pros-cons-1-25m"
source: https://www.bctengineer.com/q/semester_8/power_plant_design/wind-pros-cons-1-25m
site: BCT Engineering
---

# Wind power pros/cons and output: 1.25 m blade

Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation

- Asked in: 2073 Bhadra, 2+4 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/wind-pros-cons-1-25m
- Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1

## Question

List out the advantages and disadvantages of wind power. Estimate electric power output from a wind turbine that has turbine blade length of 1.25 m and wind speed of 16 m/sec. Assume that air density is 1.23 kg/m³ and power coefficient is 0.3.

## Short answer

Advantages are renewable, clean, low operating cost, quick installation, and land use below turbines; disadvantages are variability, limited sites, noise, visual impact, and bird risk. Using P = 0.5 rho A v^3 Cp with blade radius 1.25 m and Cp 0.3, the output is about 3.71 kW.

## Answer

#### Advantages of wind power
- Renewable and clean; no fuel cost and no CO₂ emission in operation.
- Low operating cost; quick to install; modular.
- Land around turbines can be used for farming.
- Good for remote and hybrid (wind–solar–hydro) systems.

#### Disadvantages of wind power
- Output is variable and unpredictable ($P \propto v^3$); needs storage or backup.
- Suitable sites are limited; high capital cost per kW for small units.
- Noise, visual impact, danger to birds.
- Low air density at high altitude reduces power.

#### Power output
$$
P = \frac{1}{2}\rho A v^3 C_p, \qquad A = \pi r^2
$$
Given: $r = 1.25$ m, $v = 16$ m/s, $\rho = 1.23$ kg/m³, $C_p = 0.3$.

$$
\begin{aligned}
A &= \pi \times 1.25^2 = 4.909\ \text{m}^2 \\
P_w &= 0.5 \times 1.23 \times 4.909 \times 16^3 \\
&= 0.5 \times 1.23 \times 4.909 \times 4096 = 12{,}365\ \text{W} \\
P &= 0.3 \times 12{,}365 = 3{,}710\ \text{W}
\end{aligned}
$$

**Answer:** Electric power output $\approx 3.71$ kW.

## Check yourself

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

1. Why does wind output need storage or backup?
   A. Output is variable and, since P is proportional to v^3, changes strongly with wind speed
   B. Turbines emit CO2
   C. Fuel cost is high
   D. Turbines cannot be installed quickly
   Answer: A. Variable wind and the cube law make output unpredictable. (Key point: Variability disadvantage)

2. For blade length 1.25 m, the swept area is about
   A. 1.56 m^2
   B. 4.91 m^2
   C. 9.82 m^2
   D. 3.93 m^2
   Answer: B. A = pi x 1.25^2 = 4.909 m^2. (Key point: Swept area)

3. With v = 16 m/s, rho = 1.23 and Cp = 0.3, the output is about
   A. 12.4 kW
   B. 3.71 kW
   C. 1.24 kW
   D. 37.1 kW
   Answer: B. Wind power 12.365 kW x 0.3 = 3.71 kW. (Key point: Power output)

## Close variants set in other exams

- [Wind power pros/cons and output: 1.5 m blade](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Awind-pros-cons-1-5m) — Power Plant Design, chapter 1, asked 2×

## Related in Power Plant Design

- [Wind turbine merits and output: 5.5 m blade](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Awind-merits-numerical-5-5m) — Power Plant Design, chapter 1
- [Wind turbine output: 6 m blade, 8 and 16 m/s](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Awind-numerical-6m-8ms) — Power Plant Design, chapter 1, asked 3×
- [Wind turbine output: 12 m blade, 18 m/s](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Awind-numerical-12m-18ms) — Power Plant Design, chapter 1, asked 3×
- [Wind turbine output: 6.5 m blade, 9 and 18 m/s](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Awind-numerical-6-5m-9ms) — Power Plant Design, chapter 1, asked 3×

## Related in other subjects

- [Wind turbine power, tip speed ratio and energy](https://www.bctengineer.com/question.md?key=semester_6%2Fenergy_resources%3Awind-turbine-power-energy-numerical) — Energy Resources, chapter 4