Wind Energy Converters

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Questions and Answers

What are the three factors that determine the output from a wind energy converter?

Wind direction, blade shape, and generator type

Wind speeds, cross-section of wind swept by rotor, and overall conversion efficiency (correct)

Generator efficiency, wind velocity, and blade material

Rotor size, wind turbulence, and transmission system type

Why can't a wind turbine extract all of the wind's energy?

Because the wind turbine is not efficient enough

Because the wind would have to be brought to a halt, preventing the passage of more air through the rotor (correct)

Because the blades are not designed to capture all the wind's energy

Because the generator is not powerful enough

What is the maximum percentage of the available energy in wind that a 100% efficient aerogenerator can convert into mechanical energy?

80%

90%

60% (correct)

70%

What is the typical percentage of the theoretical maximum that well-designed blades can extract?

70% Signup and view all the answers

What is the formula for the kinetic energy of any particle?

1/2 mV^2 Signup and view all the answers

What is the formula for the amount of air passing in unit time, through an area A, with velocity V?

A.V Signup and view all the answers

What is the formula for the mass m of air traversing the area A swept by the rotating blades of a wind mill type generator?

m = ρ.A Signup and view all the answers

What is the principle behind the working of a wind mill?

Converting kinetic energy of the wind to mechanical energy Signup and view all the answers

What is the primary function of plants in energy plantation?

To act as solar collectors and store energy Signup and view all the answers

What is the minimum number of times more energy stored annually by natural photosynthesis process compared to the world's annual energy consumption?

What is the primary purpose of energy farms?

To replace fossil and nuclear energy sources Signup and view all the answers

Which of the following is NOT a benefit of energy farms?

Requires regular maintenance Signup and view all the answers

What is the percentage of total forest area in India?

25% Signup and view all the answers

What is the primary goal of the program run by the Indian Institute of Science, Bangalore?

To grow monoculture plantations of fast-growing species Signup and view all the answers

What is used to generate energy from various types of biomasses?

Gasifiers and sterling engines Signup and view all the answers

What is the capacity of projects taken up under DNES at various places in the country?

5M W Signup and view all the answers

What is the main disadvantage of the upward machine?

Less efficient Signup and view all the answers

What is the advantage of the downward machine?

Allows the use of free yaw-system Signup and view all the answers

What is the effect of the tower on the blades in the downward machine?

Produces wind-shadow-effect Signup and view all the answers

What type of wind-mill is mounted on a vertical shaft?

Vertical Axis Wind-Mill Signup and view all the answers

What is the shape of the rotors of Savonious wind turbines?

S-type Signup and view all the answers

What is the disadvantage of the Savonious wind mill when the convex surface faces the wind?

Slows down the speed of the turbine Signup and view all the answers

Why are Savonious wind mills not preferred for electric power generating purposes?

Because of low speed Signup and view all the answers

What is the advantage of providing 4-blades in a Savonious wind mill?

Eliminates the effect of wind direction Signup and view all the answers

What is the primary advantage of the Darrieus wind-mill?

The generator can be mounted on the ground. Signup and view all the answers

What is the range of capacity of Darrieus wind-mills?

4 to 14 MW Signup and view all the answers

What is a disadvantage of the Darrieus wind-mill?

It is not self-starting and requires a power source to start. Signup and view all the answers

What is a characteristic of Darrieus wind-mill blades?

They are curved and C-shaped. Signup and view all the answers

What is an advantage of wind energy?

It is a reliable and cost-effective form of energy. Signup and view all the answers

What is a problem that Darrieus wind-mills can experience?

Stalling when wind speed is high. Signup and view all the answers

What is a benefit of wind energy?

It is a renewable form of energy. Signup and view all the answers

What is a characteristic of the Darrieus wind-mill?

It has a vertical axis. Signup and view all the answers

What is the primary function of acid formers in anaerobic digestion?

To break down complex organic compounds into simple organic acids Signup and view all the answers

What is the optimal pH range for fermentation and biogas generation?

6.5 to 8 Signup and view all the answers

What is the effect of increasing temperature on anaerobic digestion?

It increases the gas yield rate Signup and view all the answers

What type of bacteria are involved in methane formation?

Anaerobic bacteria Signup and view all the answers

What is the equation that represents anaerobic digestion?

CxH yO 2 + [x-y/4-2/2]H20 --> [x/2-y/8+z/4]CO2 + [x/2+y/8-z/4]CH4 Signup and view all the answers

What is the temperature range for thermophilic bacteria?

About 55°C Signup and view all the answers

What is the purpose of heating digesters in cold climates?

To maintain a temperature range suitable for anaerobic digestion Signup and view all the answers

What is the equation that represents the anaerobic digestion of cellulose?

(C6H10 O5)n + nH2O -› 3nCO2 + 3nCH4 Signup and view all the answers

Study Notes

Factors Determining Wind Energy Converter Output

Three factors determine the output from a wind energy converter: wind speeds, the cross-section of wind swept by the rotor, and the overall conversion efficiency of the rotor, transmission system, and generator or pump.
No device can extract all of the wind's energy, as the wind would have to be brought to a halt, preventing the passage of more air through the rotor.
The maximum possible energy conversion is around 60% of the available energy in wind, but well-designed blades can extract up to 70% of the theoretical maximum.

Power in the Wind

The power in the wind can be computed by using the concept of kinetics.
The wind mill works on the principle of converting kinetic energy of the wind to mechanical energy.
The kinetic energy of any particle is equal to one half its mass times the square of its velocity (1/2 mV^2).

Up-ward and Down-ward Rotors

The rotor can be classified as upward and downward machines.
Upward machines have the rotor located in front of the tower, while downward machines have the rotor located behind the tower.
Downward machines allow the use of free yaw-system and allow the blades to deflect away from the tower when loaded, but they suffer from wind-shadow-effect of the tower on the blades.
Upward machines produce higher power, eliminate the effect of tower shadow on the blades, and result in lower noise, lower fatigue on the blades, and smoother power output.

Vertical Axis Wind-Mill

In this system, the rotor is mounted on a vertical shaft.
Two common configurations of vertical axis wind-mills are the Savonious wind mill and the Darrieus wind-mill.
The Savonious wind mill has an S-type rotor, supported at top and bottom by two circular plates, with curved blades fixed on a central pipe.
The Darrieus wind-mill has 2 or 3 thin curved aerofoil section, C-shaped blades, with both ends fixed to the vertical shaft.
The advantages of the Darrieus wind-mill include the ability to mount the generator on the ground, no requirement for yaw mechanism, and high efficiency (35-40%).

Advantages and Disadvantages of Wind Energy

Advantages of wind energy include:
- Pollution-free electrical energy generation
- Renewable and available free of cost
- Suitable for rural, offshore, and onshore areas
- Reliable and cost-effective for large capacity units
- No transportation required
Disadvantages of wind energy include:
- Noise and lower power density compared to horizontal axis wind-mills

Energy Plantation

Energy plantation is a means of extracting maximum solar energy by growing plants.
Plants are grown especially for their fuel value and act as solar collectors.
Energy farms are economical, free from pollution, and require no maintenance.
They are the best alternatives for present fuel crisis and to replace fossil and nuclear energy sources.

Biogas Generation

Biogas generation involves three phases: enzymatic hydrolysis, acid formation, and methane formation.
The phases involve the conversion of cellulose biomass into simple compounds, acid formation, and methane formation by anaerobic bacteria.
The anaerobic digestion process is represented by a general equation, and the digestion process is influenced by temperature, pH value, and other factors.

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Description

This quiz covers the factors that determine the output from a wind energy converter, including wind speed, cross-section of wind swept by the rotor, and conversion efficiency.