WIND POWER SYSTEM
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WHAT IS WIND ENERGY?
- It is a form of solar energy
- Energy from a moving air
- Turbulent masses of air rush to even out the differences in atmospheric pressure created when the sun heats the air more in one place than in another place.
WHAT IS WIND POWER SYSTEM?
- Is an electro-mechanical power system that converts the energy of wind to rotary motion to produce mechanical (windpumps) or electrical (wind turbines or aero generator) power.
APPLICATION OF WIND POWER SYSTEM
A. Mechanical application (windmills) – for water pumping (domestic and agricultural usage, drainage) and mills.
B. Electrical application (wind turbines or aero-generator) – for electricity generation
- Battery charging
Factors to Consider in Site Selection for Wind Power System
- Average wind speed
- Local topography
- Presence of obstacles and height
- Free from the risk of accidents, noise, and interference with telecommunications
Advantages of Wind Power System
- Free source of fuel
- Long life expectancy
- Environment friendly
- Source is abundant
- Less liable to theft
- Mechanically simple
- Less maintenance required
Technical Details on Wind Power System
In 1927 Afred Betz of Germany computed a precise formula for the power that is available from the wind. Part of the formula shows that
- The power in the wind is proportional to the cube of the wind speed.
- The power in the wind is proportional to the area swept by the rotor.
- The power in the wind is proportional to the density of the air.
- A perfect wind system extracts a maximum of only 59.3% of the total power in the wind.
If air with mass m is moving with velocity, it has a kinetic energy expressed by:
E = ½ m V² Ev = ½ Þ V²
The power that flows with air, through area A is,
P theoretical= ½ Þ V² x VA = ½ Þ A V³
For the horizontal axis, rotary type, A = πD²/4
Maximum power Pmax = 0.593/2 Þ A V³ Betz formula
By rule of thumb;
P avail = 0.1 A V³
Wind into watts
The actual power will depend on several factors, such as the type of machine and rotor used, the sophistication of blade design, friction losses, the losses in the pump or other equipment connected to the wind machine, and there are also physical limits to the amount of power which can be extracted realistically from the wind.
So, modifying the formula for ‘Power in the wind’ we can say that the power that is produced by the wind machine can be given by:
Where:
PM is power (in watts) available from the machine
Cp is the coefficient of performance of the wind machine
P = power in watts
Þ = density of air in kg/m³ (1.2 kg/m³)
V = wind speed or velocity in meters per second
A = cross-sectional area of the rotor m²
Factors that affect air density
- Altitude
- Temperature
- Atmospheric pressure
ALTITUDE CORRECTION FACTORS FOR AIR DENSITY
Basic Parts of Wind Power System
- Rotor
- Tail vane
- Gear box (aero-generator/wind turbine)
- Racker arm (windpump)
- Generator (aero-generator/wind turbine)
- pump rod
- pump
Types of Tower
- 3-legged steel tower
- 4-legged steel tower
- Guyed-lattice
- concrete
Type of Rotor
- Blade type (horizontal axis type)
- Savonius (vertical axis type)
- Darrieus (vertical axis type)
Terminologies
- Solidity - the percentage of the area of the rotor, which contains material rather than air
- Tip-Speed Ratio – ratio of the blade tip velocity that of the wind
- Torque - is the twisting or rotary force produced by the rotor
- Power Coefficient (Cp)– is the ratio of the actual power converted by the rotor to that of the wind. Maximum Cp is 0.593 . In actual practice good rotor s will have Cp of 0.20-0.40 .
- TSR (λ) =Blade Tip Speed /Wind Speed
- Blade Tip Speed = RPM x Pi x Rotor Diameter or 2 x Pi x rotor radius x RPM
How To Find The Tip Speed:
1. Measure the rotor radius (length of one blade)
2. Speed = distance divided by time.
The distance traveled is the circumference (2Πr).
3. Speed: V =2Πr/T (time)
The blades travel one circumference
(2Πr) in a rotation time of T (seconds).
Now you see why we need to know how long it takes to make one full Revolution!
OTHER IMPORTANT FORMULAS FOR WIND ENERGY SYSTEM
HYDRAULIC POWER OUTPUT
P = 0.5 x Air density x power coef x trans. eff x vol. eff x rotor sweep area x wind velocity^3
TORQUE
Ts = Pi x Tr
where
Tr =running torque
Ts = starting torque
WINDSPEED
Vs = Vr/ 0.564
Where
Vs = starting windspeed
Vr = running windspeed
Windpumps
It is obviously important to match the water pumping demand with the available wind and hence decide upon a suitable rotor size. To calculate the demand we need to know the following data:
The head to which the water is to be pumped - in metres
volume of water to be pumped per day - in metres cubed
For water at sea level the approximate energy requirement can be calculated using the following equation:
E = 0.002725 x volume x head (in kilowatt-hours)
Drag-Type Machine
Drag-type machines, such as drag sail turbines or certain older designs, generate power primarily based on the drag force exerted by the wind on the turbine blades. They work by capturing wind energy through resistance. The wind pushes against the turbine blades, causing them to rotate.
Cd = D/2ρV²A
Where;
Cd = Drag coefficient
V = Wind Speed (m/s)
A = Vane area (m²)
D = Drag Force
Lift-Type Machine
Lift-type machines, such as most modern horizontal axis wind turbines (HAWTs), generate power based on the lift force created by the shape and pitch of the blades as the wind moves over them. hey use the aerodynamic principle of lift, where the shape of the blades creates a pressure difference between the upper and lower surfaces, resulting in rotation.
Cl = L/2ρV²A
Where;
Cl = Lift coefficient
V = Wind Speed (m/s)
A = Vane area (m²)
L= Lift Force
COEFFICIENT FOR THE EFFECT ON WIND SPEED OF DIFFERENT GROUND ROUGHNESS
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