Wind GeneratorsTom ReboldMonterey Peninsula Collegetrebold@mpc.edu

Need to know…•Basic Electricity Measurements

•Power Calculations ▫Power in wind, electricity, and movement of

water

•Wind Tower Design (engineering statics)

•Wind generator blade design (aerodynamics)

•Water Pump Design (hydraulics)

Electrity: Three Main Invisible Quantities

•Voltage, V, Volts▫Provides the “push”

•Current, I, Amperes (Amps)▫Flow of Electrons▫Amount of Current is dependent on Voltage

and Resistance•Resistance, R, Ohms ()

▫Limits the amount of current

Safe Levels

•Voltage: 30 V▫Voltages inside a computer do not exceed 12 V,

except at the power supply and power switch, which are at 120 V.Be careful in these areas!

•Current: 5 mA (0.005 Amperes)

Voltage Can Be Provided From…•A battery

Voltage Can Be Provided From…•A generator

Current•…is simply the flow of electrons•Direction depends on convention

Conventional Current Flow (+) to (-)

Electron Current Flow (-) to (+)Electron flow is from (-) to (+) (flow of electrons)Conventional flow is from (+) to (-) (hole flow)

Resistors – Basic Specs•Can be rated by…

▫Resistance (Ohms, )▫Tolerance (% of nominal value)▫Power Rating (Watts)

•Schematic Symbol…

Resistors – Types•Fixed

Variable (Potentiometer, Rheostat)

Resistors – Color Code

Resistors –Colour Code Example

3 3 102

5%(gold)

1st band: orange = 3 2nd band: orange = 3 3rd band: red = 2 (i.e. 102) 4th band: gold = 5%

33 x 102

= 3300

= 3.3 k

Resistors – Typical Power Ratings

Ohm’s Law

R

VI

“Current (I) is proportional to Voltage (V) and inversely proportional to

Resistance (R)”

RIV I

VR

UNITS: 1 Volt across 1 Ohm produces 1 Amp of current

Calculate the current in this circuit using Ohm’s Law

3

6VI

R

VI

Calculate the current in this circuit using Ohm’s Law

1.5

6VI

Calculate the current in this circuit using Ohm’s Law

3

3VI

Calculate the current in this circuit using Ohm’s Law

300

6VI

How Many Volts across Resistor?

2A

300

Ohm’s Law, Including Power

Reproduced by permission of Tony van Roon, 2002 http://www.uoguelph.ca/~antoon

How Many Watts dissipated by Resistor?

2A

300

P=I2R

1.5

6VI

P=I2R = V2/R = IV

How Many Watts dissipated by Resistor?

Water Pump

Wind Generator

I

P=I2R = V2/R = IV

For your Wind generator, same calculations apply

To find the power delivered to our pump, we will have to measure V and I

Complete System Drawing

Fuse

Pump

10 ft wire

Wind and Hydro Power Calculations•How much power is in the wind?

•How much power does it take to pump a liter of water 2 m uphill in 5 minutes?

•How can we evaluate how effective our wind system is at pumping water?

Engineering a Power Conversion System

Wind Electrical Pumping

Power Power Power

Each conversion results in a loss of power

50 W 5 W 1 W

This system has an overall efficiency of 1/50 or 2%In subsequent designs, engineers would try to improve the efficiency

The Power in the Wind • From basic physics we have “Kinetic Energy”

▫K = ½ M V2

K = energy in Joules (or N-m, or even KW-hr) M = mass, kg V = velocity of object, m/s

• In the context of wind, we can determine the mass of the cylinder of air that hits our generator in a certain time interval.

• Power is the amount of Kinetic Energy we capture divided by the time we are gathering it. ( Watts)

Hydraulic Power

•In order to pump a mass m kg of water h meters uphill, we require an amount of energy equal to ▫E = m g h (Joules) where g = 9.8

m/s2

•To pump uphill in T seconds, would require a power of ▫P = E/T (Watts)

•Suppose m = 1 kg, d = 2 m, T = 60 s▫P = 1 x 9.8 x 2 / 60 = .3 W

Tower Design

•In ENGR 8You can determinetension in cables!

•Keep tower simple. 2x4 with 4 cordsattached to stakes

•Mount motor using steel bands and screws

Thoughts on Propeller Blade Design•http://www.practicalaction.org/docs/energ

y/blades_manual.pdf

Balance

•By all means, make sure you balance your blades before testing!

•Use some small weights, coins, anything to make sure the blades are evenly weighted.

•Otherwise your generator could quickly destroy itself!

Pump Construction•http://www.ircwcc.org/manual/PUMP/PUMPS.

HTMhttp://bb_ops.tripod.com/RC_Combat/Hind_Pump.htm