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Wind Generators Tom Rebold Monterey Peninsula College [email protected] 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 (W) ▫ 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 Electron flow is from (-) to (+) (flow of electrons) Conventional flow is from (+) to (-) (hole flow) Electron Current Flow (-) to (+) Conventional Current Flow (+) to (-) Resistors – Basic Specs • Can be rated by… ▫ Resistance (Ohms, W) ▫ 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 W = 3.3 k W Resistors – Typical Power Ratings Ohm’s Law “Current (I) is proportional to Voltage (V) and inversely proportional to Resistance (R)” V I R V I R V R I UNITS: 1 Volt across 1 Ohm produces 1 Amp of current Calculate the current in this circuit using Ohm’s Law 3W I 6V V I R Calculate the current in this circuit using Ohm’s Law 1.5 W I 6V Calculate the current in this circuit using Ohm’s Law 3W I 3V Calculate the current in this circuit using Ohm’s Law 300 W I 6V How Many Volts across Resistor? 300 W 2A Ohm’s Law, Including Power Reproduced by permission of Tony van Roon, 2002 http://www.uoguelph.ca/~antoon How Many Watts dissipated by Resistor? 300 W 2A P=I2R How Many Watts dissipated by Resistor? 1.5 W I 6V P=I2R = V2/R = IV For your Wind generator, same calculations apply Water Pump Wind Generator I P=I2R = V2/R = IV To find the power delivered to our pump, we will have to measure V and I Complete System Drawing 10 ft wire Pump Fuse 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 Each conversion results in a loss of power Wind Power Electrical Power Pumping Power 50 W 5W 1W 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=mgh (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 8 You can determine tension in cables! • Keep tower simple. 2x4 with 4 cords attached to stakes • Mount motor using steel bands and screws Thoughts on Propeller Blade Design • http://www.practicalaction.org/docs/energy/bla des_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.HTM http://bb_ops.tripod.com/RC_Combat/Hind_Pump.htm