Renewable Energy

• Solar• Hydroelectric• Wind• Wave

• All originate with the sun

Sun emits EM E at av rate (P)= 3.9 x 1026 J/s

R

• E is radiated in all directions in a spherical shape from the sun.

• Insolation = incoming solar radiation.

• Intensity -power/m2 hitting Earth.

• I = power/Area.

• A = 4r2.

• r orbit ~ 1.5 x 1011m.

• on Earth ~ 1380 W/m2.

What happens to Insolation

Amount of Energy at surface

• Amount hitting surface & absorbed varies:

• Angle of rays (max I when 90o to surface)

• season,

• cloud cover,

• type color of surface,

• reflection

Solar Energy• Solar Panels Photovoltaic PV Cells• heating only. Produce current

Solar PV 1:30

• http://www.youtube.com/watch?v=Sur89b7afso

Clip 1:30

Solar Themal 1:30Clip 1:30

• http://www.youtube.com/watch?v=64mtITOuXiA

4. A solar panel is installed to heat 1.4 m3 of water from 20 – 50oC. If the average power from the sun hits it with 0.9 kW/m2,

• a. Determine the number of Joules needed to heat the water.

• b. Estimate the area of the solar panel needed to heat the water in 2 hours.

• The density of water is 1000 kg/m3,assume an ideal panel.

• 1.8 x 10 8 J.• A = 28 m2.

Solar

Advantage• Renewable• Clean

Disadvantage• Night and Clouds• Requires large Area.

Hydroelectric - Dams

• Falling water spins turbine PE >>KE >> Electric

• Can calculate energy• mgh is E of water

Mass is also density x volume.

• At home look at example Hamper pg 192 – 193.

Hydro elec 3 min

• http://www.youtube.com/watch?v=wvxUZF4lvGw

Clip 2:15

Pumper Storage German Version 2.5 min

• http://www.youtube.com/watch?v=GJ7ltJlMY9E

Hydro Sample Prb

• The flow rate of water over a dam of height 40-m is 500 L/s.

• Find the power generated.

• density of water is 1 kg/L or 1000 kg/ m3.

• Power = rate E transformed.

• GPE = mgh

• P = E/t (each second 500 L of water fall = V/t)

• P = mgh/t

• Need mass water

• D = mass/vol dV = mass sub dV for mass.

• P = (dV) gh• t

• (1 kg/L) (500 L/s) (10 m/s2) (40 m)

• P = 200,000 W

IB ProbPumped Storage

Wind Turbine

• Cylindrical volume of air with velocity v, spins blades. KE air > KE blades> elec E.

• Power P, = ½ Av3.– = air density

– A = area of blade sweeps out. Blade = radius.

– v = wind velocity

Can calculate Area circle. KE/s = ½ (r2) v3.

Power P, = ½ Av3.

Mass = () vol

Wind 1.21 min

• http://www.youtube.com/watch?v=0Kx3qj_oRCchttp://www.youtube.com/watch?v=sLXZkn2W-lk&feature=player_detailpage

2. Wind

• Wind with density of 1.2 kg/m3.goes through a windmill with 1.5m blades with vi = 8m/s. The wind slows to 3 m/s, and density changes to 1.8 kg/m3 after leaving the blades.

• Find the max power of the windmill.

• The E from the wind is the work done on the blades.

• Pi – Pf

• A = r2.

• P = ½ Av3. Solve for each speed & density.

• (2171 – 171)W = 2000 W.

Wave Poweruses up & down motion of waves (KE>PE)

• Pelamis Oscillating• Hot dog Water column

Power in waves comes from OscillationWave alternate from KE (falling ) to PE rising

• Power per lengthof wavefront

P/L = ½ A2 gv.A = amplitude (half height)g ~ 10 m/s2. v = wave velocity

3. Waves. A wave with v = 4.8 m/s and height = 10 m is 2 m long. Find the power.

• A = ampl = 5 m.

• = 1000 kg/m3.

• g = 10 m/s2.

• P/l = ½ A2 gv.

• = ½ (5 m)2(1000)(10)(4.8 m/s) = 6 x 105 W/m

• For 2 m wave = 1.2 MW

Oscillating Water Column2:45

• http://www.youtube.com/watch?v=gcStpg3i5V8

http://www.youtube.com/watch?v=mcTNkoyvLFs

Pelamis no sound 2 min

Hints.

• Often use density to get a mass.• Must approximate shapes for volume calculation.• Ep = mgh for both hydroelectric & derivation of

wave energy.• Rates L/s or kg/s often can be used somehow to

get at power which is a rate.• Ex P = mgh = Vgh. V is a flow rate.

t t t

Hwk Hamper Read 189 – 198Do pg 194-198

#13,15,16

Derivation of Equation

• A wave on the surface of water is assumed to be a square-wave of height 2A, as shown.

• The wave has wavelength λ, speed v and has a wavefront of length L. For this wave,

• (i)show that the gravitational potential energy EP stored in one wavelength of the wave is given by

• EP = ½ A2 gρL.• where ρ is the density of the water and g is the acceleration of

free fall.

• Mass water = V = 1/2 AL).

• Height fall = A• mgh = 1/2 AL) A = 1/2A2g