ENERGY, POWER 8.1 – 8.4
NON- FOSSIL FUEL PP
“SOLAR PANELS”
Two types:
Solar heating panels
Radiation enters through glass
Black absorbs heat radiation best
Insulation behind, trapped air heats up (greenhouse)
Water pumped through pipes
Works even on dull days
Energy required for pump.
ENERGY, POWER 8.1 – 8.4
Photovoltaic cells (panels)
Direct conversion from light into a p.d. and hence current
system
Efficiency appx 10% of power from Sun goes to electrical power
1 m2 panel produces appx 150 W
ENERGY, POWER 8.1 – 8.4
Power:
Real interest is the INTENSITY of the radiation from the Sun
Intensity = Power per m2
Intensity varies over the Earth depending on:
Time of day (or night!): angle of Sun with horizon
Latitude
Season
(plus cloud etc)
Angles:
A
A cos
ENERGY, POWER 8.1 – 8.4HYDROELECTRIC POWER
Large scale:
A dam produces a lake. Water flows downhill through a channel in the dam containing a turbine.
PE of water becomes KE
at the turbine.
POWER = energy / sec
Typical output:
100 – 600 MW
h
ENERGY, POWER 8.1 – 8.4
QUESTION:water flows though tube to turbine at 1 m3s-1. turbine is 50 m lower than surface. water = 1000 kgm-3 .
PE = mgh
PE/sec = mass/sec x g x h
PE/sec (= POWER) = vol/sec x density x g x h
= 1 x 1000 x 9.81 x 50 = 490500 W or 490.5 kW
ENERGY, POWER 8.1 – 8.4
Small scale:
Archimedes screw
Typical output appx 70 kW
Efficiency appx 90%
ENERGY, POWER 8.1 – 8.4
Pumped storage:
A “reserve” for when a sudden demand for extra power:
eg: half time in cup-final
2 reservoirs, tap opened and water flows from top to bottom: starts in a few minutes.
At night, (cheap electricity) turbines used in reverse as pumps and re-fill the top reservoir
Maybe 20 mins working at full capacity
ENERGY, POWER 8.1 – 8.4
Tidal Power:
Maybe 24 turbines
Producing 240 MW
(equates to normal hydroelectric power station)
ENERGY, POWER 8.1 – 8.4
WIND POWER:
Kinetic energy of wind goes to KE of turbine blades
ENERGY, POWER 8.1 – 8.4
Consider 1 second’s worth of air (a cylinder) r
v ms-1
v metres
For 1 second:
Vol air = r2v
Mass air = r2v
KE air = ½ mv2 = ½ r2v3
But this is KE/sec = POWER (in Watts)VALUE?
r = 92m, wind speed = 30mph (= 13 ms-1) air = 1.25 kgm-3 P=?
EFFICIENCY
MAX: 59%
TYPICAL 15 – 40%
ENERGY, POWER 8.1 – 8.4
TIDAL POWER:
Can only estimate the
Power available from waves
h = average height of waves (=A/2)
Vol of wave = AW
Mass of wave = vol x density = AW
PE/wave = mgh = AW x g x A/2
= WgA2/2
f waves/sec so power = fWgA2/2
P = ½vWgA2
w
v ms-
1
h
But v = for f = v/
