3. Earth’s Energy Balance
Yearly energy resources
(TWh)
Solar energy absorbed by atmosphere, oceans, Earth[1] 751,296,000.0
Wind energy (technical potential) [2]
221,000.0
Yearly energy consumption
Electricity (2005) [3]
(TWh)
-45.2
Primary energy use, non-electric (2005) [4]
-369.7
From Wikipedia, 2008-11-20:
1. Smil (2006), p. 12
2. Archer, Cristina. "Evaluation of Global Wind Power". Stanford. Retrieved on 2008-06-03. (72 TW at 0.35 capacity factor)
3. "World Total Net Electricity Consumption, 1980-2005". Energy Information Administration. Retrieved on 2008-05-25.
4. "World Consumption of Primary Energy by Energy Type and Selected Country Groups, 1980-2004". Energy Information Administration.
Retrieved on 2008-05-17.
4. Energy Generation: Solar
The total solar energy absorbed by Earth's atmosphere,
oceans and land masses is approximately 3,850 zettajoules
(ZJ) per year.
In 2002, this was more energy in one hour than the world
used in one year.
Photosynthesis captures approximately 3 ZJ per year in
biomass.
The amount of solar energy reaching the surface of the
planet is so vast that in one year it is about twice as much as
will ever be obtained from all of the Earth's non-renewable
resources of coal, oil, natural gas, and mined uranium
combined.
From Wikipedia, 2008-11-20, http://en.wikipedia.org/wiki/Solar_power
12. Energy Definitions 1
Energy: The ability to do work.
Power: The rate of energy usage.
dE (t )
P(t )
dt
E (t )
t
0 P( ) d E (0)
An energetic person is not necessarily
powerful or forceful, why?
13. Energy Measures: Units
1 Btu
777.9 ft-lbs
1055 joules=1055 watt-sec
252 calories
0.000293 kilowatt-hour
15. Energy Definitions 2
Usually measure power, then integrate to get
energy generated or used.
Mechanically, power equals force times
velocity, or torque times rotational speed,
P(t ) F (t ) x(t ) T (t ) (t )
Electrically, power equals voltage x current,
P(t ) V (t ) I (t )
17. Ampere’s Law
Charge in motion, I(t) ,
creates a magnetic flux, (t ) .
I(t)
(t )
Flux always comes out of the north pole,
according to the right-hand rule.
18. Ampere’s Law states that an electric current
produces a magnetic field. The magnetic field
curls around the current using the right-hand-rule,
that is, with your right thumb pointing in the direction
of the current, your fingers point in the direction
of the magnetic field.
I
21. Lenz’ Law states that current is induced so as to oppose a changing magnetic field.
I
I
N
S
Magnet velocity
N
S
Magnet velocity
Faraday’s Law states that a changing magnetic field produces a voltage.
For a coil with N-turns, the magnitude of the voltage is equal to
the number of turns multiplied by the rate of increase or decrease
of the magnetic flux inside the coil, V = -N(d/dt).
22. Lorentz Force Equation
Explains forces acting on charged particles in
electric and magnetic fields.
F q qv
F
qv
A charged particle moving in a magnetic field will be
deflected. If the velocity of the particle is
perpendicular to the magnetic field, the particle will
deflect perpendicularly to the plane of the velocity
and the magnetic field.
23. A Simple AC Generator
(t )
(t )
S
N
S
(t )
(t )
T
d (t )
V (t ) N
dt
N
iron
T
iron
25. Permanent Magnet DC-Motors
Permanent magnet DC-motors can also act
as DC generators. They rectify the output
voltage using a mechanical commutator.
Often the coil rotates in a magnetic field.
N
IDC
by Lorentz force eqn
S
+
VDC
-
commutator
26. A diode is needed to prevent stored
energy in the battery from driving
the motor backward.
(We will use this overall arrangement for the
experiment.)
IDC
N
S
+
VDC
-
commutator
28. Electrical Energy Storage
Two different metals and an electrolyteseparator are required for an electrochemical
cell.
According to Benjamin Franklin, a collection
of individual cells is called a battery.
Cell voltages depend on the metals involved.
29. An Electrochemical Cell Discharging
Current
Current
e-
No load voltage
Voltage
e-
qs
qd+
ions diffusing
+Electrode
Interface
Electrolyte
Interface
- Electrode
30. Cell Voltages
Non-rechargeable or primary cells
Dry cell
1.5V per cell
Rechargeable or secondary cells
Lead-acid cell
2V per cell
NiCad
1.2V per cell
NiMH
1.2V per cell
Li-ion
3.7V per cell
31. Comparison of Various Chemistries
From wikipedia, rechargeable batteries, 2008-24-2008
32. Battery Management
Some newer chemistries require great effort
for battery management systems (BMS) to
prevent cell damage due to overcharge,
overdischarge, overcurrent, overtemperature,
while maintaining charge balance among the
cells.
Older chemistries, such as lead-acid, allow
some overcharge, which works to balance the
cells. We will use lead-acid cells.
34. Energy Generation and Storage
Power = Voltage * Current
Energy = Power * Time, or
t
E (t ) P( ) d
0
E (n t ) P t P2 t P3 t Pn t
1
Windstream DC generator
DC ammeter
DC voltmeter
portable power pack
http://www.windstreampower.com/Human_Power_Generator_Series.php
35. Humans as energy sources
2008-11-20, http://www.recumbents.com/mars/tetz/E-Assist.htm, John Tetz
37. Component Matching 1
All humans have a maximum power-out point,
with an individualized torque and speed.
This maximum power point is easily matched
to a load by having gears on a bicycle. Using
gears, the human can continue to operate at
the maximum power-out point for any load.
38. Component Matching 2
A DC generator is chosen to be attached to
the bicycle wheel so that it will be able to
provide as much power as the human can
generate, assuming about 80% efficiency in
the generator.
From the human power vs time plot, a 300W
generator should be adequate for most
people.
39. DC generator power curves
2008-11-20, http://www.windstreampower.com/443902_PMDCG.php
40. Component Matching 3
The storage battery nominal voltage should
be chosen in conjunction with the DC
generator voltage output.
If the DC generator can produce 15V out,
then a single deep-cycle 12V lead-acid
battery will work. The size of the battery, and
thus the weight, depends on how much
charge and energy you want to store.
41. Energy Conversion and Usage
AC appliance
portable power pack
Kill-a-watt
AC Watt-hours out
Energy efficiency is
watt-hours removed
divided by watt-hours stored
http://www.windstreampower.com/Human_Power_Generator_Series.php
42. Inverters
Inverters are power-electronic devices that
convert DC to AC. Many families presently
have these in their automobiles. These
devices convert 12V DC to 120 Vrms AC.
The power rating of the device determines its
size and cost.
43. Component Matching 4
The inverter should be chosen so that its
input voltage matches that of the storage
battery.
Fortunately, most inverters are designed to
operate at about 12V in order to function with
standard lead-acid batteries.
44. Matching Battery to Inverter to Load
When attaching devices to the 120V AC
inverter output, it is important that the power
rating of the inverter not be exceeded.
Many inverters have some overcurrent
(overpower) protection, but users should do a
power calculation before attaching the AC
loads.
46. Measurements and Calculations
Power = Voltage * Current
Energy = Power * Time, or
t
E (t ) P( ) d
0
E (n t ) P t P2 t P3 t Pn t
1
Windstream DC generator
DC ammeter
DC voltmeter
portable power pack
http://www.windstreampower.com/Human_Power_Generator_Series.php
47. Energy Conversion and Usage
AC appliance
portable power pack
Kill-a-watt
AC Watt-hours out
Energy efficiency is
watt-hours removed
divided by watt-hours stored
http://www.windstreampower.com/Human_Power_Generator_Series.php
