Download Solid State Lighting for the Developing World

Pico Power Generation for
the Developing World
Loren Wyard-Scott 1 *
&
Dr. James Andrew Smith 2 *
1Dept.
of Electrical & Computer Engineering
University of Alberta
Edmonton, Alberta, Canada
2Dept.
of Electrical & Computer Engineering
Ryerson University
Toronto, Ontario, Canada
*Member, IEEE
Why Small Electrical
Generation Systems?
• Economics
– More affordable in isolated or low-income locations
• Reliability
– Sustainable maintenance with local resources
• Productivity
– Longer work days
– Indoor working conditions
• Literacy
– Schoolwork is possible even in the evening
Power Generation & Usage in
the Developed World
• Minority of world population
• Use a majority of energy resources
• Electrical Lighting is abundant & taken
for granted
• Pollution
problems
caused by
power
generation
Earth at night. Where are the developed nations?
Trivia!
Energy use in a typical
American Home [1]
Total energy
consumed in
America in 1995:
9.2 × 1019 J [2]
[1] Energy Kid’s Page, U.S. Department of Energy,
http://www.eia.doe.gov/kids/energyfacts/saving/efficiency/savingenergy.html,
accessed 01 Dec 2008.
[2] Beursten, Bruce E., Theodore L. Brown & Eugene Le May Jr. Chemistry:
The Central Science. Engelwood Cliffs, NJ: Prentice Hall, 1997.
More Trivia
• There are 34.2 MJ/L of automotive
gasoline [1].
• Keep this in mind as you tackle this
project!
[1]Nommensen, Arthur. List of common conversion factors
(Engineering conversion factors). IOR Energy.
Power Generation & Usage in
the Developing World
• Majority of the world’s population
• 2 billion people without modern lighting or
power
• Current Solutions
– Nothing
– Kerosene
– Diesel
• Dangers
– Fires
– Carbon Monoxide
– Sulfur Dioxide
Voting by candlelight in Haiti
Challenges Faced in the
Developing World
• Limited electricity supply
– Often no electrical grid
– Only micro energy sources (diesel, solar, hydro)
• Difficult operating conditions
– Temperature ranges
– High humidity
– Dust and dirt
• Limited replacement parts
– Limited distribution infrastructure
– Sustainability: require local businesses
Power Generation Examples
• Bicycle Dynamo
– 3 Watts
• Wind Turbine (typical):
– 1 Mega Watt
– 300,000 Bike Dynamos!
• Hydro Plant (La Grande-1, Canada):
– 1400 Mega Watts
• Coal Plant (typical):
– 500 Mega Watts
• Nuclear Plant (Pickering, Canada):
– 4100 Mega Watts
1 Mega Watt: power for 1000 North American houses
Your mission: Pico Power!
• We would like you to design and construct a
system that will provide a small amount of
light for a short duration.
• The “light” will be a Light Emitting Diode
(LED) with a current-limiting resistor, and the
duration is to be a minimum of 10 minutes.
• Moreover, during the 10 minutes, the user
needs to concentrate on reading, and so the
energy to power the light needs to be
generated before-hand and stored!
Engineering
Development Process
1.
Identification of problem
–
–
2.
What is possible?
Keep it simple & effective!
Risk evaluation
–
5.
6.
7.
8.
Prototype
What actuators and sensors? At what cost?
Determine level of functional replacement
–
–
4.
What function is missing?
Talk to the clients/users!
Identification of affordable technology
–
3.
Start
Never underestimate what can go wrong!
Prototype device, test & start again (Steps 1 -5)
Test on larger population set
International certification
Manufacture & distribute device

Test

Manufacture
End
Rapid Prototyping
• “Express - Test - Cycle” approach to design
–
–
–
–
–
–
Identify a need & design objectives
Brainstorm for solutions
Express an idea in a physical device
Test the device
Discover problems that you weren’t aware of
Repeat until you’ve met the design objectives
• Rapid prototyping systems
– Combine modular, off-the-shelf components
– Great for quick mock-ups & functional testing
– Examples
• Breadboards
• Vector board
• Speed Wire
Breadboard system
Outline of Technical Topics
Knowledge about key topics will help you succeed:
• The basics:
–
–
–
–
–
Electricity
Ohm’s Law
Power and Energy
Capacitors
Diodes (including LEDs)
• Applied electrical engineering:
–
–
–
–
–
AC and DC Generation
Rectifying
Filtering
Regulating
Life of a Power Source
Electricity Background
• Voltage [Volts]:
– A “force” that tries to move electrons
– Provided by devices such as batteries
• Current [Amperes, Amps]:
– This is the “flow” of electrons
– Carried by wires
• Resistance [Ohms]:
– Resist the flow of electrons
– Intentionally provided by resistors.
– Unintentionally provided by almost all real-world
components
Ohm’s Law
• Relates the main
electrical measures
• I=V/R
– Battery has constant
voltage [V]
– Current [I] varies
with resistance [R]
– Larger resistance
means smaller
current
Power and Energy
• Energy is measured in Joules
• Power, measured in Watts, is
Energy per unit time:
• Electrically, the power being
used in a circuit with fixed
voltage and current is:
P
E
t
P  IV
Example: if a 12V battery provides 1 Amp of current to power the stereo in
your car, it is providing 12W of power. If the stereo is on for 1 hour, the
battery provides 12W(60 minutes)(60 seconds/minute) = 43,200 Joules.
Batteries as an Energy Source
• Batteries are made of individual cells
• Series cells: more voltage
• Parallel cells: same voltage, longer life
Single Cell
Series Cells
Series & Parallel Cells
Resistances in Series & Parallel
• Resistances in
series add up.
Req  R1  R 2
• Resistances in
parallel:
Req 
Series Resistance
1
1
1

R1 R 2
Parallel Resistance
Voltage Drops
• Batteries increase circuit voltage
• Resistors & other devices “drop” voltage
– Sum of “drops” equals battery voltage
• Imagine walking on a mountain.
– Battery raises you to the top
– Resistors, etc. drop you down.
Capacitors
• Temporarily store electrical
charge
• Can rapidly discharge
current when needed
• Positive sign means it is
polarized & must be
connected right.
• Where do you find them?
– In circuit boards near
components that need steady
current
– In camera flashes
Capacitive
filtering
Capacitors in Series & Parallel
Capacitances in
parallel add
Ceq C 1C 2
• Capacitances in
series
Ceq 
1
1
1

C1 C 2
Capacitors: Energy Storage
• Like batteries, capacitors store energy.
• An ideal capacitor with a constant voltage
can store:
1
2
E  CV
2
• Capacitance is measured in Farads.
• Be aware that capacitors have a maximum
rated voltage. Exceeding this voltage can
put the capacitor (or you) in danger.
• Warning: large capacitors can store a lot of
energy. Always handle carefully!
Diodes
• Semiconductor devices
• Current flows in one direction only
• The diode’s PN junction controls
current flow
• Anode & Cathode on either side of
the junction
Anode
• If the Anode has a more positive
voltage than the Cathode, it is
“forward biased”
– Lets current through
• Otherwise it is “reverse biased”
– Will not let current through
Cathode
Diodes: The Corner Model
• A “model” is a simplified imaginary version of
the actual device
• Apply a low voltage
– It stays off
– No electrons go through
– Current is zero
• Apply a high voltage
– It turns on!
– Electrons pass through
– Current is allowed
• Voltage drop across diode is constant: Vd
Light Emitting Diode
(LED)
• Light Emitting Diode
(LED)
• Operates like a
regular diode
• The lens lets
photons out
– Converts electrons to
photons
• Higher current
– Brighter light!
LED Operation
• To control brightness,
change the current by
changing the resistance
in the circuit
• Vd depends on the LED
• 1V to 3V
• If the battery is low, the
LED will not turn on
• Too much current will
burn the LED out!
AC vs. DC Systems
• Alternating Current (AC)
systems are those that
have time-varying (usually
sinusoidal) voltage current
waveforms
• Direct Current (DC)
systems have constant
voltage and current
AC Generators
•
•
•
•
Loads run at the same frequency as generators
Requires rectifiers & filters for DC loads
Very good for long distance power transmission
Bicycle Dynamos are AC generators
DC Motors as Generators
•
•
•
•
DC motors can be driven like generators
Brushes tend to wear out
Output is constant so rectifiers are not needed
Not efficient for long distance transmission (at lower
voltages)
Rectifying I
• The process of converting an AC waveform
into another waveform that has a DC
component
• Recall that diodes operate as “one-way
valves”
• A “half-wave” rectifier is shown here:
Rectifying II
• An improvement is a “full-wave” or “bridge”
rectifier
• Positive voltage: one diode pair on
• Negative voltage: other diode pair on
Filtering I
• If periodic / alternating voltages
need to be smoothed,
capacitors can be used as
filters
– Capacitors store electrical charge,
like a bucket stores water
– Electrons are brought to the
capacitor by input current, like
drops of water into a bucket
– When needed, capacitor outputs
current like the water bucket’s
output valve
Filtering II
• The size of the capacitor, C, determines
how constant the output voltage is!
Regulating
•
Regulating is the process of controlling the
system to get the output we want
Generator output can be regulated by
•
1. Changing the mechanical input speed
2. Circuitry on the electrical output
•
7805 Regulator (5 V, 0.5 - 1.0 Amp output)
•
•
•
•
•
Place between filtered rectifier and load
Pin 1: input (7 - 30 VDC)
Pin 2: Ground
Pin 3: output (5 VDC)
Add 0.33 uF filter caps
•
7805
Pin 1 and Pin 2; Pin 3 and Pin 2
1 2 3
Life of a Power Source
• Battery life
– Inversely proportional to current
• Low current operation
– Higher resistance
– Lower current
– Weaker light & longer life
• High current operation
– Lower resistance
– Higher current
– Brighter light & shorter life
• This applies to any device that
stores electrical energy,
including capacitors!
Final Project:
Scenario & Goals
• Scenario
– A remote village of 500 people
– No night-time electricity
– Have small low-power lamps
• Objective
– Build a small power source
– 10 minute (min) lamp operation
– Preferably human-powered
– Night-time discharging
• Keep in mind:
–
–
–
–
Bas-Ravine, Haiti
Target group for the final design
What socio-economic factors affect engineering projects?
Where will the device be used?
How will the target group use the device?
Packaging for the Real World
•
KISS: “Keep it Simple, Stupid!”
– Simpler designs have less flaws
– Murphy’s Law: “If it can go wrong, it probably will.”
•
Intuitive usage
– Nobody reads the manuals
– Must be easy to recharge & operate!
•
Rugged design
– Can you drop it without breaking it?
•
Design for the local environmental conditions
– Dust, sand, snow, humidity, etc.
For more information
• Micro Hydro Installations
– http://www.green-trust.org/hydro.htm
• Light Up The World (LUTW)
– http://www.lutw.org/
• Bicycle Dynamo Rectifiers & Filters
– http://pilom.com/BicycleElectronics/DynamoCircuits.htm