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Basics of
Photovoltaics for theDeveloping World
Ethan LaRochelleEWB-Northeastern University
April 13, 2009
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Outline
Terms
Basic System Designs PV Modules
Site Assessment
Batteries Charge Controller
Wiring
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Safety First! Exposure: roof/ladder work Falls, strains and sprains
30-50 lb modules
Cuts and bumps Gloves and Class B hard hat
Burns Thermal from hot metal Acid from batteries
Electrical Hazards
20mA (AC) or >90mA (DC) is dangerous Remember there is no off switch on a panel
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PV Direct System
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Stand-Alone System
Only nee
ded
for AC power
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Grid-Tied System
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Other system Designs
Grid-tie with battery backup
Mix of previous two systems
Hybrid system
Multiple sources
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Terms and Equations
Alternating Current (AC)
Normal household
Direct Current (DC) PV modules, batteries
Power (W)
P = Potential (V) * Cu
rrent (A) Energy (Wh)
Measurement of quantity of powerused over time
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Examplesu
sing Power and Energy LED floodlight
Uses 12VDC
Draws 144mA At what rate does this
light draw power?
The light is used for 2hours. During this timehow much energy does itconsume?
The 18 LED lamp makes a greatreading light if you are within 3 to 4feet. They have an expected life of10 years or more and carry a 2 yearwarranty.
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System Design The first step in a system design is tounderstand the load requirements
Make a list of all loads and how long theywill be in use
This information will be useful during the
site assessment and design process
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PV Modules
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Types of PV Modules
PowerFilm Inc.18W at 12VThin Film
12 x 73 ~$308
BP Solar BP 380J80W at 12V
Polycrystalline
21 x 48 ~$465
SunWize SW80A80W at 12V
Monocrystalline
21 x 51 ~$470
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Types of PV ModulesMonocrystalline
Long history
Good reliabilityand efficiency
Polycrystalline
Slightly lowerefficiency than
mono
Thin Film
Reduced eff.
Can beflexible
Highershade and
heat tolerance
Low tolerance to shading
Performance decreases in highheat
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Nominal Voltages Voltages based on
batteries
12V, 24V, 36V, 48V
Voltage flow is fromhigh to low
The previousexamples of PVmodules were all 12Vnominal
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Electrical Characteristics Pmax = 175W
Vmax = 35.4V
Imax = 4.94 A
Voc = 43.6V
Isc = 5.54A
What is the nominalvoltage?
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Site Assessment
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O
rienting Solar Array For year-round average use latitude as tilt
angle
Direct true (solar) south
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Peak Su
n Hou
rs (Insolation)
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Peak Sun Hours vs. Hours of
Daylight Why does Honduras only have 5 peak sun
hours?
This is the standardized equivalent full-sunhours
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Site Assessment Short of outright physical destruction,
hard shadows are the worst possible thing
you can do to a PV module output
- Solar Living Sourcebook
Want unobstructed exposure 9AM to 3PM
Check annual change in suns path
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The Su
n Chart
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Assessment ToolsSolar Pathfinder
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Batteries
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Batteries Store energy to be used when the sun
goes down
Usually lead based
Require charge controller
Shorter life-cycle than PV modules
Automotive batteries are not ideal
Deep cycle should be used if available
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Battery Types Flooded Lead Acid
Least expensive and longest life if maintained
Sealed Lead Acid
Electrolyte suspended in gel or similarsubstance
No maintenance and wont spill Shorter life and higher cost
Can be shipped
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Safety! Batteries can produce high current
Electrical and Acid burns
Venting needed
Have baking soda to neutralize acid
Use insulated tools
Dont drop a wrench across the terminals Remove jewelry
Locate in vented enclosure with spill plate
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Battery Storage Capacity MK 8GU1H 12V, 31.6Ah Sealed Gel-HDL
($85)
How much energy canthis battery store?
Rating: 12V, 31.6Ah
12 * 31.6 = 379.2 Wh
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Example Problem Matilde wants to stay up late at night reading a
book he just checked out of his new local library.He lives in a village in Honduras that has no
electricity, but he has access to a 12V 180Wsolar module, a 12V 30Ahr battery and anywiring and other components he may need. Hehas a single 60W light bulb he would like topower. Neglecting losses and otherconfounding factors, how long will Matilde beable to stay up reading after the sun goes downif it is an average sunny day?
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O
ther things to consider Capacity depends on the rate of discharge
To maintain a healthy battery it is best not
to discharge a battery more than 50% If only car batteries are available, tie them
in parallel to increase the capacity
This will complicate the system Charge controllers are needed so the flow
of the voltage doesnt go from the batteryto the solar module during the night.
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Charge Controller
Functions:
Prevent battery overcharge
Prevent battery discharge overnight
Types
Shunt (PWM) ( < $100)
PWM ( $150 - $300)
MPPT ( $200 - $750)
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Shunt Charge Controllers
Short-circuits modules to preventovercharging
Lowest cost of three types
Can only be used up to ~20A
Good if wirelesselectronics are beingused in the system
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Wiring
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Wiring
Series
Nose-to-tail, - to +
Voltages add, Amperage constant
Parallel
+ to + and to
Voltage constant, Amperages add
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Misc.
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Mounting Systems
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Example Problems
Solar Water Pump
LED Lighting
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Acknowledgments
AltE Store
The majority of this presentation is based on
the curriculum taught in AltEs PV301 andPV302 courses
http://store.altestore.com
IEEE Foundation IEEE has funded me to take these classes
and share this information through the IEEEHumanitarian Fellowship
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Further Resources
Renewable Energy Experts Video - Water
Pumping
Video with Windy Dankoff Practical Photovoltaics: Electricity from
Solar Cells
Book by Richard Komp
Solar Energy International (SEI)
Books, workshops, etc