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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

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