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Photovoltaic Design andInstallation
Bucknell UniversitySolar Scholars Program
Presenters:
Colin Davies 08
Eric Fournier 08
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Outline
Why Renewable Energy?
The Science of Photovoltaics
System Configurations
Principle Design Elements
The Solar Scholars program atBucknell (walking tour)
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40%
85% of our energy consumption
is from fossil fuels!
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Why Sustainable Energy Matters
The worlds current energy system is built aroundfossil fuels
Problems:
Fossil fuel reserves are ultimately finite
Two-thirds of the world' s proven oil reserves arelocating in the Middle-East and North Africa (which
can lead to political and economic instability)
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Why Sustainable Energy Matters
Detrimental environmental impacts
Extraction (mining operations)
Combustion
Global warming? (could lead to significantchanges in the world' s climate system, leadingto a rise in sea level and disruption of agriculture
and ecosystems)
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A Sustainable Energy Future
Develop and deploy renewable energy sourceson a much wider scale
Bring down cost of renewable energy
Make improvements in the efficiency of energyconversion, distribution, and use
Three Methods:- Incentives
- Economy of scale
- Regulation
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Making the Change to Renewable
Energy
Solar
Geothermal Wind
Hydroelectric
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Todays Solar Picture
Germany leads solar production (over 4.5 times morethen US production) Japan is 2nd (nearly 3 times
more then US production) this is mainly due toincentives
Financial Incentives Investment subsidies: cost of installation of a
system is subsidized Net metering: the electricity utility buys PV
electricity from the producer under a multiyearcontract at a guaranteed rate
Renewable Energy Certificates ("RECs")
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Solar in Pennsylvania
Pennsylvania is in fact a leader in renewable
energy Incentives
Local & state grant and loan programs
Tax deductions
RECs (in 2006: varied from $5 to $90 per MWh,median about $20)
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Harnessing the Sun
Commonly known as solar cells, photovoltaic (PV)devices convert light energy into electrical energy
PV cells are constructed with semiconductormaterials, usually silicon-based
The photovoltaic effect is the basic physical processby which a PV cell converts sunlight into electricity
When light shines on a PV cell, it may bereflected, absorbed, or pass right through. Butonly the absorbed light generates electricity.
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Electricity
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Part 2: Learning Objectives
Compare AC and DC electrical current and
understand their important differences Explain the relationship between volts, amps,
amp-hours, watts, watt-hours, and kilowatt-hours
Learn about using electrical meters
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Electricity Terminology
Voltage (E or V)
Unit of electromotive force Can be thought of as electrical pressure
Amps (I or A)
Rate of electron flow
Electrical current
1 Amp = 1 coulomb/second = 6.3 x 1018electrons/second
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Electricity Terminology
Watt (W) are a measure of Power
Unit rate of electrical energy Amps x Volts = Watts
1 Kilowatt (kW) = 1000 watts
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Electricity Terminology
Watt-hour (Wh) is a measure of energy
Unit quantity of electrical energy (consumptionand production)
Watts x hours = Watt-hours
1 Kilowatt-hour (kWh) = 1000 Wh
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Power and Energy Calculation
Draw a PV array composed of four 75 watt
modules. What size is the system in watts ?
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Electricity Terminology
Amp-hour (Ah)
Quantity of electron flow Used for battery sizing
Amps x hours = Amp-hours
Amp-hours x Volts = Watt-hours
A 200 Ah Battery delivering 1A will last _____ hours 200 Ah Battery delivering10 A will last _____ hours
100 Ah Battery x 12 V = _____ Wh
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Types of Electrical Current
DC = Direct Current
PV panels produce DC Batteries store DC
AC = Alternating Current
Utility power
Most consumer appliancesuse AC
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Meters and Testing
Clamp on meter Digital multimeter
Never test battery current using a multimeter!
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System Types
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Part 1: Learning Objectives
Understand the functions of PV components
Identify different system types
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Photovoltaic (PV) Terminology
Cell < Module < Panel < Array
Battery stores DC energy Controller senses battery voltage and
regulates charging
Inverter converts direct current (DC )energy to alternating current (AC) energy
Loads anything that consumes energy
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Systems with DC Loads
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DC System Options
Battery backup vs. discontinuous use
LVD option in charge controller Load controllers
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Systems with AC loads
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AC System Options
Combined AC and DC loads
Hybrid system with back up generator Grid tied utility interactive system without
batteries
Grid tied interactive with battery backup
(why might you need this?)
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Grid-Tied System(With Batteries)
Complexity High: Due to the
addition of batteries
Grid Interaction Grid still supplements
power
When grid goes downbatteries supply powerto loads (aka batterybackup)
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PV Modules
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Part 3: Learning Objectives
Learn how a PV cell produces electricity fromsunlight
Discuss the 3 basic types of PV celltechnologies
Understand the effects of cell temperatureand solar insolation on PV performance
Gain understanding of module specification
Identify the various parts of a module
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Solar Cells and the PV Effect
Usually produced with Semi-conductor gradesilicon
Doping agents create positive and negativeregions
P/N junction results in 0.5 volts per cell
Sunlight knocks available electrons loose
Wire grid provides a path to direct current
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Inside a PV Cell
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Available Cell Technologies
Single-crystal or Mono-crystalline Silicon
Polycrystalline or Multi-crystalline Silicon
Thin film
Ex. Amorphous silicon or Cadmium Telluride
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Polycrystalline Silicon Modules
Less expensive to makethan single crystalline
modules Cells slightly less
efficient than a singlecrystalline (10% - 12%)
Square shape cells fitinto module efficientlyusing the entire space
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Amorphous Thin Film
Most inexpensivetechnology to produce
Metal grid replaced withtransparent oxides
Efficiency = 6 8 %
Can be deposited on
flexible substrates Less susceptible to
shading problems
Better performance in lowlight conditions that with
crystalline modules
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Selecting the Correct Module
Practical Criteria
Size
Voltage
Availability
Warranty
Mounting Characteristics Cost (per watt)
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Voltage Terminology
Nominal Voltage Ex. A PV panel that is sized to charge a 12 V battery, but
reads higher than 12 V)
Maximum Power Voltage (Vmax / Vmp) Ex. A PV panel with a 12 V nominal voltage will read 17V-
18V under MPPT conditions)
Open Circuit Voltage (Voc ) This is seen in the early morning, late evening, and while
testing the module)
Standard Test Conditions (STC) 25 C (77 ) cell temperature and 1000 W/m2 insolation
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Effects of Temperature
As the PV cell
temperatureincreases above 25C, the module Vmpdecreases by
approximately 0.5%per degree C
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Effects of Shading/Low Insolation
As insolationdecreasesamperagedecreases whilevoltage remains
roughly constant
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Other Issues
Surface temperature can be measured usinglaser thermometers
Insolation can be measured with a digitalpyranometer
Attaching a battery bank to a solar array will
decrease power production capacity
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PV Wiring
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Part 4: Learning Objectives
List the characteristics of series circuits andparallel circuits
Understand wiring of modules and batteries
Describe 12V, 24V, and 48V designs
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Series Connections
Loads/sources wired in series
VOLTAGES ARE ADDITIVE
CURRENT IS EQUAL
One interconnection wire is usedbetween two components (negative
connects with positive) Combined modules make series string
Leave the series string from a terminalnot used in the series connection
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Quiz Time
If you have 4 12V / 3A panels in an arraywhat would the power output be if that arraywere wired in series?
What if it were wired in parallel?
Is it possible to have a configuration that
would produce 24 V / 6 A? Why?
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Dissimilar Modules in Series
Voltage remains additive
If module A is 30V / 6A and module B is 15V / 3Athe resulting voltage will be?
Current taken on the lowest value
For modules A and B wired in series what wouldbe the current level of the array?
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Dissimilar Modules in Parallel
Amperage remains additive
For the same modules A and B what would thevoltage be?
Voltage takes on the lower value.
What would the voltage level of A and B wired inparallel be?
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Shading on Modules
Depends on orientation of internal modulecircuitry relative to the orientation of theshading.
SHADING can half
or even completely
eliminate the output
of a solar array!
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Wiring Introduction
PV installations must be in compliance with theNational Electrical Code (NEC)
Refer to NEC Article 690 (Solar Photovoltaic Systems) fordetailed electrical requirements
Discussion points Wire types, wire sizes
Cables and conduit Voltage drops
Disconnects
Grounding
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Wire Types
Conductor material = copper (most common)
Insulation material = thermoplastic (most common) THHN: most commonly used is dry, indoor locations
THW, THWN, and TW can be used indoors or for wetoutdoor applications in conduit
UF and USE are good for moist or underground applications
Wire exposed to sunlight must be classed assunlight resistant
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Color Coding of Wires
Electrical wire insulation is color coded to designate itsfunction and use
Alternating Current (AC) Wiring Direct Current (DC) Wiring
Color App l icat ion Color App l icat ion
Black Ungrounded Hot Red (not NEC req.) Positive
White Grounded
Conductor
White Negative or
GroundedConductor
Green or Bare EquipmentGround
Green or Bare EquipmentGround
Red or anyother color
Ungrounded Hot
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Cables and Conduit
Cable:two or more insulated conductors having anoverall covering
As with typical wire insulation, protective covering on cable israted for specific uses (resistance to moisture, UV light, heat,chemicals, or abrasion)
Condui t :metal or plastic pipe that contains wires PVC is a common conduit used
Using too many wires or too large of wires in a given conduitsize can cause overheating and also causes problems whenpulling wire
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Wire Size
Wire size selection based on two criteria: Ampacity
Voltage drop Ampacity: current carrying ability of a wire
The larger the wire, the greater its capacity to carry current
Wire size given in terms of American Wire Gauge (AWG)
The higher the gauge number, the smaller the wire
Voltage drop: the loss of voltage due to a wiresresistance and length Function of wire gauge, length of wire, and current flow in the
wire
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Safety Considerations
Unsafe Wiring
Splices outside the box
Currents in grounding conductors
Indoor rated cable used outdoors
Single conductor cable exposed
Hot fuses Disconnects
Overcurrent Protection (Fuses & Breakers)
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Safety Equipment
Disconnects Allow electrical flow to be
physically severed(disconnected) to allowfor safe servicing ofequipment
Overcurrent Protection Protect an electrical
circuit from damagecaused by overload orshort circuit
Fuses
Circuit Breakers
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Grounding
Limit voltages due to: Lightning Power line surges Unintentional contact with higher voltage lines
Provides a current path for surplus electricity to travel too(earth)
Two types of grounding: Equipment grounding
(attach all exposed metal parts of PVsystem to the grounding electrode) System ground ing(at one point attach ground to one current
carrying conductor) DC side of system => Negative to ground AC side of system => Neutral to ground
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Batteries
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Part 4: Learning Objectives
Battery basics
Battery functions Types of batteries
Charging/discharging
Depth of discharge
Battery safety
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Batteries in Series and Parallel
Series connections
Builds voltage
Parallel connections
Builds amp-hour capacity
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Battery Basics
Battery
A device that stores electrical energy (chemical energy toelectrical energy and vice-versa)
Capacity
Amount of electrical energy the battery will contain
State of Charge (SOC)
Available battery capacity
Depth of Discharge (DOD)
Energy taken out of the battery
Efficiency
Energy out/Energy in (typically 80-85%)
The Terms:
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Functions of a Battery
Storage for the night
Storage during cloudy weather
Portable power
Surge for starting motors
**Due to the expense and inherit inefficiencies of batteries it isrecommended that they only be used when absolutely necessary (i.e.in remote locations or as battery backup for grid-tied applications ifpower failures are common/lengthy)
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Batteries: The Details
Primary (single use)
Secondary (recharged) Shallow Cycle (20% DOD)
Deep Cycle (50-80% DOD)
Types:
Unless lead-acid batteries are charged up to 100%, they will loose
capacity over time
Batteries should be equalized on a regular basis
Charging/Discharging:
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Battery Capacity
Amps x Hours = Amp-hours (Ah)
Capacity:
100 amps for 1 hour
1 amp for 100 hours
20 amps for 5 hours
Capacity changes with Discharge Rate
The higher the discharge rate the lower the capacity and vice versa
The higher the temperature the higher the percent of rated capacity
100 Amp-hours =
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Rate of Charge or Discharge
Rate = C/T
C = Batterys rated capacity (Amp-hours)
T = The cycle time period (hours)
Maximum recommend charge/discharge rate =C/3 to C/5
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Cycle Life vs. Depth of Discharge
Depth Of Discharge (DOD) %
# of Cycles
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Battery Safety
Batteries are EXTREMELY DANGEROUS; handle withcare!
Keep batteries out of living space, and vent batterybox to the outside
Use a spill containment vessel
Dont mix batteries (different types or old with new)
Always disconnect batteries, and make sure toolshave insulated handles to prevent short circuiting
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Battery Wiring Considerations
Battery wiring leads should leave the batterybank from opposite corners
Ensures equal charging and discharging;prolongs battery life
Make sure configuration of battery bank
allows for proper connections to be easilymade
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Controllers & Inverters
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Part 5: Learning Objectives
Controller basics
Controller features
Inverter basics
Specifying an inverter
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Controller Basics
To protect batteries from being overcharged
Function:
Maximum Power PointTracking
Tracks the peakpower point of thearray (can improvepower production by20%)!!
Features:
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Other Controller Considerations
When specifying a controller you must consider:
DC input and output voltage
Input and output current Any optional features you need
Controller redundancy: On a stand-alone system it mightbe desirable to have more then one controller per array in
the event of a failure
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Inverter Basics
An electronic device used to convert direct current (DC)electricity into alternating current (AC) electricity
Function:
Efficiency penalty
Complexity (read: a component which can fail)
Cost!!
Drawbacks:
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Specifying an Inverter
What type of system are you designing? Stand-alone Stand-alone with back-up source (generator) Grid-Tied (without batteries) Grid-Tied (with battery back-up)
Specifics: AC Output (watts) Input voltage (based on modules and wiring)
Output voltage (120V/240V residential) Input current (based on modules and wiring) Surge Capacity Efficiency Weather protection
Metering/programming
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Solar Site
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Part 6: Learning Objectives
Understand azimuth and altitude
Explain magnetic declination
Describe proper orientation and tilt angle forsolar collection
Describe the concept of solar window
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Site Selection Panel Direction
Face south
Correct formagnetic
declination
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Orientation and Tilt Angle
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Site Selection Tilt Angle
Year round tilt = latitudeWinter + 15 lat.Summer 15 lat.
Max performance isachieved when panels
are perpendicular to thesuns rays
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Solar Access
Optimum Solar Window 9 am 3 pm
Array should have NO SHADING in thiswindow (or longer if possible)
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Solar Pathfinder
An essential tool in finding a good site forsolar is the Solar Pathfinder
Provides daily, monthly, and yearly solarhours estimates
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Practical Determinants for Site
Analysis
Loads and time of use
Local climate characteristics
Distance from power conditioning equipment
Accessibility for maintenance
Aesthetics
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Energy Efficiency
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Part 7: Learning Objectives
Identify cost effective electrical load reductionstrategies
List problematic loads for PV systems
Describe penalties of PV system components
Explain phantom loads
Evaluate types of lighting; efficiencycomparison
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Practical Efficiency Recommendations
For every $1 spent on energy efficiency, you save$3-$5 on system cost
Adopt a load dominated approach Do it efficiently
Do it another way
Do with less
Do without Do it using DC power
Do it while the sun shines
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Typical Wattage Requirements
Appliance Wattage
Blender 350
TV (25 inch) 130
Washer 1450
Sunfrost Refrigerator (7 hours aday)
refrigerator/freezer (13 hours aday)
112
475
Hair Dryer 1000
Microwave (.5 sq-ft)
Microwave (.8 1 sq-ft)
750
1400
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Improving Energy Efficiency in theHome
Space Heating: Super insulation
Passive solar design Wood stoves
Propane
Solar hot water
Radiant Floor/baseboard
Efficient windows
Domestic hot waterheating
Solar thermal Propane/natural gas
No electric heaters
On demand hot water
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Improving Energy Efficiency in theHome
Kitchen Stoves Solar cookers
Gas burners- no glowbar ignition
Microwaves
Washing machines High efficiency horizontal
axis
Cooling Ceiling fans
Window shades Evaporative cooling
Insulation
Trees
Reflective attic cover
Attic fan
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Phantom Loads
Cost the United States:
$3 Billion / year
10 power plants
18 million tons of CO2
More pollution than 6 million cars
TVs and VCRs alone cost the US $1Billion/year in lost electricity
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Lighting Efficiency
Factors effecting light efficiency
Type of light
Positioning of lights
Fixture design
Color of ceilings and walls
Placement of switches
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Incandescent Lamps
Advantages Most common
Least expensive Pleasing light
Disadvantages Low efficiency
Short life ~ 750 hours
Electricity is conducted through a filament which resiststhe flow of electricity, heats up, and glows
Efficiency increases as lamp wattage increases
FROM THE POWER PLANT TO YOUR HOMEINCANDESCENT BULBS ARE LESS THAN 2%
EFFICIENCT
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Fluorescent Bulbs
Les wattage, same amount of lumens
Longer life (~10,000 hours)
May have difficulty starting in coldenvironments
Not good for lights that are repeatedly turned
on and off Contain a small amount of mercury
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Mounting
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Part 8: Learning Objectives
Evaluate structural considerations
List hardware requirements
Pros and cons of different mounting
techniques
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General Considerations
Weather characteristics Wind intensity
Estimated snowfall Site characteristics
Corrosive salt water
Animal interference
Human factors Vandalism
Theft protection
Aesthetics
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Basic Mounting Options
Fixed
Roof, ground, pole
Integrated
Tracking
Pole (active & passive)
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Roof Mount Considerations
Penetrate the roof as little as possible
Weatherproof all holes to prevent leaks May require the aid of a professional roofer
Re-roof before putting modules up
Ballasted roof mounts work on certain roofs
Leave 4-6 airspace between roof andmodules
On sloped roofs, fasten mounts to rafters notdecking
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Building Integrated PV
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Ready for a field tour?
Questions?
If you are interested in anything you have seen today
and would like to get involved, please contact anymember of the Solar Scholars team:
Colin Davies, Eric Fournier, or Jess Scott(cjdavies, efournie, jpscott)
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The END
Thank you for participating in this lectureseries
Now lets go out into the field and take a lookat the systems that we have already
installed.
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