Photovoltaic Design and
Installation
Bucknell University
Solar Scholars Program
Presenters:
Colin Davies ‘08
Eric Fournier ‘08
Outline





Why Renewable Energy?
The Science of Photovoltaics
System Configurations
Principle Design Elements
The Solar Scholars program at
Bucknell (walking tour)
What’s wrong with this picture?


Pollution from burning fossil fuels leads to an
increase in greenhouse gases, acid rain, and the
degradation of public health.
In 2005, the U.S.
emitted 2,513,609
metric tons of carbon
dioxide, 10,340 metric
tons of sulfur dioxide,
and 3,961 metric tons
of nitrogen oxides from
its power plants.
40%
85% of our energy consumption
is from fossil fuels!
Why Sustainable Energy Matters

The world’s current energy system is built around
fossil fuels
– Problems:
Fossil fuel reserves are ultimately finite
 Two-thirds of the world' s proven oil reserves are
locating in the Middle-East and North Africa (which
can lead to political and economic instability)

Why Sustainable Energy Matters

Detrimental environmental impacts
– Extraction (mining operations)
– Combustion
 Global warming? (could lead to significant
changes in the world' s climate system, leading
to a rise in sea level and disruption of agriculture
and ecosystems)
A Sustainable Energy Future



Develop and deploy renewable energy sources
on a much wider scale
Bring down cost of renewable energy
Make improvements in the efficiency of energy
conversion, distribution, and use
Three Methods:
- Incentives
- Economy of scale
- Regulation
Making the Change to Renewable
Energy




Solar
Geothermal
Wind
Hydroelectric
Today’s Solar Picture

Germany leads solar production (over 4.5 times more
then US production) – Japan is 2nd (nearly 3 times
more then US production) – this is mainly due to
incentives

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 multiyear
contract at a guaranteed rate
Renewable Energy Certificates ("RECs")
Solar in Pennsylvania


Pennsylvania is in fact a leader in renewable
energy
Incentives
–
–
–
Local & state grant and loan programs
Tax deductions
REC’s (in 2006: varied from $5 to $90 per MWh,
median about $20)
Harnessing the Sun



Commonly known as solar cells, photovoltaic (PV)
devices convert light energy into electrical energy
PV cells are constructed with semiconductor
materials, usually silicon-based
The photovoltaic effect is the basic physical process
by which a PV cell converts sunlight into electricity
– When light shines on a PV cell, it may be
reflected, absorbed, or pass right through. But
only the absorbed light generates electricity.
Electricity
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 kilowatthours
Learn about using electrical meters
Electricity Terminology




Electricity = Flowing
electrons
Differences in electrical
potential create electron flow
Loads harness the kinetic
energy of these flowing
electrons to do work
Flowing water is a good
conceptual tool for
understanding
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 1018
electrons/second
Electricity Terminology

Resistance (R or Ω)
–
–
The opposition of a material to the flow of an
electrical current
Depends on




Material
Cross sectional area
Length
Temperature
Electricity Terminology

Watt (W) are a measure of Power
–


Unit rate of electrical energy
Amps x Volts = Watts
1 Kilowatt (kW) = 1000 watts
Electricity Terminology

Watt-hour (Wh) is a measure of energy
–
–

Unit quantity of electrical energy (consumption
and production)
Watts x hours = Watt-hours
1 Kilowatt-hour (kWh) = 1000 Wh
Power and Energy Calculation


Draw a PV array composed of four 75 watt
modules.
What size is the system in watts ?
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
Types of Electrical Current

DC = Direct Current
–
–

PV panels produce DC
Batteries store DC
AC = Alternating Current
–
–
Utility power
Most consumer appliances
use AC
Meters and Testing
Clamp on meter

Digital multimeter
Never test battery current using a multimeter!
System Types
Part 1: Learning Objectives


Understand the functions of PV components
Identify different system types
Photovoltaic (PV) Terminology

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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
Systems with DC Loads
DC System Options


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Battery backup vs. discontinuous use
LVD option in charge controller
Load controllers
Systems with AC loads
AC System Options

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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?)
Grid-Tied System
(Without Batteries)

Complexity
–

Low: Easy to install
(less components)
Grid Interaction
–
–
Grid can supplement
power
No power when grid
goes down
Grid-Tied System
(With Batteries)

Complexity
–

High: Due to the
addition of batteries
Grid Interaction
–
–
Grid still supplements
power
When grid goes down
batteries supply power
to loads (aka battery
backup)
PV Modules
Part 3: Learning Objectives

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Learn how a PV cell produces electricity from
sunlight
Discuss the 3 basic types of PV cell
technologies
Understand the effects of cell temperature
and solar insolation on PV performance
Gain understanding of module specification
Identify the various parts of a module
Solar Cells and the PV Effect





Usually produced with Semi-conductor grade
silicon
Doping agents create positive and negative
regions
P/N junction results in 0.5 volts per cell
Sunlight knocks available electrons loose
Wire grid provides a path to direct current
Inside a PV Cell
Available Cell Technologies

Single-crystal or Mono-crystalline Silicon

Polycrystalline or Multi-crystalline Silicon

Thin film
–
Ex. Amorphous silicon or Cadmium Telluride
Monocrystalline Silicon Modules



Most efficient
commercially available
module (11% - 14%)
Most expensive to
produce
Circular (square-round)
cell creates wasted
space on module
Polycrystalline Silicon Modules



Less expensive to make
than single crystalline
modules
Cells slightly less
efficient than a single
crystalline (10% - 12%)
Square shape cells fit
into module efficiently
using the entire space
Amorphous Thin Film


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Most inexpensive
technology to produce
Metal grid replaced with
transparent oxides
Efficiency = 6 – 8 %
Can be deposited on
flexible substrates
Less susceptible to
shading problems
Better performance in low
light conditions that with
crystalline modules
Selecting the Correct Module

Practical Criteria
–
–
–
–
–
–
Size
Voltage
Availability
Warranty
Mounting Characteristics
Cost (per watt)
Current-Voltage (I-V) Curve
Voltage Terminology

Nominal Voltage
–

Maximum Power Voltage (Vmax / Vmp)
–

Ex. A PV panel with a 12 V nominal voltage will read 17V18V under MPPT conditions)
Open Circuit Voltage (Voc )
–

Ex. A PV panel that is sized to charge a 12 V battery, but
reads higher than 12 V)
This is seen in the early morning, late evening, and while
testing the module)
Standard Test Conditions (STC)
–
25 º C (77 º) cell temperature and 1000 W/m2 insolation
Effects of Temperature

As the PV cell
temperature
increases above 25º
C, the module Vmp
decreases by
approximately 0.5%
per degree C
Effects of Shading/Low Insolation

As insolation
decreases
amperage
decreases while
voltage remains
roughly constant
Other Issues



Surface temperature can be measured using
laser thermometers
Insolation can be measured with a digital
pyranometer
Attaching a battery bank to a solar array will
decrease power production capacity
PV Wiring
Part 4: Learning Objectives


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List the characteristics of series circuits and
parallel circuits
Understand wiring of modules and batteries
Describe 12V, 24V, and 48V designs
Series Connections

Loads/sources wired in series
–
–
–
–
–
VOLTAGES ARE ADDITIVE
CURRENT IS EQUAL
One interconnection wire is used
between two components (negative
connects with positive)
Combined modules make series string
Leave the series string from a terminal
not used in the series connection
Parallel Connections

Loads/sources wired in parallel:
VOLTAGE REMAINS CONSTANT
– CURRENTS ARE ADDITIVE
– Two interconnection wires are used between two
components (positive to positive and negative to negative)
– Leave off of either terminal
– Modules exiting to next
component can happen
at any parallel terminal
–
Quiz Time

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
If you have 4 12V / 3A panels in an array
what would the power output be if that array
were 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?
Dissimilar Modules in Series

Voltage remains additive
–

If module A is 30V / 6A and module B is 15V / 3A
the resulting voltage will be?
Current taken on the lowest value
–
For modules A and B wired in series what would
be the current level of the array?
Dissimilar Modules in Parallel

Amperage remains additive
–

For the same modules A and B what would the
voltage be?
Voltage takes on the lower value.
–
What would the voltage level of A and B wired in
parallel be?
Shading on Modules
Depends on orientation of internal module
circuitry relative to the orientation of the
shading.
 SHADING can half
or even completely
eliminate the output
of a solar array!

Wiring Introduction

PV installations must be in compliance with the
National Electrical Code (NEC)
–

Refer to NEC Article 690 (Solar Photovoltaic Systems) for
detailed electrical requirements
Discussion points
–
–
–
–
–
Wire types, wire sizes
Cables and conduit
Voltage drops
Disconnects
Grounding
Wire Types

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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 wet
outdoor applications in conduit
UF and USE are good for moist or underground applications
Wire exposed to sunlight must be classed as
sunlight resistant
Color Coding of Wires

Electrical wire insulation is color coded to designate its
function and use
Alternating Current (AC) Wiring
Direct Current (DC) Wiring
Color
Application
Color
Application
Black
Ungrounded Hot
Red
Positive
White
Grounded
Conductor
White
Green or Bare
Equipment
Ground
Green or Bare Equipment
Ground
Red or any
other color
Ungrounded Hot
(not NEC req.)
Negative or
Grounded
Conductor
Cables and Conduit

Cable: two or more insulated conductors having an
overall covering
–

As with typical wire insulation, protective covering on cable is
rated for specific uses (resistance to moisture, UV light, heat,
chemicals, or abrasion)
Conduit: 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 conduit
size can cause overheating and also causes problems when
“pulling” wire
Wire Size

Wire size selection based on two criteria:
–
–

Ampacity: current carrying ability of a wire
–
–

Ampacity
Voltage drop
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 wire’s
resistance and length
–
Function of wire gauge, length of wire, and current flow in the
wire
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)
Safety Equipment

Disconnects
–
Allow electrical flow to be
physically severed
(disconnected) to allow
for safe servicing of
equipment

Overcurrent Protection
–
Protect an electrical
circuit from damage
caused by overload or
short circuit
 Fuses
 Circuit Breakers
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 PV
system to the grounding electrode)
System grounding (at one point attach ground to one current
carrying conductor)


DC side of system => Negative to ground
AC side of system => Neutral to ground
Batteries
Part 4: Learning Objectives
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Battery basics
Battery functions
Types of batteries
Charging/discharging
Depth of discharge
Battery safety
Batteries in Series and Parallel

Series connections
–

Builds voltage
Parallel connections
–
Builds amp-hour capacity
Battery Basics
The Terms:
 Battery
 A device that stores electrical energy (chemical energy to
electrical 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%)
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 is
recommended that they only be used when absolutely necessary (i.e.
in remote locations or as battery backup for grid-tied applications if
power failures are common/lengthy)
Batteries: The Details
Types:




Primary (single use)
Secondary (recharged)
Shallow Cycle (20% DOD)
Deep Cycle (50-80% DOD)
Charging/Discharging:


Unless lead-acid batteries are charged up to 100%, they will loose
capacity over time
Batteries should be equalized on a regular basis
Battery Capacity
Capacity:

Amps x Hours = Amp-hours (Ah)
100 Amp-hours



=
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
Rate of Charge or Discharge
Rate = C/T
C = Battery’s rated capacity (Amp-hours)
T = The cycle time period (hours)
Maximum recommend charge/discharge rate =
C/3 to C/5
Cycle Life vs. Depth of Discharge
# of Cycles
Depth Of Discharge (DOD) %
Battery Safety

Batteries are EXTREMELY DANGEROUS; handle with
care!
– Keep batteries out of living space, and vent battery
box to the outside
– Use a spill containment vessel
– Don’t mix batteries (different types or old with new)
– Always disconnect batteries, and make sure tools
have insulated handles to prevent short circuiting
Battery Wiring Considerations

Battery wiring leads should leave the battery
bank from opposite corners
–

Ensures equal charging and discharging;
prolongs battery life
Make sure configuration of battery bank
allows for proper connections to be easily
made
Controllers & Inverters
Part 5: Learning Objectives




Controller basics
Controller features
Inverter basics
Specifying an inverter
Controller Basics
Function:

To protect batteries from being overcharged
Features:

Maximum Power Point
Tracking
– Tracks the peak
power point of the
array (can improve
power production by
20%)!!
Additional Controller Features


Voltage Stepdown Controller: compensates for differing
voltages between array and batteries (ex. 48V array
charging 12V battery)
– By using a higher voltage array, smaller wire can be
used from the array to the batteries
Temperature Compensation: adjusts the charging of
batteries according to ambient temperature
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 might
be desirable to have more then one controller per array in
the event of a failure
Inverter Basics
Function:

An electronic device used to convert direct current (DC)
electricity into alternating current (AC) electricity
Drawbacks:



Efficiency penalty
Complexity (read: a component which can fail)
Cost!!
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
Solar Site
Part 6: Learning Objectives




Understand azimuth and altitude
Explain magnetic declination
Describe proper orientation and tilt angle for
solar collection
Describe the concept of “solar window”
Site Selection – Panel Direction


Face south
Correct for
magnetic
declination
Orientation and Tilt Angle
Sun Chart for 40 degrees N Latitude
Site Selection – Tilt Angle
Max performance is
achieved when panels
are perpendicular to the
sun’s rays
Year round tilt = latitude
Winter + 15 lat.
Summer – 15 lat.
Solar Access

Optimum Solar Window 9 am – 3 pm

Array should have NO SHADING in this
window (or longer if possible)
Solar Pathfinder


An essential tool in finding a good site for
solar is the Solar Pathfinder
Provides daily, monthly, and yearly solar
hours estimates
Practical Determinants for Site
Analysis





Loads and time of use
Local climate characteristics
Distance from power conditioning equipment
Accessibility for maintenance
Aesthetics
Energy Efficiency
Part 7: Learning Objectives





Identify cost effective electrical load reduction
strategies
List problematic loads for PV systems
Describe penalties of PV system components
Explain phantom loads
Evaluate types of lighting; efficiency
comparison
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
Typical Wattage Requirements
Appliance
Wattage
Blender
350
TV (25 inch)
130
Washer
1450
Sunfrost Refrigerator (7 hours a
day)
refrigerator/freezer (13 hours a
day)
112
Hair Dryer
1000
Microwave (.5 sq-ft)
Microwave (.8 – 1 sq-ft)
750
1400
475
Appliances to Avoid





Electric oven or stove
Electric space heater
Dishwasher with heaters
Electric water heater
Electric clothes dryer
Improving Energy Efficiency in the
Home

Space Heating:
–
–
–
–
–
–
–
Super insulation
Passive solar design
Wood stoves
Propane
Solar hot water
Radiant Floor/
baseboard
Efficient windows

Domestic hot water
heating
–
–
–
–
Solar thermal
Propane/natural gas
No electric heaters
On demand hot water
Improving Energy Efficiency in the
Home

Kitchen Stoves
–
–
–

Solar cookers
Gas burners- no glow
bar ignition
Microwaves
Washing machines
–
High efficiency horizontal
axis

Cooling
–
–
–
–
–
–
–
Ceiling fans
Window shades
Evaporative cooling
Insulation
Trees
Reflective attic cover
Attic fan
Phantom Loads
Phantom Loads

Cost the United States:
–
–
–
–

$3 Billion / year
10 power plants
18 million tons of CO2
More pollution than 6 million cars
TV’s and VCR’s alone cost the US $1
Billion/year in lost electricity
Lighting Efficiency

Factors effecting light efficiency
–
–
–
–
–
Type of light
Positioning of lights
Fixture design
Color of ceilings and walls
Placement of switches
Incandescent Lamps

Advantages
–
–
–
Most common
Least expensive
Pleasing light

Disadvantages
–
–
Low efficiency
Short life ~ 750 hours
Electricity is conducted through a filament which resists
the flow of electricity, heats up, and glows
Efficiency increases as lamp wattage increases
FROM THE POWER PLANT TO YOUR HOME
INCANDESCENT BULBS ARE LESS THAN 2%
EFFICIENCT
Fluorescent Bulbs





Les wattage, same amount of lumens
Longer life (~10,000 hours)
May have difficulty starting in cold
environments
Not good for lights that are repeatedly turned
on and off
Contain a small amount of mercury
Light Emitting Diode (LED) Lights

Advantages
–
–
–
–
Extremely efficient
Long life (100,000 hours)
Rugged
No radio frequency
interference

Disadvantages
–
–
Expensive (although
prices are decreasing
steadily)
A relatively new
technology
Mounting
Part 8: Learning Objectives

Evaluate structural considerations

List hardware requirements

Pros and cons of different mounting
techniques
General Considerations

Weather characteristics
–
–

Site characteristics
–
–

Wind intensity
Estimated snowfall
Corrosive salt water
Animal interference
Human factors
–
–
–
Vandalism
Theft protection
Aesthetics
Basic Mounting Options

Fixed
–
–

Roof, ground, pole
Integrated
Tracking
–
Pole (active & passive)
Pole Mount Considerations

Ask manufacturer for wind loading
specification for your array
–
–
–

Pole size
Amount of concrete
Etc.
Array can be in close proximity to the house
without penetrations to roof structure
Tracking Considerations

Can increase system performance by:
–
–

15% in winter months
40% in summer months
Adds additional costs to the array
Passive Vs. Active

Passive:
–
–

Have no motors, controls, or gears
Use the changing weight of a gaseous refrigerant
within a sealed frame member to track the sun
Active:
–
Linear actuator motors controlled by sensors
follow the sun throughout the day
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 and
modules
On sloped roofs, fasten mounts to rafters not
decking
Building Integrated PV
Ready for a field tour?

Questions?
If you are interested in anything you have seen today
and would like to get involved, please contact any
member of the Solar Scholars team:
Colin Davies, Eric Fournier, or Jess Scott
(cjdavies, efournie, jpscott)
The END

Thank you for participating in this lecture
series

Now lets go out into the field and take a look
at the systems that we have already
installed.