Photovoltaic Design and Installation

1
Photovoltaic Design and Installation

• Bucknell University Solar Scholars Program

Presenters Colin Davies 08 Eric Fournier 08
2
Outline

• Why Renewable Energy?
• The Science of Photovoltaics
• System Configurations
• Principle Design Elements
• The Solar Scholars program at Bucknell (walking
  tour)

3
Whats 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.

4
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85 of our energy consumption is from fossil
fuels!
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Why Sustainable Energy Matters

• The worlds 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)

6
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)

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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
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Making the Change to Renewable Energy

• Solar
• Geothermal
• Wind
• Hydroelectric

9
Todays 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")

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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 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.

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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

• 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

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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 1018
  electrons/second

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Electricity Terminology

• Resistance (R or O)
• The opposition of a material to the flow of an
  electrical current
• Depends on
• Material
• Cross sectional area
• Length
• Temperature

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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 (consumption
  and 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 appliances use AC

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Meters and Testing

• Clamp on meter Digital
  multimeter
• Never test battery current using a multimeter!

23
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 lt Module lt Panel lt 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

26
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(Without Batteries)

• Complexity
• Low Easy to install (less components)
• Grid Interaction
• Grid can supplement power
• No power when grid goes down

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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 down batteries supply power to
  loads (aka battery backup)

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PV Modules
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Part 3 Learning Objectives

• 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

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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

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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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Monocrystalline Silicon Modules

• Most efficient commercially available module (11
  - 14)
• Most expensive to produce
• Circular (square-round) cell creates wasted space
  on module

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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

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Amorphous Thin Film

• 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

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Selecting the Correct Module

• Practical Criteria
• Size
• Voltage
• Availability
• Warranty
• Mounting Characteristics
• Cost (per watt)

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Current-Voltage (I-V) Curve
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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 º C (77 º) cell temperature and 1000 W/m2
  insolation

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Effects of Temperature

• As the PV cell temperature increases above 25º C,
  the module Vmp decreases by approximately 0.5
  per degree C

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Effects of Shading/Low Insolation

• As insolation decreases amperage decreases while
  voltage remains roughly constant

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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

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PV Wiring
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Part 4 Learning Objectives

• List the characteristics of series circuits and
  parallel 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 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

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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

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Quiz Time

• 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?

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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?

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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?

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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!

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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

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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 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

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Color Coding of Wires

• Electrical wire insulation is color coded to
  designate its function and use

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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

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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 wires
  resistance 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 allow for safe servicing of
  equipment

• Overcurrent Protection
• Protect an electrical circuit from damage caused
  by overload or short 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 PV system to the grounding electrode)
• System grounding (at one point attach ground to
  one current carrying conductor)
• DC side of system gt Negative to ground
• AC side of system gt 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
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)

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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 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)
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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

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Battery Capacity
Capacity

• Amps x Hours Amp-hours (Ah)

100 amps for 1 hour 1 amp for 100 hours 20 amps
for 5 hours
100 Amp-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

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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
of Cycles
Depth Of Discharge (DOD)
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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
• Dont mix batteries (different types or old with
  new)
• Always disconnect batteries, and make sure tools
  have insulated handles to prevent short
  circuiting

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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

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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
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)!!

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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

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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
  might be desirable to have more then one
  controller per array in the event of a failure

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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!!

79
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

80
Solar Site
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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

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Site Selection Panel Direction

• Face south
• Correct for magnetic declination

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Orientation and Tilt Angle
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Sun Chart for 40 degrees N Latitude
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Site Selection Tilt Angle
Max performance is achieved when panels are
perpendicular to the suns rays

• Year round tilt latitude
• Winter 15 lat.
• Summer 15 lat.

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Solar Access

• Optimum Solar Window 9 am 3 pm
• Array should have NO SHADING in this window (or
  longer if possible)

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Solar Pathfinder

• An essential tool in finding a good site for
  solar is the Solar Pathfinder
• Provides daily, monthly, and yearly solar hours
  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

89
Energy Efficiency
90
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

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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

92
Typical Wattage Requirements
93
Appliances to Avoid

• Electric oven or stove
• Electric space heater
• Dishwasher with heaters
• Electric water heater
• Electric clothes dryer

94
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

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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

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Phantom Loads
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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 1 Billion/year
  in lost electricity

98
Lighting Efficiency

• Factors effecting light efficiency
• Type of light
• Positioning of lights
• Fixture design
• Color of ceilings and walls
• Placement of switches

99
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
100
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

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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

103
Mounting
104
Part 8 Learning Objectives

• Evaluate structural considerations
• List hardware requirements
• Pros and cons of different mounting techniques

105
General Considerations

• Weather characteristics
• Wind intensity
• Estimated snowfall
• Site characteristics
• Corrosive salt water
• Animal interference
• Human factors
• Vandalism
• Theft protection
• Aesthetics

106
Basic Mounting Options

• Fixed
• Roof, ground, pole
• Integrated
• Tracking
• Pole (active passive)

107
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

108
Tracking Considerations

• Can increase system performance by
• 15 in winter months
• 40 in summer months
• Adds additional costs to the array

109
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

110
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

111
Building Integrated PV
112
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)

113
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.