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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

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Photovoltaic design and installation

Photovoltaic Design and Installation

Bucknell University Solar Scholars Program


Colin Davies ‘08

Eric Fournier ‘08


  • 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
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.

Photovoltaic design and installation


85% of our energy consumption is from fossil fuels!

Why sustainable energy matters
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 matters1
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
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
Making the Change to Renewable Energy

  • Solar

  • Geothermal

  • Wind

  • Hydroelectric

Today s solar picture
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
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
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.

Part 2 learning objectives
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

Electricity terminology
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 terminology1
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 terminology2
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 terminology3
Electricity Terminology

  • Watt (W) are a measure of Power

    • Unit rate of electrical energy

  • Amps x Volts = Watts

  • 1 Kilowatt (kW) = 1000 watts

Electricity terminology4
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
Power and Energy Calculation

  • Draw a PV array composed of four 75 watt modules.

  • What size is the system in watts ?

Electricity terminology5
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
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
Meters and Testing

Clamp on meter Digital multimeter

  • Never test battery current using a multimeter!

Part 1 learning objectives
Part 1: Learning Objectives

  • Understand the functions of PV components

  • Identify different system types

Photovoltaic pv terminology
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

Dc system options
DC System Options

  • Battery backup vs. discontinuous use

  • LVD option in charge controller

  • Load controllers

Ac system options
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?)

Grid tied system without batteries


Low: Easy to install (less components)

Grid Interaction

Grid can supplement power

No power when grid goes down

Grid-Tied System(Without Batteries)

Grid tied system with batteries


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)

Grid-Tied System(With Batteries)

Part 3 learning objectives
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

Solar cells and the pv effect
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

Available cell technologies
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
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
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
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

Selecting the correct module
Selecting the Correct Module

  • Practical Criteria

    • Size

    • Voltage

    • Availability

    • Warranty

    • Mounting Characteristics

    • Cost (per watt)

Voltage terminology
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

Effects of temperature
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
Effects of Shading/Low Insolation

  • As insolation decreases amperage decreases while voltage remains roughly constant

Other issues
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

Part 4 learning objectives
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

Series connections
Series Connections

  • Loads/sources wired in series



    • 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
Parallel Connections

  • Loads/sources wired in parallel:



    • 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
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?

Dissimilar modules in series
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
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
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
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
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

Color coding of wires
Color Coding of Wires

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

Cables and conduit
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

  • 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 wire’s resistance and length

    • Function of wire gauge, length of wire, and current flow in the wire

Safety considerations
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


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


Circuit Breakers

Safety Equipment


  • 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

Part 4 learning objectives1
Part 4: Learning Objectives

  • Battery basics

  • Battery functions

  • Types of batteries

  • Charging/discharging

  • Depth of discharge

  • Battery safety

Batteries in series and parallel
Batteries in Series and Parallel

  • Series connections

    • Builds voltage

  • Parallel connections

    • Builds amp-hour capacity

Battery basics
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
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
Batteries: The Details


  • Primary (single use)

  • Secondary (recharged)

  • Shallow Cycle (20% DOD)

  • Deep Cycle (50-80% DOD)


  • 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
Battery 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

Rate of charge or discharge
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
Cycle Life vs. Depth of Discharge

# of Cycles

Depth Of Discharge (DOD) %

Battery safety
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 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

Part 5 learning objectives
Part 5: Learning Objectives

  • Controller basics

  • Controller features

  • Inverter basics

  • Specifying an inverter

Controller basics
Controller Basics


  • To protect batteries from being overcharged


  • Maximum Power Point Tracking

    • Tracks the peak power point of the array (can improve power production by 20%)!!

Additional controller features
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
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
Inverter Basics


  • An electronic device used to convert direct current (DC) electricity into alternating current (AC) electricity


  • Efficiency penalty

  • Complexity (read: a component which can fail)

  • Cost!!

Specifying an inverter
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

Part 6 learning objectives
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
Site Selection – Panel Direction

  • Face south

  • Correct for magnetic declination

Site selection tilt angle
Site Selection – Tilt Angle

Year round tilt = latitude

Winter + 15 lat.

Summer – 15 lat.

Max performance is

achieved when panels

are perpendicular to the

sun’s rays

Solar access
Solar Access

  • Optimum Solar Window 9 am – 3 pm

  • Array should have NO SHADING in this window (or longer if possible)

Solar pathfinder
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
Practical Determinants for Site Analysis

  • Loads and time of use

  • Local climate characteristics

  • Distance from power conditioning equipment

  • Accessibility for maintenance

  • Aesthetics

Part 7 learning objectives
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
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

Appliances to avoid
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


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

Improving energy efficiency in the home1

Kitchen Stoves

Solar cookers

Gas burners- no glow bar ignition


Washing machines

High efficiency horizontal axis


Ceiling fans

Window shades

Evaporative cooling



Reflective attic cover

Attic fan

Improving Energy Efficiency in the Home

Phantom loads1
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
Lighting Efficiency

  • Factors effecting light efficiency

    • Type of light

    • Positioning of lights

    • Fixture design

    • Color of ceilings and walls

    • Placement of switches

Incandescent lamps


Most common

Least expensive

Pleasing light


Low efficiency

Short life ~ 750 hours

Incandescent Lamps

Electricity is conducted through a filament which resists the flow of electricity, heats up, and glows

Efficiency increases as lamp wattage increases


Fluorescent bulbs
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


Extremely efficient

Long life (100,000 hours)


No radio frequency interference


Expensive (although prices are decreasing steadily)

A relatively new technology

Light Emitting Diode (LED) Lights

Part 8 learning objectives
Part 8: Learning Objectives

  • Evaluate structural considerations

  • List hardware requirements

  • Pros and cons of different mounting techniques

General considerations
General Considerations

  • Weather characteristics

    • Wind intensity

    • Estimated snowfall

  • Site characteristics

    • Corrosive salt water

    • Animal interference

  • Human factors

    • Vandalism

    • Theft protection

    • Aesthetics

Basic mounting options
Basic Mounting Options

  • Fixed

    • Roof, ground, pole

    • Integrated

  • Tracking

    • Pole (active & passive)

Pole mount considerations
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
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 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
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

Ready for a field tour
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.