Photovoltaic Design and Installation

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 finiteTwo-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 kilowatt-hours

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


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


Resistance (R or Ω) – The opposition of a material to the flow of an

electrical current – Depends on

Material Cross sectional area Length Temperature


Watt (W) are a measure of Power – Unit rate of electrical energy

Amps x Volts = Watts 1 Kilowatt (kW) = 1000 watts


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 ?


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


Understand the functions of PV components Identify different system types

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

Systems with DC Loads

DC System Options

Battery backup vs. discontinuous use LVD option in charge controller Load controllers

Systems with AC loads

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)

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


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

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 – 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

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


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

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

Parallel Connections

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

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

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 useAlternating Current (AC) Wiring Direct Current (DC) Wiring

Color Application Color Application

Black Ungrounded Hot Red (not NEC req.) Positive

White Grounded Conductor

White Negative or Grounded Conductor

Green or Bare Equipment Ground

Green or Bare Equipment Ground

Red or any other color

Ungrounded Hot

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– 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

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


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

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%)

The Terms:

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

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:

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 =

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

Depth Of Discharge (DOD) %

# of Cycles

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


Controller basics Controller features Inverter basics Specifying an inverter

Controller Basics

To protect batteries from being overchargedFunction:

Maximum Power Point Tracking– Tracks the peak

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

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

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

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:

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


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

Year round tilt = latitudeWinter + 15 lat.Summer – 15 lat.

Max performance isachieved when panelsare perpendicular to thesun’s rays

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


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

475

Hair Dryer 1000

Microwave (.5 sq-ft)

Microwave (.8 – 1 sq-ft)

750

1400

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


Evaluate structural considerations

List hardware requirements

Pros and cons of different mounting techniques

General Considerations

Weather characteristics– Wind intensity– Estimated snowfall

Site characteristics – 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.

Photovoltaic Design and Installation

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