Photovoltaic Design and Installation

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Osborne Lawrence
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1 Photovoltaic Design and Installation

2 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.

3 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.

4 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

5 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)

(could lead to significant changes in the world' s climate system,

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)

7 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

8 Making the Change to Renewable Energy Solar Geothermal Wind Hydroelectric

9 Today s Solar Picture Germany leads solar production (over 4.5 times more then US production) Japan is 2 nd (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")

10 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

11 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.

12 Electricity

13 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

14 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

15 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 electrons/second

16 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

17 Electricity Terminology Watt (W) are a measure of Power Unit rate of electrical energy Amps x Volts = Watts 1 Kilowatt (kw) = 1000 watts

18 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

19 Power and Energy Calculation Draw a PV array composed of four 75 watt modules. What size is the system in watts?

20 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

21 Types of Electrical Current DC = Direct Current PV panels produce DC Batteries store DC AC = Alternating Current Utility power Most consumer appliances use AC

22 Meters and Testing Clamp on meter Digital multimeter Never test battery current using a multimeter!

23 System Types

24 Part 1: Learning Objectives Understand the functions of PV components Identify different system types

25 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

26 Systems with DC Loads

27 DC System Options Battery backup vs. discontinuous use LVD option in charge controller Load controllers

28 Systems with AC loads

29 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?)

30 Grid-Tied System (Without Batteries) Complexity Low: Easy to install (less components) Grid Interaction Grid can supplement power No power when grid goes down

31 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)

32 PV Modules

33 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

34 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

35 Inside a PV Cell

36 Available Cell Technologies Single-crystal or Mono-crystalline Silicon Polycrystalline or Multi-crystalline Silicon Thin film Ex. Amorphous silicon or Cadmium Telluride

37 Monocrystalline Silicon Modules Most efficient commercially available module (11% - 14%) Most expensive to produce Circular (square-round) cell creates wasted space on module

38 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

39 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

40 Selecting the Correct Module Practical Criteria Size Voltage Availability Warranty Mounting Characteristics Cost (per watt)

41 Current-Voltage (I-V) Curve

42 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 (V max / V mp ) Ex. A PV panel with a 12 V nominal voltage will read 17V- 18V under MPPT conditions) Open Circuit Voltage (V oc ) 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/m 2 insolation

43 Effects of Temperature As the PV cell temperature increases above 25º C, the module V mp decreases by approximately 0.5% per degree C

44 Effects of Shading/Low Insolation As insolation decreases amperage decreases while voltage remains roughly constant

45 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

46 PV Wiring

47 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

48 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

49 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

50 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?

51 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?

52 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?

53 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!

54 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

55 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

56 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 (not NEC req.) Positive White Green or Bare Red or any other color Grounded Conductor Equipment Ground Ungrounded Hot White Green or Bare Negative or Grounded Conductor Equipment Ground

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,

57 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

58 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

59 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)

Protect an electrical circuit from damage

60 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

61 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

62 Batteries

63 Part 4: Learning Objectives Battery basics Battery functions Types of batteries Charging/discharging Depth of discharge Battery safety

64 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

65 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

66 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)

67 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

68 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

69 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

70 Cycle Life vs. Depth of Discharge # of Cycles Depth Of Discharge (DOD) %

71 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

72 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

73 Controllers & Inverters

74 Part 5: Learning Objectives Controller basics Controller features Inverter basics Specifying an inverter

75 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%)!!

76 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

77 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

alternating current (AC) electricity Drawbacks:

78 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

81 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

82 Site Selection Panel Direction Face south Correct for magnetic declination

83 Orientation and Tilt Angle

84 Sun Chart for 40 degrees N Latitude

85 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.

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

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

88 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

91 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 Appliance Blender 350 Wattage TV (25 inch) 130 Washer 1450 Sunfrost Refrigerator (7 hours a day) refrigerator/freezer (13 hours a day) Hair Dryer 1000 Microwave (.5 sq-ft) Microwave (.8 1 sq-ft)

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

95 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

96 Phantom Loads

97 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

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

101

102 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 The END

Designing Stand Alone Systems. Overview, components and function, Elements in Design

Designing Stand Alone Systems. Overview, components and function, Elements in Design Designing Stand Alone Systems Overview, components and function, Elements in Design What Stand Alone System Does Loads that are Reasonable for a Stand Alone System to Power: Yes or No Dishwasher? Refrigerator