Photovoltaic Components and System Configurations
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Photovoltaic Components and System Configurations
Dave ClickFlorida Solar Energy Center
January 26, 2009
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Solar Photovoltaic System (SPS)
Solar Photovoltaic System (690.2) The total components and subsystems that, in
combination, convert solar energy into electrical energy suitable for connection to a utilization load.
loadutilization
energysource inversion &
conditioning
energyconversion
InverterCharger
Controller
PV Arrayenergydistribution
loadcenter
batteryenergystorage
electricutilitynetwork
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Solar Photovoltaic System (SPS) Components
PV Array: An electrical assembly of photovoltaic modules that convert sunlight to DC electricity.
Inverter: A device that converts DC power from batteries or PV arrays into utility-grade AC power.
Energy Storage: Electrical or other storage devices sometimes used to store energy produced by PV arrays for later consumption.
System Charge Control: A device used to protect batteries from overcharge and overdischarge, and sometimes to provide load control functions.
Load: Energy consuming electrical appliances served by the system.
Balance of System (BOS) Components: Other equipment required to control, conduct, protect, distribute power and structurally support the system.
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The basic building blocks for PV systems include cells, modules, and arrays.
Cells, Modules and Arrays
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Solar Cell
Solar Cell (690.2) The basic photovoltaic device that generates DC electricity
when exposed to light. A typical silicon solar cell produces about 0.5 volt and up to 6 amps and 3 watts for larger area cells.
electrical load
typical crystalline silicon photovoltaic cell
(-)
(+)
phosphorous-doped (N-type) silicon layer ~ 0.3 x 10-6 mboron-doped (P-type)
silicon layer ~ 250 x 10-6 m
DC current flow
sun
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Single crystal (or monocrystalline) silicon wafers are sawn from grown cylindrical ingots.
Single Crystal Cells
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Polycrystalline (or multicrystalline) silicon wafers are sawn from cast rectangular ingots.
Polycrystalline Silicon
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Several steps are involved in turning silicon wafers into PV cells.
Cell Fabrication
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Diffusion of phosphorous gas creates a thin n-type semiconductor layer over the entire surface of a p-type wafer.
Establishing the P-N Junction
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The different materials, processes, and manufacturing steps produce a range of PV cell types.
Variety of Cell Types
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An I-V curve illustrates the electrical output profile of a PV cell, module, or array.
Cell Current and Voltage Output
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Photovoltaic Modules
Module (690.2) A complete, environmentally protected unit consisting of solar
cells, optics, and other components, exclusive of tracker, designed to generate DC power when exposed to sunlight.
60-Watt polycrystallinemodule
75-Watt monocrystallinemodule
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Modules are constructed from PV cells surrounded by several layers of protective materials.
Module Packaging
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Modules are available in several sizes and shapes, including squares, rectangles, triangles, flexible units, and shingles.
Module Shapes and Sizes
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PV Module Markings
690.51 Modules Modules shall be marked with identification of
terminals or leads as to polarity, maximum overcurrent device rating for module protection, and with the following ratings:
(1) Open-circuit voltage (2) Operating voltage (3) Maximum permissible system voltage (4) Operating current (5) Short-circuit current (6) Maximum power
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Module nameplates must include performance ratings for the module and may include other information used to design a PV system.
PV Module Nameplate
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Module Performance Specifications
Module performance only has meaning when the rating conditions are specified.
All PV modules are rated at Standard Test Conditions (STC): Irradiance = 1000 W/m2
Cell temperature = 25oC Module I-V parameters at STC must be on the
module listing label per NEC 690.51.
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Irradiance
Effect of Irradiance
0
1
2
3
4
5
6
0 100 200 300 400 500 600 700 800 900 1000 1100
Mo
du
le C
urr
ent (
amps
)
Irradiance (W/m2)
Cloudy, indire
ct sunlight
Clear, dire
ct sunlight
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Temperature and PV Voltage (Example)
Module Voltage at 25 degrees: 17.1 volts Temperature Coefficient: -0.077 V/deg C Module Voltage at 55 degrees: 14.8 volts
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Similar PV Devices in Series
When similar devices are connected in series, the voltages add and the current is the same as one device.
Pos (+) (-) (+) Neg (-)
Pos (+) Neg (-)
A B
Voltage (V)
Curr
ent (A
)
A, B A + B
V = VA + VB
I = IA = IB
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Similar PV Devices in Parallel
When similar devices are connected in parallel, the individual currents add, while the voltage is the same as for one device.
A
B
Pos (+)Neg (-)
V = VA = VB
I = IA + IBA, B
Voltage (V)
Curr
ent (A
) A + B
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Photovoltaic Panels
Panel (690.2) A collection of modules mechanically fastened
together, wired, and designed to provide a field installable unit.
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Several modules may be connected together to form a panel, which is installed as a preassembled unit.
PV Panel
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Photovoltaic Arrays
Array (690.2) A mechanical integrated assembly of modules or
panels with a support structure and foundation, tracker, and other components, as required, to form a direct-current power-producing unit.
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An array is a group of PV modules integrated as a single power-generating unit.
PV Array
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Photovoltaic Cells, Modules, Panels and Arrays
cell module
panelarray
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Solar cells
Module
Panel
Array
Fuses
Photovoltaic source circuits
Photovoltaicoutput circuit
Identification of Solar Photovoltaic System Components
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Inverters are available in many different configurations and ratings.
Variety of Inverters
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Alternating Current Waveforms
square wavesine wave
modified square wave
Time
Am
plitu
de
One Cycle
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Stand-alone inverters are connected to the battery bank.
Stand-alone Inverters
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Interactive inverters are connected to the PV array.
Utility-Interactive Inverters
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Utility-Interactive Inverters:Power Conditioning Units
PV array maximum power point tracking (MPPT) Power inversion from DC to AC Wave-shaping and voltage regulation Synchronous utility interfacing System control and monitoring Protective and safety features
Fuses, disconnects and surge arrestors on AC and DC sides.
Automatic disconnect when the utility is down. Must comply with IEEE 1547 and UL 1741.
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Power conditioning units are inverters that also perform other power control and conversion functions.
Power Conditioning Units
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Most sine wave inverters maintain high efficiency over a wide operating-power range.
Inverter Efficiency
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Inverter enclosures may include protective devices such as disconnects.
Inverter Disconnects
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Inverter interfaces include on-board screens, remote data monitors, and computerized data acquisition and processing software.
Inverter Data Displays
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AC modules include small inverters in place of the DC junction box.
AC Modules
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Batteries are collections of cells that produce electricity through electrochemical reactions. Cells can be configured into batteries of many different shapes and sizes.
Batteries
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Many components are common to various battery designs.
Battery Packaging
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Electrochemical reactions within a cell produce a flow of electrons from the negative terminal to the positive terminal.
Battery Discharging
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The charging reaction within a cell is the reverse of the discharge reaction.
Battery Charging
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Batteries are divided into classes based on discharge and cycle characteristics.
Variety of Batteries
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AGM batteries include fiberglass mats to absorb the electrolyte and separate the plates.
Absorbed Glass Mat Batteries
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Connecting batteries in series increases system voltage.
Batteries in Series
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Connecting batteries in parallel increases system capacity.
Batteries in Parallel
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Series and parallel connections can be combined to produce a desired system voltage level and capacity.
Batteries in Series and Parallel
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Charge controllers manage interactions and energy flows between a PV array, battery, and electrical load.
Charge Controllers
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Charge controllers protect batteries from over charging by terminating or limiting charging current.
Protecting the Battery via Charge Regulation
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Charge controllers protect batteries from over discharging by controlling discharging current.
Protecting the Battery via Load Management
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Most charge controllers include displays or LEDs to indicate battery voltage, state of charge, and/or present operating mode.
Status Displays
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Shunt charge controllers control charging current by short-circuiting the array.
Shunt Control
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Series charge controllers control charging current by opening the circuit from the array.
Series Control
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Photovoltaic System Types & Configurations
Stand-Alone Systems Operate independent of the utility grid and include
hybrid systems.
Utility-Interactive Systems Sometimes called grid-connected or grid-tied
systems. Operate connected to (i.e., in parallel with) the utility
grid. A bi-directional interface is required.
Bi-Modal Systems May operate in either utility-interactive or stand-alone
mode, but not concurrently.
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The simplest type of stand-alone PV configuration is the direct-coupled system, consisting of only an array and a DC load.
Direct Coupled Configuration
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Self-regulating stand-alone PV systems avoid the complexity of adding charge control components by precisely sizing the battery and array.
Self Regulated System Configuration
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Systems with charge control regulate the charging current into the battery. Regulation may involve disconnecting or dissipating the current inside the controller or diverting the excess current into an auxiliary load.
Regulated Configurations
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Stand-Alone PV System with Batteries and Charge Control
Charge control is required whenever the load is variable and the battery is not oversized.
Protects the battery from overcharge and overdischarge, and may provide load control functions.
DC LoadPV Array
Battery
ChargeController
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Stand-alone systems with AC loads must include an inverter, which draws DC power from the battery bank and changes it to AC power for distribution.
Stand-Alone Configurationswith AC Loads
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Hybrid systems include power sources other than the PV array and do not interact with the utility grid.
Hybrid Systems
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A utility-interactive system is controlled by the inverter, which adds AC power converted from DC power to the utility grid power at the main AC power distribution panel.
Utility-Interactive System
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Interactive System
Interactive System (690.2) A solar photovoltaic system that operates in parallel
with and may deliver power to an electrical production and distribution network. For the purposes of this definition, an energy storage subsystem of a solar photovoltaic system, such as a battery, is not another electrical production source.
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Basic Utility-Interactive or Grid-Connected PV System
DistributionPanel
PV Array Inverter/Power Conditioner
AC Loads
ElectricUtility
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Utility-interactive systems have either net-metering or dual-metering arrangements for exporting electricity to the utility grid.
Net and Dual Metering
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Interactive System
Electric production and distribution network connection
Inverter
Photovoltaic source circuits
Photovoltaic output circuit
Inverter output circuit
Inverter input circuit
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Bimodal systems can act like either a utility-interactive or a stand-alone system.
Bimodal System Configurations
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Sun Paths for 30o N Latitude
North
PointO
East
West
Zenith
June 22: 12 noon
September 23 and March 21: 12 noon
December 21: 12 noon
10 am
8 am2 pm
4 pm
4 pm
4 pm
8 am
8 am2 pm
2 pm
10 am
10 am
South
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Sun Position - Definitions
North
Point O
East
West
Zenith90 deg altitude
South0 deg azimuth
Altitude Angle ( )
Azimuth Angle ( )
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Array Orientation
Ideally: face array south at (Latitude * 0.9) degrees
(Not critical to face south at 27 for Gainesville)
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Solar Pathfinder
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Shading Concerns
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Shading Concerns
Same tree, four years later!
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