Transcript Solar 2007 Distributed Power Systems

Photovoltaic Components and
System Configurations
Dave Click
Florida 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.
energy
source
load
utilization
inversion &
conditioning
PV Array
Inverter
Charger
Controller
load
center
energy
distribution
energy
conversion
energy
storage
battery
electric
utility
network
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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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Cells, Modules and Arrays
The basic
building blocks
for PV systems
include 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
(-)
sun
typical crystalline silicon
photovoltaic cell
DC current flow
phosphorous-doped (N-type)
silicon layer ~ 0.3 x 10-6 m
boron-doped (P-type)
silicon layer ~ 250 x 10-6 m
(+)
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Single Crystal Cells
Single crystal (or
monocrystalline)
silicon wafers are
sawn from grown
cylindrical ingots.
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Polycrystalline Silicon
Polycrystalline (or
multicrystalline)
silicon wafers are
sawn from cast
rectangular
ingots.
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Cell Fabrication
Several steps
are involved in
turning silicon
wafers into PV
cells.
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Establishing the P-N Junction
Diffusion of
phosphorous
gas creates a
thin n-type
semiconductor
layer over the
entire surface
of a p-type
wafer.
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Variety of Cell Types
The different
materials,
processes, and
manufacturing
steps produce a
range of PV cell
types.
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Cell Current and Voltage Output
An I-V curve
illustrates the
electrical
output profile
of a PV cell,
module, or
array.
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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 polycrystalline
module
75-Watt monocrystalline
module
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Module Packaging
Modules are
constructed
from PV cells
surrounded by
several layers
of protective
materials.
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Module Shapes and Sizes
Modules are
available in several
sizes and shapes,
including squares,
rectangles,
triangles, flexible
units, and shingles.
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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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PV Module Nameplate
Module nameplates
must include
performance ratings
for the module and
may include other
information used to
design a PV system.
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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
Module Current (amps)
6
5
4
3
2
1
0
0
100
200
300
400
500
600
700
800
900 1000 1100
Irradiance (W/m2)
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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 (+)
Current (A)
Pos (+)
A
(-)
(+)
B
Neg (-)
V = VA + V B
I = IA = IB
Neg ()
A, B
Voltage (V)
A+B
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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.
Current (A)
A
A+B
V = VA = VB
I = IA + IB
A, B
B
Voltage (V)
Neg ()
Pos (+)
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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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PV Panel
Several modules
may be connected
together to form a
panel, which is
installed as a
preassembled unit.
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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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PV Array
An array is a
group of PV
modules
integrated as a
single powergenerating unit.
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Photovoltaic Cells, Modules,
Panels and Arrays
cell
module
array
panel
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Identification of Solar Photovoltaic
System Components
Photovoltaic source circuits
Fuses
Photovoltaic
output circuit
Solar cells
Module
Panel
Array
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Variety of Inverters
Inverters are
available in
many different
configurations
and ratings.
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Amplitude
Alternating Current
Waveforms
square wave
sine wave
modified square wave
Time
One Cycle
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Stand-alone Inverters
Stand-alone inverters are connected to the battery
bank.
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Utility-Interactive Inverters
Interactive inverters are connected to the PV array.
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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
Power conditioning
units are inverters
that also perform
other power control
and conversion
functions.
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Inverter Efficiency
Most sine wave
inverters maintain
high efficiency
over a wide
operating-power
range.
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Inverter Disconnects
Inverter
enclosures may
include protective
devices such as
disconnects.
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Inverter Data Displays
Inverter interfaces include on-board screens,
remote data monitors, and computerized data
acquisition and processing software.
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AC Modules
AC modules
include small
inverters in
place of the DC
junction box.
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Batteries
Batteries are
collections of cells
that produce
electricity through
electrochemical
reactions. Cells can
be configured into
batteries of many
different shapes and
sizes.
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Battery Packaging
Many components
are common to
various battery
designs.
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Battery Discharging
Electrochemical
reactions within a
cell produce a flow
of electrons from
the negative
terminal to the
positive terminal.
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Battery Charging
The charging
reaction within a
cell is the reverse
of the discharge
reaction.
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Variety of Batteries
Batteries are
divided into
classes based
on discharge
and cycle
characteristics.
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Absorbed Glass Mat Batteries
AGM batteries
include fiberglass
mats to absorb the
electrolyte and
separate the plates.
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Batteries in Series
Connecting batteries in series increases system
voltage.
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Batteries in Parallel
Connecting batteries in parallel increases system
capacity.
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Batteries in Series and Parallel
Series and parallel connections can be combined
to produce a desired system voltage level and
capacity.
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Charge Controllers
Charge controllers manage interactions and energy
flows between a PV array, battery, and electrical
load.
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Protecting the Battery via
Charge Regulation
Charge controllers
protect batteries
from over charging
by terminating or
limiting charging
current.
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Protecting the Battery via
Load Management
Charge controllers
protect batteries
from over
discharging by
controlling
discharging current.
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Status Displays
Most charge
controllers include
displays or LEDs to
indicate battery
voltage, state of
charge, and/or
present operating
mode.
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Shunt Control
Shunt charge
controllers control
charging current
by short-circuiting
the array.
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Series Control
Series charge
controllers
control charging
current by
opening the
circuit from the
array.
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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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Direct Coupled Configuration
The simplest type of
stand-alone PV
configuration is the
direct-coupled system,
consisting of only an
array and a DC load.
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Self Regulated System Configuration
Self-regulating standalone PV systems
avoid the complexity
of adding charge
control components
by precisely sizing the
battery and array.
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Regulated Configurations
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.
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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.
PV Array
Charge
Controller
DC Load
Battery
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Stand-Alone Configurations
with AC Loads
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.
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Hybrid Systems
Hybrid systems
include power
sources other
than the PV
array and do not
interact with the
utility grid.
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Utility-Interactive System
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.
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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
AC Loads
PV Array
Inverter/Power
Conditioner
Distribution
Panel
Electric
Utility
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Net and Dual Metering
Utility-interactive systems have either net-metering
or dual-metering arrangements for exporting
electricity to the utility grid.
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Interactive System
Photovoltaic output circuit
Inverter input circuit
Inverter output circuit
Photovoltaic source
circuits
Electric production
and distribution
network connection
Inverter
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Bimodal System Configurations
Bimodal systems
can act like either
a utility-interactive
or a stand-alone
system.
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Sun Paths for 30o N Latitude
June 22: 12 noon
September 23 and March 21: 12 noon
Zenith
10 am
2 pm
10 am
8 am
December 21: 12 noon
8 am
2 pm
East
10 am
8 am
4 pm
2 pm
North
4 pm
Point
O
South
4 pm
West
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Sun Position - Definitions
Zenith
90 deg altitude
East
Altitude Angle (
)
Azimuth Angle ()
North
Point O
South
0 deg azimuth
West
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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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