3.1 Uee2521 RRP
3.1 Uee2521 RRP
3.1 Uee2521 RRP
Dr. R. Ramaprabha
Associate Professor, Department of EEE
SSN College of Engineering, Chennai
connected PV systems.
implemented in buildings.
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Lecture Outline
• Introduction
• PV Systems in Buildings
• Inverter
• On-site Storage
• Other Issues
• Utility Applications
3
Introduction
• Photovoltaics can be used in grid-connected mode in two
ways:
– Arrays installed at the end use site, such as on
rooftops
– Utility-scale generating stations
• This unit deals with the related technical, economic and
other issues to be considered, and examines various
government and utility programs worldwide.
• A technical guide for the connection of photovoltaic and
other renewable energy generators to local electricity
networks in Australia has been produced by the
Australian Business Council for Sustainable Energy
4
Introduction
• Grid-connected PV overtook stand-alone systems as the largest
global market sector in 2000 as indicated in Fig. for International
Energy Agency member countries, although off-grid applications
continue to dominate in Australia.
website www.iea-pvps.org
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Introduction
• Globally, there are some extremely large grid-connected systems,
including 4 MWp and 5 MWp installations near Hemau, Bavaria and
near Espenhain, Saxony, respectively.
• A huge 64 MWp system is under discussion for Moura, Portugal.
Currently, the largest in Australia is at Singleton in NSW. It is a
ground-mounted 400 kWp PV ‘farm’ that produces 550 MWh per year,
and was commissioned in 1998.
• The largest Australian rooftop array is on the roof of the Queen
Victoria Markets in Melbourne. This was commissioned in 2003, uses
1328 PV laminates, each 1.59 × 0.79 m2, and incorporates a public
viewing board that displays the output (City of Melbourne, 2004).
• The system is rated at 200 kWp and is expected to generate 252
MWh/year.
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PV Systems in Buildings
• PV systems can provide power for a number of functions
in a building:
– Architectural - for both electricity generation and
roofing, walls, windows, skylights or shading devices.
– Demand-side management - for offsetting daytime peak
loads.
– Controls - for direct driving of fans, pumps, ‘smart’
windows etc.
– Hybrid energy systems - supplementing other sources
for lighting, heat pumps, air conditioners, emergency
power supplies etc.
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PV Systems in Buildings
• Fig. shows an integral photovoltaic system in a grid-connected
home.
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PV Systems in Buildings
• Development of appropriate products to meet such functions is
opening up a large market, since buildings consume a major portion
of generated electricity.
• A wide range of specific building-integrated PV (BIPV) products are
now on the market especially for roofs, façades and as architectural
elements in atria etc.
• To date, however, normal modules are most commonly placed on
roofs to supplement grid power.
• For a household system, the essential components are:
– PV modules,
– Grid-interactive inverter, so that the electricity is utility-compatible
– Metering equipment to feed and measure the power exchange
between the house and the grid.
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Inverter
• As for stand-alone PV systems, an inverter, or power
conditioning unit, is needed, since photovoltaic arrays
generate DC power at low voltage.
• Two main types of inverters can be used to achieve AC
power at the voltage used in the main grid.
• These are:
– Line-commutated - where the grid signal is used to
synchronize the inverter with the grid.
– Self-commutated - where the inverter’s intrinsic
electronics lock the inverter signal with that of the grid.
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Inverter – cont..
• An alternative division of the available products is by application:
– Central inverters are designed to convert the output of all the
parallel strings of modules in large arrays, with total power in the
range 20 - 400 kW. Self-commutated designs based on insulated
gate bipolar transistors (IGBTs) or field effect transistors (FETs)
are now dominant.
– String inverters accept power only from a single string, with total
power in the range 1 - 3 kW.
– Multi-string inverters include various independent DC - DC
converters, which feed their outputs to a common inverter. These
allow the acceptance of power from module strings with different
configurations or orientations, each able to operate at its own
maximum power point.
– AC module inverters sit behind individual modules, resulting in an
integrated AC module.
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Inverter – cont..
• An Australian (Standards Australia) and various international
standards (Appendix E) apply to grid-connected inverters. Issues to
be considered when selecting an inverter include:
– Efficiency - An improvement of 1 % can result in 10 % more power
output over a year. Some designs pay particular attention to
partial-load efficiency. Inverters with line-frequency transformers
can achieve a power conversion efficiency of 92 %, whereas those
with a high-frequency transformer can yield 94 %, although in
general higher efficiency is possible if the transformer can be
avoided. In addition to operating efficiency, standby power losses
during periods of negligible load need to be assessed.
– Safety (particularly via disconnect modes) - Run-on or ‘islanding’,
for instance, can result in the grid being energized, even when
disconnected. Isolation transformers are therefore commonly
used. Similarly, protection is required against over-currents,
surges, under- or over-frequency, under- or over-voltages for DC
input and AC output.
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Inverter – cont..
– Power Quality - The harmonic content must be low, with the Australian
standard specifying total harmonic distortion (THD) limits of 5 % for current
2 % for voltage, to protect both loads and utility equipment.
• The harmonic spectra are usually monitored up to about 50 harmonics,
but inverters using high frequency commutation can produce distortion
outside that range.
• The waveform and power factor must be acceptable to the utility.
• DC injection, which is inherently prevented by inverters with line-
frequency transformers but not by transformer-less or high-frequency
transformer designs, would saturate the utility transformers and cause
outages. Hence, Standards Australia specifies that for a single phase
inverter, the DC output current of the inverter must not exceed the
greater of 0.5 % of its rated output current or 5 mA.
• The waveform must be close to sinusoidal at 50 Hz (or 60 Hz in the USA),
the frequency must be within about 0.5 Hz of 50 Hz, while the acceptable
power factor range is typically 0.95 leading to 0.95 lagging. In Australia,
the power factor must be within the range 0.8 leading to 0.95 lagging.
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Inverter – cont..
– Compatibility with the array - The array’s maximum power voltage at
standard operating conditions must be compatible with the inverter
nominal DC input voltage.
• The maximum array open circuit voltage should also be well within the
inverter’s tolerable voltage range.
• Maximum power point trackers are commonly included with grid-
connected inverters to control the operating voltage of the array.
Several different tracking algorithms are in use, including ‘constant
voltage’, ‘perturbation and observation’, and ‘incremental
conductance’, each with its particular advantages and disadvantages
– Electromagnetic Interference - This must be low enough to comply
with relevant local requirements.
– Lightning and voltage impulse protection - These must comply with
local rules.
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Inverter – cont..
– Presentation - Items to check include compliance with relevant
electrical codes, size, weight, construction and materials, protection
against local weather conditions, terminals, and instrumentation.
Inverter costs vary considerably and have been falling in recent years, but
tend towards 20% of the overall cost of systems smaller than 5 kWp or 10%
for larger systems.
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On site Storage
• On-site storage is not essential for grid-connected systems, since it is
possible to sell excess power to the grid during daylight and buy
power at night.
• However, the addition of storage to PV systems can greatly increase
their value.
• Storage can be provided on site, typically via batteries or, for larger
systems, via pumped hydro, providing storage for peak period use.
• In the longer term, such technologies as flywheels, fuel cells,
underground caverns, superconducting magnets, compressed air, ice
or hydrogen may offer economical storage options.
• A household size D battery and flywheel storage system are
illustrated in Fig.
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Flywheel storage
Other Issues
• Other issues that need to be addressed for household photovoltaic systems
include
– Aesthetics - colour, size, shape, tilt, pattern, transparency
– Solar access - current and future shading, partial, complete or time of day,
from trees or buildings
– Building codes - roof structure, strength of mounting, zoning for
generation, light reflection
– Insurance issues - fire resistance, roof loading, safety, damage to grid or
other utility users
– Maintenance - routine and emergency, component replacement
– Impact on utility - overloading distribution transformers, power factor,
harmonics, isolation of PV (DC) current, disconnection mechanisms,
grounding, metering
– Contract with utility - buyback rates, equipment approvals, billing
arrangements.
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Summary
• Photovoltaics can be used in grid-connected mode in two ways:
rooftop & Utility-scale generating stations
• This unit deals with the related technical, economic and other issues
to be considered, and examines various government and utility
programs worldwide.
• PV systems can provide power for a number of functions in a
building includes Architectural, Demand-side management , Controls
& Hybrid energy systems.
• A wide range of specific building-integrated PV (BIPV) products are
now on the market especially for roofs, façades and as architectural
elements in atria etc.
• For a household system, the essential components are PV modules,
Grid-interactive inverter, and Metering equipment.
• Various approaches to rooftop mounted PV arrays are available.
32
Summary – cont..
• Two main types of inverters can be used to achieve AC power at the
voltage used in the main grid are Line-commutated & Self-
commutated.
Reference
Applied Photovoltaics
by