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GRID CONNECTIVITY OF RENEWABLE
ENERGY SOURCES ISSUES & SOLUTION
Swathi venugopal
Semester; 8
Electrical & Electronics
RIT, Kottayam
Date; 22/02/13
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More than 400 cities
50 million people globally
Major icons went dark
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GRID CONNECTIVITY OF RENEWABLE ENERGY SOURCES ISSUES & SOLUTION
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Increasing oil
prizes
Exhaustible sourcesReleases
GH gases
Increasing co2
SO2+NOX+H2O+O2=ACID RAIN
NITROGEN OXIDE + VOC = SMOG
Global warming
Effect Of Combustion Of Fossil Fuels?
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Declining Fossil Fuel Supplies
Environmental Concerns
Increasing Cost of Fossil Fuels
Business Opportunities
Energy Security
Energy independence
Reasons for Renewable Energy in India why and why now??
“1 MW of wind plant in one year can displace 1500 tons of
CO2, 6.5 tons of SO2 and 3.2 tons of NOx. (REPP report,
Washington July 2003)”
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The vision of Indian renewable energy program
“To develop new and renewable energy technologies,
processes, materials, components, sub-systems,
products and services at par with international
specifications, standards and performance parameters
in order to make the country a net foreign exchange
earner in the sector and deploy such indigenously
developed and/or manufactured products and services
in furtherance of the national goal of energy
security”.
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Generating units
Transmission
network
Distribution
network
Consumers
Features And Structures Of Electrical
Power Systems
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Features And Structures Of Electrical
Power Systems
Electricity Demand (Inc. Losses) Is Varying ..
Minimum at night and increasing to a peak during working hours.
During working days and weekends/holidays
seasonal variations
.
Generators Must Be Scheduled To Match These
Variations Throughout The Year
To maintain an AC power system at its nominal
frequency , “Instantaneous Power Supplied = Demand .”
Done by control of generation regulation/ load following Controlled automatically or by a central electricity system operator
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Grid connectivity renewable energy issues and solutions .
Renewable Energy Generation
Characteristics
Grid Connectivity
REIssues And Solutions .
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Comparison
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Most RE resources are location specific.
• Renewable-generated electricity may need to be
transported over considerable distances.
• Beneficial combinations of renewable sources may
not always be practicable.
CHALLENGES WITH INTEGRATING INTO
ELECTRICAL POWER SYSTEMS
Lack of flexibility
• Balancing supply and demand
• Uncertainty in predicted out-put.
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Transmission
GeneratorsTransmission Network
Distribution Network
Distribution Generators
Consumers
Transmission
Generators
DISTRIBUTED GENERATORS
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What is an efficient grid connection ?
Respect the power quality of the grid
Respect the grid protection plan
Allow control and clear monitoring
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Lack of standerds
1. Central Electricity Authority
2. Central Electricity Regulatory
Commission
3. State Electricity Regulatory
Commissions
.
Exist only for connecting
voltage levels of 33 kv &
above to the grid
“ Viable standards of grid connectivity to be framed ”
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Voltage fluctuation and regulation
Extended under voltage causes “brownouts”
Extended overvoltage decreases the life of
equipment's.
DG systems are not only affected by voltage
fluctuations, but can cause voltage fluctuations
themselves
INTEGRATING INTO ELECTRICAL POWER
SYSTEMS ISSUES & SOLUTIONS
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1. Grid-derived voltage fluctuations
Inverters - ‘voltage-following’
• Avoid this happening, Low Voltage Ride-through Techniques
(LVRT) could be incorporated into inverter design
inject reactive power during voltage sags
Reduce network voltage by drawing reactive power during voltage
rise.
provide current that is out of phase with the grid voltage so provide
power factor correction.
Disconnect DG when the grid voltage moves outside set parameters.
Ensure suitable power quality
Antislanding.
Automatic disconnection will cause overloading of other generators
Inverters -‘voltage-regulating’ mode
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2. Voltage imbalance
Voltage imbalance is when the amplitude of each
phase voltage is different in a three-phase system or
the phase difference is not exactly 120°.
High RE penetrations, the cumulative size of all
systems connected to each phase should be as equal
as possible.
3. Power output fluctuation
Short-term fluctuations
Affect power quality
Continuous tap-changing and capacitor switching
increased number of switching surge
Long-term fluctuations
Require back-up generation to maintain power
supply.
Geographical dispersal
Forecasting
Storage
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4. Voltage rise and reverse power flow
Voltage
max
min
Substa
tion
Overhead line
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Ensuring PV systems are smaller than the daytime load,
Use dynamically controlled inverter (DCI) to gradually reduce PV
output
Use of a minimum import relay (MIR) to disconnect the RE system,
Use of a reverse power relay (RPR) to disconnect the system on
low voltage and reverse power flow
Decreasing the network’s series impedance , to reduce voltage
drop.
Requiring customer loads to operate at improved power factor
Requiring customers with large loads to incorporate some form of
load-shedding scheme,
The use of storage units
To minimize voltage rise and reverse power flow
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Power factor correction
Poor power factor -increases line losses & makes voltage
regulation more difficult.
voltage-following have unity power factor
voltage-regulating mode provide power factor correction.
Grid connectivity renewable energy issues and solutions .
Unintentional islanding
Occurs when DG delivers power to the
network even after circuit breakers have
disconnected from main grid.
grid inverter technology has developed to
include anti-islanding features as per local
regulations and standards
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Unbalanced supply-demand lead to frequency fluctuation
High penetration of intermittent energy make control more
difficult.
DG inverters can provide frequency control in milliseconds,
Only when they can inject power into the network
DG linked to thermal plant are restricted in their ability to
provide frequency regulation because of their thermal loads.
Inverters disconnect from the grid when the frequency moves
outside set limits (as a form of islanding detection),
Ability to provide frequency support may be compromised.
All DG will also disconnect, exacerbating the power imbalance
Leads to complete system shutdown
.“New frequency ride through systems that do not interfere with the anti-
islanding protection systems will need to be developed”
Frequency variation and regulation
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Harmonics
Transformers
• Overheating leads to insulation
failure
• Reverse power flow capability?
Switchgear
• Overheating leads to insulation
failure
Cables• Overheating leads to insulation
failure
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Harmonics
HARMONIC REDUCTION
voltage-source inverters can provide the harmonic
support but do so at an energy cost
There are a variety of harmonic compensators that are
likely to be cheaper.
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1. Very low penetration (typically 5-10% of connected load)
Can be tolerated without significant problems
2. Moderate level penetration (10-20% of connected load)
• Minimizing VAr flows, power factor correction, increased
voltage regulation and careful consideration of protection.
More significant issues arise .
More DG may be accommodated by making changes to
the network
3. High levels of penetration, (Network dependent)
Require significant overall design and communications
infrastructure changes – for coordinated protection and power flow
control.
Under research and development
Generalization
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No market
Utility culture & framework
Lack of expertise
Limited role for private sector
Capital costs vs. variable energy costs
Transmission access & strength of grid
What are the other key barriers ?
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Promote market development
Support utility RE procurement
Encourage private investment
Provide long-term contracts
Value RE attributes
Facilitate access to Electricity grid
Train RE designers and operators
What are the Strategies to overcome
barriers ?
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GUIDE LINES
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1. CONNECTION OF REPS TO THE GRID
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2. SAFETY CONSIDERATIONS
Incorporate an anti islanding function
Install a lockable switch at an easily accessible position –
manually isolate REPS from grid
Update circuit diagram regularly and display at
appropriate locations
Establish a direct communication channel between owner
and utility
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3. EQUIPMENT PROTECTION
Carry out assessments on the new fault levels due
to connection of REPS
Incorporate the following features
auto switching & auto reclosing
facility to isolate REPS from DS when fault occur
protection facilities against transient abnormalities in the grid
stable and fast responding voltage & frequency regulators
Protection facilities to avoid unsynchronized connections
4 pole CB to provide complete isolation from DS when REPS
is not in service.
Automatic reconnection facility after the fault is removed
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3. POWER QUALITY
inverter with power conditioning feature to control THD & PF
Isolation transformer on the output side of inverter to avoid the
injection of DC to DS
Fast responding frequency and voltage regulator.
Design REPS with three phase inverter or three
identical single phase inverter to supply current Which
is balanced over the three phases to the grid –
minimize voltage & current unbalance
Install the following features
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Policy implementation & enforcement
Renewable energy market promotion
Pricing of electricity
Cost sharing
What is the the need for government
involvement?
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Centralized power
YESTERDAY
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GRID CONNECTIVITY OF RENEWABLE ENERGY SOURCES ISSUES & SOLUTION
Price of non renewable energy source is increasing
day by day , where as the availability is reducing day
by day.
It is mandatory that we have to depend on renewable
energy sources
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Centralized power Off grid power
plant
TODAY
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High initial capital costs
Electricity production is dependent on availability of
source
Electricity production may not match when household
requires .
Electricity requiring either batteries to store electricity
(especially if there is no grid connection and/or an
agreement with your electricity retailer to purchase
surplus electricity from you).
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TOM0RROW
GRID TIED SYSTEM
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DECENTRALIZED GENERATION / FUTURE
INTEGRATION
Additional energy supply systems (esp using RE)
in the medium and low voltage level is highly visible
Configuration of an intelligent distributed electricity
system as the most important alteration.
In Europe it is called “decentralized generation”.
Aims at generating the energy where it is
required
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Should avoid interferences and overcharge in
circuits
storage facilities
Energy management
Accumulator systems.
capacitors
compressed-air stores
interactions between different electricity levels.
communication,
information, control, metering, services, planning,
optimization
forecast
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4
7
Central GeneratingStation
Step-Up Transformer
DistributionSubstation
ReceivingStation
DistributionSubstation
DistributionSubstation
Commercial
Industrial Commercial
Gas Turbine
DieselEngine
Cogeneration
Cogeneration
Turbine
Fuel cell
Micro-turbine
Wind Power
Residential
Storage
Photovoltaic systems
Control Center
Operators,
Planners & Engineers
2. Communications and Information Infrastructure
GRID CONNECTIVITY OF RENEWABLE ENERGY SOURCES ISSUES & SOLUTION
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CONCLUSION
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Wind energy , tidal energy ,and solar PV are not dispatchable unlike NRE
Integrating this RE to power system is a difficult process Grid tied system is becoming a must New Technologies will need to be developed. Promote off – grid (mainly solar pv ) for sustainable
economyAdvantages of grid tied system is predominating over disadvantages
Save energy save environment
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Integration of Renewable Energy into Present and Future Energy Systems-Ralph Sims (New Zealand), Pedro Mercado (Argentina), Wolfram Krewitt †(Germany)
Vergnet S.A. Integration Of A Wind Farm Into The Utility Grid
Eric ANDRIEU, Electric Al Design Département Manager Pierre
PESNEL,Export Manager
Grid integration of renewable energy sources GermanP. Kammer, A. Kober BTU Cottbus Cottbus, y
Renewable Energy Sources (RES) Grid Integration: Key Issues and Challenges Bharat Singh
REFERENCE
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Addressing Grid-interconnection Issues With Variable Renewable Energy Sources Summary Document Report for Asia Pacific Economic Cooperation (APEC)
Renewable Energy Technologies Solutions Grid Connected Systems IRENA Workshop
Grid connection of Renewable Energy CHALMERS ENERGY CONFERENCE 2012 Peter Konings – SEIAPI / APEG
Renewable Energy in India: Progress, Vision and StrategyMinistry of New and Renewable Energy Government of India
Fractional Order Modeling & Control Strategies for Grid-Connected Renewable Energy SourcesMajor Professor : Dr. Chen
Renewable Energy Grid Connection Dave Fleming
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