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Electric Vehicle Grid Integration Research Analyzing PHEV Impacts on Distribution Transformers in Hawaii
Tony MarkelMike KussMike Simpson
Electric Vehicle Grid IntegrationNational Renewable Energy Laboratory
May 4, 2011
National Renewable Energy Laboratory Innovation for Our Energy Future
NREL Role in Grid Integration of Vehicles
• Understanding usage profiles, benefits, and battery life
• Integration with renewable resources
• Interoperability with grid – standards development and testing
• Exploring grid services technology
2
Innovation for Our Energy Future
PEV Grid Integration Research Spectrum
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• Renewable Electricity Futures Study
– Future forecast and energy dispatch
Days to Years
Minutes to Days
Subsecondto Minutes
> 20
15 ‐ 20
10 ‐ 15
5 ‐ 10
2.5 ‐ 5
1.25 ‐ 2.5
< 1.25
2050 PEV Daily FixedEnergy Demand
(GWh)
• Transformer Distribution System Impacts
– Loads and temperatures of distribution components
• Component Interoperability Testing – Operational response and
communications for management
Innovation for Our Energy Future
• Customer: • U.S. Department of Energy’s Hawaii Clean Energy Initiative
(HCEI)• Also working directly with the Hawaii Electric Company (HECO)
and HCEI Transportation Working Group• Status:
• Completed forecasting of impacts on distribution grid residential transformers due to various EV charging scenarios
• Remaining work:• Currently under discussion but could include deployment of
managed charging system
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EV Distribution System Impacts
NATIONAL RENEWABLE ENERGY LABORATORY Preliminary - 01/17/11 5
Under what PHEV penetration scenarios will distribution transformer
impacts occur?
How might TOU rates affectthe distribution system impacts?
How does public charging availability affect residential charging loads?
Key Questions
NATIONAL RENEWABLE ENERGY LABORATORY Preliminary - 01/17/11
How Transformers Degrade
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• Chemical bonds within voltage-insulating paper & oil breaks downabove 110°C
• The reaction depends upon time (linear) and temperature (exponential)• Hotspot temperature θh determines reaction rate:• The aging rate for a transformer has beenempirically determined and published inIEC 60076 and IEEE C57.91:
http://cenvironment.blogspot.com/2009/12/electrical‐transformers‐utility‐poles.htmlhttp://www.sayedsaad.com/fundmental/index_transformer.htm
Top‐oil TFunction of load& ambient temp
Hotspot T riseFunction of load
NATIONAL RENEWABLE ENERGY LABORATORY Preliminary - 01/17/11
Approach
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• Annual ambient temperature data• Consumer vehicle travel profile data• Household electrical load data
Remix travel and load inputs to create a spectrum of results
Predict thermal profile and aging of residential transformer using IEEE/IEC models
TOU Pricing and Opportunity
Charging included as external factors
NATIONAL RENEWABLE ENERGY LABORATORY
20houses / 25kVA transformer
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With high penetration of PEVs and many houses per transformer, some overloading can occur.
100%
Rated Transformer Insulation Temp
TransformerRated Load
*Home Charging Only
penetration of EVs with 2.6 kWh of charge required per PEV (36 vehicles) @ 3.3 kW charge rate.
Preliminary results from 1/17/2011Thermal model and transformer aging rates from IEC 60076 and IEEE C57.91
3-5 15-208-12Light load Heavy load
NATIONAL RENEWABLE ENERGY LABORATORY Preliminary - 01/17/11
Aging Rate as a function of Transformer Mileage
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Green - “transformer upgrade likely unnecessary”Yellow - “transformer upgrade likely necessary” Red - “transformer upgrades definitely necessary”
40-50% penetration assuming ~12 homes per transformer
NATIONAL RENEWABLE ENERGY LABORATORY Preliminary - 01/17/11
Smart Communications Reduces Transformer Time-at-Temperature
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• Simple 1-way communication tells vehicles to delay charging when transformer temperature rises above 98°C threshold
• Temperature input could be measurement- or model-based• Smart Grid extends capacity of 25kVA transformer
2.3 kWh per PEV3.6 kWh per PEV chargingcontinuesovernight
NATIONAL RENEWABLE ENERGY LABORATORY Preliminary - 01/17/11 11
The impact of PHEVs on distribution transformers is linked to several factors.
The strongest seem to be,• Number of households per transformer• PHEV penetration rate
o Vehicle mileage per transformer• Charging rate
Key Findings
Several moderating steps can be taken, • Daytime public charging reduces the amount of energy
needed to be delivered through residential transformers• Low to moderate levels of TOU pricing adoption shifts load to
reduce coincident load peakso High levels of TOU adoption may create new peaks
• Limited demand management control based on transformer thermal state offers significant transformer capacity expansion
• Distributed renewables located near PEV loads?
NATIONAL RENEWABLE ENERGY LABORATORY Preliminary - 01/17/11
A tool to track PEV roll-out and grid impacts
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National Renewable Energy Laboratory Innovation for Our Energy Future13
Solar Wind
Biofuels
InterfaceUtility
Energy Storage
Plug-in Electric
Vehicles
Renewable Fuels for Plug-in Hybrid Electric VehiclesProvides Integrated Low CO2 Solution
Communication
Credit: Envision Solar
Credit: Solar Electrical Vehicles
Unless noted photo credits: NREL
National Renewable Energy Laboratory Innovation for Our Energy Future
Charge Management Simulations Connect NREL Commuting to Renewables
• 20% penetration of PEVs => 24% miles electrified• All charging completed within work day hours• Grid capacity requirements minimized and matched to solar
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Wait Time (hr)
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mut
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Time Waiting for Charge to Begin
0 4 8 12 16 20 240
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Time of the Day
PE
V P
ower
(kW
)
Charging of NREL Garaged PEVs
ImmediateStaggeredSolar Array
NATIONAL RENEWABLE ENERGY LABORATORY 15
Questions?Tony Markel
National Renewable Energy [email protected]
