Within-Day Recharge of Plug-In Hybrid Electric Vehicles: Energy Impact of Public Charging Infrastructure Dr. Jing Dong and Dr. Zhenhong Lin Oak Ridge National Laboratory TRB 91 st Annual Meeting, Washington, D.C. January 22-26, 2012
Introduction Plug-in hybrid electric vehicle (PHEV) partially substitute electricity for gasoline a bridging technology towards battery electric vehicle (BEV) Public charging opportunities provide PHEV drivers with more flexibility further improve fuel economy This study is intended to assess the effect of public charger availability in increasing PHEV s share of driving on electricity capture within-day recharge behavior, considering real world travel activities 2 Managed by UT-Battelle
Background PHEV operates through a hybrid powertrain Charge depleting (CD): battery as the major energy source Charge sustaining (CS): engine as the major energy source CD range: the distance that a PHEV can travel in CD mode, designated by PHEV-[miles] Charging infrastructure Charging time and power, collectively, determine the amount of the electricity transferred to the battery Voltage Ampere circuit Charge power Charging time (10kWh) Level 1 120 volt 15 Amp 1.44 kw 7 hours Level 2 240 volt 30 Amp 6 kw 1-2 hours Level 3 480 volt 200 Amp 90 kw Less than 10 minutes 3 Managed by UT-Battelle
GPS Travel Data Obtained from NREL s Transportation Secure Data Center Collected continuously using passive GPS tracking devices Household travel survey conducted in Austin, Texas, USA One-day travel data of 229 vehicles Travel distances of 1652 trips and the intermediate dwell times Cumulative Travel Distance (mile) 35 30 25 20 15 10 5 Trip length Dwell time Daily VMT 0 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 Time 4 Managed by UT-Battelle
GPS Travel Data: Travel Pattern Daily VMTs and trip lengths Cumulative distribution determine vehicle s energy consumption 40% of daily VMT are less than 20 miles 97% of the trips are less than 20 miles a PHEV-20 can operate in CD mode more often if public charging is available 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 20% 30% Max Dwell time Dwell Time 0 1 2 3 4 5 6 7 8 9 10 11 12 Dwell time (hours) Cumulative distribution 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Dwell time between two consecutive trips limits the charging time Trip length Daily VMT 0 10 20 30 40 50 60 70 80 90 100 Travel distance (miles) 20% of the stops last more than 2 hours (to fully charge a PHEV-20 by a Level 2 charger) 30% of the vehicles are continuously parked for more than 7 hours (to fully charge a PHEV-20 by a Level 1 charger) 5 Managed by UT-Battelle
Methodology: Energy Consumption Power split PHEV with blended-mode operation Operate in the CD mode until the CD range is exhausted Electricity consumption: E e = d cd r cd,e Gasoline consumptions: E g = d cs r cs,g + d cd r cd,g Energy cost: E e price e + E g price g CD range CD mode CS mode (mile) Gasoline, r cd,g (gallon/mile) Electricity, r cd,e (kwh/mile) Gasoline, r cs,g (gallon/mile) 10 0.0095 0.1800 0.0237 20 0.0082 0.1975 0.0238 40 0.0057 0.2386 0.0244 Source: Automomie model developed by Argonne National Laboratory 6 Managed by UT-Battelle
Methodology: Within-Day Recharge Assumption: Recharging PHEV will not interfere with existing travel routines. The remaining CD range indicates the battery s state of charge. In the following example, the CD range of a PHEV-10 is extended by 10 miles if recharged once and 16 miles if recharged twice. Distance (mile) 35 Travel distance 30 Remaining CD range, recharge once 25 Remaining CD range, recharge twice 20 15 10 5 1 st recharge 2 nd recharge 0 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 Time 7 Managed by UT-Battelle
Methodology: Within-Day Recharge (cont d) Charger network coverage the probability that a charger is available at a certain stop User s decision on recharging perceived benefit and cost associated with the recharge Benefit includes gasoline cost savings, refueling burden relief etc. Cost comprises electricity cost and the perceived recharge burden. bounded rationality driver will recharge when the benefit-cost ratio is greater than a bounded rationality threshold. Travel distances in CD and CS modes can be computed to estimate energy consumptions and cost. 8 Managed by UT-Battelle
Result: Home vs. Public Charging Scenarios Home & Public: charged at home and public charger available Public only: no charger at home and public charger available Home only: charged at home and no public charger Gasoline Use (gallon/mile) 0.025 0.020 0.015 0.010 0.005 0.000 PHEV10 PHEV20 PHEV40 Home & Public Public only Home only PHEV-40 consumes less gasoline than PHEVs with smaller battery packs. For PHEV-10 and -20 (but not for PHEV-40), relying solely on public charging consumes less gasoline than home charging only. 9 Managed by UT-Battelle
Result: Public Charger Network Coverage Scenario: Assume a fleet of PHEV-20 All vehicles are fully charged when leaving home. Public charger availability varies from 0 to 100%. Public charging opportunities encourage within-day recharge behavior. Gasoline Use (gallon/mile) 0.018 0.016 0.014 0.012 0.010 0.008 0.006 0.004 0.002 0.000 10 Managed by UT-Battelle 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Charger Network Coverage (%) 200 180 160 140 120 100 80 60 40 20 0 Electricity Use (Wh/mile) Gasoline Electricity
Result: Public Charger Network Coverage Gasoline consumption: Fully covered public charger network provides more than 30% reduction in gasoline use PHEV-10 with 50% charger coverage consumes less gasoline than PHEV-20 (no public charger) Energy cost: Electricity price: $0.11/kWh Gas price: $2.55/gallon Higher charger coverage results in more energy cost savings Greater savings are observed for PHEV-10 and -20 than for -40. Gasoline Use (gallon/mile) Cost Savings (cent/mile) 0.025 0.020 0.015 0.010 0.005 0.000 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0% 0% 10% 10% 20% 20% 30% 40% 50% 60% 70% 80% 90% Charger Network Coverage (%) 30% 40% 50% 60% 70% 80% 90% Charger Network Coverage (%) 100% 100% > 30% PHEV-10 PHEV-20 PHEV-40 PHEV-10 PHEV-20 PHEV-40 11 Managed by UT-Battelle
Conclusions This study estimates PHEV energy consumption based on GPS tracking data considers within-day recharge, constrained by travel activities and charger availability 12 Managed by UT-Battelle Key findings Providing public charging service reduces PHEV gasoline consumption and energy cost Public charging offers greater benefits for PHEVs with a smaller battery pack (within-day recharges compensate battery capacity)
Thanks! Q & A 13 Managed by UT-Battelle