3. Technical Background

The purpose of this section is to provide charging infrastructure, distribution system impact, and tariff-related information relevant to this proceeding. A number of technical issues are presented to provide background for purposes of answering charging option questions presented in section 5 and as a starting point for discussion among parties.

The technical information provided here is in addition to the information provided in the Commission's Policy and Planning Division's May 22, 2009 white paper.8 This white paper outlines electric vehicle drive train options, battery capacity options, battery chemistry options, and related infrastructure support requirements that distinguish PHEVs from BEVs. It also includes a limited analysis of the impact of a given vehicle population scenario on total energy demand, peak load, and net greenhouse gas emissions. Stakeholders submitted comments to the Policy and Planning Division on this white paper, which served to further clarify the technical information in the white paper.9

3.1. Vehicle Connection to Electric Vehicle Supply Equipment Options

This rulemaking invites academic, utility industry, automotive industry, local governments, and consumer comment on PHEV and BEV charging preferences, in addition to inviting stakeholder comment on applicable charging infrastructure codes and standards. We briefly explain the technical aspects of charging electric vehicles to give context to the questions that later follow.

A factory-model PHEV or BEV houses a charger that converts alternating current (AC) from an electrical circuit into direct current (DC) and regulates the current voltage directed to the on-board battery for storage.10

The electric vehicle charge time and Electric Vehicle Service Equipment (EVSE)11 sub-circuit size determine the amount of energy (kWh) drawn per charge. As the electric vehicle market matures, electric vehicles may demonstrate improved energy conversion efficiencies, depending on factors including vehicle weight, drive train options, and driving conditions. Like household electric appliances, higher efficiency electric vehicles will use less energy (kWh) to provide the same energy service.

The difference between the vehicle battery state of charge and battery capacity determines energy needed per charge.12 To draw power from an electricity sub-circuit at the residence or a commercial or public charging facility, the electric vehicle can either (1) use a mobile cordset EVSE to connect to a dedicated wall plug and a 120 Volt (V) sub-circuit (1.4 kW, 15 Amps (A) or 20 A), or (2) connect to a cord attached to a permanently mounted EVSE premise unit connected to a 240V sub-circuit (typically, 3.3 kW - 6.6 kW, up to 19.2 kW, 80 A).13 A DC charging option includes an additional charger in the EVSE that bypasses the vehicle charger for higher power distribution (for example, 120 kW, up to 800 kW).14

A second electric meter or sub-meter needed to separate vehicle load from the normal residential load is external to the vehicle and to the EVSE premises unit. An external communication bridging device is one of several options that could transmit homeowner and/or utility program messages through the Advanced Meter Initiative (AMI) meter and a communication platform to the uniquely identified vehicle. This rulemaking may explore whether the interface between the utility and the electric vehicle should include communication signals that include (but are not limited to) utility time variant pricing signals, demand response signals, and voltage ramping and regulation signals.

A mix of charging level options at standardized charging facilities (standard 120V (Level 1), 240V (Level 2) and DC charging options) will likely be required to support a mass electric vehicle market.15 Many electric vehicle drivers may prefer Level 2 off-peak charging in order to charge larger BEV batteries within a reasonable time and expedite smaller PHEV battery charging. However, Level 1 charging is as ubiquitous as a standard 120V outlet. Level 1 and Level 2 charging at residential EVSE facilitates off-peak charging when electricity demand, driving demand, and electricity cost of service are low. Night time vehicle charging is convenient for a homeowner and has the potential to integrate increased levels of intermittent off-peak wind energy, flatten the electricity system load curve, and realize generation, transmission, and distribution system efficiencies.

However, some drivers may prefer daytime opportunistic charging at a residential, commercial, or public charging facility. 16 Daytime charging may be necessary to make electricity refueling as convenient as gasoline refueling, and may be a requirement for a mass electric vehicle market. The potential adverse impact of daytime charging, however, is that if it occurs during peak load time (approximately noon to 7:00 p.m.), this could have a negative impact on the grid, causing more expensive and polluting peak generation units to operate.

This rulemaking will also explore centralized charging as a potential charging option to complement decentralized residential charging. DC charging may offer a charge rate adequate to enable a geographically centralized electricity refueling model similar to the gasoline filling station model for conventional vehicles. Replaceable battery swapping stations located in urban areas, exurban areas, and along highways are another means of making electricity refueling time and location similar to the gasoline filling station model.17

Another technical issue relates to the fact that charging facilities will be located in multiple utility service territories, which may require an entity/entities (e.g., electric utilities, electric vehicle service providers, and/or clearing houses) to establish an electric vehicle usage billing system. This rulemaking may look at issues relating to the necessity of such a system to accurately track electricity fuel consumption to apply utility tariffs and track net greenhouse gas emissions reductions. A billing system may be preferable to a uniform statewide electric vehicle tariff; stakeholders note that utility tariffs are unique because of service cost differences due to geographic and regulatory factors.18

We note that early PHEV consumer behavioral research indicates after-market converted-PHEV drivers prefer charging at multiple times and locations, including daytime charging.19 Again, this rulemaking is an opportunity to invite charging behavior research findings to analyze infrastructure performance requirements. We also welcome electric vehicle user input via their representative associations.

3.2. Potential Near-Term Electrical Distribution System Impacts

This rulemaking is also an opportunity to examine system-dependent analyses of transformer stress due to localized electric vehicle load, and discuss whether cost increases due to such load should be incorporated into utility distribution maintenance budgets in general rate cases or other cost of service proceedings. It is also an opportunity to assess demand response load management programs, tariffs, and other technologies that may be of use to avoid acute distribution system impacts. In the long term, pending electric vehicle market commercialization, other system impact costs may include transmission line upgrades and total energy procurement attributable to electric vehicle usage.

In our July 15, 2009 electric vehicle workshop in R.08-12-009, we were warned that distribution system impacts, more so than transmission and generation system impacts, may arise in the early electric vehicle market. There is some evidence that in certain neighborhoods, clusters of early adopters of electric vehicles exist. Under certain charging voltage and timing assumptions, an average of less than one PHEV per household could increase asset overloading on the neighborhood transformer.20 A commonly used 25 kilovolt-ampere (kVA) neighborhood transformer serves the typical household load for five to seven homes. Level 2 charging (for example, at 6.6 kW) for a BEV can increase the load served by the transformer by the equivalent of an additional household load; a PHEV charging at 120V (1.4 kW) is the equivalent of a third of a household load. DC charging, if as ubiquitous and used as often as a gasoline filling station, may place acute stress on multiple local circuits and transformers. Distribution system stress is particularly of concern if customers charge when they arrive home after work when the transformer would otherwise cool down with declining household evening load.21 Consequently, vehicle charging level and charging timing is relevant to the rate of transformer capacity and transformer aging. For electric reliability purposes, this Commission intends to address this important issue to see how to encourage sequential charging during hours that will not adversely impact local circuits and transformers.

8 See Section 7 herein, regarding Commission Staff White Paper and comment incorporation into the rulemaking's evidentiary record. Commission Staff White Paper, Light-duty Vehicle Electrification in California: Potential Barriers and Opportunities, Commission Policy and Planning Division, (May 22, 2009). http://www.cpuc.ca.gov/NR/rdonlyres/AD8A4A5E-6ED9-4493-BDB6-326AB86A028E/0/CPUCPPDElectricVehicleWhitePaper2.pdf.

9 Stakeholder comments on Commission staff's white paper are available online: http://www.cpuc.ca.gov/PUC/energy/ev_comments.htm.

10 A typical on-board electric vehicle charger converts AC to DC at 3-5 kilowatts (kW). A common on-board battery capacity size for a PHEV is 8-15 kilowatt-hours (kWh), while a typical battery capacity size for a BEV is 25-33 kWh. Battery capacity is influenced by the amount of "usable" battery capacity specified under warranty. Battery capacity may decline over time and under certain climate conditions, although manufacturers are working on improving lifespan over deep-cycle testing. The smaller battery size in the PHEV is due to the vehicle's dual fuel sources, electricity and gasoline, natural gas, biofuels, or other alternative fuel options. The BEV relies solely on stored power in the battery.

11 The EVSE premises unit houses circuit insulation, fault (fuse), Ground Fault Circuit Interrupt (GFCI), a pilot circuit to activate charging and define the energy per charge, and a safety switch to protect against "hot" vehicle decoupling. All components of the EVSE premises unit and EVSE installation requirements are subject to the Society of Automotive Engineers (SAE) J1772 Standard, the United Laboratories (UL) certification processes, the National Electric Code (NEC) and California Electric Codes (CEC).

12 This assumes the vehicle owner charges to full capacity from the battery state of charge. The state of charge is a function of vehicle miles driven in all electric range (i.e., total energy consumed in all-electric range), driving conditions, and vehicle efficiency (miles/kWh). A minimum state of charge in a PHEV is the point at which the vehicle switches from charge depleting to charge sustaining mode.

13 Stakeholders note mismatches between the vehicle onboard chargers and available energy are likely. The lesser of the "available line current" or "charger size" determines the power that is delivered and used. Certain battery size, voltage, and charging level data is from Scholer, Rich - J2293 Task Force, "Messages and Categories" presentation, Ford Motors.

14 The plug between the electric vehicle and the electricity source uses a SAEJ1772 EVSE plug standard which is a conductive 5-pin coupler.

15 The SAE J 1772 documents classify 120V and 240V charging options as Level 1 charging and Level 2 charging, respectively. Source: Scholer, Rich, http://www.cpuc.ca.gov/NR/rdonlyres/851ED8D2-7E45-4964-989E-6FC30F4DC265/0/RichScholerFord.pdf. PHEV and BEV owners may demand a range of charging facility options depending on vehicle drive type, range limitations for all electric range, driving patterns, charging time of day preference, total charge time preference, and preferred primary charging location.

16 The cost of higher incremental greenhouse gas emissions associated with "peaker" power plants would be reflected through the price per ton of carbon dioxide equivalent as determined by the carbon market. As an alternative to daytime charging, drivers may participate in demand response emergency load shedding programs during high load hours to avoid adding to on-peak demand.

17 Better Place is an electric vehicle service provider company proposing a battery swap facility option. See Becker, Thomas. "Electric vehicles in the United States: A new model with forecasts to 2030," Center for Entrepreneurship and Technology, University of California at Berkeley, July 2009, http://cet.berkeley.edu/dl/CET_Technical_Brief_Economic.pdf.

18 Pacific Gas and Electric Company, "Comments of Pacific Gas and Electric Company on CPUC Policy and Planning Division White Paper," July 1, 2009, p. 5, http://www.cpuc.ca.gov/NR/rdonlyres/BE381C44-94FC-46BC-BDBE-CDE00D9DE05F/0/PGECommentsPEVWhitePaper.pdf.

19 Kurrani, Heffner, Turrentine, "Driving Plug-In Hybrid Electric Vehicles: Reports from U.S. Drivers of HEVs converted to PHEVs, circa 2006-07," Institute of Transportation Studies, University of California at Davis, 2007, p. 17.

20 Alexander, Marcus, Electric Power Research Institute (EPRI), "Effects of electric transportation on the electricity grid," (July 15, 2009), R.08-12-009 Presentation to Commission Smart Grid proceeding Workshop 4, http://www.cpuc.ca.gov/NR/rdonlyres/5F5E1729-1688-48C0-8A5B-FD5B47A161DA/0/CPUCpresentationMarcusAlexander2009_07_15.pdf.

21 EPRI notes "it is possible that in some neighborhoods 2 or 3 PHEVs per household could be present even in the near-term market, which would shorten the transformer life to 1/10th of its expected value if high rate charging was used," EPRI, "Re: Comments from EPRI on the Commission Staff's White Paper," (July 1, 2009), p. 4, http://www.cpuc.ca.gov/NR/rdonlyres/4EFB4601-CDC7-45E3-B9F0-F3AA5E5D119F/0/EPRICommentsonCPUCElectrificationWhitePaper7109.pdf.

Previous PageTop Of PageNext PageGo To First Page