Time-of-Use Rates and Electrical Planning for EV Charging in California
California's three investor-owned utilities — Pacific Gas & Electric (PG&E), Southern California Edison (SCE), and San Diego Gas & Electric (SDG&E) — each operate mandatory or opt-in time-of-use (TOU) rate schedules that directly affect the cost and infrastructure logic of residential and commercial EV charging. Understanding TOU rate structures, their interaction with electrical capacity planning, and their relationship to California's grid management policies is essential for anyone sizing circuits, specifying charger hardware, or evaluating panel upgrades for EV use. This page covers TOU rate definitions, the electrical planning decisions they drive, scenario-based comparisons, and the boundaries that determine when more advanced grid integration is warranted. For a foundational understanding of how electrical systems support EV infrastructure across the state, see California Electrical Systems: Conceptual Overview.
Definition and scope
Time-of-use rates are electricity pricing structures in which the per-kilowatt-hour (kWh) cost varies according to the time of day, day of week, and season. The California Public Utilities Commission (CPUC) has mandated a phased transition to default TOU rates for residential customers of PG&E, SCE, and SDG&E, formalized through CPUC Decision 15-07-001 and subsequent rate proceedings (CPUC TOU Rate Policy).
Under TOU structures, peak periods — typically 4 p.m. to 9 p.m. on weekdays — carry rates substantially higher than off-peak periods. For example, SCE's TOU-D-PRIME rate, designed specifically for EV owners, separates a "super off-peak" window (9 p.m. to 8 a.m.) from peak and mid-peak windows, creating strong financial incentives to shift charging to overnight hours (SCE TOU-D-PRIME Rate Schedule).
Scope of this page: This page addresses TOU rates as they apply within California under the jurisdiction of CPUC-regulated investor-owned utilities. Municipal utilities — such as the Los Angeles Department of Water and Power (LADWP) or Sacramento Municipal Utility District (SMUD) — operate under separate ratemaking authorities and are not covered here. Federal rate regulations, interstate transmission pricing, and EV charging at locations served by rural electric cooperatives fall outside this page's coverage. The regulatory context for California electrical systems page addresses the broader statutory and agency framework.
How it works
TOU pricing interacts with EV charging electrical planning through three distinct mechanisms:
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Load-shifting incentive: Off-peak kWh rates can be 50–70% lower than peak rates depending on the utility and rate tier. This price differential creates a direct incentive to install charger controls — either smart EVSE with scheduling features or an energy management system — that restrict charging to approved windows.
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Demand charge exposure (commercial and multi-unit contexts): Commercial TOU schedules often include a demand charge component measured in dollars per kilowatt of peak demand. A 19.2 kW Level 2 charger or a DC fast charger operating during peak windows can significantly increase a monthly demand charge. Commercial EV charging electrical systems require separate demand charge analysis beyond simple kWh pricing review.
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Panel and circuit sizing interaction: Because TOU incentives favor concentrated overnight charging, the electrical panel and dedicated circuit must be sized for the full rated amperage of the EVSE — not an averaged load. A 48-amp Level 2 charger requires a 60-amp dedicated circuit per NEC Article 625 continuous-load rules (125% of continuous load = 60A). If multiple vehicles charge simultaneously in off-peak windows, load management for multiple EV chargers becomes the controlling design factor.
The process for aligning TOU rate selection with electrical planning follows a structured sequence:
- Identify the applicable utility and rate schedule options (residential vs. commercial, EV-specific vs. general TOU).
- Assess existing panel capacity to confirm available amperage for overnight charging loads.
- Determine EVSE type (Level 1 at 12A, Level 2 at 16–80A, or DCFC) and its circuit requirements.
- Select a smart EVSE or network-connected charger with scheduling capability aligned to the utility's off-peak window.
- Confirm permitting requirements with the local authority having jurisdiction (AHJ) — California Electrical Code (CEC) Article 625 governs EVSE installations, and all new dedicated circuits require inspection.
Common scenarios
Scenario A — Single-family residence, PG&E TOU-EV2-A rate:
A homeowner installs a 48-amp Level 2 charger. PG&E's EV2-A rate offers super off-peak pricing from 11 p.m. to 7 a.m. The EVSE is programmed to begin charging at 11 p.m., completing a full charge by 6 a.m. The 60-amp dedicated circuit and subpanel are sized for the full 48-amp continuous draw. No demand charge applies under residential rate schedules.
Scenario B — Multi-unit dwelling, SDG&E EV-TOU rate:
A 20-unit apartment complex installs 10 Level 2 chargers. SDG&E's commercial EV rates carry demand charges. Simultaneous off-peak charging from all 10 chargers at 7.2 kW each produces a 72 kW load — potentially triggering a service entrance upgrade. A load management controller staggers charging to cap peak demand, reducing demand charge exposure. Multi-unit dwelling EV charging electrical planning addresses this scenario in detail.
Scenario C — Workplace charging, SCE TOU-EV-9 rate:
Workplace chargers operate primarily during peak hours (8 a.m. to 5 p.m.). SCE's TOU-EV-9 rate for commercial EV service includes both energy and demand components. Workplace charging at peak aligns with grid stress periods. Demand response programs allow large commercial sites to curtail charger output during grid emergency signals, which can reduce rate surcharges or generate bill credits.
Scenario D — Solar + storage integration:
A solar-integrated EV charging system charges a battery storage system during daylight off-peak hours, then discharges stored energy into the EV charger during evening peak hours, bypassing utility peak rates entirely. Electrical planning must account for inverter capacity, battery output amperage, and interconnection rules under CPUC Rule 21 (CPUC Rule 21).
Decision boundaries
Several threshold conditions determine which TOU rate strategy and electrical infrastructure path applies:
Residential vs. commercial rate classification: Single-family and small multi-family accounts below certain demand thresholds qualify for residential TOU schedules (no demand charge). Accounts exceeding the utility's commercial service threshold — or requesting service above a specific amperage — move to commercial schedules that include demand charges. This boundary is utility-specific and set by tariff schedule, not by a fixed statewide rule.
Level 2 vs. DCFC planning threshold: Level 2 EVSE (up to 80A, 240V) operates within reach of standard residential and light commercial service. DC fast chargers begin at approximately 50 kW and require three-phase power, a separate metered service, and in most cases a utility interconnection study (utility interconnection for EV charging). The choice between Level 2 and DCFC is the primary determinant of service upgrade scope. A comparison of Level 1, Level 2, and DCFC electrical requirements is covered in detail at Level 1 vs. Level 2 vs. DCFC: Electrical Differences.
Smart charger vs. managed charging system threshold: A single EV charger in a single-family home can be managed through EVSE-native scheduling. Sites with 3 or more chargers, mixed loads, or demand charge exposure require a dedicated energy management system with dynamic load control. The California Energy Commission (CEC) and CPUC have jointly issued guidance on managed charging through programs such as the Clean Vehicle Rebate Project and the EV Charge Network program (CEC Clean Transportation Program).
Rebate and incentive eligibility: TOU rate enrollment is often a condition of utility EV charging rebates. PG&E, SCE, and SDG&E each administer rebate programs — some funded through CPUC-approved public purpose programs — that require enrollment in a qualifying TOU rate as a precondition. Details on available programs are covered at EV charging electrical rebates and incentives in California. The California Electrical Systems home page provides a navigational overview of all related topics.
Electrical planning for TOU-optimized EV charging is not a standalone decision. Panel capacity, circuit sizing, EVSE selection, permitting under the CEC and local AH
References
- National Association of Home Builders (NAHB) — nahb.org
- U.S. Bureau of Labor Statistics, Occupational Outlook Handbook — bls.gov/ooh
- International Code Council (ICC) — iccsafe.org