Residential EV charging cost patterns across time-of-use rates

Why hourly cost patterns matter beyond simple $/kWh

Utility rate marketing typically quotes a single average per-kilowatt-hour (kWh) price. That number conceals an important fact: for TOU rate structures, the price a household actually pays depends entirely on when the EV charges. A reference 2026 Tesla Model Y Long Range at 12,000 mi/yr consumes approximately 3,120 kWh of charging per year, representing roughly 20–30% of a typical US household's annual electricity usage. That volume is large enough that the hour-of-day the charging happens materially shapes the household bill.

The specific hour-by-hour cost curve each utility imposes also determines what charging flexibility looks like. On some utilities, a window as narrow as 4–6 hours overnight offers deep super-off-peak discounts and the rest of the day is comparably expensive. On others, roughly half the day is off-peak at a more modest discount. These two patterns produce very different optimal household behaviors even when the average per-kWh rate is similar.

The analysis below walks through four specific utility territories representing the range of US TOU rate designs, then quantifies what the hourly pattern means in actual annual dollars.

Reference EV annual charging cost by territory

Translating the hourly cost curves above into annual household impact requires two assumptions: the vehicle's annual kilowatt-hour consumption (3,120 kWh for a 2026 Tesla Model Y Long Range at 12,000 mi/yr) and the fraction of charging that falls in each rate tier. The analysis below assumes an optimally-scheduled driver who charges 100% overnight within the super-off-peak or deepest-discount window available on each utility — the best-case scenario representing a driver who has fully adopted smart charging and whose vehicle is routinely plugged in overnight.

Even under this optimal scheduling assumption, the spread across territories is substantial.

The optimal overnight charging window

Each utility's deepest-discount window has a specific shape. Three of the four utilities analyzed above offer their deepest discount during a narrow overnight window (midnight to roughly 5–8 AM); one (Eversource) offers a longer but shallower off-peak period extending from midnight through noon. These differences matter for households whose vehicles may not always be plugged in during a specific narrow window.

• Xcel Colorado EV Service · 5-hour super off-peak (midnight–5 AM) at $0.08/kWh. Requires reliable overnight plugging-in by midnight to capture full savings. Charging that spills into 5–6 AM lands in the mid-peak tier at $0.14/kWh.
• Ameren Missouri EV Overnight · 5-hour super off-peak (midnight–5 AM) at $0.07/kWh. Same structural pattern as Xcel but on a dedicated EV sub-meter, so household non-EV usage stays on standard rate without peak-hour exposure.
• PG&E EV2-A · 15-hour super off-peak (midnight–3 PM) at $0.32/kWh. Very wide super off-peak window makes timing less critical, but absolute price is still high even at the discount.
• Eversource Massachusetts R-4 TOU · 12-hour off-peak (midnight–noon) at $0.19/kWh. No "super off-peak" tier; the off-peak rate applies uniformly across the window.

The practical implication: households on Xcel or Ameren need disciplined overnight charging timing to realize the posted discount; households on PG&E or Eversource have more scheduling flexibility but face higher absolute rates even at discount tiers.

The charging-timing penalty quantified

What happens when charging isn't perfectly timed? The question matters because real-world households don't always plug in overnight — forgotten plug-in events, mid-day top-ups after errands, visitors needing a quick charge, teen drivers charging after school. The dollar impact of these timing deviations varies dramatically by utility.

Three distinct patterns emerge from the chart. On high-rate utilities like Pacific Gas & Electric EV2-A, the gap between a disciplined overnight charger ($998/yr at 100% off-peak) and a casual charger ($2,028/yr at 100% peak) exceeds $1,000/yr. On Xcel Colorado, the same discipline matters but the absolute dollar impact is smaller ($250/yr spread). On Ameren Missouri's EV sub-meter rate, the entire household cost range is modest regardless of charging timing because the maximum rate stays reasonable.

The practical lesson: on expensive-market utilities (California, Northeast), smart charging automation and consistent overnight plug-in habits are high-value. On moderate-rate midwest utilities, timing discipline matters but failure to achieve perfect timing is less costly. On sub-metered EV rates, the structure essentially removes the timing-penalty risk entirely.

Seasonal and weekday-weekend variation

The 24-hour cost curves shown above represent summer weekday patterns, which is when most TOU rates impose their highest peak prices. Three additional patterns shape real-world annual charging cost.

Weekends typically have no peak period. On most US EV TOU rates, Saturday and Sunday charge at off-peak or super off-peak rates all day, regardless of hour. For households with weekend-heavy driving (recreational use, errand concentration), weekend charging is often the cheapest available window across all 168 hours of the week.

Winter peak hours shift earlier. Summer peak windows on most US utilities run approximately 4–9 PM to capture air-conditioning load. Winter peak windows on the same utilities often shift to 6–9 AM and 5–8 PM to capture heating load. Households that establish an overnight charging routine in summer may inadvertently charge during morning winter peak windows without realizing the rate structure has shifted.

Shoulder seasons (spring/fall) often have the deepest discounts. Some utilities (notably Xcel Colorado) extend their super-off-peak window during low-demand months, offering 6–8 hour super-off-peak windows instead of the 4–5 hour summer window. Households that charge primarily during spring and fall benefit from the extended discount availability.

5-year compound charging cost projections

Annual cost differences compound meaningfully over typical EV ownership horizons. The chart below projects cumulative home charging cost over 5 years across three scenarios on four representative utilities: the optimal case (100% off-peak timing), the moderate case (70% off-peak), and the unmanaged case (40% off-peak, 60% at mixed higher-rate tiers). All three scenarios use the same reference vehicle (Tesla Model Y Long Range) and same mileage (12,000 mi/yr).

The lesson is consistent across utilities: smart charging automation that captures the optimal window represents meaningful 5-year savings even in low-rate midwest markets, and transformative savings in high-rate California or Northeast markets.

Smart charging automation that captures the savings

The dollar savings documented above are realizable only to the degree that charging actually happens during the correct window. For households attempting to manage this manually (checking the clock, remembering to plug in by a specific time, unplugging before peak hours start), consistent capture is realistically 60–80% of the theoretical maximum. Smart charging automation can push realized capture to 95%+ with minimal household effort.

Four tiers of smart charging automation are commonly available in 2026:

• Vehicle-based scheduling. Nearly every 2022+ EV allows the driver to set a "charge start time" in the vehicle's own menu or mobile app. The driver plugs in whenever convenient; the vehicle delays start until the scheduled hour. Zero additional hardware cost; requires only user discipline to set the schedule correctly for the local utility rate.
• Charger-based scheduling. Smart Level 2 chargers (ChargePoint Home Flex, JuiceBox 40, Wallbox Pulsar Plus, Emporia EV Charger) support independent scheduling that works regardless of vehicle. Useful for households with mixed vehicles or vehicles whose own scheduling is unreliable. $500–$800 charger cost already common.
• Utility managed charging program enrollment. ConnectedSolutions (MA/RI), SmartCharge NY, Charging Perks (CO), and similar programs schedule charging on the household's behalf and pay the household for allowing it. The EV charger VPP guide covers the full program landscape; the key point here is that enrolled households automatically capture optimal charging windows without needing to manage timing themselves.
• Dynamic rate automation. Utilities with hourly or real-time pricing (ComEd Hourly, Griddy-style markets) require automation that reads the live price and starts/stops charging accordingly. ChargePoint Home Flex, Emporia EV Charger, and some vehicle apps support this. Essential for hourly rates; irrelevant for standard TOU rates.

For households on standard TOU rates (Archetypes B and C in the Utility Rate Evaluation Framework), vehicle-based scheduling (tier 1) captures nearly all available savings at zero incremental cost. For households on managed charging programs or hourly rates, charger-based or utility-managed automation is worth the hardware investment.

Further economic considerations

Several additional factors shape whether the documented cost patterns translate directly to household savings beyond the mechanics covered above.

The combined rate-plus-vehicle optimization effect. Rate-side savings compound favorably with vehicle efficiency choices. A household on Pacific Gas & Electric EV2-A driving a Tesla Model Y (26 kWh/100mi) at 100% super off-peak sees roughly $980/yr in home charging cost. The same household driving a less efficient 2026 Rivian R1S (approximately 42 kWh/100mi) at the same mileage would see $1,572/yr — a $592/yr efficiency penalty on expensive-market utilities. On low-rate Ameren Missouri, the same efficiency difference translates to only $130/yr. Vehicle efficiency matters more on high-rate utilities, which has implications for vehicle selection in high-electricity-cost markets.

Daytime workplace or public charging shifts the math. Households whose vehicles charge primarily at workplace Level 2 or during midday errand runs at commercial Level 2 charging are often paying flat commercial rates (typically $0.20–$0.35/kWh) rather than residential TOU rates. For these households, the residential TOU analysis above doesn't directly apply — and the economics typically favor shifting more charging home when possible to access the TOU rate structure.

Solar households capture the pattern differently. Households with rooftop solar generation offset grid-sourced electricity with on-site generation. If charging happens during solar generation hours (midday), the effective per-kWh cost drops to the marginal grid-tie cost, which is near zero in net-metering states and even lower in some tariff structures. For solar households, the "optimal charging window" shifts from overnight to midday — the inverse of the standard TOU recommendation. The Utility Rate Evaluation Framework discusses solar interactions in more detail.

Hourly real-time pricing represents a different optimization problem. Utilities offering hourly or real-time pricing (ComEd Hourly in Illinois, retail choice markets in Texas and the Northeast) impose an entirely different charging-cost pattern than fixed TOU rates. Hourly prices can swing from $0.04/kWh during low-demand overnight to $0.50+/kWh during grid stress events. The patterns in this case study (24-hour cost curves) are structural simplifications of what hourly pricing actually looks like. Households on these rates benefit from charging automation that responds to live pricing signals rather than fixed clock-based schedules.

Rate case activity can shift these patterns substantially. The cost curves and annual projections above reflect Q3 2026 published rates on each utility. Rate case decisions typically occur every 1–3 years and can change peak hours, discount tiers, or supply portions by 20–40%. Massachusetts specifically has had unusually volatile basic service supply resets (every 6 months) through 2024–2026; California, Colorado, and the Northeast IOUs are all mid-cycle in rate cases that may shift these numbers through 2027–2028.

The utility rate equity question. Deeply discounted EV TOU rates (Xcel Colorado's $0.08/kWh super off-peak, Ameren Missouri's $0.07/kWh EV-only rate) concentrate benefit on households that can shift usage overnight — typically higher-income, single-family-home demographics with new EVs. The fixed-cost infrastructure of the grid is paid by all ratepayers. Regulators in several deep-dive territories are actively debating how to balance EV-friendly rate design against broader equity considerations. The cost patterns documented here reflect today's structure; future rate case decisions may compress some of the deeper discounts observed through 2026.

Method. Hourly rate patterns in Chart 1 reflect summer weekday structures for each utility as published in Q3 2026 tariffs; actual rate schedules vary by season and may include surcharges or riders not fully reflected. Annual cost calculations assume a reference 2026 Tesla Model Y Long Range at 26 kWh/100mi, 12,000 miles per year, 100% home charging. Deepest-discount rates for Chart 2 reflect each utility's best available EV rate under optimal scheduling; real-world households typically land 10–25% higher due to incomplete timing capture. The charging-timing penalty curve (Chart 3) models linear interpolation between off-peak and peak rates; actual multi-tier rates (PG&E, SCE) have intermediate tier pricing that produces slight non-linearities not captured in the simplified model. 5-year projections (Chart 5) assume rates held constant over the 5-year window; actual rate case activity will shift these numbers. Weekday/weekend/seasonal variations in Chart 4 reflect typical rate design patterns; some utilities deviate from the shown pattern. All numbers are estimates for guidance; individual household outcomes vary with specific vehicles, mileage, charging schedule compliance, and utility rate structure as of the actual purchase/enrollment date.