EV Charging Schedule Optimizer

The EV Charging Schedule Optimizer determines the cheapest charging window based on your departure time, electricity rates, and vehicle battery specifications.

When to Charge: Peak vs Off-Peak Pricing Explained

TOU electricity pricing divides the day into rate tiers that reflect the cost of generating and distributing power during different demand periods. The mechanics are straightforward: when millions of households run air conditioning, cook dinner, and watch television between 4 pm and 9 pm, the grid strains to keep up. Utilities meet that demand by firing up expensive peaker plants — often natural gas turbines — that cost far more per kWh to operate than baseload generators. TOU pricing passes those cost differences through to consumers as an incentive to shift flexible loads to cheaper hours.

A typical US time-of-use structure looks like the following breakdown.

• Off-peak (9 pm or midnight to 6 or 7 am): The cheapest window, when grid demand drops to its daily minimum. Rates often fall 40% to 70% below peak prices.
• Shoulder or mid-peak (6 am to 4 pm): Moderate pricing. Some utilities collapse this into two tiers; others use a flat rate for the entire daytime period.
• Peak (4 pm to 9 pm): The most expensive window, coinciding with residential demand surges. This is the worst time to charge an EV at home.

The exact hours and rate levels vary by utility, season, and region. California utilities like PG&E shift their peak window later in summer (when air conditioning demand extends into the evening) and offer EV-specific plans with extended off-peak windows. Arizona's APS offers one of the country's steepest TOU spreads at $0.07 off-peak versus $0.24 peak. In the UK, Economy 7 and Octopus Go tariffs provide 7 to 8 hours of deeply discounted overnight rates. To see exactly how much these rate differences affect your monthly bill, check the residential and TOU rates for your specific region.

How the Optimizer Calculates Your Best Window

The scheduling algorithm works backward from the departure time to find the latest possible start that still completes charging before the car is needed. Starting as late as possible keeps the most charging hours within the cheapest rate window.

The core calculation follows three steps.

1. Energy required: Multiply the usable battery capacity by the difference between the target and current SoC, then divide by charger efficiency (typically 90% for Level 2). For a 75 kWh battery charging from 30% to 80%: 75 x 0.50 / 0.90 = 41.67 kWh drawn from the wall.
2. Charging duration: Divide the energy required by the charger's power rating. At 11.5 kW: 41.67 / 11.5 = 3 hours 37 minutes.
3. Start time: Subtract the duration from the departure time. For a 7:00 am departure: 7:00 am minus 3h 37m = 3:23 am start.

If the calculated start time falls within the off-peak window, the entire session charges at the cheapest rate. If the session would need to begin before the off-peak window starts — say, because the battery needs 9 hours on a Level 1 charger but off-peak only runs for 7 hours — the optimizer flags the overlap and shows the blended cost. In that scenario, upgrading to a faster Level 2 charger can compress the session into the off-peak window entirely.

Common Scheduling Pitfalls and Fixes

Scheduled charging sounds simple in theory: plug in, set a timer, wake up to a charged car. In practice, several issues can trip up even experienced EV owners. The following troubleshooting flow covers the most common problems and their solutions.

Pitfall: Off-peak window is too short for the required charge. This happens most often with Level 1 charging (1.4 kW) or when a large battery needs a deep charge (e.g., 10% to 90% on a 100 kWh pack). Two fixes apply: reduce the target SoC to 80% (recommended for daily driving anyway, and better for long-term battery health), or increase the charger power. Moving from Level 1 to even a modest 7.7 kW Level 2 circuit typically cuts charging time by 80%, fitting almost any session into a 7-hour off-peak window.

Pitfall: Utility does not offer a TOU plan. Some utilities — particularly rural cooperatives and municipal providers — charge a flat rate around the clock. In that case, scheduling provides no financial benefit and the vehicle can charge at any time. However, flat-rate utilities sometimes offer separate EV tariffs on a dedicated meter. Check with your provider, as these programmes are expanding rapidly across the US.

Pitfall: Weekend and holiday schedules differ. Many TOU plans have different rate windows on weekends — some utilities charge off-peak rates all day Saturday and Sunday. If the vehicle's built-in timer only supports a single schedule, set it for the weekday off-peak window (the more expensive scenario) and accept that weekend charging may cost less regardless of timing. Smart chargers with app-based scheduling often support separate weekday and weekend programmes.

Pitfall: Vehicle timer and charger timer conflict. If both the vehicle and the smart charger have scheduling enabled, they can interfere with each other — the charger may delay power delivery while the vehicle simultaneously delays its own charging request, resulting in the session never starting. The fix is simple: use one timer or the other, not both. Most EV owners find the vehicle's built-in departure scheduling more reliable, since it accounts for battery pre-conditioning in cold weather.

How Smart Chargers and Vehicle Timers Work

Two independent systems can control when an EV charges: the vehicle's onboard scheduling software and the charging station's own timer or smart features. Understanding which to use — and when — avoids confusion and ensures sessions happen as planned.

Most modern EVs include a departure-time feature accessible through the infotainment system or companion app. Set the time the car needs to be ready, and the vehicle's BMS calculates when to begin drawing power. Tesla's system, for example, factors in cabin pre-conditioning (heating or cooling the interior using grid power rather than battery), so the car is both charged and climate-ready at departure. Hyundai and Kia's systems allow setting different schedules for different days of the week. Ford's FordPass app supports location-based scheduling — the car recognises the home charger and only applies the delayed start at that location.

Smart chargers (ChargePoint Home Flex, Wallbox Pulsar Plus, Grizzl-E Smart, Emporia Level 2) add another layer of control. These units connect to WiFi and offer app-based scheduling, energy monitoring, and sometimes integration with utility TOU rate data. Some models — notably the ChargePoint and Wallbox — support dynamic load management, adjusting charging speed based on household demand to avoid tripping the main breaker. The smart charger comparison guide covers the features and trade-offs of popular models.

For most owners, the vehicle's built-in scheduling is the simpler choice. Smart charger scheduling becomes valuable when managing multiple EVs on a single circuit, when the utility offers a demand-response programme that requires the charger to communicate with the grid, or when the owner wants granular energy tracking that the vehicle does not provide.

From Industrial Meters to Smart EV Tariffs

Time-varying electricity pricing is not a modern invention. Utilities have charged industrial customers different rates for peak and off-peak consumption since the early 20th century, when mechanical demand meters recorded maximum power draw during billing periods. The concept was simple: factories that ran heavy equipment during the day, when everyone else also needed power, paid more than those willing to operate overnight shifts.

Residential TOU pricing emerged much later. In the 1970s, the US energy crisis prompted experimental TOU programmes aimed at flattening residential demand curves. These early programmes required special meters that tracked consumption by time period — expensive to install and maintain. Adoption was slow and largely voluntary through the 1980s and 1990s.

The rollout of digital smart meters in the 2010s changed the economics. Smart meters record consumption in 15-minute or hourly intervals and transmit data wirelessly, making TOU billing practical at scale. California mandated TOU as the default residential rate structure in 2020, and several other states followed with optional TOU programmes. The growth of residential solar and battery storage added another dimension: net metering credits and export rates now also vary by time of day in some markets.

EV-specific tariffs represent the latest evolution. Recognising that EVs are large, flexible loads that can charge at any hour, utilities began offering dedicated EV rates with deeper off-peak discounts than standard TOU plans. The UK's Octopus Intelligent Go tariff, launched in 2022, introduced smart integration: the tariff communicates with compatible chargers and vehicles to automatically shift charging to the cheapest half-hour slots, even interrupting and resuming sessions as prices fluctuate. This model — where the tariff and the charger coordinate dynamically — is likely the future of residential EV charging in markets with variable wholesale pricing.

Weeknight TOU Scheduling for a California Commuter

A Tesla Model 3 Long Range owner in the San Francisco Bay Area plugs in at 6 pm with 30% battery remaining after the day's commute. The departure time is 7 am, and the utility (PG&E EV-B rate) charges $0.16/kWh off-peak (midnight to 3 pm) and $0.42/kWh peak (4 pm to 9 pm).

Energy required: 75 kWh x (0.80 - 0.30) = 37.5 kWh. With 90% charger efficiency: 37.5 / 0.9 = 41.67 kWh from the wall. At 11.5 kW, this takes 41.67 / 11.5 = 3.62 hours, or 3 hours 37 minutes. The optimal start is 7:00 am minus 3 hours 37 minutes = 3:23 am — well within the midnight-to-3-pm off-peak window.

At the off-peak rate, the session costs 41.67 x $0.16 = $6.67. Charging immediately at peak rates would cost 41.67 x $0.42 = $17.50. The nightly saving of $10.83 compounds to over $238 per month across 22 workdays. Over a year, that is nearly $2,860 saved by a simple timer adjustment.

UK Economy 7 Schedule with a Large-Battery SUV

A Kia EV9 owner in southern England charges on an Economy 7 tariff: 7.5p/kWh from midnight to 7 am, and 35.5p/kWh at all other times. The vehicle has a 96 kWh usable battery, an 11 kW onboard charger, and currently sits at 35% SoC. The target is 80% for a 7:30 am school run.

Energy required: 96 x (0.80 - 0.35) = 43.2 kWh. With efficiency: 43.2 / 0.9 = 48.0 kWh. Charging time at 11 kW: 48.0 / 11 = 4.36 hours, or 4 hours 22 minutes. The optimal start time is 7:00 am (allowing a 30-minute buffer before departure) minus 4 hours 22 minutes = 2:38 am. The entire session fits within the midnight-to-7-am off-peak window.

Off-peak cost: 48.0 kWh x 7.5p = 360p = £3.60. At the standard rate, the same session would cost 48.0 x 35.5p = 1,704p = £17.04. The daily saving of £13.44 totals £295.68 per month. Even with the larger battery, the 7-hour Economy 7 window provides ample time at 11 kW. A vehicle with only a 7.4 kW onboard charger would need 6 hours 29 minutes for the same session — still within the window, but with less margin.

Time-of-Use Rate

A time-of-use rate structure charges different per-kWh prices depending on when electricity is consumed. The cheapest tier (off-peak) typically covers overnight hours when grid demand is lowest, while the most expensive tier (peak) covers late afternoon and evening hours when demand surges. TOU plans are the primary mechanism through which EV owners reduce home charging costs, and most modern smart meters support them.

Smart Charger

A smart charger is a Level 2 EVSE with WiFi or cellular connectivity that enables remote scheduling, energy monitoring, and sometimes dynamic load balancing through a companion app. Smart chargers differ from basic (dumb) units in their ability to respond to external signals — time-of-use rate schedules, utility demand-response events, or solar production data from a home energy system.

Departure-Time Scheduling

Departure-time scheduling is a vehicle-side feature that delays the start of a charging session so that the battery reaches the target SoC just before the owner needs the car. The vehicle's software calculates the required charging duration, subtracts it from the set departure time, and begins drawing power at the computed start time. Some implementations also pre-condition the cabin (heating or cooling) using grid power rather than battery reserves, so the vehicle is both charged and comfortable at departure.

Finding the optimal charging window starts with knowing the rates — compare residential and TOU electricity prices across regions to see how your area stacks up. For a broader view of how daily charging patterns interact with battery longevity, the battery degradation estimator models the effect of SoC range, temperature exposure, and charging frequency on long-term capacity retention. And for drivers weighing overall EV running costs, comparing total fuel expenditure against a petrol equivalent puts scheduling savings in context.