How do I estimate shifted kWh?

Use telematics or charger logs to measure energy delivered during controllable windows over a representative month. Aggregators can export these figures directly.

Can I include vehicle-to-grid exports?

Yes. Treat exported energy as shifted kWh with the peak rate equal to the avoided retail tariff and the off-peak rate equal to any remuneration or opportunity cost during discharge.

Why might demand savings be zero?

If you leave demand inputs blank or set either the reduction or rate to zero, the calculator conservatively assumes no demand-charge benefit to avoid overstating savings.

How to Calculate EV Managed Charging Savings

Managed charging software lets fleets reshuffle load into cheaper time-of-use (TOU) windows and cap simultaneous charging to avoid demand charges. Finance teams need a transparent calculation to translate those operational controls into dollars saved per month. This walkthrough outlines the required inputs, formulas, and validation steps so savings claims can withstand procurement, utility, and sustainability reviews.

The approach complements tariff risk assessments in the EV demand charge exposure guide and energy arbitrage thinking from the battery arbitrage walkthrough, helping teams build integrated electrification business cases.

Definition and scope

Managed charging savings represent the difference between what a fleet would have paid at baseline charging behaviour and what it pays after shifting energy to off-peak TOU windows and smoothing peaks to reduce demand charges. Savings are calculated monthly, in dollars, and separated into energy and demand components to match utility invoices.

The calculation assumes vehicles still receive the same total energy (kWh) per month; only the timing changes. It also assumes the managed profile remains within charger and electrical service constraints documented during design.

Variables and units

Gather the following data in consistent units:

E_shift – Energy shifted from peak to off-peak windows (kWh/month).
r_peak – Peak energy rate ($/kWh).
r_off – Off-peak energy rate ($/kWh).
ΔP – Reduction in monthly peak demand due to managed charging (kW).
r_d – Demand charge rate ($/kW).
S_E – Energy savings ($/month).
S_D – Demand savings ($/month).
S_T – Total savings ($/month).

If TOU schedules change seasonally, gather rates for the specific billing cycle. Use metered demand reduction rather than modelled values when possible. When EVs backfeed via vehicle-to-grid (V2G), treat exported energy as part of E_shift with r_peak equal to the avoided retail rate.

Formulas

Calculate savings with two linear expressions:

S_E = E_shift × max(r_peak − r_off, 0)

S_D = ΔP × r_d

S_T = S_E + S_D

The max operator prevents negative savings if off-peak rates ever exceed peak rates. Demand savings require both a non-zero ΔP and demand charge rate; otherwise S_D is zero. Keep results to two decimal places to match utility billing conventions.

Step-by-step workflow

1. Establish the baseline

Determine monthly kWh delivered under uncontrolled charging and the coincident peak demand at the service meter. Pull these from utility interval data or charger management systems. Confirm the tariff’s TOU rates and demand charge structure.

2. Measure managed performance

After deploying managed charging, track the kWh shifted into off-peak windows and the new peak demand. Many platforms report these directly; otherwise compute them by comparing interval load shapes. Adjust for any seasonal rate changes.

3. Calculate energy savings

Multiply E_shift by the difference between peak and off-peak rates. If the rate differential is negative, set S_E to zero to avoid overstating benefits. Document the rate sources for auditability.

4. Calculate demand savings

Multiply ΔP by the tariff’s demand charge rate. If your tariff has multiple demand components (e.g., distribution and transmission), compute each separately and sum. When managed charging shifts but does not reduce the billing determinant (such as ratchet clauses), set ΔP to zero for those components.

5. Combine and validate

Add S_E and S_D to obtain total monthly savings. Reconcile against utility bills to ensure demand determinants and TOU periods match the calculation. If differences arise, adjust inputs or investigate metering issues.

Validation and monitoring

Validate rate tables against utility tariffs each season, and confirm meter multipliers have not changed. Compare managed load profiles against charger schedules to ensure vehicles are actually adhering to dispatch commands. For finance, reconcile calculated savings with general ledger entries to avoid double counting incentives or credits.

Track savings intensity per vehicle or per mile to understand marginal benefits of adding more EVs. If savings erode, investigate drivers such as higher off-peak rates or insufficient staggered scheduling.

Limits and considerations

The calculation assumes the same total energy is delivered; if range anxiety causes undercharging, operational impacts may outweigh bill savings. Demand savings can disappear if a single unmanaged session sets the billing peak, so procedural compliance matters. Finally, ancillary revenues from grid services are out of scope and should be modelled separately.

Consider resilience constraints: some depots keep a minimum state of charge for backup power or emergency dispatch. Those constraints may limit E_shift and should be reflected in assumptions shared with stakeholders.

Embed: EV managed charging savings calculator

Enter shifted kWh, TOU rates, and any demand reduction to see monthly energy, demand, and total savings in dollars.

EV Managed Charging Savings Calculator

Quantify avoided energy spend and demand charges from managed EV charging that reshapes load away from peak periods.

Financial planning aid. Reconcile outputs with utility tariffs and demand metering data before booking savings in budgets.