Time-of-Use (TOU) Tariff

Time-of-Use (TOU) Tariff is a utility electricity pricing structure that divides the 24-hour day, week, and season into distinct rate periods—typically off-peak, shoulder, and peak—charging higher per-kilowatt-hour prices when grid demand is highest and lower rates overnight or during midday renewable generation surpluses.

How it is measured and specified

Under a Time-of-Use schedule, a utility assigns volumetric energy prices (expressed per kWh in local currency) to fixed time blocks—for example, a low overnight off-peak charging window (such as 23:00–06:00), intermediate daytime shoulder hours, and high-cost late-afternoon or early-evening peak hours (such as 14:00–19:00 or 17:00–21:00), often differentiated further between summer/winter seasons and weekdays versus weekends.

For a behind-the-meter battery energy storage system performing daily TOU arbitrage, the net economic value per discharged kilowatt-hour is not simply the gross price difference between the peak tariff (P_peak) and off-peak charging tariff (P_off-peak). Because round-trip efficiency (RTE) losses require more than 1 kWh of charging input to deliver 1 kWh of peak discharge, the effective net spread per discharged kWh is P_peak − (P_off-peak / RTE), before subtracting cyclic battery degradation and O&M costs.

How it matters when sourcing from China

Even when a commercial buyer sources LFP cabinets or containers directly from Chinese Tier-1 manufacturers at competitive FOB prices, TOU arbitrage alone frequently fails to generate a positive Net Present Value (NPV) if the local utility's peak-to-off-peak tariff spread is narrow. As explained in how battery and storage TCO is modelled, our studies evaluate the exact local tariff spread alongside round-trip efficiency losses and degradation rather than assuming every battery pays for itself:

Narrow Spread Without Demand Charges (Negative Arbitrage-Only NPV): In the 3 MWh Middle East & Africa hospital ESS TCO study, the utility tariff offers an off-peak charging rate of $0.023/kWh against a blended avoided peak energy value of $0.11/kWh (at 92% RTE and 85% DoD). Over 15 years, energy-arbitrage savings alone yield a negative NPV (−$874,973), proving that the hospital procurement case must be justified by critical-care outage avoidance or diesel runtime displacement rather than TOU spread alone.
Compressed Municipal Spread: Similarly, in the 100 kWh South African museum battery storage TCO study, charging at an off-peak tariff of ZAR 1.85/kWh and discharging against a peak tariff of ZAR 2.00/kWh at 92% RTE leaves almost no net arbitrage margin once efficiency losses are deducted, making unquantified load-shedding resilience the decisive factor.
Stacked TOU Arbitrage + Peak Shaving (Positive NPV): Conversely, in the 750 kWh EU bottling plant ESS TCO study, combining a €0.09/kWh off-peak charging tariff and a €0.11/kWh peak-to-off-peak spread (€17,154 Year-1 arbitrage savings at 92% RTE across 260 days/yr) with €33,300/yr in monthly peak shaving demand-charge reductions produces a positive 10-year NPV of €23,115 and an 8.3-year simple payback.

What to confirm before procurement

Calculate your efficiency-adjusted net TOU spread (P_peak − P_off-peak / RTE) using your actual utility tariff schedule before requesting Chinese BESS quotations.
Check whether the off-peak charging window is wide enough (in hours) to recharge the battery at its rated C-rate without triggering an off-peak demand spike.
Confirm that the supplier's Energy Management System (EMS) supports multi-window seasonal and weekday/weekend TOU dispatch schedules.