Time-of-Use Battery Savings: Peak Shaving Strategies That Work

Quick Answer

Time-of-use (TOU) battery savings represent the single biggest financial benefit of home battery storage. By strategically charging during off-peak hours and discharging during expensive peak periods, homeowners routinely save 40-70% on their electricity bills. With peak rates in many markets exceeding $0.40-0.50/kWh and off-peak rates below $0.15/kWh, the rate differential alone can justify a battery investment within 5-8 years.

Key Takeaways

Peak-to-off-peak rate spreads of $0.20-0.35/kWh create substantial arbitrage opportunities for battery owners, especially in California, New York, and other high-cost markets
Automated TOU optimization through smart battery apps eliminates the need for manual scheduling and maximizes daily savings
Summer months provide the highest savings due to extended peak windows and elevated rates, with some homeowners saving $200-300/month
NEM 3.0 makes battery storage essential for new California solar installations, as export credits dropped by 75-80%
Strategic partial charging during shoulder periods can capture additional savings between peak and off-peak rates
Combining TOU optimization with solar self-consumption doubles the effective savings compared to either strategy alone

Understanding Time-of-Use Rate Structures

Time-of-use pricing is the foundation of battery savings strategy. Utilities divide each day into two or three pricing tiers:

Peak periods (highest rates, typically $0.35-0.55/kWh): Usually 4-9 PM on weekdays when grid demand peaks from air conditioning, cooking, and electronics use. Some utilities split this into “peak” and “super-peak” during summer.

Off-peak periods (lowest rates, typically $0.10-0.18/kWh): Usually 11 PM to 7 AM when grid demand is lowest and renewable energy may even create surplus. This is your charging window.

Shoulder/mid-peak periods (moderate rates, typically $0.20-0.30/kWh): Transition hours between peak and off-peak. Some strategies can capture value here too.

The key metric is the rate spread — the difference between peak and off-peak rates. A $0.30/kWh spread with a 13.5 kWh battery and 90% efficiency yields roughly $3.65 in daily arbitrage value, or about $1,330 annually before degradation.

Peak Shaving Strategy #1: Simple Daily Cycling

The most straightforward approach charges your battery completely during off-peak hours and discharges fully during peak hours. This requires minimal configuration and works with any battery system.

Daily savings calculation:

Battery capacity: 13.5 kWh (e.g., Powerwall 3)
Round-trip efficiency: 90%
Usable energy: 13.5 × 0.90 = 12.15 kWh
Rate spread: $0.45 peak - $0.15 off-peak = $0.30/kWh
Daily value: 12.15 × $0.30 = $3.65
Annual value: $3.65 × 365 = $1,332

For a deeper dive into calculating these savings precisely, use our peak shaving calculator which accounts for your specific rate structure.

Peak Shaving Strategy #2: Solar-Enhanced Arbitrage

When you pair your battery with solar panels, the economics improve dramatically. Instead of buying off-peak grid power to charge your battery, you use free solar energy — reducing your effective charging cost to zero.

Enhanced savings with solar:

Charging cost: $0 (solar surplus)
Discharge value at peak rate: 12.15 kWh × $0.45 = $5.47/day
Annual value: $5.47 × 365 = $1,997

This nearly doubles the simple arbitrage value because you eliminate the off-peak charging cost entirely. The home battery payback calculator can model this combined scenario.

The critical timing shift: Without a battery, your solar peaks at noon when rates may be low. The battery stores that noon surplus and delivers it at 6 PM when rates peak. This time-shift is the core value proposition.

Peak Shaving Strategy #3: Demand Charge Management

Some utilities charge commercial and residential customers based on their highest 15-minute power draw (measured in kW). A battery can “shave” these peaks by supplementing grid power during high-demand moments.

Even if your utility doesn’t currently have demand charges, the strategy is worth understanding because many utilities are transitioning toward demand-based pricing. A battery installed today positions you ahead of this trend.

Demand charge savings example:

Peak demand without battery: 8 kW
Peak demand with battery: 4 kW (battery supplies the rest)
Demand charge: $15/kW/month
Monthly savings: (8-4) × $15 = $60
Annual savings: $720

Seasonal TOU Optimization

Rate structures change seasonally, and your battery strategy should adapt accordingly.

Summer Strategy (June-September)

Summer offers the highest savings potential due to extended peak windows and elevated rates. Key adjustments:

Extend discharge window: Summer peaks may last 5-6 hours instead of 3-4
Pre-cool your home: Use excess solar/off-peak power to cool your home before peak hours, then reduce AC during peak
Save battery for late afternoon: Solar production drops after 4 PM, but peak rates may continue until 9 PM

Winter Strategy (October-May)

Winter savings are typically lower but still meaningful:

Shorter peak windows: May only need 60-70% of battery capacity
Shifted peak times: Winter peaks often shift to morning (6-9 AM) and early evening (5-8 PM)
Heating optimization: Electric heating creates high morning demand — your battery can cover this

Utility-Specific TOU Strategies

California (PG&E, SCE, SDG&E)

Under NEM 3.0 battery savings rules, California homeowners with new solar installations receive dramatically reduced export credits. Battery storage is now essential to capture value:

PG&E EV2-A rate: Peak $0.42-0.55/kWh, off-peak $0.14-0.18/kWh
SCE TOU-D-PRIME: Peak $0.38-0.52/kWh, off-peak $0.12-0.16/kWh
Recommended strategy: Charge from solar during midday, discharge 4-9 PM

New York (ConEdison)

ConEdison’s smart charge rate offers significant TOU spreads:

Summer peak: $0.25-0.35/kWh
Off-peak: $0.08-0.12/kWh
Additional value from NYC’s Local Law 97 compliance

Texas (Oncor, CenterPoint)

Texas doesn’t have traditional NEM, but TOU plans from retail providers like Griddy and Energy Ogre create opportunities:

Wholesale price spikes during summer can exceed $2-5/kWh
Battery owners can avoid these spikes entirely
Grid frequency regulation payments may be available

Smart Battery Automation

Modern battery systems include intelligent automation:

Tesla Powerwall: “Time-Based Control” mode automatically optimizes charge/discharge based on your TOU schedule. Set it once and it adjusts daily.

Enphase IQ: The Enphase App provides “Savings Mode” that learns your consumption patterns and rate schedule to maximize TOU savings.

Sonnen eco: ” Sonnen ecoLinx” integrates with smart home systems for predictive optimization based on weather forecasts and usage patterns.

FranklinWH: The energy management system automatically prioritizes between solar, battery, and grid based on real-time rate optimization.

Measuring Your TOU Savings

Track your battery’s actual performance with these metrics:

Daily arbitrage value: kWh discharged × peak rate minus kWh charged × off-peak rate
Self-consumption ratio: Percentage of solar energy used on-site vs exported
Grid independence score: Percentage of total consumption met by solar + battery
Monthly bill comparison: Same-month year-over-year comparison controls for seasonal variation

Most battery apps provide these metrics automatically, but calculating them independently from your utility bill gives you a reality check.

Common TOU Strategy Mistakes

Mistake 1: Charging from grid when solar is available. Always prioritize solar charging over grid charging. The only exception is if off-peak rates are literally $0 (some plans offer this for limited hours).

Mistake 2: Ignoring weather forecasts. On cloudy days, your solar won’t produce enough surplus to fully charge the battery. Pre-charging from the grid during off-peak hours before a cloudy day prevents running out during peak.

Mistake 3: Discharging too early. If your peak window starts at 4 PM, don’t start discharging at 2 PM. You’ll run out of battery before the most expensive hours.

Mistake 4: Not recalibrating seasonally. Rate structures change, your consumption changes, and days get longer or shorter. Review your strategy quarterly.

Mistake 5: Forgetting about degradation. A 13.5 kWh battery at year 10 might only have 10.5 kWh of capacity. Account for this in your long-term savings projections.

Financial Modeling for TOU Savings

For a precise financial model, you need:

Your utility’s exact TOU schedule and rates for all seasons
Your hourly consumption profile (available from your smart meter)
Solar production estimate (PVWatts or similar)
Battery specifications (capacity, efficiency, degradation rate)
Rate escalation assumption (typically 2-4% annually)

Our home battery payback calculator handles all of these inputs and generates a year-by-year projection including degradation and rate escalation.

FAQ

How much can I save with TOU rate optimization using a home battery?

Most homeowners save 40-70% on their electricity bills by strategically charging their battery during off-peak hours and discharging during peak hours. In high-rate areas like California, annual savings can exceed $2,000.

What is the best charging and discharging schedule for TOU rates?

The optimal schedule charges your battery during the cheapest off-peak window (typically 11 PM to 7 AM), holds charge during shoulder periods, and discharges during the peak window (typically 4-9 PM). Smart battery systems automate this based on your utility’s rate schedule.

Should I adjust my battery strategy seasonally?

Yes. Summer months usually have higher peak rates and longer peak windows, so your battery provides more value. In winter, peak windows may shift earlier. Most smart battery apps automatically adjust for seasonal TOU changes.

Do all utilities offer time-of-use rates?

Most major utilities now offer TOU rate plans, especially for solar customers. Under NEM 3.0 in California, TOU rates are mandatory for new solar installations. Check with your utility for available rate schedules.

Can I use solar directly during peak hours instead of a battery?

Solar production typically declines during late afternoon peak hours (4-7 PM), which is exactly when rates are highest. A battery bridges this gap by storing midday solar surplus and discharging during peak evening hours when solar alone can’t meet demand.

What’s the difference between peak shaving and load shifting?

Peak shaving reduces your maximum demand (measured in kW) to lower demand charges, while load shifting moves energy consumption from expensive to cheap time periods (measured in kWh). Home batteries primarily do load shifting on TOU plans, but can also provide peak shaving for commercial applications.