Time-of-Use Arbitrage: How Batteries Save Money on Electricity Rates

What Is TOU Arbitrage?

Arbitrage is why many homeowners add storage. Is solar plus battery worth it?

Time-of-use (TOU) arbitrage is the practice of storing electricity when rates are low and using that stored energy when rates are high, capturing the price difference as savings. Solar batteries make this strategy possible by storing cheap solar energy produced during low-rate periods and discharging it during expensive peak periods. This financial mechanism is the primary economic driver for battery storage in markets with significant TOU rate spreads.

Understanding how TOU arbitrage works helps you evaluate battery economics in your specific utility territory and optimize your battery settings for maximum savings.

How It Works

A typical TOU arbitrage day for a solar battery owner looks like this:

1. Morning off-peak (6 AM - 9 AM): Battery may charge from grid at low rates if not full from overnight
2. Midday solar (10 AM - 3 PM): Solar panels power home and charge battery with free solar energy
3. Afternoon peak (4 PM - 9 PM): Battery discharges to power home, avoiding expensive peak rates
4. Night off-peak (10 PM - 5 AM): Home draws cheap grid power; battery charges if rates are favorable

Savings Example

Consider a California home under NEM 3.0 with these rate periods:

• Off-peak rate: $0.12/kWh (midday solar charging)
• Peak rate: $0.45/kWh (evening discharge)
• Daily battery cycle: 10 kWh

Daily savings calculation:

• Value of peak energy avoided: 10 kWh x $0.45 = $4.50
• Cost to charge battery: 10 kWh x $0.12 = $1.20
• Net daily savings: $4.50 - $1.20 = $3.30
• Annual savings: $3.30 x 365 = $1,205

Over 10 years, this generates $12,050 in cumulative savings, approaching the net cost of a single battery after the federal tax credit.

Where TOU Arbitrage Matters Most

Net metering policies affect the math. Compare net metering vs battery storage.

TOU arbitrage provides the strongest returns in markets with large peak-to-off-peak rate spreads:

• California (NEM 3.0): 30-40 cent/kWh spreads between midday and evening
• Arizona (APS/SRP): Significant summer peak rate premiums
• Nevada (NV Energy): Growing TOU rate adoption
• Hawaii: Extreme rate differentials, though solar export value is also high
• Texas (some utilities): Variable but potentially large spreads

Optimizing Arbitrage Settings

Tax credits reduce battery costs. Federal solar tax credit guide.

Most battery systems offer configurable operating modes:

Self-Consumption Mode: Maximizes solar self-use by storing excess solar and discharging during evening peaks. Best for markets with poor net metering.

Time-Based Control: Charges during cheapest rate periods and discharges during most expensive periods. Optimizes for rate arbitrage.

Backup-Only Mode: Keeps battery fully charged for outages, minimizing arbitrage savings but maximizing backup readiness.

Balanced Mode: Combines self-consumption and backup priorities for moderate savings and outage protection.

Advanced Arbitrage Strategies

Sophisticated users can further optimize returns:

• Weather-based pre-charging: Charge battery from grid before forecasted cloudy days when solar production will be limited
• Seasonal schedule adjustments: Modify charging patterns as daylight hours and rate periods change seasonally
• Peak shaving for demand charges: Commercial customers with demand charges can save additional money by limiting peak power draw
• Virtual power plant participation: Some utilities pay premium rates for battery discharge during grid emergencies

Maximizing Your Solar Savings

TOU arbitrage is the key financial mechanism that makes batteries viable in markets without full retail net metering. By shifting solar energy from low-value midday periods to high-value evening peaks, batteries capture value that would otherwise flow to the utility at minimal compensation.

To maximize savings, understand your utility's specific rate structure, configure your battery's operating mode appropriately, and monitor performance to ensure settings optimize for your actual usage patterns. As battery costs continue declining and TOU spreads widen, arbitrage economics will only improve for prepared homeowners.