Affiliate disclosure

WattSage is reader-supported. As an Amazon Associate we earn from qualifying purchases. This page contains affiliate links to tools that pair with the calculator. See our Affiliate Disclosure. Disclaimer: this calculator provides estimates only, not financial advice. Actual results vary based on installer pricing, utility rate changes, and usage patterns.

Quick scenario presets

Not sure where to start? Click a preset to load typical values for common U.S. homeowner profiles:

Your home & system

Default $12,500 = typical 13.5 kWh install. See full cost breakdown →
U.S. average is 28 kWh/day. Check your utility bill.
What you pay per kWh overnight (cheapest hours).
What you pay per kWh during peak hours (4–9 PM).
How many kWh per day your battery shifts from peak to off-peak. Max = your battery capacity.
E.g., CA SGIP ~$2,000–$4,000, MA ConnectedSolutions ~$7,500 over 5 yrs, NY NYSERDA ~$1,500. See all programs →
Average number of power outages you experience per year.
Estimated out-of-pocket cost per outage without a battery.

Your estimated results

Net cost after incentives
$8,750
30% federal credit +
state rebate applied
Annual savings
$1,822
Payback period
4.8 years
15-year total savings
$27,330
Return on investment (15-yr)
312%

Based on your inputs, a 13.5 kWh home battery would pay for itself in approximately 4.8 years through daily arbitrage savings and avoided outage costs. Over a 15-year ownership period, you'd save an estimated $27,330 — a 312% return on your $8,750 net investment.

Calculation breakdown:
  • Daily arbitrage savings: $1,022/yr
  • Avoided outage costs: $800/yr
  • Federal tax credit (30%): −$3,750
  • State rebate: −$0

How the calculator works

The WattSage ROI calculator uses the following methodology:

  1. Net cost = Installed cost − (Installed cost × 0.30) − State incentive. The 30% federal Residential Clean Energy Credit (IRC §25D) is applied automatically to all systems with ≥3 kWh capacity that are charged by solar at least once per year.
  2. Annual arbitrage savings = Daily kWh shifted × (peak rate − off-peak rate) × 365 days × 0.90 round-trip efficiency factor. This represents the savings from charging your battery at off-peak rates and discharging during peak rates.
  3. Annual outage savings = Outages per year × cost per outage × 0.85 (battery covers ~85% of typical outages; you may be away from home or the battery may be depleted for the other ~15%).
  4. Payback period = Net cost ÷ Annual savings (arbitrage + outage avoidance).
  5. 15-year lifetime savings = Annual savings × 15 years, with a 0.5% annual degradation factor applied to arbitrage savings (battery capacity fades over time).
  6. ROI % = (Lifetime savings − Net cost) ÷ Net cost × 100.

This calculator intentionally excludes inflation, electricity rate increases, and battery replacement costs. In practice, electricity rates have risen 4–6% annually in most U.S. markets over the past decade, which would make the actual ROI higher than what's shown here. Battery replacement (if needed at year 12–15) would lower it.

Tools to validate your inputs

For the most accurate ROI estimate, install a home energy monitor for 30 days before getting installer quotes. Real per-circuit data beats any calculator.

Top Pick

Sense Energy Monitor (with Solar)

The single best tool for accurate battery sizing and ROI validation. 30 days of per-circuit data lets you replace "estimated daily kWh" with your actual usage pattern.

Check price on Amazon →

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Budget Pick

Emporia Vue 3 Energy Monitor

Half the price of the Sense with 16 circuit-level sensors included. Best value option for getting accurate per-circuit data before talking to installers.

Check price on Amazon →

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