Solar Battery Calculator

Calculate batteries needed for solar backup from daily usage and backup hours needed.

By Konstantin Iakovlev · Updated September 2026 · Source: IRS — Residential Clean Energy Credit (not available for property placed in service after Dec. 31, 2025)

kWh
$

Batteries Needed

1

Installed Cost

$12,000.00

The 30% residential clean energy credit (Section 25D) that once covered home battery storage expired December 31, 2025 under the One Big Beautiful Bill Act, so a 2026 installation pays the full cost. State and utility storage incentives still exist in many markets and can be worth more than the old federal credit.

Battery Analysis

Backup Energy Needed10.0 kWh
Batteries Required1
Total Cost$12,000.00
Est. Payback~22.8 years

Use the Solar Battery Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only. Results are estimates from the numbers you enter and the assumptions described on this page; check them against local building codes, product specifications and current prices, and have structural, electrical or gas work designed or checked by a licensed professional.

How It Works

Sizing a battery comes down to how much power you need to keep flowing when the grid drops or the sun isn't cooperating. As outages from extreme weather and grid strain grow more common, getting that figure right is what separates real energy independence from a system that quits halfway through the night.

You enter your daily energy use in kWh, straight from a utility bill, and the hours of backup you want. Backup energy is daily use ÷ 24 × hours. Each battery is counted at 90% of its rated capacity, a typical usable depth of discharge, so a 13.5 kWh unit supplies about 12.15 kWh, and the tool rounds up to whole batteries. The payback figure assumes grid power at $0.16/kWh and that the battery shifts about 30% of your usage away from peak rates; it is a rough guide, since savings depend heavily on time-of-use pricing and net-metering rules.

Always-on electronics draw a quiet 'phantom load' that adds up over a day, so fold it into your usage rather than ignoring it. Backup duration is the figure people most often shortchange; think through peak-demand windows and which appliances truly have to stay on. It's also worth sizing with tomorrow in mind, since adding something like EV charging later will reshape what your battery bank needs to cover.

Example: 8 Hours of Backup on 30 kWh a Day

  1. 1 Step 1: Enter 30 kWh of daily use, 8 hours of backup and a 13.5 kWh battery at $12,000 installed.
  2. 2 Step 2: Backup energy needed = 30 ÷ 24 × 8 = 10.0 kWh.
  3. 3 Step 3: One 13.5 kWh battery supplies about 12.15 kWh usable (90%), which covers the 10.0 kWh, so one battery is enough: $12,000 installed.
  4. 4 Step 4: Estimated payback = $12,000 ÷ (30 kWh × 365 × $0.16 × 30%) = $12,000 ÷ $525.60 ≈ 22.8 years, before any state or utility storage incentive; the federal 30% credit ended with 2025.

Source: IRS — Residential Clean Energy Credit (not available for property placed in service after Dec. 31, 2025) · Last updated: September 2026

Frequently Asked Questions

How many solar batteries do I need for my home?
It depends on your daily use and how many hours you want covered. At the calculator's default 30 kWh a day, 8 hours of backup needs 10 kWh, which one 13.5 kWh battery (12.15 kWh usable) covers; 12 hours needs two and a full 24 hours needs three. Limiting backup to essential circuits cuts the load and stretches each battery further.
How much does a solar battery system cost?
Installed prices vary with the product and installer, so use your quote; the calculator's default is $12,000 per battery. Battery storage qualified for the 30% federal 25D credit only through December 31, 2025; that credit has since expired, so systems placed in service in 2026 pay the full cost unless a state or utility incentive applies. The calculator multiplies the per-battery price by the number of batteries, so enter an average if your quote prices a second unit lower.
Is a solar battery worth the investment?
It depends on your utility rates and whether you have time-of-use pricing or poor net metering. If you pay high peak rates ($0.30+/kWh), batteries can save money by storing cheap solar energy. For backup power, the value depends on how often and how long you lose power.

You might also need

Solar Panel Savings Calculator

Estimate solar panel system cost, payback period, and 25-year savings with state incentives (the federal 25D credit ended after 2025).

Electricity Bill Calculator

Calculate your monthly electricity bill by adding appliances and their usage. Find your biggest energy consumers.

Carbon Footprint Calculator

Estimate your annual carbon footprint from driving, electricity, flights, and diet. Compare to the US average.