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Solar + Battery Backup Calculator

Hybrid grid-tied solar with home battery — outage protection and TOU optimization

✓ Free estimate — no signup required

Solar + Battery vs. Grid-Tied vs. Off-Grid

Grid-Tied Only

  • Lowest cost
  • No outage backup
  • Depends on net metering
  • Best ROI in most cases

Solar + Battery ✓

  • Outage backup (hours–days)
  • TOU optimization
  • Still grid-connected
  • $8k–$30k+ premium

Full Off-Grid

  • Complete independence
  • Highest cost
  • Best for remote sites
  • Generator backup often needed

A battery-backup solar system is the sweet spot for most homeowners: you keep the cost efficiency of grid connection while gaining resilience against outages. The battery automatically takes over during grid failures, keeping critical loads running without any manual action.

Battery sizing note: This calculator estimates solar panel needs. For battery sizing, see the reference table below — or use 1 battery per 10–15 kWh of daily consumption you want to back up.
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Battery Backup Scenarios

How much battery storage do you need? Depends on what you want to back up:

Essential Loads Only

$8,000–$12,000
What's backed up
Fridge, lights, internet, select outlets
Daily load
5–10 kWh
Battery storage
1 battery (13.5 kWh)
Backup runtime
12–24 hours

Comfort Backup

$18,000–$30,000
What's backed up
Essentials + HVAC (moderate use)
Daily load
20–30 kWh
Battery storage
2–3 batteries (27–40 kWh)
Backup runtime
24–48 hours

Extended Whole-Home

$28,000–$50,000
What's backed up
Full home for multi-day outage
Daily load
30–50 kWh
Battery storage
3–5 batteries (40–67 kWh)
Backup runtime
2–5 days (with solar recharge)

Cost ranges are for battery-only additions to an existing solar system. Combined solar + battery system costs add $10,000–$35,000+ for panels.

Battery for Time-of-Use Optimization

In states with time-of-use (TOU) electricity rates — California, Arizona, Massachusetts, and others — electricity costs 2–3× more during peak hours (typically 4–9 PM). A home battery can charge from solar during the day and discharge during peak hours, maximizing the value of your solar production even if your utility has reduced net metering rates.

TOU states with best battery ROI:

★California★Arizona★Massachusetts★New York★Maryland★Nevada

Solar Battery Backup — Frequently Asked Questions

What is a solar battery backup system?▾
A solar battery backup system (also called a hybrid system) combines grid-tied solar with a home battery. Your panels charge both the battery and power your home. When the grid fails, the system automatically disconnects from the utility and switches to battery power — providing seamless backup for critical loads. Unlike a full off-grid system, you remain connected to the grid for normal times and can draw from it when the battery is low.
How much battery do I need for solar backup?▾
It depends on what you want to back up and for how long. A single Tesla Powerwall 3 (13.5 kWh) can run essential loads (refrigerator, lights, outlets, internet) for 12–24 hours. For whole-home backup through a multi-day outage, 2–4 batteries (27–54 kWh) is more appropriate. Most installers recommend starting with essential-load backup (1–2 batteries) and sizing up if needed.
What is the difference between backup mode and self-consumption mode?▾
In backup mode, the battery reserves capacity specifically for outages — it stays partially or fully charged and discharges only when the grid goes down. In self-consumption (or TOU optimization) mode, the battery charges from solar during the day and discharges in the evening to offset expensive peak-rate electricity. Many systems let you set a minimum backup reserve (e.g., 20–50%) while still running self-consumption.
Does adding a battery change the solar system size I need?▾
Sometimes. If you're adding battery primarily for backup, your panel sizing stays the same (sized to offset your consumption). If you're using the battery for time-of-use (TOU) optimization — charging cheap overnight grid power or maximizing solar self-consumption — you might add extra panel capacity to ensure the battery fills each day. Battery-only systems (no solar) can also be charged from grid electricity to shift load.
What are the top home battery options for solar backup?▾
The leading home battery systems in 2025 include: Tesla Powerwall 3 (13.5 kWh, AC-coupled), Enphase IQ Battery 5P (5 kWh, DC-coupled microinverter-native), LG RESU Prime (9.6–16 kWh), Franklin WH (15 kWh, bidirectional EV-charging capable), and SolarEdge Home Battery (10 kWh, DC-coupled). All use lithium iron phosphate (LFP) chemistry with 10-year warranties. Prices range from $8,000–$15,000 installed per unit.

Related Solar Resources

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Grid-Tied Solar Calculator

Standard solar without battery — most common setup

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Off-Grid Solar System Calculator

Fully independent solar with no utility connection

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How Many Solar Panels Do I Need?

Complete solar sizing guide

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How Solar Calculators Work

Methodology and assumptions behind the estimates

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Solar Savings by State

Compare battery + solar ROI across states

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Main Solar Panel Calculator

Full calculator with all states and custom inputs

Solar + Battery Savings by State

→California→Texas→Florida→Arizona→Nevada→North Carolina→Georgia→Colorado→New York

Disclaimer: Battery backup sizing depends on your specific loads, usage patterns, utility rate structure, and outage risk tolerance. This tool provides planning-level estimates only. Consult a licensed solar installer for a detailed battery backup assessment. Battery costs change rapidly — verify current pricing with installers.