A home battery sizing calculator helps you determine exactly how much battery storage capacity your home needs, whether you want to maximize solar self-consumption or ensure reliable backup power during outages. Enter your solar production, electricity usage, or essential backup loads to get a recommended battery size, cost estimate with the 30% federal tax credit, and a comparison of popular battery systems.
Calculator Mode
From your solar system or installer estimate
Average US home uses ~30 kWh/day
Check with your utility company
Typical: 30-50% if away during the day
Typical: $10,000-$15,000 installed
Essential Loads Checklist
Percentage of total capacity that is actually usable
Self-Consumption Analysis
ROI & Savings Analysis
Savings assume 3% annual electricity rate increase. Actual payback varies based on time-of-use rates and utility policies.
Backup Power Requirements
Battery Units Needed
Popular Home Battery Comparison
| Battery | Capacity | Usable | Power Output | Est. Cost | Units Needed |
|---|---|---|---|---|---|
| Tesla Powerwall 3 | 13.5 kWh | 12.2 kWh | 11.5 kW | $12,500 | — |
| Enphase IQ 5P | 5.0 kWh | 4.5 kWh | 3.84 kW | $5,500 | — |
| LG RESU Prime | 16.0 kWh | 14.4 kWh | 7.0 kW | $11,000 | — |
| Generac PWRcell | 9.0 kWh | 8.1 kWh | 4.5 kW | $10,000 | — |
Prices are approximate installed costs and may vary by region and installer. Usable capacity based on 90% DoD. All batteries carry 10-year warranties.
Cost Estimate Range
Based on $800-$1,200/kWh installed. The 30% Investment Tax Credit is available through 2032.
How to Use the Home Battery Sizing Calculator
Choosing the right home battery storage system can be confusing with so many options on the market. This calculator takes the guesswork out of the process by analyzing your specific energy situation and recommending the ideal battery capacity, whether your goal is to store excess solar energy or keep critical appliances running during power outages.
Step 1: Choose Your Calculator Mode
Start by selecting your primary goal. Solar Storage mode is for homeowners with solar panels who want to capture excess daytime production for evening use instead of exporting it to the grid. Backup Power mode is for anyone who wants to size a battery system to keep essential loads running during grid outages, regardless of whether they have solar panels.
Step 2: Enter Your Energy Details
In Solar Storage mode, enter your daily solar production and electricity usage in kWh — you can find these on your solar monitoring app and utility bill. Set your electricity rate and indicate whether your utility offers net metering, as this significantly affects the financial benefit of battery storage. If your utility pays full retail credit for exported solar, a battery provides less financial benefit but still offers backup protection.
In Backup Power mode, check the essential loads you want to power during an outage. The calculator includes common household appliances with their typical daily energy consumption. Select your desired backup duration — 24 hours is a good starting point for most homeowners, while areas with frequent extended outages may want 48 hours of backup.
Step 3: Understand Depth of Discharge
Depth of discharge (DoD) represents how much of a battery's rated capacity is actually usable. Modern lithium-ion batteries typically allow 80-90% DoD. A 13.5 kWh battery at 90% DoD provides 12.15 kWh of usable energy. The calculator accounts for this automatically, so the recommended capacity is the total rated capacity you need to purchase, not just the usable amount.
Step 4: Review Results and Compare Batteries
Click "Calculate Battery Size" to see your recommended battery storage capacity, cost estimates including the 30% federal Investment Tax Credit, and how many units of each popular battery brand you would need. In Solar Storage mode, you will also see a detailed ROI analysis showing annual savings, payback period, and self-consumption rate improvements. The battery comparison table shows how many units of Tesla Powerwall, Enphase IQ, LG RESU, and Generac PWRcell systems you would need to meet your requirements.
Tips for Accurate Sizing
For the most accurate results, use actual data from your solar monitoring system and utility bills rather than estimates. Remember that battery needs can vary seasonally — summer air conditioning and winter heating loads differ significantly. Consider sizing your system slightly larger than the minimum recommendation to account for battery degradation over its 10-year warranty period, as lithium-ion batteries typically lose 2-3% capacity per year.
FAQ
Is this home battery sizing calculator really free?
Yes, completely free with no signup required. All calculations run locally in your browser — no data is sent to any server. Use it as many times as you need to compare different battery configurations and scenarios.
Is my data safe when using this calculator?
Absolutely. Everything runs entirely in your browser using JavaScript. No personal information, electricity usage data, or location details are transmitted anywhere. You can even use the calculator offline once the page loads.
How many kWh of battery storage does the average home need?
For solar self-consumption, most homes need 10-15 kWh of battery storage to capture excess daytime solar production for evening use. For whole-home backup, you typically need 20-40 kWh depending on which loads you want to power and how long you need backup to last.
What is depth of discharge and why does it matter?
Depth of discharge (DoD) is the percentage of a battery's total capacity that can actually be used. Most lithium-ion home batteries have an 80-90% usable DoD, meaning a 13.5 kWh battery provides only 10.8-12.15 kWh of usable energy. This calculator accounts for DoD automatically.
How much does a home battery system cost?
Home battery systems typically cost between $800-$1,200 per kWh of storage capacity installed. A single Tesla Powerwall (13.5 kWh) costs around $12,000-$15,000 installed. The 30% federal ITC tax credit applies when batteries are paired with solar panels, significantly reducing your net cost.
What is the 30% federal tax credit for home batteries?
The Investment Tax Credit (ITC) under the Inflation Reduction Act allows a 30% tax credit on home battery storage systems, even standalone installations without solar panels. The 30% rate is available through 2032, stepping down to 26% in 2033 and 22% in 2034.
Which home battery brand is best?
The best battery depends on your needs. The Tesla Powerwall 3 (13.5 kWh) is the most popular for whole-home backup. The Enphase IQ Battery 5P (5 kWh) is modular and pairs well with Enphase microinverters. The LG RESU Prime (16 kWh) offers the most capacity per unit. All are reliable lithium-ion systems with 10-year warranties.
How long will a home battery last during a power outage?
Backup duration depends on your battery capacity and which loads you power. A single 13.5 kWh battery running only essential loads (refrigerator, lights, WiFi, phone charging) at about 3 kWh/day can last roughly 3-4 days. Running more appliances like HVAC or an electric stove will drain the battery much faster.