Energy Resilience Guide

Battery Backup Sizing Guide

Add a battery to your plug-in solar system and you have stored energy ready when the grid goes down. Use our calculator to find the right battery size for your needs — then learn how solar panels keep it charged for free.

Backup Power
during outages
$200–$600/yr
typical savings
Self-Recharging
via solar panels

How Battery Backup Works with Plug-In Solar

A plug-in solar system paired with a portable battery station creates a self-contained energy loop. During the day, your solar panels generate power — some goes directly to your home circuits, the rest charges the battery. At night or during an outage, the battery powers your critical devices.

Step 01

Solar Generates

Your plug-in solar panels convert sunlight to electricity. Power flows into your home circuits, reducing your grid draw. Excess power charges your battery via a solar input port.

Step 02

Battery Stores

The battery station stores energy as DC power. Most portable stations accept 200–1,200W of solar input and can be fully charged in 2–6 hours of peak sunlight.

Step 03

You Stay Powered

When the grid goes down, plug your critical devices directly into the battery station. It provides clean AC power — no noise, no fumes, no fuel required.

Battery Sizing Calculator

Select the appliances you want to keep running during an outage, set how many hours of backup you need, and we'll recommend the right battery size.

Critical

🧊
Refrigerator
150WCRITICAL
🏥
Medical Device (CPAP/Nebulizer)
60WCRITICAL
💧
Sump Pump (small)
400WCRITICAL

Lighting & Communication

💡
LED Lights (5 bulbs)
50W
📱
Phone Charging (2 phones)
20W
💻
Laptop
65W
📡
WiFi Router / Modem
15W
📺
TV (40–55")
80W

Comfort

🌀
Ceiling Fan
75W
❄️
Portable AC (small)
900W
🔥
Space Heater (small)
750W
🍽️
Microwave (brief use)
1000W

Work from Home

🖥️
External Monitor
30W
🔦
Desk Lamp (LED)
10W

Your Backup Requirements

Usage pattern

All devices run at the same time, the entire duration — worst-case estimate.

4h
1h6h12h
Total load
All at once (worst case)
Spread out (~2.5× longer)
Active estimate + 20% buffer

Select appliances above to see your battery recommendation

This estimate assumes all selected devices run simultaneously and continuously. If devices are used at different times or intermittently, your battery will last significantly longer.

Estimates assume 80% battery depth of discharge and 90% inverter efficiency. Real-world results vary.

Battery Size Comparison

How long can each battery size power common appliances? These estimates assume 80% depth of discharge and average appliance wattage.

Battery SizeFridge OnlyFridge + LightsFridge + Laptop + LightsEst. PriceExample Model
500Wh2.7h2.0h1.5h~$350Entry-level portable
1,000Wh5.3h4.0h3.0h~$700Mid-range portable
1,500Wh8.0h6.0h4.5h~$1,100Mid-range with battery
2,000Wh10.7h8.0h6.0h~$1,500Premium plug-in solar
3,000Wh16.0h12.0h9.1h~$2,200High-capacity system
5,000Wh26.7h20.0h15.1h~$3,500Large portable / stackable
10,000Wh (10kWh)53.3h40.0h30.2h~$6,500Whole-room backup / modular

Estimates assume 80% depth of discharge (DoD). Fridge = 150W avg. Lights = 50W (5 LED bulbs). Laptop = 65W. Actual runtime varies by appliance age, temperature, and usage patterns.

How Much Solar Do You Need to Recharge Your Battery?

Plug-in solar panels can recharge your battery during the day, making your backup system self-sustaining during extended outages. The formula is simple: divide your battery capacity by your panel wattage times peak sun hours.

Recharge Time (hours) =
Battery (Wh) ÷ Panel Wattage (W)
Assumes peak sun conditions. Multiply by 1.25× for real-world efficiency losses.

A 400W plug-in solar array generates roughly 1,600–2,000Wh on a sunny day (4–5 peak sun hours). That's enough to fully recharge a 1,000Wh battery and offset $0.30–0.50 of grid electricity simultaneously.

400W
1× 400W panel
1,600–2,000Wh
Daily generation
1,000Wh in ~2.5 hrs
Recharge time (5 sun hrs)
800W
2× 400W panels
3,200–4,000Wh
Daily generation
2,000Wh in ~2.5 hrs
Recharge time (5 sun hrs)
1,600W
4× 400W panels
6,400–8,000Wh
Daily generation
5,000Wh in ~3 hrs
Recharge time (5 sun hrs)
2,400W
6× 400W panels
9,600–12,000Wh
Daily generation
10,000Wh in ~4 hrs
Recharge time (5 sun hrs)

Peak sun hours vary by location: 3–4h in the Pacific Northwest, 4–5h in the Midwest, 5–6h in the Southwest. Use the higher end for summer estimates.

Frequently Asked Questions

Ready to Build Your Resilience Plan?

Now that you know your battery size, use the Buyer's Guide to compare systems spec by spec — or jump straight to the Savings Calculator to see your payback timeline.