How much battery storage do I need for emergency backup power?

For essential loads (fridge, lights, phones), plan for 3,000-5,000 Wh/day. A 3-day outage without solar recharging needs 9-15 kWh usable capacity. Adding a 2-4kW solar array significantly extends coverage through daily recharging.

Can I run my refrigerator on solar during a power outage?

Yes. A typical refrigerator uses 100-150W and runs intermittently, consuming about 1-2 kWh/day. A 5 kWh battery (LiFePO4) combined with a 400-800W solar array can run a refrigerator indefinitely during daylight hours and overnight with adequate battery storage.

Emergency Power Calculator — Battery & Solar for Power Outages

How to Use This Calculator

Check the essential appliances you need to keep running during a power outage, set the outage duration, and the calculator tells you the minimum battery capacity (kWh) and solar panel count to stay powered.

Prioritize your loads

During an outage, focus on life-safety and health first: refrigerator to prevent food spoilage, medical devices (CPAP, oxygen concentrator), phone charging for emergency communication, and basic lighting. Add comfort loads (fans, TV) only after essentials are covered.

Battery vs generator for outage power

A solar + battery system provides silent, fuel-free, maintenance-free backup power that starts instantly. Generators require fuel storage, regular maintenance, emit fumes, and are noisy. For outages under 3 days, a properly sized battery system is often the better choice. For extended outages (hurricane season, etc.), a hybrid approach — battery + small generator — provides the best resilience.

Typical Emergency Load Reference

Refrigerator150W × 24hrs = 3,600 Wh/day

CPAP (without humidifier)30-40W × 8hrs = 320 Wh/night

LED lights (4 fixtures)40W × 6hrs = 240 Wh/day

Phone charging (2 phones)20W × 4hrs = 80 Wh/day

WiFi router15W × 24hrs = 360 Wh/day

Laptop65W × 4hrs = 260 Wh/day

A "fridge + lights + phones" configuration uses roughly 3,900 Wh/day. A 5kWh battery (LiFePO4, 80% DoD = 4kWh usable) provides approximately 1 day of this load without any solar recharging.

FAQ

How much battery do I need for a 3-day power outage? ▼

For essential loads (fridge, lights, phones), plan for 3,000-5,000 Wh/day. For a 3-day outage with no solar recharging, you need 9,000-15,000 Wh of usable capacity. With LiFePO4 batteries at 80% DoD, that's 11-19 kWh of installed capacity — roughly 2-3 Powerwall-equivalent batteries. Adding a 2-4kW solar array can significantly extend outage coverage through daily recharging.

Can solar panels charge batteries during a grid outage? ▼

Yes — but only with the right equipment. Standard grid-tie inverters shut down during outages (for safety). You need either: (1) a hybrid inverter with backup/island mode capability, (2) an off-grid inverter with battery storage, or (3) a whole-home backup system like Tesla Powerwall, Enphase IQ Battery, or SunPower SunVault. These systems automatically disconnect from the grid during outages and allow solar to continue charging the battery.

What is a critical loads panel? ▼

A critical loads panel (or backup panel) is a subpanel that contains only your essential circuits — refrigerator, a few lights, phone chargers, and medical devices. During an outage, the battery system powers only this subpanel rather than your entire home. This dramatically reduces battery size requirements and cost. A critical loads panel typically costs $500-1,500 to add during a solar+battery installation.

Emergency Power Calculator

How to Use This Calculator

Prioritize your loads

Battery vs generator for outage power

Typical Emergency Load Reference

FAQ

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