Solar Generator Sizing Calculator

Use our Solar Generator Sizing Calculator above to estimate the battery capacity needed to power your appliances during a power outage. Choosing the correct solar generator size is one of the most important factors in building a reliable backup power system.

Solar generators are typically rated in watt-hours (Wh) or kilowatt-hours (kWh). The larger the battery capacity, the longer your appliances can run. Many homeowners focus on wattage alone, but runtime is equally important when sizing a backup power solution.


How the Calculator Works

The calculator estimates the battery capacity required based on your power consumption and desired runtime.

Battery Capacity (Wh) = Running Watts × Runtime Hours

To account for inverter losses, battery reserve, and real-world operating conditions, it’s wise to add an additional 20–25% safety margin.

ApplianceWattsHoursRequired Battery
Refrigerator70085,600 Wh
CPAP Machine608480 Wh
Router & Modem50241,200 Wh

Common Solar Generator Sizes

500–1,500 Wh

  • Phones
  • Laptops
  • Routers
  • Small electronics

2,000–3,000 Wh

  • Refrigerators
  • CPAP machines
  • Internet equipment
  • Lighting

4,000–6,000 Wh

  • Multiple appliances
  • Freezers
  • Sump pumps
  • Extended outage coverage

10,000+ Wh

  • Whole-home backup
  • Large battery systems
  • Multi-day outages

What Appliances Can a Solar Generator Run?

ApplianceTypical Watts
Refrigerator100–800
Freezer200–700
Television100–300
CPAP Machine30–90
Microwave1,000–1,500
Coffee Maker800–1,200
Sump Pump800–1,500
Well Pump1,000–2,500

Solar Generator vs Battery Capacity

Many people confuse watts, watt-hours, and kilowatt-hours.

A 2,000-watt inverter can power a 2,000-watt appliance, but a 2,000 Wh battery can only run that appliance for about one hour before the battery is depleted.

Understanding the difference between power output and stored energy is essential when choosing the right solar generator.


Example Calculations

Refrigerator During an Outage

700W × 8 Hours = 5,600 Wh

Refrigerator + Freezer

1,200W × 8 Hours = 9,600 Wh

CPAP Machine Overnight

60W × 8 Hours = 480 Wh


Frequently Asked Questions

What size solar generator do I need for a refrigerator?

Most refrigerators require between 1,500 and 6,000 Wh of battery capacity depending on runtime requirements and compressor cycling.

What size solar generator do I need for a sump pump?

Many sump pumps require 800–1,500 running watts and may have significantly higher startup surge requirements.

Can a solar generator power a house?

Large solar generators and battery systems can power portions of a home or even an entire house depending on energy consumption and battery capacity.

How many solar panels do I need to recharge a solar generator?

The answer depends on battery size, panel wattage, sunlight conditions, and charging goals.

Is a solar generator worth it for emergencies?

For many homeowners, solar generators provide quiet, low-maintenance backup power without the need to store gasoline or propane.

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