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GeneratorRuntime.com

Solar Generator Size Calculator

What size solar generator or portable power station do you need? List your devices to get the battery capacity and the continuous output to look for.

Your devices (per day)

For cycling appliances (fridges, freezers, pumps), enter the hours the motor actually runs, not 24. Fridge and freezer presets assume about 10 running hours a day (≈40% duty) — an editable planning assumption.

Assumptions
%

Planning assumption (default 85% for AC loads) — not a manufacturer spec.

%

Planning assumption (default 20%): capacity you won't drain.

How much solar would I need to recharge this each day?

h

Equivalent full-strength sun, not daylight hours.

%

Planning assumption.

Estimated panel wattage

≈ 213 W

800 Wh ÷ (5 h × 75%). Estimate only — check the station's solar input limits.

Already own a station? Calculate its runtime.

How this calculation works

  1. Daily energy = running watts × hours per day × quantity, added for every device. Your inputs, or labeled typical values.
  2. Battery energy needed = daily energy ÷ conversion efficiency. Efficiency is a planning assumption.
  3. Minimum capacity = battery energy ÷ (1 − reserve). Reserve is a planning assumption.
  4. Continuous output = all running watts added together, assuming everything can be on at once. Calculated estimate.
  5. Surge = continuous output + the single largest startup extra, assuming only one motor starts at a time — we don't add every startup value together. Calculated estimate.

Many products marketed as "solar generators" are battery power stations that can be recharged from solar panels. Compare your result with the station's published capacity (Wh), continuous output (W) and surge rating. Meeting the numbers doesn't guarantee every motor or compressor will start.

Need to estimate charge time? Use the Solar Recharge Time Calculator. Sizing a fuel generator instead? Try the Generator Sizing Calculator.

Solar generator sizing FAQ

›What size solar generator do I need for a refrigerator?

Measure or estimate the fridge's daily energy. A typical full-size fridge might average 150 W running about 40% of the time — around 1,440 Wh a day — though real models vary widely. After efficiency and reserve, that points to roughly a 2,000 Wh station for one day. The station also needs enough continuous output for running watts and enough surge rating for the compressor's startup.

›How many watt-hours do I need for an outage?

Add up each device's watts × hours used per day, then multiply by the number of days you want to cover without recharging. Divide by efficiency and leave a reserve. This calculator does that for one day; multiply the result for longer outages or add solar to recharge.

›What is the difference between Wh and W?

Watts (W) are the rate of power at a moment — what the station's output must handle. Watt-hours (Wh) are energy over time — how much the battery stores. A 100 W device running 8 hours uses 800 Wh.

›Why does inverter size matter?

The inverter's continuous rating limits how many watts you can run at once, regardless of battery size. A large battery with a small inverter can't run a microwave; a big inverter with a small battery runs it only briefly. Motor loads also need enough surge capacity to start.

›How much solar do I need to recharge a power station every day?

Divide the daily energy you use by your location's peak sun hours and the real-world solar yield. Example: 1,000 Wh ÷ (5 peak sun hours × 75%) ≈ 270 W of panels. Stay within your station's solar input limits.