Before the Battery

Evidence page

Battery backup for a refrigerator

Short answer: plan on roughly 1,000–1,900 Wh per day at the outlet for a typical US refrigerator, then divide by about 0.765 — a conservative Before the Battery planning factor — to get the stored capacity you need. With that factor, a nominal 1,000 Wh station represents about 10–18 hours across that daily-use range; a nominal 2,000 Wh station represents about 19–37 hours. Compressor startup compatibility remains a separate pass/fail gate. Beyond 48 hours, daily recharge decides the answer, not capacity.

A kitchen during a power cut, lit only by daylight, refrigerator closed.
The situation this guide sizes: a kitchen without mains power and a refrigerator that must stay cold.

Published 8 August 2026 · Last reviewed 30 August 2026

By Alexis Marchais, engineer and independent decision-system builder.

How this guide calculates

Daily energy at the outlet = annual kWh ÷ 365. Required stored capacity = daily energy × planning days ÷ 0.765. Cycle closure is checked daily: recharge per day must at least match energy used per day.

Observed / model inputs

  • The kWh-per-year figure printed on your refrigerator's EnergyGuide label, or 24 hours of readings from a plug-in power meter.
  • Measured steady running watts and the highest startup surge the meter records over a full day.
  • Realistic daily recharge in Wh, estimated for your location and season rather than taken from panel nameplate watts.

Before the Battery planning assumptions

  • 85% AC delivery: only about 85% of stored energy reaches an AC load after conversion losses.
  • 10% retained reserve: the last 10% of the pack is never planned against.
  • Combined, these give the 0.765 planning factor used across this site. It is a conservative Before the Battery assumption, not an externally proven universal constant.
  • Running watts are never derived from kWh per day; an average energy rate is not a continuous output requirement.

The arithmetic, in full

Every figure below comes from your own EnergyGuide label, not from an assumed appliance profile. The example uses 500 kWh per year, a common mid-size US refrigerator.

  • 500 kWh/year ÷ 365 = 1,370 Wh per day at the outlet.
  • A 24-hour outage therefore needs 1,370 Wh delivered as AC.
  • Conversion losses: only about 85% of stored energy reaches an AC load. 1,370 ÷ 0.85 = 1,612 Wh.
  • Safety reserve (a Before the Battery planning assumption): 10% of the pack is never planned against. 1,612 ÷ 0.90 = 1,791 Wh of stored capacity.

So a nominally “2,000 Wh” station is a one-day refrigerator machine, not a three-day one. Multiply the daily figure by three and the same arithmetic asks for roughly 5,400 Wh — a different class of hardware entirely.

The decision boundary

Past about 24 hours, the question stops being “how big” and becomes “does the cycle close”. Energy has to come back every day at least as fast as it is used. A 200 W solar panel in real winter conditions might return 400–600 Wh per day; a refrigerator asks for 1,370. That gap does not shrink by buying a larger battery — it is an architecture problem, and the honest answer is an installed system, a generator, or a shorter planning horizon.

Capacity is not compatibility

Watt-hours decide duration. Watts decide whether anything happens at all. A refrigerator compressor draws a steady running load and a much larger startup surge for a fraction of a second. A station can hold plenty of energy and still stall on that surge, which is why this publication treats startup as a separate pass/fail gate and refuses to derive running watts from kWh per day — an average energy rate is not a continuous output requirement.

What to measure

  1. The EnergyGuide kWh/year figure, or 24 hours on a plug-in power meter.
  2. Steady running watts while the compressor is running.
  3. The highest startup watts the meter records over a full day.
  4. What can realistically recharge, in Wh per day, during an outage.

Run it on your own numbers

Open the refrigerator outage check — it applies exactly the arithmetic above, shows every line of it, and abstains when the declared situation cannot be answered honestly. See also the methodology for where these factors come from.

Reproducible dataset

Every figure on this page comes from the same published arithmetic: annual kWh converted to daily outlet energy, then divided by the 0.765 combined planning factor. Fifteen worked cases are published with their downloads so you can check the math yourself.

Refrigerator outage sizing table: 15 transparent scenarios — formula, assumptions, gate states, XLSX and CSV.

Primary sources

Merchant marketing is never used as a primary source for generic arithmetic. Specific product or model specifications still require dated OEM documentation plus independent measured evidence.

  1. How to use the EnergyGuide label when shopping for home appliancesUS Federal Trade Commission

    Supports: That the kWh-per-year figure on the EnergyGuide label is the correct starting input for annual refrigerator energy use.

  2. ENERGY STAR certified residential refrigerators (product finder)US Environmental Protection Agency

    Supports: The range of certified annual consumption figures behind the typical 1,000–1,900 Wh per day band used on this site.

  3. Keep your food safe during emergenciesUSDA Food Safety and Inspection Service

    Supports: The food-safety holding times that make refrigerator and freezer backup a time-bounded problem rather than an open-ended one.

  4. PVWatts CalculatorUS National Renewable Energy Laboratory

    Supports: That realistic daily solar yield is location- and season-dependent, and must be estimated rather than assumed from panel nameplate watts.

Browse all guides, diagnostics and research — the refrigerator cluster: the sizing table, the outage check and the method behind them.