What size solar array do you actually need?
Uses the appliances and hours/day you set up in the House calculator. Tell us where you are and get the array size that actually covers it — full daily energy use, not just an overnight recharge, adjusted for real sun hours where you live.
Your appliances
7 of 11 House appliances count toward the numbers below.
Array size is limited by roof space and budget, so Luxury is excluded by default. 4 selected items also can't realistically run off a battery/solar system (pumps, big motors, heavy resistive loads) and are sized out regardless of tier.
United States highlighted — hover any country for its sun-hour figures, click one we have data for to select it.
~4.7 peak sun hours/day (annual), area-averaged across the country — your exact spot will run higher or lower.
- Continuous
- 1,730 W
- Peak (surge)
- 3,230 W
That's the inverter rating a system needs to run this directly off solar during the day — anything smaller can't keep up with the load, regardless of array or battery size.
Using each appliance's own hours/day from your House setup — edit those there for a more accurate number.
To cover 32.34 kWh of daily use — whether drawn directly during the day or from the battery overnight — at United States's ~4.7 annual peak sun hours and 75% real-world system efficiency (panel angle, temperature, and conversion losses).
Sizing on the annual average splits the difference — switch to Winter above for the conservative number.
How this calculator works
Solar array sizing answers one specific question: given how much energy I use each day and where I live, how many watts of panels does that take? We total your selected appliances' running watts, multiply by how many hours a day they're powered, and divide by your selected country's average peak sun hours and a 75% real-world efficiency factor (panel angle, temperature, and conversion losses).
Why daily hours, not just an overnight recharge figure: it's tempting to size the array on just “how much battery did last night use” — but if a fridge runs 24 hours a day, the array has to produce energy for the daytime hours too, whether that power goes straight to the fridge or through the battery first. The array's job is to generate a day's worth of energy within its sun-hours window, full stop — so the input that matters is total daily watt-hours, not a fraction of the day.
The Winter/Summer toggle matters more than it looks: at high latitudes the seasonal swing is enormous — Germany averages about 5 peak sun hours a day in summer but under 1 in winter, a 5x difference in array size for the same daily energy. If your outage scenario is a winter storm, size on the winter figure; an array that keeps up in December keeps up all year.
This page intentionally stops at sizing — it doesn't point you at specific panels yet, since we're still building out that catalog honestly rather than recommending products we haven't vetted. Want just the battery capacity and inverter rating, without the solar array question? Use the battery calculator.
Why people add solar to battery backup
A battery alone is a fixed amount of energy — once it's empty, it's empty until you find an outlet. Solar panels turn that into a renewable supply: free recharging every sunny day, indefinitely, with nothing to refuel or store, and whatever the panels produce while appliances are running gets used directly, cutting how hard the battery has to work. The trade-off is weather-dependence — a wall outlet recharges a battery in under an hour any time, while solar only works when the sun's out, and a bad-weather stretch means falling back on stored battery capacity.
Data sources
Sun-hour figures: NASA POWER — 20-year monthly climatology (2001–2020) of all-sky surface shortwave downward irradiance, in kWh/m²/day — the standard peak-sun-hours planning figure.We area-average it over a grid of points sampled inside each country's borders. Winter means December–February north of the equator and June–August south of it; summer is the reverse.
Map geometry: world-atlas, derived from Natural Earth — the same public-domain dataset most published maps use.
US state-level figures: NREL PVWatts v8 (NSRDB) — Simulated for a 1kW, south-facing, 20°-tilt rooftop system at each state's largest city, using NREL's National Solar Radiation Database climatology.Selecting United States unlocks a state dropdown with a real per-state figure instead of the national average — annual only, since that's what the source publishes at state grain.
National and state averages both hide real regional spread — Arizona and Washington State are different solar countries in everything but name, and even within a state (coastal vs. inland California, humid-east vs. arid-west Texas) the figure can run 20-25% off. Treat these figures as planning numbers, and check a site-specific tool before buying hardware.
Frequently asked questions
How big a solar array do I need?
Total your appliances' running watts, multiply by how many hours a day they're actually powered, and divide by (your location's peak sun hours × ~75% for real-world losses). A location with 5 peak sun hours needs a meaningfully smaller array than one with 3 for the same daily energy — this calculator adjusts for that automatically based on the country you select.
Does the array need to cover daytime use, or just recharge the battery overnight?
Both, and they're the same number. Whether an appliance draws power directly off the panels at noon or from the battery at midnight, that energy has to come from the array's production within its sun hours either way — a fridge running 24 hours a day needs the same size array whether you think of it as 'powering itself during the day, recharging the battery at night' or just 'using X watt-hours a day.' Sizing on total daily energy use — not just an overnight recharge figure — is what actually captures daytime direct use.
What's a peak sun hour, and why does my country matter?
A peak sun hour is the equivalent of one hour of sunlight at 1,000 W/m² — the standard panels are rated against. It's not the same as daylight hours; a cloudy 14-hour summer day might only deliver 3 peak sun hours. Countries and regions vary hugely — sunny, low-latitude places like Australia, Egypt, or the Southwest US see 5–6.5+ peak sun hours a day, while northern Europe often sees under 3. The same daily energy use takes roughly twice the array in a low-sun country as a high-sun one.
Why does selecting the United States show a state dropdown?
A national US average blends Arizona's 6.5+ peak sun hours with Alaska's 3, which isn't useful for sizing anything specific. Once you pick United States, a state selector appears with a real per-state figure from NREL PVWatts — noticeably more accurate than the country-wide number, though still a single-city estimate rather than a full area average, so it's annual-only (no winter/summer split at state grain) and can still run 20-25% off in states with a real internal climate split.
How much worse is solar in winter?
It depends almost entirely on latitude. Near the equator, winter and summer are nearly identical. In the northern US or central Europe, winter delivers a third to a fifth of summer's sun — Germany averages about 5 peak sun hours a day in summer and under 1 in winter. If your outages come with winter storms, size the array on the winter figure; an array that keeps up in December keeps up all year.
Is solar better than a gas generator?
They solve different problems. Solar recharges a battery for free and indefinitely, with no fuel to store or go stale — but it only works when the sun's out, and array + battery costs more upfront per watt than a gas generator. Gas generators refuel in minutes any time of day but need a fuel supply, which can run out in a long regional outage. Many households in outage-prone areas end up with both.