The framing that makes this simple
A battery is a bucket. It has a fixed size, you empty it, and then it is empty.
Solar is an allowance. Every day it puts a certain amount back, and if the allowance is bigger than your daily spend, the outage can last indefinitely.
So the question is never "how much solar do I need" in the abstract. It is two questions: how much energy do I use per day, and how many peak sun hours does my location get. Everything else is arithmetic.
Step 1 — your daily energy
Not your peak watts. Watt-hours across 24 hours, which is a much smaller and much more useful number.
| Tier | What it covers | Daily energy |
|---|
| Communications only | Router, modem, phones, a few lights | ~300–500 Wh |
|---|
| Food and essentials | Fridge, lights, devices, a laptop | ~1,200–1,800 Wh |
|---|
| Food plus a freezer | Above, plus a chest freezer | ~2,000–3,000 Wh |
|---|
| Essentials plus a pump | Above, plus a well pump or sump pump | ~3,000–4,500 Wh |
|---|
These are working estimates assembled from the appliance figures Champion and Honda publish, combined with typical duty cycles. They are a starting point for planning, not measurements of your house — an old fridge in a hot garage will be well above the range, a new one below it. The full wattage chart has the underlying numbers.
Notice what is absent. Heating, air conditioning, electric water heating, electric cooking and clothes drying are all missing, because they are kilowatt-hours per hour rather than per day. No portable solar setup covers them, and pretending otherwise is how people end up disappointed by equipment that was never going to work.
Step 2 — your peak sun hours
A peak sun hour is one hour of sunlight at 1,000 W/m² — the intensity panels are rated at. A location with 5 peak sun hours does not get five hours of daylight; it gets a whole day whose total energy equals five hours at full intensity.
Using it is straightforward: a 200W panel in a location with 5 peak sun hours produces roughly 1,000Wh a day before losses.
| Location | Annual average peak sun hours per day |
|---|
| Arizona | 6.5 |
|---|
| California | 5.6 |
|---|
| Texas | 5.3 |
|---|
| Florida | 5.3 |
|---|
| Minnesota | 4.3 |
|---|
| New York | 4.0 |
|---|
| Washington | 3.8 |
|---|
| National average | ≈ 5.0 |
|---|
State figures as published by Unbound Solar's peak sun hours map, which draws on NREL's PVWatts data from the National Solar Radiation Database. These are annual averages — a December figure is substantially lower than a June one at every latitude, and that seasonal swing matters more than the state-to-state difference. For your own location and month, NREL's PVWatts calculator is the free authoritative tool.
Step 3 — the arithmetic, and the derating
The formula is: panel watts = daily Wh ÷ peak sun hours ÷ 0.7.
The 0.7 is the part people leave out. Between the panel's rating and the energy that reaches your battery you lose output to cell temperature, imperfect angle, cable resistance, charge-controller conversion and dirt on the glass. Assuming you collect about 70% of the theoretical figure is a conservative planning assumption rather than a measured one.
| Daily need | At 4 peak sun hours | At 5 peak sun hours | At 6 peak sun hours |
|---|
| 500 Wh | ~180 W | ~145 W | ~120 W |
|---|
| 1,500 Wh | ~535 W | ~430 W | ~360 W |
|---|
| 2,500 Wh | ~890 W | ~715 W | ~595 W |
|---|
| 4,000 Wh | ~1,430 W | ~1,145 W | ~955 W |
|---|
Calculated as daily Wh ÷ peak sun hours ÷ 0.7 and rounded. The derating factor is a planning assumption, not a measurement; real conditions vary considerably day to day.
The middle row is the one most households land on, and it is worth sitting with. Sustaining a fridge, lights and devices indefinitely takes roughly 400–550W of panel — two decent folding panels, not one. A single 200W panel covers about half of it.
Step 4 — check the battery can take it
Two limits, both in your station's manual, and both capable of making the panels you bought useless:
- Maximum solar input in watts. A station that accepts 200W will accept 200W no matter what you connect. This is the most common way money gets wasted here.
- Battery capacity relative to the overnight load. Solar produces nothing after dark, and a fridge keeps cycling. The battery has to be big enough to carry from sunset to sunrise on its own.
A rough pairing that works: battery capacity at least equal to your daily energy, and panel wattage from the table above. That gives you a full day of margin if a day comes in badly.
Season is the thing that breaks plans
The state figures above are annual averages, and every one of them hides a large seasonal swing. Winter days are shorter, the sun is lower, and storm systems are thicker — which is exactly when outages happen in most of the country.
So a system sized on annual averages will underperform in the season you most need it. Two responses, both legitimate:
- Oversize the panels. Excess capacity in June costs nothing and rescues December.
- Pair solar with a generator. Solar covers indefinite summer outages silently; the generator covers the ice storm. That combination is more robust than either alone and it is what we would actually recommend for most of the country.
What cloud actually costs you goes into the numbers, and solar versus gas makes the case for the pairing.
The honest summary
- For communications and lights — one 100W to 200W panel and a 500Wh to 1kWh battery. This works, everywhere, all year.
- For a fridge and essentials — 400W to 500W of panel and a 1.5kWh to 2kWh battery. The common case, and two panels rather than one.
- For a freezer and a pump as well — 800W or more of panel and 3kWh of battery, which is a large and expensive folding-panel array. Consider a generator for the recharge instead.
- For heating, cooling or electric cooking — not solar. Not at portable scale, not with any number of folding panels.
And the practical shortcut: work out your daily watt-hours first. Almost everyone who is disappointed by a solar backup setup skipped that step and bought by headline capacity instead. Matching capacity to outage length is the companion to this page.
