Will a CPAP run on solar overnight?

Not directly — panels make nothing at night. The battery runs the machine and the panel refills it by day. To replace one dry night (about 64Wh) you need roughly 21W of panel at 4 peak sun hours; to replace a humidified night (about 320Wh), roughly 107W.

Our pick for this

We earn a commission on these links at no extra cost to you. It does not change the runtime figures above — the maths is shown so you can check it.

Bluetti Elite 100 V2
Pairs with 200W of panel
1,024Wh gives about 12 dry nights of buffer, which is what makes a solar setup survive a run of cloudy days rather than break even on paper.
Check price on Amazon

Power-draw figures for the machines below are provisional estimates, not yet our own meter readings. See how we test.

The question behind the question is whether the setup breaks even — whether a day of sun puts back what a night of therapy takes out. For dry therapy that bar is remarkably low.

How the pieces fit

A "solar generator" is a battery with a charge controller. The panel charges the battery; the battery runs the CPAP. Nothing runs off the panel directly overnight, and a panel sized to run the machine in daylight is not the same as one sized to refill the battery.

So there are two separate sums: does the battery cover the night (see what size you need), and does the panel replace what the night cost.

Panel wattage to break even

Use peak sun hours — the hours of equivalent full-output sun, typically 3 to 5 a day depending on latitude and season — and allow about 25% for charge-controller and conversion losses.

panel watts = nightly Wh ÷ (peak sun hours × 0.75)

Panel needed to replace one night's use
Peak sun hours	Dry (64Wh)	Humidified (320Wh)
3 (winter, higher latitude)	28W	142W
4 (typical)	21W	107W
5 (summer, clear)	17W	85W

Assumes 75% combined charging efficiency and eight hours a night at 8W dry / 40W humidified. Draw figures are provisional pending our own meter testing — see How We Test.

What this means in practice

For dry therapy, a single 100W panel is comfortable overkill — roughly four to five times break-even. That margin matters, because it is what carries you through an overcast day.

For humidified therapy, a 100W panel is break-even at best and loses ground in poor weather. 200W is the sensible figure if you intend to run the heater indefinitely.

Build in margin deliberately. Break-even on paper means the first cloudy day puts you into deficit, and the deficit compounds.

Panels are rated optimistically

A 100W panel is rated under laboratory conditions. In the field, angle, temperature, dust and haze commonly cost 10-25%. Flat on the ground in summer is worse than it sounds; tilted toward the sun is worth more than another panel.

Can I plug a CPAP straight into a solar panel?: No. Panel output swings with sun and cloud, and a CPAP needs stable regulated power. The panel charges a battery and the battery runs the machine.
What size solar panel do I need for a CPAP?: About 21W at 4 peak sun hours to replace a dry night, or about 107W for a humidified one. In practice buy 100W for dry use and 200W if you run the humidifier.
Will solar keep up with a CPAP on a cloudy day?: An overcast day can cut output by 75% or more. For dry therapy the margin on a 100W panel usually absorbs that; for humidified use it does not, which is why the battery needs to hold more than one night.

What to actually buy