Why winter output is lower
- Shorter days. There are simply fewer hours of light.
- A lower sun. Light arrives at a shallow angle and passes through more atmosphere.
- Cloud. Storms that cause outages usually bring heavy cloud with them.
- Snow cover. A layer of snow blocks almost all output until it is cleared.
- Shade. A low sun throws long shadows from trees and buildings that are no problem in summer.
Estimating a winter day
daily energy (Wh) = panel watts × peak sun hours × yield
A peak sun hour is one hour of full-strength sunlight. Summer days in much of the United States and southern Canada deliver 5 or more. A clear midwinter day at northern latitudes may deliver 1 to 3, and an overcast one well under 1. Look up monthly figures for your own location with the tools linked below.
| Panels | 1 sun hour | 2 sun hours | 4 sun hours |
|---|---|---|---|
| 100 W | 75 Wh | 150 Wh | 300 Wh |
| 200 W | 150 Wh | 300 Wh | 600 Wh |
| 400 W | 300 Wh | 600 Wh | 1,200 Wh |
| 800 W | 600 Wh | 1,200 Wh | 2,400 Wh |
The table uses a 75% yield. For scale, a modem and router use about 480 Wh a day, and a fridge and freezer together about 1,800 Wh.
What that means in practice
On a dull winter day, 200 W of panels will keep phones, lights and the internet going but will not run a fridge. Keeping up with a fridge and freezer on a two-sun-hour day would take about 1,200 W of panels, and that is a lot of panel to set out in the snow.
So size the battery to carry you through the outage on its own. Treat solar as a way to stretch it by a day or two, or to recover between storms.
Setting panels up in winter
- Tilt them steeply. In winter the sun is low, so a steep tilt of around 60 degrees from flat catches more light and helps snow slide off.
- Face them toward the midday sun. That is south in the northern hemisphere.
- Clear snow with a soft brush. Do not scrape the glass or use hot water.
- Check for shadows through the day. A shadow across one corner can cut the output of the whole panel.
- Weigh them down. Portable panels catch the wind easily.
Keep the battery warm
Panels like the cold. Batteries do not. Many lithium power stations will not accept a charge below 32°F (0°C), and some shut down in deeper cold. Run the solar cable through a window gap or a door seal and keep the power station indoors. Seal the gap with a towel.
Check before you connect
- Maximum solar input in watts. Extra panel capacity above this is wasted.
- Voltage range. Panels wired in series add their voltages, and cold weather raises panel voltage further. Exceeding the input limit can damage the unit.
- Current limit in amps for panels wired in parallel.
- Connector type. Many panels use MC4 connectors, and power stations often need an adapter cable.
Sources
Related
Reviewed October 2026 by Lee Palmer. This guide is general information, not professional advice. Suggest a correction.