Solar lights rely on batteries that get recharged by miniature photovoltaic panels like the ones in residential electricity-generating arrays. The panels convert ultraviolet sunlight to electricity, and it follows that when days are shorter and cloudier, they don't have as much sunlight to convert. That doesn't necessarily mean that your solar lights won't work in winter, though. One of the determining factors is panel efficiency, which may actually be better in winter than summer.
Higher Efficiency, Less Sunlight
Cold weather is a plus when it comes to photovoltaic panels, and although it makes more of a difference for large solar arrays, the cold is a boon for the tiny panels that power your solar lights, too. Even the most efficient panels produce 0.25 percent less power for each degree as the temperature rises above 77 degrees Fahrenheit. This means that in the heat of the summer, when sunlight is abundant, the panels on your solar lights are actually producing less power than on a sunny day in winter.
The problem is that every location in North America experiences less sunlight in winter. Winter deficiencies increase as you move north; the farther north you are, the shorter the days and the closer the sun stays to the horizon. In addition, the winter months are generally cloudier than the summer months, particularly in the Pacific Northwest and the northern Midwest. This means less direct sunlight and less charging time for the batteries that power your lights.
Making the Most of Winter Sunlight
As long as you have some sunlight in the winter months, you may still be able to light your garden with solar landscape lights and your house and garden features with solar flood lights. Recent improvements in solar lights include better reflectors to produce more light, batteries that can hold up to 2.5 times more charge and one-piece construction that seals out moisture and protects the delicate circuitry. Moreover, you can buy light kits with remote panels that you can place in sunny spots 15 feet or more from the lights they power.
Because the lights must stay on longer in winter while having less time to charge, though, they may not remain on all night. It may be prudent to connect them to a timer that shuts them off after midnight.
It's important to clear the PV panels for your lights whenever it snows. The panels won't generate electricity under a blanket of snow, and if you allow snow to melt on the panels, the resultant ice scatters incident light and reduces electricity generation to a fraction of the panel's potential. If you won't be around to service the lights and panels in the winter, it may be best to put them into storage until spring.