Solar lights are easy to set up and require no electricity, making them a simple and eco-friendly addition to your outdoor landscaping. Cloudy days will interfere with these lights, however, slowing, though not stopping, their ability to charge. While solar lights' abilities vary by manufacturer, most are able to stay shining through the occasional cloudy day, though using them after long periods without adequate sunlight can eventually weaken their charging capabilities.
Solar lights operate on power packs that contain solar panels, control systems and batteries, usually nickel cadmium or lead acid batteries. The panels collect sunlight, and the control systems process the sunlight into power. The batteries then store the power until you are ready to use the lights. The time needed to fully charge batteries will vary among solar light manufacturers, as will the time the lights run when the batteries are charged. Cloudy days will impact these estimates.
Clouds diffuse sunlight, which cuts the productivity of your lights' panels. The panels will still charge during cloud cover, but not as efficiently as on a sunny day. When clouds cover the sun, the systems' power production is cut by about half. The U.S. Department of Energy estimates that in the winter, when days are shorter and generally cloudier, your lights will operate for a 30- to 50-percent shorter amount of time than in the sunnier seasons.
Many solar lights are able to store sufficient power to operate properly over several cloudy days, but when you operate your lights without fully charging the battery, you risk reducing the overall life of the battery. While the solar panels in your lights generally are weather-resistant, you should avoid using your solar lights in prolonged periods of bad weather, particularly if you live in a region with harsh winters. You can conserve power by switching your lights off; they will continue to collect solar energy even when turned off.
Although you can't control the weather, proper positioning and maintenance of your solar lights will ensure they soak up as much energy as possible, even on cloudy days. Make sure they are in an area where they receive maximum sunlight all day long, not blocked by shadows from vegetation or buildings. Also, keep your solar panels clean. Bird droppings and other debris will hinder their ability to collect sunlight. Always be sure to turn the power switch to off when you store your lights.
Under the right conditions, clouds can actually increase the amount of power your lights' panels absorb. When puffy cumulus clouds cover the sun, at times the sunbeams will penetrate holes in the clouds. When this happens, your panels absorb not only the direct sunlight, but also the sunlight reflected off the cloud. Most solar panels are designed to handle such bursts of energy, which usually do not last long.