The short answer is, nothing. Your solar panels are built to withstand weather conditions of all the seasons with extreme heat in the summer to extreme cold in the winter.
This all depends on how much snow is piled up on the solar panels. With a light coating, some electricity can still be produced. However, if there are several inches of snow piled up on the solar panel, most likely the solar panel will not produce any electricity.
For your safety, we do not advise cleaning off your solar panels, especially if they are on your roof. Snow will typically slide off the solar panels in several days if the conditions are correct. Also, the electricity production during the several days when the solar panels are covered up, will be nominal in comparison to the total yearly production of your solar system. You may also damage your solar system if the snow is removed incorrectly.
Solar panels are more efficient (produce more electricity) during colder temperatures. However, because of shorter days during the winter, total production is usually less than spring or summer.
Just remember, spring is just around the corner and NOW is a great time to start planning for your own solar system!