Although the unit with light sensor turns on and off depending on the light, they are not solar powered. You still need to plug them in a power unit, but they are extremely economical and environmental friendly and you will save a lot of money compared to traditional holiday lighting solutions.
Also, you can adjust a timer, which are easy to find and relatively inexpensive anymore if you only want them to start at a certain time.
For more info check out our Ultimate Guide to Laser Xmas Lights – http://laserchristmaslightshq.com/ultimate-guide-christmas-laser-lights/
Or our Holiday Projector Guide explaining the five highest quality and most affordable projectors on the market – http://laserchristmaslightshq.com/best-laser-light-projectors/