only as reliable as your fixtures, batteries, panels and the availability of sunlight, long enough to recharge the battery. One or several? Individual or multiples powered from the same source. Not as easy to string 12/24vDC to each light and still get the power you need. Mounts for panels can be pricey and still need to be high enough to not be vandalized.
You need at least 3 or 4 days capacity in your batteries to handle the shady/cloudy days. Resource is out there to calculate based on your location and sun days.