Solar street lights have the advantage that each unit is independent of mains power and each other. So the lights can be installed one at a time and start working immediately. However they are expensive to purchase compared to mains powered lights. A 30 Watt Solar Street Light is about $4,000. Also the batteries require to be replaced every few years.
The power produced by the solar panels can only be used for the individual street light. Much of the time the panel will be producing surplus power which cannot be stored by the on-board battery. One way to harness this would be to install a standard 12 Volt outlet on the base of the pole, so local residents could use surplus power to charge small appliances.