Like most great ideas, Solar Street Lighting is an elegantly simple idea.
Collect energy from the sun
Store the energy in batteries so you can use it during the night
Add some intelligence (a controller) to manage the care and feeding of your batteries and tell the lights what to do
So what differentiates one solar lighting system from another? Why do some outdoor solar lighting systems provide reliable all-night lighting for 10 years while other's struggle to make it through the night?
System is the important word here. The components of the system need to be well integrated and balance with each other and with the environment in your location. That's why off the shelf solutions are non-starters for public lighting projects.
The best solar street lights also tap into technologies that focus on efficiency and weather-ability.
High efficacy LED fixtures translate to an easier load for your solar components
Battery formulations that are well suited to temperature extremes in your location and that can be deeply cycled without reducing battery life
Controls that monitor and protect your battery reserve and prevent blackouts
Success depends on a planning process that includes an assessment of needs, solar characteristics of your location, photometric analysis and optimization of the system's components.