Solar street light
Solar street lights are raised light sources which are powered by solar panels generally mounted on the lighting structure or integrated in the pole itself. The solar panels charge a rechargeable battery, which powers a fluorescent or LED lamp during the night.
Most solar lights turn on and turn off automatically by sensing outdoor light using solar panel voltage. Solar streetlights are designed to work throughout the night. Many can stay lit for more than one night if the sun is not available for a couple of days. Older models included lamps that were not fluorescent or LED. Solar lights installed in windy regions are generally equipped with flat panels to better cope with the winds.
Latest designs use wireless technology and fuzzy control theory for battery management. The street lights using this technology can operate as a network with each light having the capability of performing on or off the network.
Solar street lights consist of 4 main parts:
The solar panel is one of the most important parts of solar street lights, as the solar panel will convert solar energy into electricity. There are 2 types of solar panel: mono-crystalline and poly-crystalline. Conversion rate of mono-crystalline solar panel is much higher than poly-crystalline.Solar panel are varies from wattage systems.
LED is usually used as lighting source of modern solar street light, as the LED will provide much higher Lumens with lower energy consumption. The energy consumption of LED fixture is at least 50% lower than HPS fixture which is widely used as lighting source in Traditional street lights. LEDs lack of warm up time also allows for use of motion detectors for additional efficiency gains.
Battery will store the electricity from solar panel during the day and provide energy to the fixture during night. The life cycle of the battery is very important to the lifetime of the light and the capacity of the battery will affect the backup days of the lights. There are usually 2 types of batteries: Gel Cell Deep Cycle Battery and Lead Acid Battery and many more. Lithium-ion batteries are also popular these days as they are compact in size and not prone to theft (cannot be used in other applications like lead acid batteries).
Strong Poles are necessary to all street lights, especially to solar street lights as there are often components mounted on the top of the pole: fixtures, panels and sometimes batteries. However, in some newer designs, the PV panels and all electronics are integrated in the pole itself. Wind resistance is also a factor.
Also there are some accessories, like foudation cage and battery box.
Each street light can have its own photo voltaic panel, independent of other street lights. Alternately, a number of panels can be installed as a central power source on a separate location and supply power to a number of street lights. 
All In One type Solar street lights are also gaining popularity. In this type the Solar panel, Lithium-ion battery and LED light are fitted together in a compact way. This enhances battery protection against theft and also the entire unit is weather proof.
City of Las Vegas was the first city in the world that tested new EnGoPlanet Solar Street lights that are coupled with kinetic tiles that produce electricity when people walk over them.
- Solar street lights are independent of the utility grid. Hence, the operation costs are minimized.
- Solar street lights require much less maintenance compared to conventional street lights.
- Since external wires are eliminated, risk of accidents are minimized.
- This is a non polluting source of electricity
- Separate parts of solar system can be easily carried to the remote areas
- It allows the saving of energy and also cost.
- Initial investment is higher compared to conventional street lights.
- Risk of theft is higher as equipment costs are comparatively higher.
- Snow or dust, combined with moisture can accumulate on horizontal PV-panels and reduce or even stop energy production.
- Rechargeable batteries will need to be replaced several times over the lifetime of the fixtures adding to the total lifetime cost of the light.
The charge and discharge cycles of the battery is also very important considering the overall cost of the project.
- "A New Intelligent Control Terminal of Solar Street Light". ieeexplore.ieee.org. Retrieved 2011-07-12.
- "A Study on energy efficient & Solar PV street lighting system" (PDF). fosetonline.org. Retrieved 2011-07-12.[dead link]