Solar street light

Solar street lights are raised light sources which are powered by photovoltaic panels generally mounted on the lighting structure. The photovoltaic panels charge a rechargeable battery, which powers a fluorescent or LED lamp during the night.

Features  Most solar panels turn on and turn off automatically by sensing outdoor light using a light source.[1] 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.[1]

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.[2]

Components  
Solar powered street lights[3]Solar street lights consist of 5 main parts:

Solar Panel  Solar panel is one of the most important parts of solar street lights, as 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.

Lighting Fixture  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.

Rechargeable Battery  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.

Controller  Controller is also very important for solar street light. A controller will usually decide to switch on /off charging and lighting. Some modern controllers are programmable so that user can decide the appropriate chance of charging, lighting and dimming.

Pole  Strong Poles are necessary to all street lights, especially to solar street lights as there are components mounted on the top of the pole: Fixtures, Panels and sometime batteries. And wind resistance should also be taken into consideration when choosing the pole.

Types  
Solar street light at the bus stopEach 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.[4]

Advantages  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 is minimized.[4]
This is a non polluting source of electricity
Separate parts of solar system can be easily carried to the remote areas
Disadvantages  Initial investment is higher compared to conventional street lights.
Risk of theft is higher as equipment costs are comparatively higher.[4]
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.
Implementation in the Sunderbans  Solar street lights were installed in the Sundarban Tiger Reserve (STR) in August 2008 and April 2009 with assistance from the Forest Protection Committee and the STR officials. Each household in the region were provided with a home light connection by the WWF so that the people feel responsible for the security of the installed solar street lights.[5]