Street lights have been in use since the Roman and Greek civilizations. Before the invention of incandescent lamps, oil lamps, candle lighting and gas lamps were used to illuminate the streets for public safety. In 1878, the first electric street light was used in the cities of France. With time, cheaper and brighter incandescent lamps replaced arc lights. Today, conventional street lights use high-pressure sodium lamps.
Street lights have been in use since the Roman and Greek civilizations. Before the invention of incandescent lamps, oil lamps, candle lighting and gas lamps were used to illuminate the streets for public safety. In 1878, the first electric street light was used in the cities of France. With time, cheaper and brighter incandescent lamps replaced arc lights. Today, conventional street lights use high-pressure sodium lamps.
Components and Terminology of a solar street light system
Luminary:
Any lighting unit which houses one lamp or more than one lamps along with the parts which are designed to distribute the light and to protect and power the lamps is called a luminary. A solar street light also has a similar light-giving body.
Solar panel:
A solar panel is composed of many solar cells that generate power to run a solar street light. It is a device that is used to absorb sunlight and convert solar energy into electricity to light up solar lights. The two main types of panels are:
- Polycrystalline
- Mono crystalline
Polycrystalline panels are commonly used due to their affordability and they offer the same performance even in high temperatures. Monocrystalline panels are expensive and can perform better in cold climates.
Battery
A solar battery is a type of battery that gets charged with energy from solar panels. Modern solar street lights use:
- Li-ion batteries
- LiFePO4 batteries
Lithium ion batteries work on 3.7 volt and these are the same batteries used to operate mobile phones, laptops and digital cameras. The average voltage of a lithium iron phosphate battery is 3.2 volt. This technology is also being used to run some latest cellphones and laptops.
Both these batteries work well for a solar street light as they can charge faster and the advantage of batteries with less voltage is that the solar panel does not have to generate a lot of current to charge the battery. One of the reasons why modern solar street lights are priced higher than traditional solar street lights is because they use either lithium ion or LiFePO4 batteries instead of lead acid batteries.
Controller
Solar controllers are charge regulators that regulate the flow of current going from the solar panels to the batteries. They prevent backflow of current from the battery to the panel and also overcharging and undercharging of batteries. Solar street lights use:
- MPPT controller
- PWM controller
MPPT controllers are highly priced, more efficient and work better in cooler conditions. PWM controllers work well in smaller power systems and are cheaper.
Types of solar street lights
All in one or fully integrated solar street light
The solar street lights in which all the components are integrated into one single unit are called all in one solar street lights. Traditional all in one solar street lights use SLA (sealed lead-acid battery) but their modern counterparts prefer lithium-ion or LiFePO4 batteries. All in one solar street lights with motion sensors are energy efficient and priced reasonably.
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Luminary:
Luminary of an all in one solar street light is a casing which houses components including a light source, a solar panel, a battery and a controller.
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Solar panel:
Polycrystalline panels are widely used in all in one solar street lights
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Battery:
lithium-ion or LiFePO4 batteries are commonly used here because of their high efficiency and compact size.
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Controller:
PWM or MPPT controllers are used here, alongside motion sensor, although some all in one solar street lights do come without motion sensor built in.
Integrated or all in two or split solar street light
Earlier, solar street lights with lead-acid batteries were known as ‘split solar street lights.’ In the current scenario, integrated solar street lights are also known as split solar street lights.
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Luminary:
Luminary of an integrated solar street light includes only battery, controller and LED.
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Solar panel:
Solar panels come as a separate unit in an integrated solar street light system and Polycrystalline panels are widely used in Integrated solar street lights
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Battery:
Lithium-ion(Li-ion) or Lithium iron phosphate (LiFePO4) batteries are used here to give a full night backup.
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Controller:
MPPT controller are most commonly used for Integrated solar street light to give a full night backup. Some of the earlier version and some current versions of these lights do use PWM charge controller.
Modern split solar street lights use lithium-ion or LiFePO4 batteries instead of lead-acid batteries. Due to their cost-effectiveness and efficiency, polycrystalline panel with MPPT or PWM controller is used. Some of the integrated solar street lights work in a time-based manner where they give out full brightness for the first few hours and then operate at a lower brightness until morning.