How do solar street lights work?

Solar street lights are very popular across the world and are known for being efficient and effective outdoor light sources.  However, apart from people associated with the solar industry, not many know how these lights work.  In fact, only a few solar light users can explain the components of a solar street light.  Once you understand the working principle, it becomes easier to make smart solar purchases and to operate the solar light system.

Working principle

Alexandre Edmond Becquerel, a French physicist, discovered the photovoltaic effect in 1839, which explained how solar energy could be converted into electrical energy. Solar street light consist of photovoltaic panels, what is commonly known as solar panels.  Multiple solar cells make up a solar panel and a solar cell consists of multiple layers of crystalline silicone and chemicals, which create layers of negatively-charged electrons and positively charged spaces.

When placed under direct sunlight, solar cells absorb sunlight and the electrons are activated and pushed into the positive spaces.  An electrical circuit is formed and direct electricity is produced when the electrons pass through this circuit.  This electricity is stored in a rechargeable battery which is connected to the solar panel through a charge controller.  At dusk, photoreceptors on the solar lamp sense the lack of sunlight and start supplying the stored electricity to the light source.

Solar cells do not produce any power after sundown and solar street lights work from dusk to dawn using the electricity generated during the day.  The lights automatically shut off at daybreak when the photoreceptors sense presence of sunlight.  This process keeps repeating every day.  Solar street lights are wireless as they require only solar energy to function and are always installed on lighting structures for the panels to receive maximum sunlight and for wider coverage of the light.


Solar panel

As explained above, solar panel is one of the most important parts of a solar street light.  A solar panel’s job is to absorb sunlight and convert it into electricity. Solar panels made of single crystals of silicon are known as monocrystalline solar panels, conversion rate of which is much higher than polycrystalline solar panels that consist of several silicon crystals.  However, polycrystalline solar panels are commonly used because of their affordability and ability to perform in high temperatures.

Lighting fixture

Modern solar street lights use LED as their lighting source as LEDs are known to provide much higher Lumens with lower energy consumption.  Street lights with HPS light fixture require at least 50% more energy for illumination than LEDs.  LED emits zero ultraviolet rays when compared to fluorescent and incandescent lights.  LEDs do not need any warm-up time to turn on which works in favour of motion-sensor solar street lights.

Rechargeable battery

Solar street lights use rechargeable batteries that get charged with energy from solar panels and help to illuminate the fixture during night.  Lead acid batteries were the common choice in traditional solar street lights.  The latest designs have integrated lithium batteries into the luminary unit itself, making it easy to install the lights on walls.  Both lithium-ion and lithium iron phosphate (LiFePO4) batteries charge faster, are compact and have higher number of charging cycles.

Charge controller

Controllers help in protecting the rechargeable battery by regulating the voltage.  Charging process stops at dusk and controllers prevent the backflow of current during that time.  Controllers decide when to switch on/switch off charging, thereby preventing overcharging and over-discharging of batteries.  MPPT controllers are priced at a higher range and are more efficient.  PWM controllers are perfect for smaller power systems and are cheaper.


Solar street lights must be installed at a height and strong poles are required to accommodate the entire lighting unit.  Sturdy brackets are used to fasten the fixture on the pole.  Thermally galvanized steel poles are used which last for around 40 years without rusting.  The hoisted pole is secured on the ground with concrete.  Most of the modern solar street lights can be mounted on sturdy walls also if there is sufficient sunlight to fall on the panels.

Type of solar street lights

All in one solar street light: 


solar street light all in one

This light comes at affordable prices and is the preferred lighting choice for smaller spaces.  Most of all in one solar street lights come with motion sensors and the solar panel, controller, battery and LED are integrated into a single unit.   They turn on at dusk and after around 30 seconds’ wait, they go down to 20% brightness.  The sensors detect movement and increase the brightness to 100%.  Again, after a time delay, the brightness gets adjusted back to 20% if no motion is detected.

Integrated solar street light: 

solar street light 20 watt

This light is generally used to light up large spaces such as public roads, streets, gardens, play areas or any corners or areas with no access to a power grid.  Integrated solar street light comes with separate solar panel and rest of the components are moulded into a single unit.  While one of the models remain at full brightness from dusk to dawn, another one works at full brightness in the first few hours and then at a reduced brightness for the rest of the night.

Working pattern and all the components of both these solar street lights are the same.  The lights are housed in durable metal and plastic material and waterproofed with IP65.  Solar street lights are being widely used for safety and decorative purposes and also to improve quality of life.  Depending on your lighting preferences, there are many solar street lights available with different designs and technical specifications.