Solar powered LED streetlights can conserve a vast amount of electricity and ensure overall sustainability. Unlike in the case of the traditional streetlights, solar power is an inexhaustible environment-friendly and non-polluting source of energy.
By Potshangbam July
Solar LED streetlights are being widely adopted in the face of growing concerns about global warming and the need for energy-efficient lighting solutions. The demand for solar powered LED streetlights can be attributed to their energy efficiency, long life span, clean energy, low CO2 emissions, etc. Other key factors are lower maintenance costs during their operational life span and easy installation. With the increased implementation of Internet of Things (IoT) solutions, the solar powered LED streetlight will be the next big thing in the lighting industry. This segment is expected to grow at a significant rate, backed by favourable policy measures by the government.
How solar LED streetlights work
Solar LED streetlights use energy from the sun, which is renewable, or rather, inexhaustible. They operate with the use of photovoltaic cells that absorb the sun’s energy during the day and convert it into electrical energy, which is stored in batteries. At night, the stored energy is used to light up lamps. The process is continuous, whereby the battery gets recharged during the day and discharged at night. The solar cells are turned on/off automatically by sensors that gauge the climatic conditions. Even on a day when sunlight is not available, the lamps can be lit at night, based on energy stored in the battery. The whole setup does not require any line voltage, metering or transformer. Besides, these streetlights are very safe with 12/24 volt circuits, and there have hardly been any cases of electric shock.
The design of solar LED streetlights
The design of the entire streetlight system includes various components, such as the solar panel, the LED luminaire, the rechargeable battery, the charge controller, the pole and interconnecting cables. Components like LEDs, PV panels and batteries are independent of each other in the system, and they can be switched off or on, as necessary.
Solar panel or PV cell: These cells are the most essential parts of street lighting. They come in two versions— mono crystalline and poly crystalline. The mono crystalline cell has a higher energy conversion rate than the poly crystalline cell. Both are instrumental in converting solar energy to electrical energy, and can be used in a wide range of applications.
LED lights: LEDs have been incorporated in streetlights as they use less power (watts) per unit of light generated (lumens). They operate at a much lower temperature; hence, the energy consumption of LED lights is much lower than that of high pressure sodium based lamps, which are commonly used in conventional streetlights. Besides, LED lights are capable of producing directional light, which prevents loss of energy and generates a brighter light. They have a life span of 50,000-100,000 hours, which is much longer than all other types of lights.
| Some of the key players in the global solar LED street lighting market Signify Holding
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Rechargeable batteries: Two types of batteries are used—gel cell deep cycle batteries and lead acid batteries. The lifetime and capacity of these batteries should be given priority as they can affect the backup power if not chosen wisely.
Controller: This is an important device that switches the streetlight on and off, as per the requirements. It also keeps a check on the battery status and prevents it from overcharging or undercharging. Now controllers are available as pre-programmed options in compact designs. Typically, they comprise an MCU, battery charger, secondary power supply, LED lamp driver, etc.
Pole: A strong pole of 2.66mt is required for a solar powered LED streetlight. Components like fixtures, batteries and panels are installed on the pole.
Interconnecting cable: The cable is required to interconnect various components on top of the pole. It is used to connect the solar panel, the controller of the LED light and the battery, in sequence. The size and length of the cable depends on the current being carried to the LED lights and the height of the pole.
Why opt for solar LED streetlights for public lighting
Safety and security are the major concerns with regard to public lighting. Solar based LED streetlights are the ideal choice for public lighting as they stay lit up through the entire night or on dark cloudy days, regardless of power outages or grid failure. LEDs provide more lumens per watt than traditional lights, and produce a whiter light that results in good visual acuity. High consumption of energy in street lighting has been a concern, which translates into a high level of harmful emissions. LEDs use one-fifth the power of incandescent lighting, a third of the power that HID or metal halide lamps use, and half what fluorescent lamps consume, all of which controls energy wastage. They release no toxic elements into the environment as they use the DC power provided by the solar panel, which is clean and renewable energy.
The solar LED streetlights are a good alternative to wire based lighting. Being wire-free, they are independent of the utility grid. They enable a saving on cable costs, which is cost effective not only in the short-term but also in the long term. They automatically get turned on/off at dusk and dawn, which avoids the need for daily monitoring. They reduce maintenance expenditure to a certain level, which is a major problem with public lighting.
The biggest advantage of using PV panels in LED streetlights is that it is easy to adjust their position in any direction to use peak sunlight, and hence absorb solar radiation to the maximum.
Tech innovations
Solar LED streetlights with IoT based control systems eliminate the need for manual monitoring activities. The system allows civic authorities to monitor the status of the battery’s charge level and solar voltage from a remote location. Accordingly, the brightness of the light can be either increased or decreased. Further, the solar voltage used the previous day, the remaining solar voltage, and the charging percentage of the battery can be checked through the control system.
LED solar streetlights also provide information in real-time, sending alerts if the system is out of order. Light dependent resistor (LDR) sensors are used in circuits where required to sense the presence of light. These work on the principle of photo conductivity. When light falls on the LDR, the resistance decreases, and increases in the dark. This provides an analogue input value to the control circuit. The value can be used to switch the LED streetlight on or off, automatically. An infrared sensor can sense the motion of the pedestrians or cars in the area, based on the heat or thermal radiation from an object or person. Some solar LED streetlights use kinetic energy, generated from the footsteps of the pedestrians, to charge the batteries and power the lights.
Adoption of solar LED streetlights in India
The adoption of solar LED streetlights is ramping up in India with increased support from the government, which has launched various schemes and programmes, such as the Solar Mission, Prakash Path, etc. The Street Lighting National Programme (SLNP), which was launched on January 5, 2015, is a significant initiative. Its main aim is to replace all the energy consuming conventional streetlights with smart and energy efficient LED variants. Besides, the government is promoting energy efficiency by offering LED products at subsidised prices.
Interestingly, the adoption of solar LED street lighting in rural areas is high. These rural areas are constantly facing problems due to inadequate electrification and long transmission lines. Such lighting systems are ideal since they do not depend on the power utilities. The penetration of solar LED streetlights has also accelerated due to a dramatic drop in the prices of LED technology, PV panels, and other components. LED technology, coupled with solar resources, can change the street lighting landscape, because of the advantages from the economic, environmental and energy perspectives.
