New solar LED streetlights are relatively maintenance free, and come with computerised controllers for timed switching on/off and for dimming
By Richa Chakravarty
Wednesday, August 20, 2014: Solar streetlights are energy efficient sources of lighting that require no utility lines. They not only save money but are also the greener option. Every solar streetlight comes with a self-contained solar power assembly that runs the fixture. The assembly comprises solar modules, a vented aluminium panel pan, a welded rear channel mounting bracket, a battery storage console with sealed batteries, all the control electronics, and the aluminium power bracket to bolt on to any pole or wall.
What’s new in the market
Today, almost all solar streetlights use LED lights, as they consume less power and can be customised to suit a low voltage DC power requirement. The efficiency of LEDs is now 100 lm/W, and they offer a more accurate colour rendering while also starting instantly. Unlike high density discharge (HID) lamps, which take time to heat up once switched on, LEDs turn on instantly. Also, an LED lighting system has a lens on the LED array, which is designed to focus its light in a designed beam pattern.
Currently, it’s the solar LED streetlights—which are available in various beam profiles, correlated colour temperatures (CCT) and with different wattages—that are in demand. Lights with computerised controllers (for switching the lights on/off and dimming them) are also available. Moser Baer has launched its Asterion solar streetlights that range from 10 W to 45 W with excellent lumens packages and CCT availability of 4000 K and 6500 K. To guarantee a 50,000-hour lifetime, Moser Baer has designed these streetlights such that the LED junction temperature can be controlled under 70°C and the heat sink temperature variations can be restricted to less than 4°C.
“While traditional streetlights have very high maintenance costs or need re-lamping after 5000-8000 hours, the use of LEDs in solar streetlights makes the system maintenance free. Their excellent colour rendering index (CRI >85-90) along with the highly safe features of LEDs have made these the ‘in’ thing in the streetlight market,” says Shiv Nath, group COO, Moser Baer.
Advanced LED streetlights are also equipped with very efficient secondary optics that not only direct the light in the desired pattern (like a batwing optical pattern, for instance) but also increase the uniformity to minimise the black patches across the road.
“LED streetlights powered by solar energy are completely electronic systems now. This technological shift has helped in reducing/minimising huge transmission and distribution losses. Due to the high light output, LED lamps can be dimmed as much as 50 per cent when first installed with a minimal compromise on light output. In addition, they can be scheduled to dim as circumstances allow, such as at low traffic times, in unpopulated areas, in the middle of the night, etc. For example, streetlights can be dimmed by 60 per cent between 11 p.m. and 5 a.m. to save energy. Also, with on/off scheduling capabilities based upon photocell or pre-programmed commands, they can be easily programmed to operate based on the changing sunrise/sunset times, reducing lamp burn time,” explains Shiv Nath.
Moser Baer will soon launch a smart on/off and automatic dimming control feature for its lights. The smart technology will also control the staggered usage of powered streetlights. “This technology will further reduce power consumption, extend lamp life, and reduce power and maintenance expenses,” says Shiv Nath.
Gautam Solar Pvt Ltd has also launched solar LED streetlights of 9 W, 12 W, 24 W, 30 W and 36 W, with an aluminium body and toughened glass. “These streetlights have microcontroller-based open circuit and short circuit protection for the lamp,” informs Shubra Mohanka, director, Gautam Solar Pvt Ltd.
Kotak Urja Pvt Ltd also offers solar streetlights with super bright LED lamps that have a photometric design for the rectangular beam pattern. “Their high intensity, high uniformity and glare-eliminated light is perfect for streetlight applications. There is no hassle of bulb replacements; hence, these lights are perfect for roads, expressways and highways,” states Raghunandan, vice president, Kotak Urja Pvt Ltd.
In February 2014, Systellar Innovations launched its range of solar LED streetlights, ranging between 10 W and 40 W, with an in-built microprocessor-controlled LED driver and PWM charge controller. Systellar has provided a separate red coloured LED to indicate when the PV panel is dirty, so that users clean the solar panels well in time.
Tata Power Solar offers solar LED/CFL streetlights with the solar module/array of 35 Wp to 150 Wp. CFL preheat and LED thermal management technology gives these streetlights a long life. These lights have a smart battery management system with battery charging and low battery/load cut-off indicators. Built-in reverse polarity, battery over-charge/deep-discharge, over load/short circuit and open circuit protection makes these streetlights reliable.
Philips also offers solar LED streetlights with quality mono- and poly-crystalline silicon solar panels. Their high lumen LED modules have maximum efficacy. The streetlights have been designed with low-voltage solar controller technology with dimming capabilities for power-save management. They have highly efficient controllers to charge the batteries and intelligent microprocessor-controlled algorithms for light management that ensure maximum uptime.
Integrated solar charge controllers: Manufacturers have embarked on innovative mechanics and aesthetic designs to make streetlights more suitable for the requirements of customers. The latest innovations include LED streetlights with integrated solar charge controllers within the LED light. This reduces the failure of charge controllers and also cuts down the additional wiring costs required to connect these to the luminaire. Earlier, the charge controllers were external and would get damaged regularly due to exposure to the atmosphere.
Solar streetlights with smart battery control systems: Today, solar LED streetlights have become smarter, with battery charge regulators that integrate an advanced control system specially designed to maintain the battery status over many years. With smart battery control systems, these solar streetlights ensure four or more days of continuous operation. Usually, lithium ion batteries are used with these streetlights, providing an extendible life with plug-and-play installation. These intelligent battery control management systems optimise energy usage and avoid waste.
“Although lithium ion batteries cost three times more than any other battery, they have a life of 10 years, which can match the efficiency level of solar panels. Three years ago, solar streetlights came with bulky batteries that could run just for one day. But today, we can design the battery size as per the application. This can increase efficiency and, at the same time, reduce the costs,” says Raghunandan.
A consumer has the option of using either an 11 W CFL run by a 75 Ah lithium ion battery, or use a 6W LED with a lithium ion battery that is half the size of that used in a CFL fixture. So it is not just about energy harvesting but also smart management, while reducing costs. Manufacturers are exploring the ferrite-based batteries to substitute lithium ion batteries in order to reduce the cost structure, but they still have a long way to go.
Instead of the bulky batteries with separate battery boxes used earlier, batteries are today integrated within the structure along with the solar panels.
So, solar streetlights currently come as standalone structures.
Centralised solar streetlights: Users are also exploring centrally operated solar streetlights. These could be either AC or DC operated, and have a common solar panel installation with charger, inverter or battery bank. In such installations, a separate panel is mounted for a group of streetlights that are connected to a central power source. These streetlights are preferred because they are easy to monitor and maintain.
How to choose the right product
Local solar radiation levels are a very important factor influencing the accurate design of solar streetlights. Hence, the particular country, state or even city for which the streetlights are being selected, is a very important factor. Different places have different solar radiation hours (peak sun time). The design of the solar panel and battery for the solar LED street lighting system depends on the peak sun time.
Right choice of light source: The intensity of light required is another important factor that should be considered. Also, one should decide on the accurate lighting time required in the night. Based on the hours required, the design and configuration varies. Also, the light source used should be the most efficient, that is, one that consumes the minimum energy and minimises wastage. The height of the streetlight pole is also an important factor, as a higher pole will require a stronger light source (LED) to illuminate the road.
Suitable battery: The batteries used should be of the delayed discharge variety with more charge/discharge cycles.
Maintenance factor: Another important factor that consumers should consider is the maintenance of these streetlights; this is something that most people do not take into account, leading to the misconception that “solar streetlights fail easily.” Ensure that the facilities and resources of the vendor include an optimal solution so that the maintenance is easily taken care of. The company from which the light has been purchased should provide onsite services for the lights installed.
Optical design and performance: A user must evaluate the optical design and performance of the product when considering solar LED streetlighting. The light distribution pattern, uniformity and optical efficiencies of competing products are important parameters that need to be compared. “Focusing on illuminance levels on the road and optical distribution, rather than a lumens per fixture and lumens per watt number, is the best way to evaluate,” shares Shiv Nath.
As these streetlights are located outdoors in harsh environments, the housing of the battery, the hardware and the surface finish should be taken care of. For example, going for solar streetlights that are only painted is not a wise decision. Buyers should check that the poles and the surface of the streetlights are properly galvanised so as to avoid rust formation. “Along with the features and the light source, buyers should also look for the warranty and service support,” suggests Shubra Mohanka.
Moser Baer’s Asterion LED solar streetlight
Gautam Solar’s 9 W/12 W LED streetlights
Kotak Urja’s LED solar streetlights
Systellar Innovations’ solar LED streetlights
Tata Power’s LED/CFL solar streetlights
Philips’ solar LED streetlights
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