Solar Street Lighting System Types
A solar street light is an outdoor light fixture that harnesses the radiant energy from the sun to drive its light engine. Whether to create driving visibility, improve traffic safety or enhance pedestrian security, solar street lighting is a practical, simple and cost-effective supplement to grid-tied lighting solutions.
Besides, grid-independent operation eliminates the need for trenching, underground wiring, and connections to the utility grid, making solar street lights the first choice for installations in harsh environments and remote locations. No carbon emissions, no energy bills and minimal ongoing costs. Even in urban areas, these compelling advantages of solar street lights appeal to a number of outdoor lighting applications such as illumination of secondary roads, residential streets, driveways, pathways, parking lots and building perimeters.
A typical solar street lighting system consists of a solar panel, a solar charge controller, a battery bank, a light assembly and a light pole or support structure where these components (except for the battery bank in some cases) are mounted.
The solar panel is a major component of a solar street light. The main function of the solar panel is to convert sunlight into electrical energy. This energy is then stored in solar rechargeable batteries.The conversion efficiency of the solar panel is inversely proportional to the size of the solar panel.
Solar panels are comprised of several individual solar cells. There are two types of solar cells worth mentioning (we will not cover thin-film panels as they are much less efficient and not able to perform up to the task): mono-crystalline and poly-crystalline. Compared to poly-crystalline, the conversion rate of mono-crystalline solar cells is much more appropriate for solar street light performance.
Solar Charge Controller
The solar controller is the heart of the solar system. This device decides when to switch on or off the lighting and charging. The main function of smart controllers is to control lighting, dimming and battery charging. The smart controller prevents the solar battery from overcharging and undercharging. By receiving the energy from solar panels it continuously charges the battery during the day. During the night the controller supplies the stored power to run the LED street lights. Smart controllers can support single load or multiple loads.
Smart solar controllers provide excellent energy generation, performance optimization and monitoring of each street light unit via cloud based software. The smart controller has a built-in communication network and dedicated software for control and proactive maintenance of the entire street light network.
They can be divided into three categories: simple ON/OFF control, pulse width modulation (PWM), and maximum power point tracking (MPPT). The ON/OFF control is designed to protect the battery from overcharge or undercharge, and prevent reverse current. PWM controls the amount of current charging the battery and provides trickle charging. MPPT is a more advanced approach that is commonly used in solar street lightings systems for high efficiency battery charging.
Solar Rechargeable Battery
The solar battery is a type of electrical battery. Its main function is to store electricity from the solar panel during the day in order to provide energy for the LED lamp at night. The capacity and lifetime of the battery is very important as they provide backup power for low energy periods – days without sun. A good smart solar street lighting system has a temperature probe that monitors the battery and optimizes its performance (battery temperature and depth of discharge voltage) to prolong battery life cycle.
The two most prevalent battery technologies used in solar street lights are lead-acid and lithium-ion.
Lead-acid batteries have a cycle life of 1500 – 2500 cycles, a lifespan of 3 – 5 years, a depth of discharge (DOD) or round trip-efficiency (RTE) of 70 – 90%, and an energy density around 30 Wh/kg to 50 Wh/kg depending on the lead density. Lead-acid batteries take between 12 and 16 hours to reach 100% capacity, which is an allowable disadvantage because solar radiation usually lasts for many hours during a day and the slow charge rate allows efficient charging of the batteries.
Lithium ion batteries have the highest energy density and the longest cycle life of all battery chemistries. The lithium-ion battery is a lithium-ion transfer cell in which lithium ions, the working ionic component of electrochemical reactions, shuttle between the anode and the cathode through the electrolyte.
Lithium ion batteries are typically used in integrated solar street lights which require an energy storage solution with a long cycle life, high energy density and small footprint. In addition to these advantages, lithium ion batteries exhibit qualities such as high DOD, good thermal stability, high charging efficiency, and short discharge time.
Smart solar street lights use new LED technology which delivers much higher lumen for less energy used. LED lights with lower wattage than traditional style fixtures are more efficient and have lower power consumption while providing higher luminosity levels and zero UV emissions. LED fixtures are also less prone to failures with an average number of 50,000 working hours, whereas traditional street lights range from 5,000 to 8,000 working hours with much higher failure rate. The energy consumption rate of LED fixture is at least 50% lower than high pressure sodium (HPS) fixtures.
Solar Street Lighting System Types
Generally, there are four types of solar street lighting systems.
1. Off-Grid Type Solar Street Lighting System
Most of the solar light projects are coming soon in the area where there is no electricity wiring. Moreover, the installation of these electric wiring is tough and requires lots of manpower and money.
Moreover, solar light is a better option. In off-grid type street light each pole has an independent unit. It contains the power source (the solar panel), a battery, a light controller and a LED light. In fact, you can put this unit anyplace (with the exception of an area where there is no sunlight, obviously).
2. Grid-Tie Solar Street Lighting System
(i) Grid-Tie (Single Inverter)
The grid-tie (single inverter) solar street light is the one where a sun-oriented arrangement is set up in a focal area. This gives energy to an arrangement of LED road lights. The transmission lines supplies fuel to these lights. In my opinion, this option is better if you need to have a sunlight based arrangement.
(ii) Grid-Tie (Micro Inverter)
The grid-tie (micro inverter) solar street light have individual inverters on each pole for LED solar street light. In this system, there is no need of big solar arrangement. It was essential to have the sun oriented part of these pathway lights observable to the people while continuing the connection.
3. Solar&Wind Hybrid Solar Street Lighting System
This solar street light is a combination of solar and wind energy. When we combine the both, it will produce more energy. The wind and sunlight both produce the energy at the different time. The wind is dominating in winters whereas sunlight is more in summers. For this reason, this solar street light is successful in harsh climatic conditions. In addition, this technology has many advantages as compared with the other systems.
4. All-In-One Solar Street Lighting System
The all-in-one solar street lighting system is manufactured and designed by expert team. Actually, this solar street lighting system has automatic motion sensors with settings of dimmer and motion sensor which helps to save energy. That is why it is on the top list.