How do solar street lights work?

Working Principle of Solar Street Lights

The working principle of solar street lights involves multiple aspects of technology and design, while smart solar street lights add more intelligent features based on this. Below is a detailed explanation:

Traditional Solar Street Lights Working Principle

1. System Components:
   • Solar Panels: Convert solar energy into electrical energy.
   • Battery: Stores the electrical energy generated during the day for use at night.
   • Controller: Manages the charging of the solar panel and the discharging of the battery.
   • LED Light Source: Provides illumination.
   • Light Pole and Fixture Housing: Supports the entire system while providing protection and aesthetic value.
2. Daytime Charging:
   • Photovoltaic Effect: Solar panels use the photovoltaic effect of semiconductor materials to convert sunlight into electricity. Common semiconductor materials include monocrystalline silicon, polycrystalline silicon, and amorphous silicon.
   • Monocrystalline Silicon Panels: Highest conversion efficiency, reaching over 20%, suitable for areas with insufficient sunlight.
   • Polycrystalline Silicon Panels: Slightly lower conversion efficiency, about 10% to 15%, but with lower costs, suitable for areas with abundant sunlight.
   • Amorphous Silicon Panels: Require lower light conditions, with a conversion efficiency of about 6% to 8%, suitable for environments with insufficient indoor or outdoor lighting.
   • Charging Process: The controller monitors the output voltage and current of the solar panel as well as the charging state of the battery to ensure efficient charging.
   • Charging Modes:
     • Switch Type: Simple switch control, suitable for small systems.
     • PWM Type: Pulse Width Modulation adjusts the width of the charging pulses to control the charging current, suitable for medium-sized systems.
     • MPPT Type (Maximum Power Point Tracking): Dynamically adjusts the operational point of the solar panel to remain at maximum power output, suitable for large systems.
   • Temperature Compensation: The controller adjusts charging parameters based on ambient temperature to avoid charging efficiency drops due to high temperatures or difficulties due to low temperatures.Compensation formula:Vcomp = Vref + k(T – Tref)
     • Vcomp: Compensated charging voltage
     • Vref: Reference charging voltage
     • k: Temperature compensation coefficient, usually -3 mV/°C
     • T: Actual ambient temperature
     • Tref: Reference temperature, usually 25°C
3. Nighttime Discharge:
   • Light-Controlled Switch: When the sun sets and the light intensity decreases, the open-circuit voltage of the solar panel drops to a preset value, prompting the controller to automatically start the discharge process.
   • Light Control Threshold: Typically set around 1.8V; when the open-circuit voltage of the solar panel falls below this value, the controller initiates discharge.
   • Discharge Process: The battery powers the LED light source through the controller, illuminating the streetlight. The controller ensures that the battery does not get over-discharged under any conditions (including extended rainy days).
   • Discharge Modes:
     • Constant Current Discharge: Maintains a constant output current, suitable for LED light sources.
     • Constant Voltage Discharge: Maintains a constant output voltage, suitable for some traditional light sources.
     • Smart Dimming: To further save energy, the controller can be set to a time-based dimming mode, reducing the power of the LED light source to half or even a third of its rated power during late night hours when fewer people are around, thus extending the battery life and the lighting time of the streetlight.

     Time-based dimming: For example, full power (100%) from 18:00 to 22:00, and half power (50%) from 22:00 to 06:00.

Smart Solar Street Lights Working Principle

1. System Components:
   • Solar Panels: Similar to traditional solar street lights, responsible for converting solar energy into electrical energy.
   • Battery: Stores electrical energy for nighttime use.
   • Controller: Not only manages the charging and discharging process but also incorporates more intelligent functions.
   • LED Light Source: Provides illumination.
   • Sensors: Includes light sensors, temperature sensors, humidity sensors, infrared sensors, etc., used for collecting environmental data.
   • Communication Module: Such as ZigBee wireless communication module, enabling remote monitoring and control.
   • Location Module: Such as GPS and BeiDou dual-mode positioning module, used to obtain the location information of the streetlight.
2. Intelligent Control:
   • Dual Timing: Utilizes a radio wave receiving module and BeiDou satellite timing module to achieve dual timing, ensuring time accuracy.
   • Timing Error: Usually less than 1 second.
   • Sunrise and Sunset Time Calculation: Obtains the latitude and longitude of the streetlight’s location through the GPS and BeiDou dual-mode positioning module, combining algorithms to calculate the local sunrise and sunset times, thus controlling the on and off time of the streetlight.
   • Sunrise and Sunset Time Algorithm: Based on astronomical algorithms of the Earth’s rotation and revolution, it has high accuracy.
   • Light Intensity Monitoring: Light sensors continuously monitor ambient light intensity to ensure that the streetlight is turned on or off under appropriate lighting conditions.
   • Light Intensity Threshold: Generally set around 100 lux; when the ambient light intensity falls below this value, the controller initiates discharge.
   • Temperature and Humidity Monitoring: Temperature and humidity sensors monitor environmental conditions, helping the controller adjust charging and discharging strategies to ensure normal operation under various weather conditions.
     • Temperature Range: -20°C to 60°C
     • Humidity Range: 0% to 100%
   • Pedestrian Detection: Infrared or microwave human sensing sensors detect whether there are pedestrians passing by, adjusting the brightness of the streetlight based on pedestrian density to save energy.
     • Sensing Distance: Generally around 10 meters.
     • Sensing Angle: Usually around 120°.
   • Remote Monitoring: The ZigBee wireless communication module enables remote monitoring and control, allowing administrators to check the status of the streetlight via the internet and perform fault diagnosis and maintenance.
     • Communication Distance: ZigBee communication distance can reach over 100 meters.
     • Communication Rate: 250 kbps
3. Hardware Design:
   • Solar Panels: Fixed installed at the top of the streetlight pole, commonly using monocrystalline silicon, polycrystalline silicon, and amorphous silicon panels. Some designs also include automatic tracking functions to keep the panels facing the sun to improve power generation efficiency.
   • Automatic Tracking: Achieved through motors and sensors, adjusting the angle once every hour.
   • Battery: Model usually SP12-38, matched with solar panels, connected to LED lights via an inverter to power the streetlight.
     • Capacity: 12V 38Ah
     • Cycling Times: Over 1000 times
   • Controller: Utilizes a high-performance ARM Cortex-M3 32-bit RISC core, operating at a frequency of 72MHz, with built-in high-speed memory and rich I/O ports. The controller collects data through various sensors and performs comprehensive processing for intelligent control.
     • Working Voltage: 5V
     • Working Current: 100mA
     • Memory: 128KB Flash, 20KB SRAM
   • Pushing Rod Control System: In some designs, electric push rods can control the retraction and extension of the solar panels to prevent the effects of sand and snow, improving power generation efficiency and extending the panel’s lifespan.
     • Electric Push Rod Model: YNT-01
     • Stroke: 300mm
     • Speed: 10mm/s
   • LED Light Folding Mechanism: Controls the folding of LED lights via an electric push rod to reduce energy consumption when lighting is not needed.
     • Folding Angle: 0° to 90°

Software Design

1. Program Initialization: The system initializes at startup, loading preset parameters and configurations.
   • Initialization Time: Typically around 10 seconds.
   • Time Setting: Obtains accurate time information through the GPS and BeiDou dual-mode positioning module to set the light switching times.
   • Time Accuracy: ±1 second
2. Data Collection: Sensors real-time collect data on light intensity, temperature, humidity, pedestrian density, etc., and send it to the controller.
   • Collection Frequency: Once per minute.
3. Data Processing: The controller comprehensively analyzes the collected data to decide the on/off status and brightness adjustments of the streetlights.
   • Processing Time: Typically around 1 second.
4. Communication Protocol: ZigBee wireless communication protocol is used for data transmission, enabling remote monitoring and control.
   • Protocol Version: ZigBee 3.0
   • Network Topology: Star, tree, and mesh networks
5. Fault Diagnosis: The controller has fault diagnosis capabilities, able to detect the system’s status and promptly discover and handle faults.
   • Fault Detection Time: Typically around 10 seconds.
   • Fault Alarm Method: Sends alarm messages via LED indicators and ZigBee modules.

Common Technical Details（Adjustable and customizable）

1. Solar Panels:
   • Conversion Efficiency: Monocrystalline silicon 20% or more, polycrystalline silicon 10% to 15%, amorphous silicon 6% to 8%.
   • Output Voltage: 12V or 24V.
   • Output Current: Changes according to panel area and light intensity.
2. Batteries:
   • Capacity: 12V 38Ah.
   • Charge/Discharge Efficiency: 85%.
   • Depth of Discharge: 80%.
3. Controller:
   • Working Voltage: 5V.
   • Working Current: 100mA.
   • Temperature Compensation Coefficient: -3 mV/°C.
   • Overcharge Protection Voltage: 14.4V (for 12V system), 28.8V (for 24V system).
   • Over-discharge Protection Voltage: 10.5V (for 12V system), 21V (for 24V system).
   • Light Control Threshold: 1.8V.
   • Time-based Dimming: 100% power in the first half of the night, 50% power in the second half.
4. LED Light Source:
   • Lumen Efficacy: 100 ~160 lm/W (1W LED).
   • Lifetime: 50000 hours.
   • Startup Time: Instant.
   • Working Voltage: 12V or 24V.
   • Working Current: Changes based on power.
5. Sensors:
   • Light Sensor: Light intensity threshold of 100 lux.
   • Temperature Sensor: Temperature range of -20°C to 60°C.
   • Humidity Sensor: Humidity range of 0% to 100%.
   • Infrared Sensor: Sensing distance of 10 meters, sensing angle of 120°.
6. Communication Module:
   • ZigBee Module: Communication distance over 100 meters, communication rate of 250 kbps.
   • GPS and BeiDou Dual-Mode Positioning Module: Timing error less than 1 second, time accuracy of ±1 second.
7. System Design:
   • Daily Power Consumption: For example, using a 70W ceramic metal halide lamp, with 8 hours of daily use, daily consumption is 560Wh.
   • System Efficiency: 0.6.
   • Longest No-Sunshine Period: 3 days.
   • Solar Panel Capacity Calculation Formula:Wp = (Q × 365) / (η × I0 × G)
     • Wp: Capacity of the solar panel (Wp)
     • Q: Daily power consumption (560Wh)
     • η: System efficiency (0.6)
     • I0: Standard solar radiation intensity (1000 W/m²)
     • G: Solar radiation on the inclined solar components (MJ/m²)
8. Smart Dimming:
   • Time-based Dimming: 100% power in the first half of the night, 50% power in the second half.
   • Adaptive Dimming Based on Light Intensity: Dynamically adjusts the brightness of the LED light source based on environmental light intensity.

Advantages

1. Environmental Protection and Energy Saving:
   • Zero Emissions: Does not consume conventional electricity, reducing dependence on fossil fuels and lowering carbon emissions.
   • Efficient Utilization: Maximizes the use of solar energy through intelligent control, minimizing energy waste.
2. Safety:
   • Low Voltage DC Power Supply: Prevents safety hazards associated with high voltage power supply.
   • Multiple Protections: The controller is equipped with various protection functions such as overcharge, over-discharge, short circuit, and reverse connection protections to ensure safe operation of the system.
3. Flexibility:
   • Automatic Adjustment: Automatically adjusts the brightness of the streetlight based on ambient light intensity and pedestrian density to meet needs at different times.
   • Remote Control: Administrators can remotely monitor and control streetlights via the internet, improving management efficiency.
4. Economy:
   • Easy Installation and Maintenance: No need to trench or lay cables, resulting in lower installation and maintenance costs.
   • Low Long-term Operating Costs: Although the initial investment is higher, the long-term operating costs are low, with a long service life and overall good economic benefits.
5. Applicable Scope:
   • Urban Roads: Widely used in urban secondary roads, parks, residential areas, villas, and other locations.
   • No Electricity Areas: Especially suitable for areas without electricity such as the western regions, border defenses, and islands, providing safe and environmentally friendly lighting solutions.

Through the detailed explanation above, I hope you have a more comprehensive understanding of the working principles, core values, and features of solar street lights and smart solar street lights.

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