Abstract: Solar energy possesses the advantages of energy conservation, environmental friendliness, and convenience. By designing a rational solar channel lighting system, we not only address the issue of insufficient lighting during the day in the channel but also achieve energy savings.
Keywords: solar energy, photovoltaic conversion, channel lighting, solar panel, controller, battery, inverter
Foreword
The sun is a vast, enduring, and inexhaustible energy source. Solar energy is both primary energy and renewable energy. It is abundant, free to use, without transportation costs, and pollution-free. It offers the benefits of energy conservation, environmental protection, and convenience.
Based on the amount of solar radiation received, China can be roughly divided into five regions. Shenzhen, located in the subtropical zone, has mild winters and hot summers. It falls under category three, with an annual sunshine duration of 2200 to 3000 hours, making it highly suitable for utilizing solar energy.
Direct applications of solar energy include photothermal conversion, photovoltaic conversion, and photochemical conversion. Indirect and comprehensive applications are even more diverse. Photovoltaic conversion primarily involves solar panels and solar power supply systems; photothermal conversion includes water heaters, solar cookers, dryers, etc.; photochemical conversion is mainly applied to photosynthesis and photoelectrochemistry, which remains largely in the experimental research phase.
First, Introduction to the Solar Channel Lighting System
1. Background of Solar Channel Lighting Installation
Shenzhen has numerous overpasses longer than 40 meters. Due to insufficient lighting, these passages become dark during the day, particularly after the streetlights are turned on and remain dim for over an hour or on rainy days when the lights are turned off. For the safety of citizens, the passages need to be illuminated 24 hours a day. However, the existing channel lights can only provide illumination at night. Reconnecting the lines for daytime lighting would require significant investment and pose construction challenges. A solar photovoltaic system offers a convenient and efficient solution for small-scale power supply.
Additionally, in recent years, Shenzhen has faced tight electricity supplies, prompting the government to advocate energy conservation. Thus, installing a solar channel lighting system becomes essential.
2. Channel Conditions
Let us take the southern channel of the Honghu Interchange as an example to discuss the system's composition. The southern channel of the Honghu Interchange is 40 meters long and 6 meters wide. The distance from the channel to the solar installation site is approximately 15 meters. Originally, there were three sets of 250W high-pressure sodium lamps with nighttime power supply.
3. System Principle
Solar photovoltaic conversion refers to the process where the radiant energy of the sun is converted into electrical energy through a semiconductor material, commonly known as the "photovoltaic effect." The principle of the solar channel lighting system is illustrated in Figure 1. The main components include solar cell arrays, controllers, batteries, inverters, and lamps.
Figure 1: Schematic Diagram of Solar Channel Lighting System
The original channel lamps have a total power of 750W. The solar cell power and battery capacity required for solar-powered operation are substantial, resulting in a high system cost. Additionally, running a single set of lamps continuously for 24 hours*365 days significantly reduces their lifespan. Therefore, to ensure stable lighting, a solar channel lighting system was added. When the mains power is available at night, the original channel lights are activated; during power outages or daytime, the solar-powered channel lights illuminate, ensuring continuous lighting throughout the day and night.
Second, Comparison and Selection of DC/AC Loads
If DC loads are selected, the inverter can be omitted to improve energy efficiency. However, given the channel length of 40 meters, the voltage drop from the battery to the end lamps (approximately 60 meters) results in a 10% loss at 24V DC. Furthermore, controlling DC low voltages with high currents leads to significant losses, complicating voltage boosting technologies. Additionally, low light efficiency (45Lm/W), short lifespans (5000 hours), and difficulties in purchasing such equipment make DC loads less practical.
In contrast, while AC loads may have slightly lower utilization rates, the inverter conversion efficiency exceeds 90%, minimizing losses. AC loads are more practical and convenient, so AC loads were chosen.
Third, Selection of Light Sources and Lighting Arrangement
After comparing the efficacy, lifespan, price, and versatility of various light sources, 5*25W high-efficiency energy-saving lamps were selected. The lighting fixtures were arranged as follows:
Figure 2: Lighting Arrangement
Fourth, Solar Panels
Solar panels are the primary components of solar photovoltaic conversion. The peak power (Pk) of the solar cell module is determined by the local average solar radiation intensity and the electrical load requirements at the end of the system.
1. Peak Power Selection (Estimation Formula):
Pk = Lamp power × Number of lamps × Daily usage time ÷ Effective daily sunshine hours ÷ Actual solar cell array power coefficient ÷ Battery conversion efficiency ÷ Inverter efficiency
Pk = 25(W) × 5(set) × 12(H) ÷ 5(H) ÷ 0.7 ÷ 0.85 ÷ 0.9 = 560.22W
Among these:
1) The lighting time of the mains-powered channel lights is adjusted seasonally by theodolites. Solar channel lights operate for 11 to 14 hours per day, averaging 12 hours.
2) The actual power factor of the solar cell array considers the charging efficiency of the solar panel and losses during charging, set at 0.7.
Therefore, the solar panel power was chosen to be 600W (75W × 8pcs).
3) The installation tilt angle is 33° to 35°, facing south. This not only facilitates maximum solar energy absorption but also allows rain to naturally clean the solar panels.
Fifth, the Controller
The controller uses a PWM pulse-width modulation controller with the following features:
1. Overcharge Protection: When the battery voltage exceeds 28V, charging stops;
2. Over-discharge Protection: When the battery voltage drops below 22V, the load is disconnected;
3. Battery Charging Temperature Compensation;
4. Positive Pole Reverse Connection Protection;
5. Short Circuit Protection;
6. Overload Protection;
7. Overheat Protection (with heat sink);
8. Lightning Protection;
9. Small Power AC Supplementary Charging System: During rainy days when solar energy is insufficient and the battery voltage falls below DC 22V, AC 220V mains power is converted to DC 24V in the evening to recharge the battery;
10. Mains Detection and Switching: When mains power is available at night, the mains-powered channel lights illuminate, and the controller shuts off the solar-powered channel lights. When mains power fails or during the day, the controller detects the absence of mains signals and activates the solar-powered channel lights. This ensures that the channel is illuminated for 24 hours without relying on a manual control switch.
These enhancements ensure reliable and efficient operation of the solar channel lighting system.
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