Abstract: Solar energy, characterized by energy conservation, environmental friendliness, and convenience, offers a promising solution to lighting problems in passageways. By designing a well-thought-out solar-powered lighting system, we can not only address the issue of inadequate lighting during the day but also achieve significant energy savings.
Keywords: solar energy, photoelectric conversion, passageway lighting, solar panel, controller, battery, inverter
Preface:
The sun is an immense, enduring, and inexhaustible source of energy. As a primary and renewable energy resource, solar energy is abundant, free of charge, and pollution-free. Its advantages in terms of energy conservation, environmental protection, and convenience make it an ideal energy source for the future.
In China, according to the amount of solar radiation received, the country can be roughly divided into five categories. Shenzhen, located in the subtropical zone with warm winters and hot summers, falls under category three, receiving between 2200 and 3000 hours of sunshine annually. This makes Shenzhen an ideal location for utilizing solar energy effectively.
Solar energy can be utilized directly through photothermal conversion, photoelectric conversion, and photochemical conversion. Indirect and comprehensive applications of solar energy are even more diverse. Photoelectric conversion primarily involves solar panels and solar power supply systems, while photothermal conversion includes applications such as water heaters, solar cookers, and dryers. Photochemical conversion, though still largely experimental, is primarily used in photosynthesis and photoelectrochemistry.
Introduction to the Solar Passageway Lighting System:
1. Background of Installation:
Shenzhen is home to numerous overpasses longer than 40 meters, some of which suffer from insufficient lighting. These passageways tend to be darker during the day, especially after the streetlights are turned off, posing safety risks for pedestrians. To ensure continuous illumination, the original channel lights could only operate at night. Relaying the lines for mains-powered lighting would require significant investment and effort. However, installing a solar photovoltaic system offers a more practical solution with convenient construction.
Additionally, given the recent tight power supply situation in Shenzhen and the government's call for energy conservation, it became necessary to install a solar passageway lighting system.
2. Channel Conditions:
For instance, the southern passageway of the Honghu Interchange is 40 meters long and 6 meters wide. The distance from the passageway to the solar installation site is approximately 15 meters. The existing three sets of 250W high-pressure sodium lamps provide nighttime lighting.
3. System Principle:
Photovoltaic energy conversion refers to the process where the radiant energy of the sun is converted into electrical energy via semiconductor materials, commonly known as the "photovoltaic effect." The principle of the solar passageway lighting system is illustrated in Figure 1. The main components include solar cell arrays, controllers, batteries, inverters, and lamps.
Figure 1: Schematic Diagram of the Solar Passageway Lighting System
The original channel lights consume a total of 750W of power. The solar cell power and battery capacity required for solar-powered operation are substantial, resulting in a high system cost. Moreover, running a single set of lights for 24 hours every day throughout the year significantly reduces their lifespan. Thus, to ensure consistent lighting, a solar passageway lighting system was added. During mains-powered nights, the traditional channel lights remain on; when the mains fails or during the day, the solar-powered lights take over to ensure continuous illumination.
Comparison and Selection of DC/AC Loads:
Choosing DC loads would eliminate the need for an inverter, improving energy efficiency. However, given the 40-meter-long passageway, the distance from the battery to the end lamp is approximately 60 meters, leading to a 10% voltage drop in the 24V DC line. Additionally, controlling low-voltage DC with high currents results in significant losses, making voltage boosting technologies complex. Furthermore, DC lights have low luminous efficiency (45Lm/W), short lifespans (5000 hours), and are difficult to purchase.
On the other hand, while the utilization rate of AC loads may be slightly lower, the inverter's conversion efficiency exceeds 90%, with minimal losses. AC loads are more practical and convenient, so AC loads were selected.
Selection of Light Sources and Lighting Arrangement:
After comparing the efficacy, lifespan, price, and versatility of various light sources, five 25W high-efficiency energy-saving lamps were chosen. The lighting fixtures were arranged as follows:
Figure 2: Lighting Arrangement
Solar Panels:
Solar panels are the key components of solar photovoltaic conversion. The peak power (Pk) of the solar cell module depends on the local average solar radiation intensity and the electrical load requirements at the end.
1. Peak Power Selection (Estimation Formula):
Pk = Lamp Power × Number of Lamps × Daily Usage Time ÷ Effective Daily Sunlight Hours ÷ Actual Solar Panel Usage Power Coefficient ÷ Battery Conversion Efficiency ÷ Inverter Efficiency
Pk = 25(W) × 5(sets) × 12(hours) ÷ 5(hours) ÷ 0.7 ÷ 0.85 ÷ 0.9 = 560.22W
Among them:
1) The lighting time of the mains channel lights is adjusted seasonally by the theodolite, with solar channel lights operating 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, taken as 0.7.
Therefore, the solar panel power was chosen to be 600W (75W × 8 pieces).
3) The installation tilt angle is 33° to 35°, facing south, which not only facilitates maximum solar absorption but also allows rain to naturally clean the solar panels.
Controller:
The controller uses a PWM pulse width modulation controller with the following features:
1. Overcharge Protection: Stops charging when the battery voltage exceeds 28V;
2. Overdischarge Protection: Disconnects the load when the battery voltage drops below 22V;
3. Battery Charging Temperature Compensation;
4. Positive Pole Reverse Connection Protection;
5. Short Circuit Protection;
6. Overload Protection;
7. Overheat Protection (with heatsink);
8. Lightning Protection;
9. Small Power AC Supplementary Charging System: When there is insufficient solar energy due to rainy weather and the battery voltage falls below DC 22V, the high-frequency rectifier converts AC 220V mains into DC 24V to recharge the battery;
10. Detecting Mains and Switching: When mains power is available at night, the mains channel lights turn on and the solar channel lights are turned off by the controller. When the mains fails or during the day, the controller detects the absence of mains power and switches on the solar channel lights. This ensures continuous illumination in the channel, surpassing the functionality of a simple switch.
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