In traditional coal mine street lighting design, there are common problems such as long power supply distance and poor cable laying environment. The usual solution is to use box type substations for power supply. According to the Urban Road Lighting Design Standard (CJJ45-2006), the design of street lighting usually adopts TN-S or TT grounding systems. However, regardless of which grounding system is used, the impact of high/low voltage grounding faults on the street lighting distribution system, street lighting sensitivity verification, selection of mainline circuit breakers, cable selection, and cable laying must be considered. Solar street lighting, as a new type of green street lighting, has significant advantages over traditional street lighting methods in terms of energy conservation and environmental protection, and does not need to consider the aforementioned issues in traditional street lighting design. It is suitable for road lighting on secondary roads and below; Compared with wind solar complementary street lighting, its structure is simple and maintenance costs are not high. Coal mine surface roads are usually secondary roads, and solar street lights are obviously very suitable for lighting coal mine surface roads.
1. Solar street light system and working principle
The solar street light system usually consists of several parts, including LED light source (including driver), solar panel, battery pack (including battery pack insulation box), solar street light controller, street light pole (including foundation), etc. Its working principle is: under the control of the solar street light controller, the solar panel charges the battery during the day, and the battery pack supplies power to the LED light source at night, controlling the opening and closing of the LED light source. The solar street light controller can ensure that the battery pack is not damaged due to overcharging or discharging under any conditions (sufficient sunlight or long-term rainy days), and has functions such as light control, time control, sound control, temperature compensation, lightning protection, and reverse polarity protection.
2. Design examples
2.1 Basic Design Information
The access road to a certain coal mine is located at longitude 114 ° 01 ‘~114 ° 06’ east and latitude 31 ° 46 ‘~31 ° 52’ north, with an altitude of 990 meters. The average sunshine time in the region is 4.04 hours, and the longest continuous rainy day is 7 days. The total length of the access road is 1709.712 meters, with a pavement width of 9.0 meters and a roadbed width of 12.0 meters. The pavement structure is asphalt concrete.
2.2 LED light power calculation
Due to the design of the road being a secondary road, according to the “Urban Road Lighting Design Standard” CJJ 45-2006, the average illuminance on the road surface is required to be maintained at 15lx, and the illuminance uniformity is not less than 0.35. The street lights should be arranged on one side, using cut-off type lamps. The designed solar street lights have a height of 10 meters, a spacing of 30 meters, a overhanging length of 2 meters, and an elevation angle of 10 °, totaling 55 sets.
According to the formula for road lighting illuminance:
Among them, Eav is the illuminance, taken as 15 Lx, Φ Is the luminous flux, k1 is the maintenance coefficient, k2 is the utilization coefficient, k3 is the lamp efficiency, Weff is the effective width of the road surface, and S is the distance between street lamps. Take k1=0.6, k2=0.7, and k3=0.9. After calculation Φ= 9 375Lm, check relevant samples and confirm that the LED light power is 100 W.
2.3 Battery capacity calculation
The working voltage of the LED is 24 V, and the discharge current of each 100W LED lamp is 4.17 A (100 W/24 V ≈ 4.17 A); Assuming a constant current driving power consumption of 20% for LED lights, the actual discharge current is 5 A (4.17 A × 1.2 ≈ 5 A); Each LED light works for 10 hours a day and consumes 50Ah of electricity (5 A) × 10 h=50 Ah).
To meet the discharge requirement of continuous rainy and cloudy weather for 7 days (including the discharge on the night before rainy and cloudy weather for 8 days), the battery needs to store a capacity of 400 Ah (50 Ah) × (7+1)=400 Ah. Considering factors such as battery capacity degradation and seasonal temperature changes, a battery with a discharge capacity of 90% is calculated to be 444 Ah (400 Ah/0.9 ≈ 444 Ah), so a total of 3 150 Ah/24 V batteries are required.
2.4 Calculation of battery panel capacity and inclination angle
Assuming that each LED light works for 10 hours a day (taking 7pm to 5am the next day as an example), with a maximum continuous rainy day of 7 days and a minimum of 20 days between two rainy days, the daily power generation of the battery panel must not only meet the electricity consumption of the LED light for 10 hours that night, but also be fully charged within the remaining 13 days (20-7=13) to ensure that the battery pack can provide 7 days of rainy and cloudy lighting. Therefore, the daily power generation of the battery panel needs to meet the electricity consumption of 1.57 days (1+(7+1)/14=1.57). Assuming a 24V monocrystalline silicon solar panel is used with a charging voltage of 34.8V, the capacity of the solar panel Wp=50 × one point five seven × 34.8/4.04=676 W.
So, 6 120 W/24V battery panels can be selected. The battery panel with a peak power of 676 W can generate electricity after 4.04 hours of peak sunlight per day, which can meet the requirement of 5 A current LED lights working for 10 hours every night. At the same time, there is a surplus of 0.57 days of power supply per light day that can be stored in the battery, which can perfectly meet the design requirements of 7 rainy and cloudy days every 20 cycle days.
In order to effectively utilize solar energy, the installation of solar panels should determine the optimal inclination angle based on the local longitude and latitude. The coal mine is located at 114 ° 01 ‘-114 ° 06’ east longitude and 31 ° 46 ‘-31 ° 52’ north latitude. The inclination angle between the solar panels and the horizon is determined to be 39 °, and 5 ° west.
2.5 Lightning protection and grounding
Due to the design of solar street lights being DC 24V, which is a safe voltage, there is no need for electrical protection grounding. Solar street lights cannot use street lights or solar panels as lightning arresters. It is advisable to use metal lamp columns as both lightning arresters and down conductors. It is also advisable to use street light steel reinforcement foundations as lightning protection grounding electrodes, with a grounding resistance not exceeding 10 Ω. If not met, an artificial grounding electrode should be added. To prevent transient overvoltage, surge protectors are installed in the street light controller.
In summary, 55 sets of 100 W LED lamps, 55 sets of 10 m lamp posts, 330 120 W/24 V battery panels, and 165 150 Ah/24 V batteries are required.
3. Performance comparison
In order to intuitively reflect the advantages of solar street lamps, Table 1 presents a performance comparison between solar street lamps and traditional sodium lamps.
| Comparison project | Solar street lights | Traditional high-pressure sodium lamp | Comparison results |
| Lamp power | High | General | Solar street lights are more energy-efficient |
| Service life | 500 000 h | 10 000 h | Longer lifespan than high-pressure sodium lamps |
| Environmental friendliness | Pollution-free | Heavy metal pollution | Solar street lights are pollution-free and recyclable |
| Security | 50 V safe voltage | High pressure | Solar street lights are safer |
| Electricity consumption and maintenance costs | Low | High | Solar street lights are more economical |
Obviously, solar street lights have significant advantages over traditional street lights.
4. Conclusion
Although solar street lights have been widely used at present, their application in coal mines is rare. Coal mine ground roads are usually secondary roads, and solar street lights have significant advantages in their street lighting compared to traditional street lighting. This article presents the engineering application of solar street lights in the design of coal mine ground street lights to attract the attention of coal mine practitioners.