The Samoan National Medical Phase I Health Department Building project is located in the capital of Samoa, Apia, with an average annual temperature of about 28 ℃. The base area is 8360m ^ 2, the office building area is 3193.6m ^ 2, with 3 floors above ground and a height of 18.6m. 35 sets of LED solar street lights are installed outdoors.
1. Introduction to solar street lights
Solar street lights are essentially an independent photovoltaic system composed of solar photovoltaic modules, light source controllers, batteries, load lamps, etc. The street lights using AC lamps are also equipped with inverters, which can meet the lighting requirements of roads or venues.
Photovoltaic modules are crucial components in solar street lights, primarily responsible for absorbing solar energy and converting it into electrical energy.
There are various types of light source controllers, including voice control, light control, timing control, etc. The control forms of solar street lights mainly include light control on light control off, light control on time control off, and time control on time control off. In order to extend the service life of batteries, it is necessary to limit their charging and discharging conditions to prevent overcharging and deep charging. In areas with large temperature differences, qualified controllers should also have temperature compensation functions.
Solar street lights should use energy storage batteries that are suitable for deep discharge and have a long cycle life. The design of battery capacity should comprehensively consider the design life of the battery, the imbalance of inclined surface radiation, photovoltaic module power, system efficiency, etc. The backup power supply period for solar street lights should be 3 days and 7 days. The power of solar cells must be more than 4 times higher than the load power to ensure the normal operation of the system. The voltage of solar cells should exceed the working voltage of the battery by 20% to 30% to ensure normal charging of the battery. The battery capacity must be more than 6 times higher than the daily load consumption.
2. Installation and debugging of LED solar street lights
2.1 Installation of LED solar street lights
2.1.1 Installation of lamp pole foundation
The foundation of the lamp post is the most important basic link of solar street lights, which requires the use of reinforced concrete. Its depth and width should meet the wind resistance requirements of the lamp post height and photovoltaic modules. The depth of the anchor bolt embedded in the concrete should be greater than 20 times its diameter, and it should be firmly welded with the main reinforcement; The rust on the anchor bolts should be removed, and the threaded parts should be protected; The center distribution diameter of the foundation flange bolt is consistent with the center distribution diameter of the flange hole at the base of the lamp post; The bolt adopts double nuts and spring washers. Grounding protection for street light system: The casing of electrical equipment such as metal lamp poles, solar cell module frames, brackets, and metal chassis should adopt grounding protection. The grounding body needs to be buried in the soil under the concrete foundation and welded. The welding should be firm and treated with anti-corrosion. The grounding wire connected to electrical equipment is connected with galvanized bolts. When welding is not possible for non-ferrous metal grounding wires, bolt connections can be used.
2.1.2 Installation of photovoltaic modules and controllers
(1) The installation of photovoltaic modules should be reliable, fastened with anti vibration screws, and the azimuth angle of the southern hemisphere modules should be due north. The inclination angle should be determined according to design requirements. Solar street lights rely on solar radiation for operation, so the installation location requires sufficient sunlight. The layout of street lights should be combined with local actual conditions and meet relevant standard requirements. Samoa is located in the southern hemisphere, with high light intensity in the due north direction. When installing, be careful not to be obstructed by tall buildings or trees in this direction.
(2) The controller is installed on the lamp post of the street lamp to prevent sunlight or rain.
2.1.3 Battery installation
The battery is buried underground and placed in a waterproof box, considering waterproofing and theft prevention. According to the local situation, only concrete cover plates were used during the installation of the project.
2.2 LED solar street light debugging
The LED solar street light in the Samoa Ministry of Health building consists of four components: controller, battery, solar photovoltaic panel, and LED street light. The battery adopts a 12V-85Ah model, with a solar panel power of 75W and an LED street light of 30W. The controller can measure parameters such as charging capacity, current, discharge capacity, battery voltage, and adjust the discharge power of the LED street light.
2.2.1 Preliminary determination of control mode and verification
Solar street light suppliers suggest using a combination of light control and time control for discharge. When the illumination is less than 10lux, the LED street light will automatically start after a delay of 30 seconds. The time control method is shown in Table 1.
| Discharge time/min | Discharge power/W |
| 240 | 30 |
| 300 | 15 |
| 60 | 30 |
According to the time control method, calculate the discharge watt hour:
Discharge watt hour=4 × 30+5 × 15+1 × 30=225Wh;
The rated voltage of the battery is 12V;
Discharge ampere hour=225 ÷ 12=18.75Ah.
Using control software to read internal data from the controller, it was found that the average discharge ampere hour per day is 18.2Ah, and the calculated discharge ampere hour is basically consistent with the actual discharge ampere hour.
Using control software to read the daily charging ampere hours of the controller (with clear weather selected for measurement and analysis), it was found that the total charging ampere hours were 13Ah.
By comparing the daily discharge ampere hour and charging ampere hour, it was found that the discharge ampere hour was 18.2Ah and the charging ampere hour was 13Ah. The daily discharge ampere hour is greater than the charging ampere hour, combined with the battery capacity of 85Ah.
Calculated: 85 ÷ (18.2-13) ≈ 17 days,
It indicates that the solar street lights will not be able to discharge according to the set requirements after 17 days (if encountering cloudy and rainy days midway, it will be less than 17 days). The lifespan of a battery depends on the depth of discharge, and the greater the depth of discharge, the shorter its service life. According to the set time control method, the daily discharge ampere hour is greater than the charging ampere hour, which increases the discharge depth of the battery and shortens its lifespan.
2.2.2 Correction of control parameters and verification confirmation
A solution was proposed and a detailed analysis was conducted to address the issues with the parameter settings involved in the manufacturer’s suggested light control+time control method. In order to achieve practical on-site functionality and enhance the service life of batteries, three solutions are proposed.
Option 1: Increase solar photovoltaic panels; Option 2: Reduce the daily discharge time of LED lights; Option 3: Reduce the discharge power of the LED light.
According to the actual situation, option one has been ruled out because the 75W solar photovoltaic panels have already been installed, and it is unrealistic and uneconomical to replace them. Option 2 is to reduce the daily discharge time of LED lights. This solution can be applied to three areas on site where the light intensity is not very good, because the light on the south facade of the building (the south facade of the building in the southern hemisphere is blocked) is relatively weak. By reducing the daily discharge time of LED lights, a balance between daily charging ampere hours and daily discharging ampere hours can be achieved, reducing the depth of battery discharge. Option three is to reduce the discharge power of the LED lights. Considering the local situation, there are basically no night entertainment activities in Samoa. Therefore, it is more appropriate to reduce the discharge power and reduce the illumination of the LED lights. The specific control mode adjustment is shown in Table 2.
| Discharge time/min | Discharge power/W |
| 240 | 15 |
| 300 | 15 |
| 60 | 15 |
Calculate the discharge watt hour based on the above time control method:
Discharge watt hour=4 × 15+5 × 15+1 × 15=150Wh;
The rated voltage of the battery is 12V;
Discharge ampere hour=150 ÷ 12=12.5Ah ＜ 13Ah.
After adjustment, the daily charging ampere hour is greater than the daily discharge ampere hour, which can reduce the discharge of the battery
Depth increases the service life of the battery.
If encountering the most unfavorable situation of continuous cloudy and rainy days and unable to charge, the time for the battery to discharge is calculated as follows:
The capacity of the battery is 85Ah, calculated at a discharge efficiency of 50%.
Discharge days=85 × 50% ÷ 18.2=2.33 days (calculated based on the originally set daily discharge ampere hour of 18.2Ah).
Discharge days=85 × 50% ÷ 12.5=3.4 days (calculated based on the adjusted set parameter of daily discharge ampere hour of 12.5Ah).
By adjusting the discharge time and power parameters of the on-site solar street lights through Scheme 2 and Scheme 3, the overall lighting functionality requirements of the outdoor street lights can be achieved, and the purpose of extending the service life of the battery can be achieved. After determining the parameters, actual observation and verification were carried out, which was consistent with theoretical calculations, and the debugging of LED solar street lights was accurately completed.
3.Conclusion
Through follow-up observation of the installation, debugging, and application of LED solar street lights in the Samoa Ministry of Health building, a method for installing and debugging LED solar street lights has been developed. By comparing theoretical calculations with actual observation data, and combining with application scenarios, the parameter settings for discharge time and discharge power have been determined. This installation and debugging plan has certain reference value for similar projects.