Case Study: how to design a project with all in one solar street lights

2021/7/6 9:32:54

Here is a real-life inquiry from Oman.

First email

Since there is lack of detailed information for designing a project, so we ask for more information, and the customer sends them in attachments

Second email

We spent some time to study and organize the information from the emails

At last, the customer’s requirements are listed below

1. 100w rated wattage, all in one solar led street lights for a roadway project
2. The road is 12-meter width
3. Mounting height 10 meters
4. minimum required illumination level at the ground: 5 lux
5. 12 hours/day, full power operation
6. 5 days of autonomy
7. materials are suitable for continuous 55 Celsius (the testing method is in Chapter 5)
8. IP65 waterproof.

The engineering process started firstly from checking the existed IES files to guarantee the 5 lux optical requirement on the ground

let’s go through the steps one by one

design a project with all in one solar street lights

Step 1: check IES datasheet

Our 100w happens to be tested at the mounting height 10 m ( MH = 10 m), and it central illuminance can reach around 8 lux,

(tips: if the mounting height is 7 meters in your project, you need to multiply factor 2.041 in the right column to get relevant lux data on the ground)

100w road surface isolux diagram

Step 2: adjust the distance between the poles

Solar street lights throng one side of the street

After adjustment

In the course of simulation of engineering, IES files and Dialux can help engineers to get appropriate pole distance pretty easily.

process?

1. load the 100w IES file into software Dialux
2. Set the pole position: both sides or only one side?. (in this case, only one side installation is allowed)
3. Input basic parameters: road width, mounting height, preliminary pole distance, and the number of lamps per pole.
4. Try a different value of pole distance on the basis of using minimum streetlights, until you get “minimum 5 lux on the ground”

Installed at one side – diaLux simulation

In the end, we decide 25 meters is the best pole distance. And at this time, the minimum illuminance is about 7 lux.

Step 3. Calculate the battery size

So far, optical parameters and installation positions have all been determined.

Next, we need to size the solar battery according to requirements, 12 hours/day and 5 days backup

1. The LED modules in this 100w model require working current 1.34A.
2. 12 hours full power operation consumes battery power 1.34A x 12H = 16.08AH
3. for 5 days backup, we need (16.08AH x 5 = 80.4 AH)
4. So we select an existed battery size: 84AH for this model.

Step 4. Calculate the solar panel size

The final step is to size the solar panel according to battery size 84AH and the peak sun hours

1. The solar irradiance in Sultanate of Oman is sufficient, its peak sun hours is about 6.5 hours
2. 84AH / 6.5 = 12.92 A, so we need 12.92A current from solar panel for 6.5 hours
3. For LifePO4 lithium battery, the charging voltage is 18v
4. 18V x 12.92A = 232.62 W, that means we need about 230 w energy from solar panel per day theoretically
5.  Since the battery is not always totally empty, so we usually multiply a coefficient, 0.7
6. 232.62 W x 0.7 = 162.84 W

Our 100w model is equipped with a 170w monocrystalline solar panel.

100w model, 10 000 lumens, and with 5 days of autonomy

So, finally, we prepare the products with recommended parameters as below

• 170W monocrystalline solar panel
• 84AH LifePO4 lithium battery
• 100w rated LED model
• 10 000 lumen
• IP65

Conclusion

All in one solar street lights is a new trendy type of solar street lights, And this trend will be strengthened as the development of sodium-ion batteries, which is even powerful than current lithium-ion batteries.

Although it may take some time for sodium-ion batteries to go out from the laboratory to real-world applications, it is worth expecting. And at that time, solar street lights will be powerful enough to replace all streetlights.