2023 Guidance of Solar Street Light Design Caculation

Solar street light is charged by solar panel in the daytime and work at night, there is a built-in lithium battery, and different solar panel and battery configuration can meet different illumination requirement. In this article, Clodesun will introduce the solar street light design calculation.

Solar Street lights Battery Design

Step 1, calculate the current:

For example 12V battery system; 60 watts solar street light power.

Current(A) = 60W ÷ 12V = 5 A

Calculate the battery capacity demand:

For example, the cumulative lighting time of a street lamp every night needs to be 7 hours (H) with a full load;

(for example, open at 8:00 p.m., close 1 road at 11:30 p.m., open 2 roads at 4:30 a.m., and close at 5:30 a.m.)

It needs to meet the lighting requirements of 5 consecutive rainy days. (5 days plus the night before the rainy day, 6 days in total)

Battery capacity = 5A × 7h × (5 + 1) days = 5A × 42h = 210 ah

Calculation of solar street lamp solar panel

3： Calculate the peak demand (WP) of the solar panel

The cumulative lighting time of the street lamp every night needs to be 7 hours (H);

★: the average daily effective illumination time of the solar panel is 4-5 hours (H);

At least 20% of the reserved amount for the solar panel needs to be reserved.
the rated power of the LED lamp in a solar streetlight is 30W at 12V.

LED brightness at night will be set as 1 hour 60% + 5 hours 100% + 6 hours 40%

3 days of autonomy, in other ways, it can support 3 rainy/cloudy days

battery type is LiFePO4 batteries, the DoD would be 80%

Step 2: Calculate the daily energy consumption of the LED lamp

the current consumption of the LED lamp = 30/12 = 2.5Amps

the total power consumption in a day = 8 hours at 100% brightness

so the daily power consumption = 2.5 x 8 = 20Ah.

Step 3: Considering the 3 days’ autonomy
if we design solar-powered streetlights that can sustain for 3 rainy/cloudy days, then we should multiply daily power consumption by days of autonomy

that will be, 20Ah x 3 = 60Ah.

Step 4: Considering the depth of discharge.

in this example, our battery type is LiFePO4, and Its DoD is 80%

so the battery size should be 60Ah/80% = 75Ah

Solar Street Light Solar Panel Design

The electricity generated by solar panels should be used to make up for the electricity that was used last night, and at the same time, the electricity to be used tonight should be fully charged, that is,

Solar panel power generation = daily power consumption * 2

Solar panel power generation = solar panel power * installation site sunshine peak hours * power generation efficiency

Solar panel power=daily power consumption*2/(peak hours of sunshine at installation location*generation efficiency)

The peak sunshine hours of the installation site can also be found on the Internet, we will take 4 (most places are around 4 hours unless other places with particularly good sunshine can reach 5 hours).

The power generation efficiency of solar systems is generally 70-75%.

Solar Street Light Pole Height Design

The height of the solar power street light directly affects the illumination range of the led lamps. The higher the light pole, the wider the illumination range according to the Pythagorean theorem.

Scenic spots and parks are generally suitable for installing solar power street lights of about 7 meters, At night, the traffic of pedestrians and vehicles on rural roads is not large, so it is generally installed by one-sided interactive lighting, and the installation distance is about 20-25 meters. If it is less than 20 meters, part of the lighting will be affected. In addition, one more street light should be installed at the corner to avoid lighting blind spots.

solar power street light installation 3D photometric drawing

If you want to install a solar power street light with a pole height of 8 meters, you must ensure that the distance between the street lights is 25-30 meters. You should use the cross-lighting method for installation on both sides. This method is mostly used for road lighting with a width of 10 -15 meters.

For roads with 12-meter light poles, the longitudinal spacing of solar power street lights is generally recommended to be 30-50 meters. Symmetrical lighting on both sides should be used, and the road lighting width needs to exceed 15 meters.

Solar Street Lighting  Installation Design?

Different countries and regions have different geographic locations and latitudes. and we may set different battery capacities and solar panel sizes for the solar streetlights. When people install solar street lights someplace, on one side, the solar panel can face the sun directly, but on the other side, the solar panel can not face the sun, so if the solar panel can be adjustable, it will absorb more solar energy, which can maximize the conversion of solar energy while the lower quality solar led street light panel is fixed, causing low conversion rate of solar and the using areas are also limited, so when we design solar street light project, we need to confirm that the sun can face the solar panel on both side of the road

And we also need to consider the amount of traffic or activity in the area that needs illumination. For example, if solar street lights are installed on highways or airports, the traffic of people and vehicles is very busy and the lighting illuminations are relatively high. For example, especially on the highway, the client usually requires 100% 12 hours at night and last 3-4 rainy days. Conventional solar street lights can not meet the lighting requirements. then we need to consider enlarging the size of the solar panel and the capacity of the battery, another method is to increase the capacity of the solar street light battery and reduce the power of the LED.

When solar street lights are installed in parks and village roads, the traffic of people is not very busy, and the illumination requirements are not high. The government can consider using conventional solar street lights at this time in order to save costs and energy.

Conclusion

Before we start a solar street light project, we need to know the factors that affect the working solar power street light system, Like the width and lanes of the road, Lux level, working hours per day, local sunshine conditions, average continuous rainy days, and the highest or lowest environment temperature. With these conditions, a scientific and reasonable solar power system can be designed.