How to Control the Cost of Solar Lights?

As we all know, when we choose a solar streetlight, we need to make some preparation. For example, we need to know where to install the lights? What is the road situation, one lane, two lanes? How many constant rainy days? And what is the lighting plan at nights.

After knowing all these data, we can know how big solar panel and battery we will use, and then we can control the cost.

Let’s take an example, for a 12v, 60W streetlight, if it will work for 7 hours every night, and there are 3 constant rainy days, and the daylight ratio is 4 hours. The calculation is as follow.


1. Capacity of the Battery

a.Calculate the current

Current =60W÷12V5A

b. Calculate the capacity of battery

Battery=Current* working time everyday* constant rainy days=105AH.

We need to pay attention, 105AH is not the final capacity, we still need to consider the over-discharge and over-charge issue. In the daily use, 140AH is only 70% to 85% compared to the standard.

The Battery should be 105÷0.85=123AH.


2. Solar Panel Wattage

Before calculating the solar panel wattage, we should know that solar panel is made of silicon chips. Regularly one solar panel will have 36pcs silicon chips in parallel or in series. The voltage of each silicon chip is about 0.48 to 0.5V, and the voltage of the whole solar panel is about 17.3-18V. Besides, during the calculation, we need to leave 20% space for the solar panel.

Solar panel wattage ÷working voltage=(current×working time every night×120%).

Solar panel Wattage Min=5A×7h×120%)÷4h×173V182W

Solar panel Wattage Max=5A×7h×120%)÷4h×18V189W

However, this is not the final wattage of solar panel. During the working of solar lights, we also need to consider the wire loss and the controller loss. And the actual solar panel should be 5% more compared to the calculation data 182W or 189W.

Solar panel Wattage Min182W×105%=191W

Solar panel Wattage Max189W×125%=236W

All in all, in our case, battery should be more than 123AH, and the solar panel should be between 191-236W.

When we choose the solar streetlights, based on this calculation formula, we can figure out the capacity of the solar panel and batteries by ourselves, This can help us to save the cost to some extent, which will also bring us good outdoor lighting experience.

Post time: Jan-14-2021