How do you calculate battery and solar panel size?

Solar street lights have become more and more popular in the market this year, especially in regions or countries with sufficient solar energy, where the market share is getting higher and higher. Correspondingly, the market is flooded with LED solar street lamps of uneven quality. Some low-quality solar street lighting has seriously affected the customer’s experience. The most common problem is that some lamps have insufficient lighting time. Solar street lights can only turn on for 2-3 hours a day. To solve the problem of insufficient lighting time, it is necessary to select batteries and solar panels of appropriate capacity. So how do we calculate the appropriate battery and solar energy capacity?

• First calculate the current required by the entire solar street light system

For example: 12V battery system; 50W LED street light.
Current = 50W÷12V = 4.17 A

• Second, the calculation of the required capacity of the battery

For example, LED street lamp lighting time is 11 hours per night, the actual 100% load lighting is 7.5 hours (h);
(At 7:00-11:00 in the evening, turn on 100% power, at 11:00 at night-6:00 in the next day, the brightness power is 50%=25W)
Need to meet the lighting needs of continuous rainy days for 3 days. (3 days plus the lighting the night before the rainy day, total 4 days)
Battery = 4.17A×7.5h×(3 + 1) days
= 4.17A×30h = 125AH
In addition, in order to prevent the battery from overcharging and over-discharging, the battery is generally charged to about 90%; the remaining discharge is about 5%-20%. So 125AH is only about 70%-85% of the real standard in the application. In addition, the actual loss should be measured according to the different loads. The actual working current is affected by a constant current source, ballast, line loss, etc. It may increase by 15%-25% on the basis of 4.17A.

• Calculation of required power for solar panels

According to the above example, the cumulative lighting time of 50W LED solar street lights needs to be 9 hours (h) per night; at the same time, we set a daily effective solar light duration of 6 hours (the effective light duration of each area is different), Then the required solar panel capacity is:

Relax at least 20% of the extra amount required for solar panels.
WP÷17.4V = (4.17A×7.5h×120%)÷6h
WP÷17.4V = 6.26
WP=109(W)
In addition, in the solar street lamp assembly, the line loss, the loss of the controller, and the existence of the ballast or constant current source are different. In practical applications, it may be about 15%-25%. Therefore, 130W is only a theoretical value, and a 120W solar panel is generally a safe solution.

Conclusion

If you want solar-led street lights to meet the lighting time just like ordinary LED street lights, the general approach is to increase the capacity of solar panels and batteries. However, in the actual market environment, many manufacturers in order to attract customers with low prices Often cut corners, especially to reduce the capacity of the battery (because the cost of energy storage batteries in the solar street light system is the highest). If you want to buy a solar street light that meets the standards, please pay attention to the capacity of the solar panels and batteries.