## Calculation formula for solar panel and battery configuration

1: First calculate the current:
Such as: 12V battery system; 2 30W lamps, 60 watts in total.
Current = 60W÷12V＝5 A
2: Calculate the battery capacity requirement:
Such as: 9.5 hours lighting time per night for street lights, the actual full load lighting is 7 hours (h);
Example 1: 1 LED light
(e.g. turn on 100% power at 7:30 in the evening, drop to 50% power at 11:00 at night, then 100% power after 4:00 in the morning, and close at 5:00 am)
Example 2: 2 non-LED lamps (low-pressure sodium lamps, induction lamps, energy-saving lamps, etc.)
(For example, two circuits are opened at 7:30 in the evening, one circuit is closed at 11:00 in the evening, two circuits are opened at 4:00 in the morning, and the circuit is closed at 5:00 in the morning)
needs to meet the lighting needs of continuous rainy days for 5 days. (5 days plus the lighting of the night before rainy days, totaling 6 days)
Battery = 5A × 7h × (5+1) days = 5A × 42h = 210 AH
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 210AH is only about 70%-85% of the real standard in the application. In addition, the actual loss should be measured according to the different load.
The actual working current is affected by constant current source, ballast, line loss, etc. It may increase by 15%-25% on the basis of 5A.
3: Calculate the peak demand for solar panels (WP):
The accumulated lighting time of street lights every night needs to be 7 hours (h);
★: The solar panel receives an average effective light time of 4.5 hours per day (h);
Relax at least 20% of the reserve for solar panels.
WP÷17.4V = (5A × 7h × 120%) ÷ 4.5h
WP÷17.4V ＝9.33
WP＝162(W)
★: 4.5h daily sunshine time is the sunshine coefficient of the area around the middle and lower reaches of the Yangtze River.
In addition, in solar street lamp components, the line loss, the loss of the controller, and the power consumption of the ballast or constant current source are different. In practical applications, it may be about 15%-25%. So 162W is only a theoretical value, and it needs to be increased according to actual conditions.