How to calculate the configuration for solar street light ?

Solar street light is charged by solar in daytime and bright in night, there are lithium battery built-in, different configuration can meet different requirement. Let us take some examples to introduce the configuration for solar street light.

Calculate Current
For example: A solar street system, 2pcs 30W LED lamps, 12V lithium battery.
Current=60W/12V=5A

Calculate Battery Capacity
For example, the lighting time of solar street light is 9.5h each night, actually lighting with full load is 7h.

Example:
Light source is LED lamp,
Lighting with 100% full load starts from 19:30 o’clock,
Lighting with 50% load starts from 23:00 o’clock,
The next day from 4:00 o’clock recovers to light with 100% full load,
LED lamp stop to light in 5:00 o’clock (the next day).
Requiring continue to light for 5 rainy days (5 rainy days + the last night, it is 5+1=6 days).

It is 3.5 hours from 19:30 to 23:00 with 100% full load lighting.
It is 5 hours from 23:00 to 4:00 (the next day) with 50% load lighting, amount to lighting with 100% full load for 2.5 hours.
It is 1 hour from 4:00 to 5:00.
So, actual total lighting time is 3.5h+2.5h+1h=7 hours.

Then battery capacity=5A*7h*6(days)=210Ah.

In order to avoid over-discharge, battery just discharges up to 80% as usual, namely, 210Ah capacity is just 80% of actual request capacity. In addition, it would have some power wasting consumption according to different loads, actual working current is influenced by constant flow source, rectifier, line loss, etc.
Therefore, the actual battery capacity might be 210Ah*125%=262.5Ah.

Calculate Power of Solar Panel (Wp)
Solar street light need work 7h each night, while it is about average 4.5h that solar panel can touch enough sunlight. The voltage of solar panel is 17.4V.
It need configure more 20% for power of solar panel.
Wp/17.4V=(5A*7h*120%)/4.5h,
So, Wp=162W.

Please note: 4.5h average sunlight is taking China as example, most of areas is about 4.5h effective sunlight in China, accurate sunlight time need be according to accurate Country or installation location.

Moreover, it has difference for line lose, power consumption of controller, different power of rectifier or constant flow source, so, 162W is also just theoretical value, the actual need add 15%-25%, 162W*(115%-125%)=186.3W-202.5W.

Above is description for solar street configuration, different configuration need be according to different project request.

Bingsolar Power, 4th, March, 2018