How to design one solar street lamp system?

- Oct 22, 2018 -

Now solar lamps are very popular in China rural area, it is estimated that hundreds of thousands solar lamps are installed in remote area. Most of projects are financed by the local government to improve the living condition of the rural area. But there are some solar lamps can’t work well, the main reason should be the problem of system design, of course some company decrease the system design data to save cost, which is the main the reason. Anyhow, here let us talk about the design for the whole solar lamp systems.


Firstly, we should know the detailed information about the loads, that is the LED lamps. Now, mostly the lighting lamps are referred to LED. Let’s say 30W, this is enough for the rural area. The common lamp is about 120 lm/W, pls note this is for the whole lamp, not only the single chip. Like it work 12 hours at night, then the power consumption will be 30W*12 hours =360WH. There are smart way to save energy: like the first 2 hours, working at 100%, next 3 hours working at 80%, the next 5 hours working at 50%, the last 2 hours working at 80%, then the total power consumption is (2+3*0.8+5*0.5+2*0.8)*30=255WH. This will save about 1/3 energy than working 100% at whole night.

Secondly, you must calculate the panel power. You must know the meaning of “effective radiation time”, which is not the day time. Normally the effective radiation time is only 4-5 hours. So the energy from the panel will be Panel power * Effective radiation time. Like 150W panel, the effective time is 4 hours, then the energy from the panel will be 150W*4 hours =600WH. Normally the summer’s effective radiation time will be long, like in June, it will reach to 6 hours; while in winter, the effective radiation time will be only 2 hours. If you want the solar lamp can work very well, even in winter, then you must calculate like this: 150W*2hours=300WH. Also you need to consider about the tilt angle, try to get more energy in winter time;  also you need to consider about the dust on the surface of the panel; also you need to consider about the loss along the wires and solar controller conversion efficiency, so this will be a little complicated. So for one LED lamp of 30W, working for 12 hours at night, then 360WH, divided by 2 hours, then 180W panels are needed. Considering the tilt angle, dust affect, and wires and conversion loss, also there should be left some energy to charge battery full after rainy days except lamp consumption at night, maybe 300W will be suitable. But if you calculate as 4 hours effective radiation time, then 150W panel will be ok. But in winter time, especially in December, it will have some problems. Of course you can use dimming function of solar controllers, which can dim the lighting lumen to extend the lighting time.

The last, we should consider about battery. 360WH / 12V is 30AH, which means there is 30AH energy needed to supply to LED lamp. But the battery is not allowed 100% overdischarged, normally there is 30% for lead acid battery should be left for over discharging protection. And you also need to support 2 days or 3 days rainy days. Then you should calculate like this: 30AH * 3 days /0.7 = 130AH.

The above is some factors should be considered during designing one solar lamp system. Hope this will be helpful for you to set up one solar lamp system.

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