how to design a solar street light?

Solar Expert Posts: 34 ✭✭
hai folks,

i want to set up a solar street light pole with 60w/24v led lamp

autonomy: 8 hours(6pm-10pm=100% & 10pm-6am=50%)/day for three days

i plan to use kyocera 245w panel
@stc
Voc=36.9V
Isc=8.91A
Vmp=29.8V
Imp=8.23A

can i use this single large panel or i should go for two small panel?
---
battery:two 100AH AGM battery to have 50% DOD

the battery will be placed in a battery box

in hot season(jan-april) here temperature will be around 91 F

how can i maintain good temperature inside the battery box?
charge controller:Steca Solarix 15amps pwm

• Banned Posts: 17,615 ✭✭
Re: how to design a solar street light?

It's down to math again.

First of all, are you saying the lamp will be run at half power from 10 PM to 6 AM? If so that would be 4 hours * 60 Watts for 240 Watt hours plus 4 hours * 30 Watts for 120 Watt hours. Total: 360 Watt hours.

Now the batteries are 100 Amp hours, but what Voltage? If it is 12 then you have 200 Amp hours @ 12 Volts or at 50% DOD 1200 Watt hours maximum available. That's a bit shy of 3 days worth of 360 Watt hours, but you would probably have at least some charging even on cloudy days. If the light is triggered by a photocell you may have some usage on cloudy days as well.

The 245 Watt panel would need to be used on an MPPT controller. On 12 Volts that makes it (245 * 0.77 / 12) 15 Amps output. It should 'max out' a Morningstar 15 Amp MPPT controller. It will also be enough for 200 Amp hours of 12 Volt battery: 7.5% peak charge rate.

Before anyone chimes in about that not being 10% let me point out it is above the minimum 5% requirement and since this is a dedicated street light there should be no draw during charging.

But the problem is that the lamp is 24 Volts (I presume DC) and the panel does not have a high enough Vmp to properly charge a 24 Volt battery bank. It's close, and if the wiring can be kept very short and large to minimize V-drop and the panel doesn't get too hot you'll get partial charging for awhile. But expect short battery life. Normally a 24 Volt system requires a Vmp of about 35.

The Voltage issue is the only barrier I see to this working.

Oh and the expensive MPPT controller would not be needed for 24 Volts; you'd only need something like a SunSaver 10 http://www.solar-electric.com/ss-10l.html Make sure you get the 24 Volt version.
Re: how to design a solar street light?

You might want to experiment with lamp wattage (reflectors for more efficiency, etc.)...

In general, our eyes work "logrithmically"... For lights (and sound), a reduction of 1/2 from 60 Watts to 30 Watts is barely perceptible (I have tried this experiment with an LED flashlight that had a 0.5 and a 1.0 watt output level--It was almost impossible to see a difference in normal usage). A factor of 1/10 is a significant difference (if you had a 6 watt and a 60 watt fixture next to each other, the 6 watt fixture would not even be noticeable vs the 60 watt fixture).

There are some street lamp fixtures that are closer to 24 watts--And one mfg out of Europe that used motion detectors... When nothing is moving, the lamp reduces power a lot (maybe a factor of 1/10?). Of course, if you have windy weather+trees and bushes, then motion detectors are not going to be much use.

The take away for this is you can probably cut the light by 1/2, and reduce your battery+solar panel by 1/2, and people would not even notice the difference.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 891 ✭✭✭✭
Re: how to design a solar street light?
11JAGAN wrote: »
how can i maintain good temperature inside the battery box?

Bury it. Three feet down the temperature is a lot more constant year round.
• Solar Expert Posts: 3,739 ✭✭✭✭
Re: how to design a solar street light?
Bury it. Three feet down the temperature is a lot more constant year round.

Excellent advice... as long as there is no chance that it can flood. --vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i