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Solar Panel

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75% of 12 hours equals 9 hours of sunshine. Depending on your location in India the sunshine time might be less. The amount of light hitting a solar panel is independent of the sun's relative position to the globe as long as the panels are aligned with the sun for rectangular light reception.

My safety factor calculation considered that fact.

At my location the sunlight time is 12 hours per day.

Even if your location is further North than mine (14deg North) you won't have the same conditions as they are in Great Britain. (Maximum of 180 sunny days in a good year and during that time intermittent rain :) )

Regards

Hans
 
75% of 12 hours equals 9 hours of sunshine. Depending on your location in India the sunshine time might be less. The amount of light hitting a solar panel is independent of the sun's relative position to the globe as long as the panels are aligned with the sun for rectangular light reception.

My safety factor calculation considered that fact.

At my location the sunlight time is 12 hours per day.

Even if your location is further North than mine (14deg North) you won't have the same conditions as they are in Great Britain. (Maximum of 180 sunny days in a good year and during that time intermittent rain :) )

Regards

Hans

The discussion was useful . I will continue after starting this work.
 
How did you estimate 250W panel with out considering my climatic conditions? How did you work out 2500WHRS(I think it has to be expressed as AH capacity of the battery. Am I right?). What is LiFePO4.
LiFePO4 is the chemical formula for an intrinsically safe lithium battery.

Watt hours is assuming you will be using a switcher since they are far less expensive than doubling the size of an already expensive solar panel. Maximum Power Point Tracking (MPPT) can help as well.

I was taking into account climate conditions, while MPPT would definitely work with the stated panel, at least for most conditions, I am not sure about a simple switcher charger. I was figuring on 40W x 2 (typically only half of the rated is actually available power) x 24 (hours per day) / 8 (hours of light) which is 240 Watts to deliver the power in 8 hours to run your load for 24.

AHrs is how the batteries are rated, multiply by voltage and you get WHRs, how much you can get from the battery through a switcher. The AHrs required from a 24V battery would be half of that from a 12V one even thought the WHrs were the same. I would be a measure of power requirement instead of battery capacity, electric utilities charge by KWHrs not KAHrs. If I were charged in KAHrs I would get a HV service and put the step down transformer in my house! ;)

Oh enough of my babbling... for a 12V battery pack, it needs to be able to charge at 10A for 8 hours and discharge at 4A for 16 hours, or around a 100AHr pack for 1200WHrs of actual capacity. I had doubled it for the lead acid battery because I forgot as I did the calculation to remove the high load fudge factor: if you are lucky the thing only supplies half of it's 20Hr rated capacity at high drain.
 
MPPT helps more than solar tracking: 12V panels "like" to put out 17V depending on conditions.

What type of LEDs are you looking at? you should not even be considering less than 80Lm/W and you will not see anything approaching that in small indicator parts-they are usually around 1Lm/W for the better ones.
 
I was figuring on 40W x 2 (typically only half of the rated is actually available power)
You mean a 240W panel working for 8 hrs will deliver only 960 WHRs to the load?


.. for a 12V battery pack, it needs to be able to charge at 10A for 8 hours and discharge at 4A for 16 hours,
Charging and discharging to be equal. Is it not?
 
MPPT helps more than solar tracking: 12V panels "like" to put out 17V depending on conditions.

What type of LEDs are you looking at? you should not even be considering less than 80Lm/W and you will not see anything approaching that in small indicator parts-they are usually around 1Lm/W for the better ones.

Can you please convert it to candela/ watt?
 
You mean a 240W panel working for 8 hrs will deliver only 960 WHRs to the load?
You wanted guarantees. Over the course of the day you will be lucky to get half the rated power on the average.
Charging and discharging to be equal. Is it not?
In a perfect world, sure.

In the real world you are looking at a 30% loss through good batteries under perfect conditions (low charge/discharge rates and never to far). If you are using a good switcher you might only lose 10% there.
 
Can you please convert it to candela/ watt?
you can't just convert Lumens to candelas. Lumens are a measure of actual quantity of light and candelas are a measure of intensity.

Candelas are measure of intensity at a particular viewing angle at a particular distance, it is like spreading a cubic decimeter of sand over a square meter and over a square decimeter. The depth (cadelas) of the sand is far greater in the square decimeter than it is in the square meter but the volume (lumens) of the sand is the same.
 
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you can't just convert Lumens to candelas. Lumens are a measure of actual quantity of light and candelas are a measure of intensity.

Candelas are measure of intensity at a particular viewing angle at a particular distance, it is like spreading a cubic decimeter of sand over a square meter and over a square decimeter. The depth (cadelas) of the sand is far greater in the square decimeter than it is in the square meter but the volume (lumens) of the sand is the same.

The LEDs used for traffic signaling has a limited viewing angle and increased light intensity. Viewing angle and intensity are normally taken in to consideration. It is the intensity of light in the required direction that is more important than total quantity of light emitted. Right?
 
The LEDs used for traffic signaling has a limited viewing angle and increased light intensity. Viewing angle and intensity are normally taken in to consideration. It is the intensity of light in the required direction that is more important than total quantity of light emitted. Right?
**broken link removed** P/N 10193 8 degree angle and 24Cd/Lm with a 40Lm red Rebel is 960Cd @ 1W

HLMP-C008-U000 6Cd @ 8 degree angle at 20mA@2V=0.04W. If you use 160 of of them for 960Cd you get 6W and quite a few more LEDs than you could possibly fit into a traffic light.

So...which is better?
 
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it would be appropriate to compare the numbers to the old 40W incandescent bulbs that might have only been putting out 300Lm (instead of 500Lm since they are long life bulbs), losing 30-50% in the reflector and 80-90% in the color filters for 20-30Lm actually getting out of the signal fixture.
 
In the real world you are looking at a 30% loss through good batteries under perfect conditions (low charge/discharge rates and never to far). If you are using a good switcher you might only lose 10% there.

30% energy loss, I can understand. But 30% charge loss:confused:
If the total charging is always higher than discharge, then there has to be a continuous voltage build up as in the case of a capacitor? (which is not possible). Is it not?

Switcher can reduce loss outside the battery, not with in the battery. Is it not?
Then did you mean that 30% loss is in the circuit?
 
No, in the battery. Most lithiums need an extra 15-20%. Lead acids run about equal IF you charge and discharge them slowly. Check the battery charge and discharge curves
 
No, in the battery. Most lithiums need an extra 15-20%. Lead acids run about equal IF you charge and discharge them slowly. Check the battery charge and discharge curves

I thought charging is similar to water flowing in to a tank. If there 1lit flowing to the tank and 0.99 lit is flowing out per unit time then there has to be a continuous increase in level and finally an over flow. If you can kindly explain why battery is different then I could have saved time in going through the details and learning myself .
Else can you just forward this charge discharge curve which will clear my doubt.
 
To make thing easy,

Check any battery datasheet. Look at the graph fast charging will result in low capacity. I mean capacity as AH. So as uber mentioned, slow charging gets higher or more capacity. Just look at any datasheet :)
 
There various electro-chemical details as well but the most basic concept is cell resistance, and it has a positive temperature coefficient. Another thing that helps is to charge them cold.

Lead acids are notorious for poor high load performance, consequently car batteries are rated in cold cranking amps-will the thing start your car in the winter? I you look at the capacity tables you see the rated capacity is for a 20Hr life. A 100AHr battery will supply 5A for 20Hrs, but at 20A it might only last 2Hrs.
 
There various electro-chemical details as well but the most basic concept is cell resistance, and it has a positive temperature coefficient. Another thing that helps is to charge them cold.

Lead acids are notorious for poor high load performance, consequently car batteries are rated in cold cranking amps-will the thing start your car in the winter? I you look at the capacity tables you see the rated capacity is for a 20Hr life. A 100AHr battery will supply 5A for 20Hrs, but at 20A it might only last 2Hrs.

Interested to know more. Can you please suggest any website?
 
What's the backup plan when the traffic light fails? I've seen India traffic cam movies, does anyone even pay attention to traffic lights?
Something regarding safety should be way over designed so its failure rate is almost zero.
 
I was wondering why a battery is needed. It is because the electricity over there hardly ever works.
 
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