Solar lighting system in our school

[pastmaster02]

Hello! I've just recently joined Solar Panel Talk forums. I'm kinda new here. I just came to ask for some advice and help about our planned project "solar lighting system" for our school. Our project is about making an outdoor lighting system that runs from solar energy and they will only be turned on at around 6PM up to 6AM in the morning the next day so that's 12 hours of continuous lighting. We are planning to provide about 50 watts of LED lamps at 12V DC for the area (it's actually a catwalk). We are also planning to buy a solar panel array with a capacity of 100 watts peak (*12V). And to provide the storage for our energy, we are also planning on buying a 12V 100 amp-hr deep cycle battery with a 30 amp solar charge controller. Now my question is: are these components enough to make our project work?

I've imagined the connection to be something like this: solar panel array > solar charge controller > battery > LED lights

I've got more questions:
1. How long can a full charged 12V 100 Ah deep cycle battery provide power to our 12V 50 watt LED?
2. How long does it take to charge up a 12V 100 Ah battery if our solar panel array provides 100 watts peak of power at 7 sun hours?
3. Does increasing the depth of discharge of our battery affect the duration of the "on" time of our LED lamps?
4. What is the advisable depth of discharge for a 100 Ah 12V deep cycle battery?

* I'm not sure if the voltage output of the array is 12V. Some say that it can be up to 17 V. How can I determine what voltage our array provides?


Can someone teach me how to calculate the information needed to make our project successful? These are our available materials (they're kinda fixed because we are low on budget hehe):

50 watts 12V DC LED lamps (turned on for 12 hours)
100 watts peak solar panel arrays
100 Ah 12 V deep cycle battery
30 amp solar charge controller (based on the info above, can we reduce the rating of this charger? we really need to budget out money wisely)

Thank you.

[Mike90250]

How many 50w lamps will you be using.

get the math teacher at the school to help you.

# of lamps
50 w
# hours (12)

12 hr x 50w = 600wh x (number of lamps) That's how much power is burned in 1 night.

You need a battery that is 4x that number, to get long ( >5 years) life from it.

Your solar array needs to be at least 2 x ( 600wh x (number of lamps) ) you got earlier, sometimes 3x.

It's going to be expensive. Plugging in the lights will only cost you 10 cents a night, per light, solar will cost you over a dollar per night, per light.

[Sunking]

100 watt panel will only power the light for about 1 to 2 hours. I agree you need a crash course in Math, real math, not green math.

[john p]

what is neing used?
50 watts of LEDs ?
50w LED lamps? if "yes" how many??

Mabe your calcs are all wrong on what he needs to provide the power.
50w LEDs would be overkill to just light a catwalk.
mabe just 6? 1w LEDs could do this adequately??
I use 12 of the to do the perimeter of a building and find that its plenty of light.

[pastmaster02]

Thanks for your replies. We are about to use 10 pieces of 5-watt bulbs for a total of 50 W. My classmates decided to put a single LED lamp in every post in our catwalk.
Question: for a given rating of components 100 Wp solar array, 100 Amp-hr 12V battery, 30 A charge controller, and 50W lights, how long can we power the lights? Considering these components are somewhat fixed (in specs), what adjustments on powering time must we make? For example, we could just power the lights for 1 or 2 hours just like Sunking said. Is there any way to provide lighting for a minimum of 5 hours? Should we use a lower power lamps?

I know the idea of having a solar lighting system is really expensive but our professor required this project to us for our course curriculum. So we can't do much about it.
Thanks again.

[Mike90250]

....

I know the idea of having a solar lighting system is really expensive but our professor required this project to us for our course curriculum. So we can't do much about it.
Thanks again.

Well, since your professor is not grading me, I'm not going to give the answer away.

Oh, wait, I already did, in my first reply to you. You just have to do the math I laid out.

Plan on only a 20% discharge from full battery, or you will shorten the life considerably.

[pastmaster02]

Well, since your professor is not grading me, I'm not going to give the answer away.

Oh, wait, I already did, in my first reply to you. You just have to do the math I laid out.

Plan on only a 20% discharge from full battery, or you will shorten the life considerably.

Thanks again for your reply.

Total power of lamps: 50 W
Number of powered hours: 5 hours (from 12 down to 5 hours)
Energy spent in 1 night: 50 W x 5 hours = 250 W-hr

Battery: 250 W-hr x 4 = 1000 W-hr capacity. Is this equivalent to 1000 W-hr divided by 12 V = 83.3 Amp-hr? (does multiplying the energy spent by 4 mean we are using only 25% of the battery capacity? Is that good enough?)

PV array: 250 W-hr x 2 = 500 W-hr capacity (assuming the the sun is giving full power for 7 hours, is the power our array gives equal to 500 W-hr/7 hrs = 71.43 W?

[john p]

I dont know where you live but you certainly dont get 7hrs of good sunlight each day probably 4 hours. work onthat figure. if its winter it could be 2 to 3 hrs.

[pastmaster02]

I dont know where you live but you certainly dont get 7hrs of good sunlight each day probably 4 hours. work onthat figure. if its winter it could be 2 to 3 hrs.

I live in the Philippines. From what I have searched through the net, our locality has an average of 5.8 sun hours a day. I think the array will produce power at its peak at around 10AM up until between 3-4 PM. So can I use 5 hours of sun? Thanks.

[john p]

If you are in Luzon 4 hrs Visayas 4.5 Mindano 5 hrs. im near Tacloban and that is Visayas about 4.5

[pastmaster02]

If you are in Luzon 4 hrs Visayas 4.5 Mindano 5 hrs. im near Tacloban and that is Visayas about 4.5

I'm in Luzon. 4 hours is a bit short. Is that the minimum sun hours? In my computation should I use that minimum? Or can I raise it to like 5 hours or something? Thanks!

[john p]

No.. the 4 hrs would be close to best case ..
Reason .. its never clear skys all day. you have to allow for some clouds. and clouds are solar energy killers.

[Sunking]

I'm in Luzon. 4 hours is a bit short. Is that the minimum sun hours? In my computation should I use that minimum? Or can I raise it to like 5 hours or something? Thanks!

You are getting yourself into trouble here. You cannot use the AVERAGE for battery systems. You have to use the shortest month of the year. If you fail to do that you will go dark and destroy your battery.

[Sunking]

Battery: 250 W-hr x 4 = 1000 W-hr capacity. Is this equivalent to 1000 W-hr divided by 12 V = 83.3 Amp-hr? (does multiplying the energy spent by 4 mean we are using only 25% of the battery capacity? Is that good enough?)

Incorrect answer. You only discharge 20% per day. [250 wh x 5] / 12 volts = 104 AH

PV array: 250 W-hr x 2 = 500 W-hr capacity (assuming the the sun is giving full power for 7 hours, is the power our array gives equal to 500 W-hr/7 hrs = 71.43 W?

Incorrect, you do not receive 7 Sun Hours in the winter months of December and January. I assume more like 3 to 4 hours. 250 wh / .5 / 3 h = 166 watts.

[pastmaster02]

Incorrect answer. You only discharge 20% per day. [250 wh x 5] / 12 volts = 104 AH

Incorrect, you do not receive 7 Sun Hours in the winter months of December and January. I assume more like 3 to 4 hours. 250 wh / .5 / 3 h = 166 watts.

I will make adjustments to my calculations. Instead of 5 sun hours, I'm gonna use 4 hours of sun. So, 20% discharge would be the best option I'll have to prolong the battery life. I see. If that is the case, how long do you think my battery will last, considering I have one cycle of charge/discharge per day? And about halving the 250 W-hr energy, what's that for? PV array inefficiency? Thanks.

No.. the 4 hrs would be close to best case ..
Reason .. its never clear skys all day. you have to allow for some clouds. and clouds are solar energy killers.

Oh ok. So that's 4 hours of sun on my calculation. Thanks a lot!