# Building a simple solar powered outdoor light

#### navino87

Joined Apr 21, 2012
15
Requirement : To light a 14 - 20 watt DC lamp for 7 hours a day

Hello friends.. I just wanna make a simple solar powered outdoor light for my farm house where there is a frequent power cut. The temperature is generally very high in my place Today the temperature here is 109 degree.. Iam a complete newbie when it comes to this project. I have read an guide by Jeffrey Yago from the following page :http://www.backwoodshome.com/articles2/yago92.html.

From this above guide, i came to an understanding that it requires 4 main components to go ahead with this project. 1. solar array 2. charge controller 3. a battery 4. DC Lamp.

I can easily get battery and light in my place. But i have to source solar array and charge controller. The problem is i don't know which solar array and charge controller to get for lighting a 40-50 watt light. Will the following product get the job done for me??

http://in.element14.com/multicomp/mc-sp10-gcs/solar-panel-10w-17-5v-357x280x18mm/dp/1852499
http://in.element14.com/multicomp/mppt10a-12-24/battery-charger-mppt-solar-10a/dp/1852558

Please help me with selecting the right the solar array, high efficiency D.C. lamp, charge controller, and a battery. As this should be the first step to my project.

Thank you

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#### wayneh

Joined Sep 9, 2010
17,039
Work backwards from the load. You'll want the most light per watt you can find. Let's say you need 7 hours at 15W, that's 105 watt-hours of energy. Your battery voltage may need to be boosted or bucked to provide the proper voltage to the lamp, and that can be accomplished at, say, 85% efficiency. So you need 105/0.85 = 124 W•hrs. A rough estimate of battery efficiency (useful power out compared to charging power) is 50%, so you're up to 248 W•hrs of charging power.

You're charge controlling circuitry may be 90% efficient or so, meaning you'll need 248/0.9 = 275 W•hrs from your panel. Now it comes down to how much sunlight you have. The specs quoted for a panel are usually very optimistic, and you will rarely get that in reality except under ideal conditions. How many hours of full sun do you get? You may be able to get average estimates for you location, estimates that include cloud cover history.

Lacking any better estimate, let's say you get 6 hours per day of full-equivalent sunlight. Your panel needs to supply 275/6 = 46 watts continuous to get the job done. So no, that 10W panel is not adequate. You need 4-5X larger.  You mentioned heat. This reduces performance, and is a significant factor in full sun - these things get hot!

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#### russpatterson

Joined Feb 1, 2010
353
Consider LED lighting. You'll get much more light per watt. Malibu brand, available at Home Depot, Lowes, etc. makes outdoor quality lights for about $35 that are quite effective. I run a system in my yard that might fit your needs. 60 watt panel (about$220 on Amazon.com HQRP brand). 18Ah SLA battery from batteries plus and a charge controller (I've used MorningStar brand and they work well, available from Alt-e store). Then you just need your LED lights and a switch to turn them on when needed. I run 4 outdoor LED lights on that system. They usually run about 5-7 hours on a decent day like we're getting this time of year.

#### wayneh

Joined Sep 9, 2010
17,039
Consider LED lighting. You'll get much more light per watt.
I was surprised to learn this isn't necessarily so, although LEDs beat the pants off most incandescent bulbs. But there are other options. Not sure how practical they are for this kind of system.

See this reference, especially the table near the bottom.

#### navino87

Joined Apr 21, 2012
15
Thank you.. Think we will be having 10 to 11 hours of full-equivalent sunlight.. So, now i will be needing a say 50 or 60 watt solar panel. So, for 50 watt panel with 10 hours of equivalent sunlight, what is the capacity of the battery should i go for?? Also, please give me a fair idea about which lamp i should go for.. Guess, i should look for some efficient 12v lamp as the battery voltage is 12v..

TY

#### rohitd

Joined Jan 29, 2011
14
navin if you are in india as your name suggests then we have almost 10 hrs of bright light everyday on an average. so to get a good light first I woul suggest you to use surya cfl tubes 28 watts. one tube is equivalent to 40 watt normal thick tube. using cfl bulbs will also do but then the colour of light is a major factor. if you are using it indoors then use a 100watt pannel. it will cost you around 14-15K rupees. use inva tubular 150ampere another 14-15K. use a solar controller and an inverter. you will have power for everything Light, Fan, TV, Computer etc.. total cost will go to about 50-60k but it would be one time amount and you wont have the risk of overcharging the battery ever.plus government gives good subsidies for the solar and wind power.

#### evilclem

Joined Dec 20, 2011
116
Some charge controllers have in-built nightlight operation if you are chasing an auto-on at night light: http://www.electusdistribution.com....ID=7&keywords=&SPECIAL=&form=CAT&SUBCATID=361

I would definitely be using 12V lighting as this removes any need to acquire an inverter.

Battery size will depend on the bulb you choose, how many hours to run it each night and how many days of rainy weather you wish to survive.

#### navino87

Joined Apr 21, 2012
15
Thanks for the help guys..

@ rohitd : Ya, I am from India.. Bro, your setup is awesome.. But, it is purely for indore purposes.. I just want an cost efficient solar system for lighting say just 1 or 2 lamps in an remote area(agricultural land).. And is there any 12v cfl available?? I couldn't afford for an inverter for this kindda setup .. BTW, could you PM me the best place in India for sourcing best panel and control system??

@evilclem : bro, think i can live with the traditional switch system rather than going for some costlier nightlight operation control systems.. I just want to have an best, cost efficient solar system running.. A decent battery with capacity to power 1 or 2 15w lamp(12v) in summer and would be happy to survive say 2 days of rainy day..

#### Bernard

Joined Aug 7, 2008
5,774
Consider recreational vehicle, RV, or motor home supply store for 12V light fixtures. I think the ones I used had 2 15 W flourescent bulbs.

#### navino87

Joined Apr 21, 2012
15
^^ Thank you, Will look for it..

Iam planning to get a 50 watt or 75 watt solar panel. The bellow is the specification of the panel.

ELECTRICAL CHARACTERISTICS : SS-50
Nominal Power (Pm) in Watts : 50
Open Circuit Voltage (Voc) in Volts : 21.0
Short Circuit Current (Isc) in Amps : 3.17
Voltage at Maximum Power (Vmp) in Volts : 17.0
Current at Maximum Power (Imp) In Amps : 2.94
Maximum System Voltage : 1000V

PHYSICAL PARAMETERS
Solar Cells per Module (Units) : 36
Length X Width X Thickness (LXWXT)
in mm : 630X675X35
In Inches : 24.8X26.6X1.4
Weight in Kg : 5.15
Mounting Holes Pitch(Y) in mm : 310.00 In Inches : 12.2
Mounting Holes Pitch(X) in mm : 629 In Inches : 24.8
Area in Sq. Meter : 0.43 In Sq. Feet : 4.63
Junction Box : IP 65

OTHER CHARACTERISTICS
Type of cell : Mono / Multi crystalline Silicone
Front Face : Tempered Glass (Low Iron)
Encapsulate : EVA (Ethylene Vinyl Acetate)
Frame : Anodized Aluminium
Junction Box : Weather Proof Nylon 6
Temp. Coefficient : Voltage: -0.123 V/°K Current: +4.4mA / °K Power: -0.47%/°K
NOCT : 47 +/- 2 °C
ELECTRICAL CHARACTERISTICS : SS-75
Nominal Power (Pm) in Watts : 75
Open Circuit Voltage (Voc) in Volts : 21.0
Short Circuit Current (Isc) in Amps : 4.76
Voltage at Maximum Power (Vmp) in Volts : 17.0
Current at Maximum Power (Imp) In Amps : 4.41
Maximum System Voltage : 1000V

PHYSICAL PARAMETERS
Solar Cells per Module (Units) : 36 Length X Width X Thickness (LXWXT)
in mm : 900X675X35 In Inches : 35.4X26.6X1.4
Weight in Kg : 7.95
Mounting Holes Pitch(Y) in mm : 450.00 In Inches : 17.7
Mounting Holes Pitch(X) in mm : 629 In Inches : 24.8
Area in Sq. Meter : 0.61 In Sq. Feet : 6.66
Junction Box : IP 65

OTHER CHARACTERISTICS
Type of cell : Mono / Multi crystalline Silicone
Front Face : Tempered Glass (Low Iron)
Encapsulate : EVA (Ethylene Vinyl Acetate)
Frame : Anodized Aluminium
Junction Box : Weather Proof Nylon 6
Temp. Coefficient : Voltage: -0.123 V/°K Current: +4.4mA / °K
Power: -0.47%/°K
NOCT : 47 +/- 2 °C
Now, what would be the battery that would meet my requirements?? Will an 26Ah battery do the job for me?? or should i look for something better?? I seriously don't have any idea about selecting the batteries.

TY

#### wayneh

Joined Sep 9, 2010
17,039
Now, what would be the battery that would meet my requirements?? Will an 26Ah battery do the job for me?? or should i look for something better??
Again, you need to work backwards from the power needed by your load, your lights. If they're operating at 12v, each amp-hour is 12 watt-hours. Your lighting will require some number of watts and you can choose how long you need them to operate. That tells how many watt-hours you need. Divide by twelve and you've got your minimum Ahrs for your battery.

There may be a difference between rated Ahrs and actual, everyday, practical Ahrs. So you may need a battery rated higher than your needs. Maybe someone can supply the fudge factor. But you can't go wrong going larger. I wonder if an auto battery isn't most economical (more Ahrs per dollar) just because the market for them is so much larger.

#### navino87

Joined Apr 21, 2012
15
^^ Thx bro

Here goes the calculation part :

Solar array having a 75-watt name plate rating could generate 750-watt hours (75 watt x 10 hours) of power during a very sunny day. A 15-watt fluorescent lamp would operate 50 hours on this energy (750 watt-hour/15 watts), assuming no efficiency losses.

To Power a 15-watt fluorescent fixture an average of 7 hours each night. (15 watts x 7 hours)/ 12 volts = 8.75 amp-hour/day
Loss during both the battery charging and battery discharging process, and additional efficiency losses for the fluorescent ballast, charge controller, and wiring, adding at least 30 percent more to our initial calculation. (8.75 amp-hour) + (2.6) = 11.35 amp-hour/day
Are these calculations fair enough?? so, will a 26 Ah battery be enough to power 1 or max 2 12v, 15 watt CFL lamps??

TY

#### wayneh

Joined Sep 9, 2010
17,039
Battery charging alone doubles the power needed, end to end. But 30% makes a reasonable estimate of all losses after the battery.

So I believe the answer is yes, a 26 Ahr battery ought to be able to power one and maybe two CFLs. It'd be nice if someone else could doublecheck this.

I think your "full sun" estimate is optimistic ("full" to the manufacturer probably means 12-noon on the equator with crystal clear air) but that nice big panel should give a pretty good amount of power for one or two bulbs.

#### navino87

Joined Apr 21, 2012
15
Ya felt the same abt the 10 hrs full-equivalent sunlight .. Guess there will be atleast 7hrs full-equivalent sunlight at my place.. Now below is the revised calculation..

Solar array having a 75-watt name plate rating could generate 525-watt hours (75 watt x 7 hours) of power during a very sunny day. A 15-watt fluorescent lamp would operate 35 hours on this energy (525 watt-hour/15 watts), assuming no efficiency losses.

To Power a 15-watt fluorescent fixture an average of 7 hours each night. (15 watts x 7 hours)/ 12 volts = 8.75 amp-hour/day
Loss during both the battery charging and battery discharging process, and additional efficiency losses for the fluorescent ballast, charge controller, and wiring, adding at least 30 percent more to our initial calculation. (8.75 amp-hour) + (2.6) = 11.35 amp-hour/day

How long will it take to fully charge a 26Ah battery, with a panel which could generate approx. 525 watt/hr??

#### wayneh

Joined Sep 9, 2010
17,039
How long will it take to fully charge a 26Ah battery, with a panel which could generate approx. 525 watt/hr??
That's a bit complicated. The specs for your panel quote 4.4amps at peak power, 17V. That's more or less where it might operate when charging your battery, although it should slow down (lower current, higher panel voltage) as the battery approaches full charge. So ideally 26AH/4.4A=5.9 hrs.

Your charging regulator might draw the panel voltage down as low as 14-15 volts, so the current draw could be a bit higher at times, but I would still guess that a discharged battery will essentially take all day to return to full charge.

#### navino87

Joined Apr 21, 2012
15
^^ Thanks a lot for the help bro

Now coming to the solar controller part, will a Morningstar SunLight Charge Controller 10A 12V DC do the job for this setup?? morningstar seams to be the best in this market. The thing is that it is not locally available at my place. so gotta import it .. There are 4 versions available.

• 12 Volt: 10 and 20 amp ratings
• 24 Volt: 10 and 20 amp ratings
Guess the 10 amp 12 volt is the one for me.. Please guide me with selecting the best..

TY

#### wayneh

Joined Sep 9, 2010
17,039
Guess the 10 amp 12 volt is the one for me.. Please guide me with selecting the best...
I haven't looked in great detail but it appears fine. Maybe overkill but you'll probably enjoy the features.

It can handle current at >2X your panel's short circuit current, so it looks good on that count. I didn't see any spec for maximum input voltage from the panel. I doubt there is any concern at all, but it would be a nice thing to confirm.

You might consider the 20A unit. Only you can judge, but it would allow a 4X future expansion of your system and maybe doesn't add too much to the price? Again, it's your call based on price and your future plans. I think I'd stick with 12v, just for simplicity and versatility.

#### navino87

Joined Apr 21, 2012
15
Thanks wayneh and everyone ..

Ordered following and expecting it to be delivered in a week time.

Solar Panel 75Watt $111.11 Phocos Charge Controller CML20A 12/24v, 20A$28.14
Phocos CFL Lamps 15Watt $6.48 Battery 26Ah$48.14

Will update once i receive everything

As per this wiring diagram, I need to add fuses to wires leading to positive of battery and lamp. Could some1 help me with this? How to do this??

TY

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#### wayneh

Joined Sep 9, 2010
17,039
There are a lot of options for fuses and fuse holders. Some holders are meant to be mounted and some are in-line, just a fat spot in the wire.

I'd start by choosing what sort of holder you want and how to mount it as needed, and then choose a fuse to fit the holder. If you have any trouble finding the right fuse, you may have to work backwards; find the right fuse and choose a holder for it.

Do you know what current ratings you need? That will be the most important fuse rating to worry about. The second concern is how fast the fuse will blow in a over-current situation. Given a choice, I think I'd go with slo-blo for this application unless the controller instructions recommend otherwise.