# Thought for outside yard light



## budgetprepp-n (Apr 7, 2013)

I was just playing with a inverter and some led light bulbs. 
The cree 60 watt pulls 13.2 watts. The 100 watt pulls 21.6 watts 

In darkness a 60 watt or a 100 watt really gives off a lot of light. I have a tall pole with one of those blueish 
mercury lights. it breaks down all the time I would like to replace it. 

With a good deep cycle battery how big of a solar panel would it take to have the 60 or 100 watt run all night?
I have a 12 volt photo cell that would turn it on at night and off at dawn. 

This would be a self contained unit it's own battery and panel. Sound doable?


----------



## tribby01 (Jun 2, 2014)

I like that Idea Let me know how that turns out


----------



## PaulS (Mar 11, 2013)

Even with a good reflector you aren't going to get much light from a 100 watt bulb at that distance.


----------



## Kauboy (May 12, 2014)

Paul's right, the light would disperse too quickly to be very effective at ground level.

Assuming you are only interested in feasibility of the set up, and not usability, then the following may help.
If the 100w equivalent bulb draws 21.6w of power on a 12v system, then it is using 1.8 amps (w/v=a).
To run this bulb over the course of a single night with a bit of overlap to cover longer days of the year, lets assume 12 hours, then you would need a battery with a capacity of about 22 Amp hours.
(12 hours in half a day makes the math easy on a 12v system  )

On this system, with a full charge on the battery, it would be mostly depleted by morning.
That means we need to recharge the entire battery in the next 12 hours to be ready for the next night.
Now, keep in mind that charging a battery is not just a numbers game, but also a physics game.
The charging itself is not 100% efficient, and energy is lost in the conversion of flowing energy to stored energy.
Also, a panel's wattage rating is taken at peak current, but won't be what is actually pushed to the battery in the real world.
Adding all this together, the loss has been tested to impact the charging rate by about 2.5 times.

So, now for the math. First, we convert to like variables, in this case, from amp hours to watt hours.
Your 12v battery with 22AH of capacity has a total Watt Hour rating of 264WH. (v*a=w)
The formula to determine what wattage your panel will need to be to charge this up is as follows:
(264WH/12v)*2.5 = panel watts [(wh / battV) * loss = panel watts]
For your setup, you will require a panel with a minimum rating of about 55 watts.
If you factor in the fact that the panel will not be perfectly perpendicular to the sun throughout, and that cloudy conditions will affect the exchange, you will want to beef up the panel a little more than this to be safe.

If you can get a 70-ish watt panel, you should be fine.

Just be sure to get a charge controller on this system to avoid overcharging the battery and avoid the discharging of the battery by the panel overnight.

Seems like quite a lot of effort and money for one little bulb, huh?
Probably why they aren't very popular in such setups.

EDIT: I misread the original post and didn't notice that you were running this on an inverter. If that is the case, and you are running a 120v bulb, then the above won't help much. Sorry.


----------



## budgetprepp-n (Apr 7, 2013)

Kauboy said:


> Paul's right, the light would disperse too quickly to be very effective at ground level.
> 
> Assuming you are only interested in feasibility of the set up, and not usability, then the following may help.
> If the 100w equivalent bulb draws 21.6w of power on a 12v system, then it is using 1.8 amps (w/v=a).
> ...


 I don't know if the cost would be that high or not under $300 for a light that burns bright enough to light up a good size area every night in
a place where there is no electric. Like a camp ground or I'm sure it would be easy to make this portable for camping. Tie something on
a rope and go for a high tree branch. ------If this works out
That $300 is with everything new battery included.


----------



## Ripon (Dec 22, 2012)

Panels are so freekin dirt cheap compared to 18-24 months ago just go over a little and get a 100-120 watt panel and that way on dark days you'll probably still score enough juice to power up either bulb.


----------



## alterego (Jan 27, 2013)

A Couple Comments.

From Every Thing I See The Percent Of Discharge On A Battery Determine It's Life Span Over Cycle Count. If You Discharge A Battery To Nearly Dead Then Recharge Complete During The Day Your Life Span Is Greatly Diminished. So You Need To Consider The Cost Of Battery Replacement.

Also I Have Been Seeing More And More Single Panel Solar Setups For Highway Road Use Signage. Basically Doing This Same Thing. Of Course They Have Every Ones Money To Do The Work. 

Next. I Do Not Believe I Will Want Yard Lights On After SHTF This Would Draw Some Attention I Am Sure.


----------

