Solar / Battery Power for Art Project

[Ninja Nemo]

Hi all,

I've fully planned my art project except for one item: lighting! I'd like to avoid generators at all cost since I both have nowhere to store them and just don't like them. I'm looking to power about 16 CFL or LED flood lights during the nights on the playa.

Looking at other people's posts for their camps, it seems like a simple car battery, inverter, and solar panel would be sufficient for the entire week. Would I even need a solar panel to recharge the battery if I was only powering a few lights? It would be a lot easier otherwise. If not, what size solar panel would I be looking at to provide sufficient charge?

I've looked through the forums but haven't found much regarding solar power 101 (beyond this somewhat helpful / flame-ridden post viewtopic.php?f=278&t=51987) so any help would be great.

Thank you.

[Ninja Nemo]

Sorry, can't edit my original thread. I'm continuing to research. Based on what I read, I'm thinking I need less lighting as my planned flood lights are ~15 watts/each * 16 lights = way too much usage. I figure that if I can keep consumption at less than 250 watts/night, it would be best to just buy three car batteries (~3000 watts?) and leave them hooked up for the duration? I also hear that some theme camps provide recharging via solar so maybe a mid-week recharge with just 2 batteries would be enough?

Does that seem reasonable?

[TT120]

The thing to do is figure out how much current (amps) your lights and stuff will draw and then get solar panels that will match it. Get a deep cycle battery and you should be good all week.

That one you linked from HF is a 45 watt setup which means at 12 volts, it will put out about 3.75 amps. That should keep your battery charged quite nicely.

[BBadger]

If you're going the battery route, don't use car batteries; they don't have the capacity and are meant for starting engines, not continuous power usage. Use deep cycle lead-acid batteries. They provide about 6V @220AH each the Costco variety).

Still, you're not going to get far at 250W. 250W means only 5.5hours of runtime per $85 battery. That's assuming you drive it into the ground too, which you shouldn't as it isn't good for it (you want to only discharge to 50%). You'll need some means to charge them up each day, and solar is not cheap.

I'd seriously consider the generator, at least to recharge the batteries. You'll be paying a lot for anything solar that'll charge your stuff in a reasonable amount of time, and unless you're going to use them all the time outside the burn that power tech is a waste of money. The generator can be hidden a ways away from art installation with sound baffles and other stuff as needed.

[oscillator]

First step is to figure your total load for your piece. Get the specs for the lights, multiply x number of lights.

That should give you total watts. Divide watts/voltage (12VDC? 120VAC?) to get total amps.

Then figure how many hours the piece will be lit (10 hours/nights?) - this gives you total amp hours (aH). If you are running 120VAC, factor in ~15% efficiency loss for the invertor. (This is one reason a 12VDC system works well)

Your battery array should provide at least 10-20 times the aH of your piece. So if your total is say, 5aH, use a 100aH battery.

General rule of thumb = the closer you pull from a battery rating, the faster its discharge rate. So, a 10aH battery will not power a 5aH load for (2) hours. Lead acid batteries work best at a 10 - 20x discharge rate. Then factor in how batteries behave on the playa - this will also limit things a bit. Also, don't discharge batteries too low (10VDC) or you can kill it.

Example: I did a 12VDC solar-powered piece that used ~5aH. First time out, I used a 55aH deep cycle. That powered things well for ~6 hours, but at 10 hours the battery was about done. Second time out I used (4) 6VDC in series/parallel for about 200aH w/ (3) 100w panels - no problems at all and probably overkill.

For charging, figure a solar array that will supply the total aH during the charge phase. This charge phase can be all day if the panels are positioned well and you dust them off. An 85watt panel will source about 5amps @ 12VDC and would take 8 hours to recharge 40 amps.

When designing a system try to get everything matched and balanced: You want the charging system matched to the battery system. IOW, don't put 20amps into a 55aH battery. Also, get a charge controller rated 1.5 times what you think you'll need.

Regarding the 45watt HF deal: I have used them, not impressed. These were (3) 15 watt panels. As I recall each 15w panel was nearly as big as a Kyocera 85w panel.

In the past I have used these guys: http://www.affordable-solar.com/

FWIW, my current setup is (2) 85w, 15amp Morningstar charge controller, (2) 55aH Optima blue top, 300w SureSine inverter (no fan). I like not having to refuel a generator in the middle of the night, or anytime else for that matter.

Oh, this discussion is for deep-cycle lead acid batteries, not Lithium varieties.

So to recap:

total ampHours = total watts/voltage

charge batteries @ 1/10th rating

discharge batteries @ 1/10 - 1/20th rating

factor in efficiency loss for all components (10-15%)

Oh, good luck with your piece!

[Ninja Nemo]

Thanks guys, this info is really helpful.

I reassessed my situation and have decided to try to just use 2 15w (hopefully DC) floodlights powered by battery (consuming ~300w/night) and do the rest with solar lanterns I have laying around. The floodlights are the true thing lighting the piece while the solar lights will just be used to illuminate guywires and anchors. With the 2 15w lights, I figure I can run them off of a deep cycle battery and swap out a spare every 2-3 days when I go check on the piece?

At the same time, I'm planning to add solar panels to my camp for lighting since battery powered xmas lights weren't cutting it. I'm very minimal and the system would only be used to power lights and recharge camera batteries. Using oscillator's advice, I'm thinking that I can setup a solar rig at camp which hopefully will both make up for the minimal consumption at camp each day (I'm guessing less than 100w/night) and allow me to recharge one of the batteries for my piece.

One additional question - I found a 10w LED flood light as well as a 10w RGB LED flood light. I think the total # of LED's is the same, the second one can just switch between colors. Will the RGB light consume more than the other?

Thank you all for your help and come check out the Elysian Garden at the burn this year to see the fruits of my labor.

[BeachBum]

I like Oscillator's reply, don't sweat any math though, it's easy to figure out. Amp-hours x 12Volts = Watt-hours. I also like teardropper's pic in your referenced thread of how to do a very, very simple setup.

For solar panels, I picked up a couple used ones last summer off Craigslist to run my 800 lights "MegaTree" type project, though in a different lights form factor. Just get panels for charging 12V batteries (~18V PMax), not the 30Volts or so PMax panels. Search for "solar panels" and also for "solar panel" in the title of the listing. You can find these for $1.50 per Watt or less off Craigslist. Right now, in the SJ/Campbell area you can find 40W for $40, 80W for $120, ..., or down south in LA you can find 80W for $125, 100W for $150, ... Go cheap for your camp setup, $100 or $150 for the panel(s), $40 for the charge controller, $100 for the Costco 105Ah deep cell, a couple of $35 400W 12Vdc -> 120Vac inverters. Far cheaper than buying a quiet generator, and the battery setup can be used for longer hours each night.

Best wishes.

[some seeing eye]

There have been extensive discussions of this very topic - system sizing. And some good ones on this thread too. Snow Koan camp charges batteries you bring to them. They also were adding an array mid playa. Some of the campers are solar pros for a job.

[BBadger]

Note that oscillator's amp-hour estimate assumes you're powering 120VAC from 12VDC batteries -- hence the 10x factor when computing your overall capacity needs. If you're not doing that, you should just compute your energy needs from the battery's energy capacity (Volts * Amps * Hours) and the number of watts you need to get your runtime i.e. (Volts_battery*Amps_bat*hours_bat) / watts_required. Assume that you will only use 50% of the battery capacity too, or it'll damage your batteries.

[usurpedus]

really great/ helpful info on this thread

[teardropper]

My power consumption is going up, so adding another panel.
And while it's not good for battery life to run below 50%, I typically run below. It's better for me not to have even more batteries - so, since I only use this setup 2 or 3 times a year, I use em down. And I've used the pair of 6volt golf cart batteries (225 a/h) for 4 years now. If I were using them daily and depending on them, I would add more batteries. Batteries, big, 6v cart batteries are heavy. So, I'd rather use the ones I have and use them down a little more than carry more batteries.

And, yeah, BeachBum, it's simple. By evolution and, so, design. I don't use an inverter unless I absolutely have to and recommend using as many 12v DC devices, rather than 120v AC, as I can find.

KISS