Solar Array Configuration

[kowtow]

This has been a great forum to indulge in.

I'm posting to get some ideas about what I can "practically" speaking, expect from my solar panel configuration.

I have two 100W solar panels (200 watts total) with a cheapo PWM charge controller. My batteries consist of four Costco (#12852) 12v 115Ah batteries connected in parallel for a total of 460ah (conservatively 1/2 of that to be used before requiring a charge). I also have a 2.5kw DC to AC inverter for any AC that may be required.

Aside from all the "what's the power drain, blah, blah, blah" stuff that I can calculate on my own. I want to get someones advice on what a system like this will do to charge up my batteries from a drained state (50% of max capacity). I can calculate the numbers, but I would like to understand from someone who's been on the playa, what can one really anticipate in terms of hours of direct sun in general and what the charging efficiency is (I know that's a very general question) of a 200 watt system in terms of charging up this bank of batteries.

Thanks.

[Jackass]

Super slow charging, that's a lot of battery

[Jackass]

Are you going to use it for Christmas lights and a swamp cooler, or are you trying to run an A/C and microwave??

[GreyCoyote]

This has been a great forum to indulge in.

I'm posting to get some ideas about what I can "practically" speaking, expect from my solar panel configuration.

I have two 100W solar panels (200 watts total) with a cheapo PWM charge controller. My batteries consist of four Costco (#12852) 12v 115Ah batteries connected in parallel for a total of 460ah (conservatively 1/2 of that to be used before requiring a charge). I also have a 2.5kw DC to AC inverter for any AC that may be required.

Aside from all the "what's the power drain, blah, blah, blah" stuff that I can calculate on my own. I want to get someones advice on what a system like this will do to charge up my batteries from a drained state (50% of max capacity). I can calculate the numbers, but I would like to understand from someone who's been on the playa, what can one really anticipate in terms of hours of direct sun in general and what the charging efficiency is (I know that's a very general question) of a 200 watt system in terms of charging up this bank of batteries.

Thanks.

Let me take a wag at this. YMMV. But at least it's based on a little experience.

On a good day on the playa you should get about 165-170 peak watts out of your setup at the panels at high solar noon. (The "rated" watts are a lab figure, in perfectly clear and cool weather, at the equator, perfectly positioned, at high solar noon, and you won't ever hit this for very long). Next you can figure-in a few watts lost in the charge controller, and then quite a few watts lost due to battery physics (call it 15%). The length of light that is usable for solar generation on the playa is about 11 hours. So as a guess I'd figure 120 average charging watts per hour over 10 hours, for 1200 watt-hours/day. At 100 watts/hour in a 12 volt system, you're charging the batteries at the rate of 8.3 amps/hr, so call it 91 ah/day. So to take a battery at 50% capacity to fully charged you're looking at somewhere around 2-1/2 days.

Now, having made all these pretty predictions and whiz-bang guestimates, you can rest assured they will all go to hell an hour after you setup your array. Someone will kick it over, it will get dusty, some doofus will put a smilely-face sticker smack in the middle, a neighboring camp will park an RV next to it, etc. All of these will play hell with neat little calcs.

FWIW, I goofed with solar on the playa for a bit, but I finally decided it wasn't worth it for me. Yeah, it made me feel all warm inside and it was a lot of fun to mess with, but I finally realized that when push came to shove it was a lot of hooey for not enough return. I still take 4 ea 105AH batteries in the trailer, but now I charge them from the Honda. I can charge them from a deeply discharged state in about 8 hours. I have found the only time I really run off the batts is between 4 am and 9 am when the camp is trying to sleep. Otherwise, they are just there for back-up.

YMMV. As stated all this is back of the napkin stuff. I would *highly* suggest you ask the same question of the folks at Black Rock Solar and the Alternative Energy Zone. They do some big installations, and they have some hard-won, real-world, on-the-playa data they could share. Good folks, too, and they LOVE to talk about this stuff.

[BBadger]

Burning Man. Solar Power. Practical.

These things form a contradictory loop.

[Captain Goddammit]

Just aim a 250-watt halogen lamp directly at the panel, for perpetual power.

[kowtow]

Let me take a wag at this. YMMV. But at least it's based on a little experience.

On a good day on the playa you should get about 165-170 peak watts out of your setup at the panels at high solar noon. (The "rated" watts are a lab figure, in perfectly clear and cool weather, at the equator, perfectly positioned, at high solar noon, and you won't ever hit this for very long). Next you can figure-in a few watts lost in the charge controller, and then quite a few watts lost due to battery physics (call it 15%). The length of light that is usable for solar generation on the playa is about 11 hours. So as a guess I'd figure 120 average charging watts per hour over 10 hours, for 1200 watt-hours/day. At 100 watts/hour in a 12 volt system, you're charging the batteries at the rate of 8.3 amps/hr, so call it 91 ah/day. So to take a battery at 50% capacity to fully charged you're looking at somewhere around 2-1/2 days.

Thanks GreyCoyote for the great practical numbers! This was exactly what I was looking for. Since I'm new to solar, I wanted the real world stuff and in particular the playa stuff, ya to even include the stickers, dust storms, and clumsy drunks. I want to prepare as much as possible, so I can now take that real numbers and plug that into what I think I'll be using for power, because then I can work on how to supplement the solar fizz with generator time, etc. Now I can begin work on building a hush box to keep the peace on the playa.

It amazing, even with technology fossil fuels still can't be beat. Maybe that's why they've been around so long. Maybe I should burn tires at burning man then use a peltier generator to turn the heat into electricity so that I can power my cell phone to call the tire company to bring more tires, so that I can do it all over again.

[Captain Goddammit]

If you're going to do any generator charging, I think the thing to focus on is how much current you can get from your charger.
A metric shitload of charging current will do a LOT more to reduce generator run time than your solar panels will.
Usually someone chimes in saying charging at a very high rate is bad for your batteries... I say bullshit, I use those same batteries in my MV and they get charged by a pair of alternators at between 50 and 100 amps. Every battery installed in a vehicle gets charged at pretty high current.
So, I'm recommending getting as powerful a charger as you can, and do the solar just for the sport of it if you like. Electrically, it's a drop in the bucket.

[BBadger]

Usually someone chimes in saying charging at a very high rate is bad for your batteries... I say bullshit, I use those same batteries in my MV and they get charged by a pair of alternators at between 50 and 100 amps. Every battery installed in a vehicle gets charged at pretty high current.
So, I'm recommending getting as powerful a charger as you can, and do the solar just for the sport of it if you like. Electrically, it's a drop in the bucket.

Well that depends on what stage of the charging you're at. If your batteries are depleted (i.e. ~50% or so) high charge-current is just fine as you'll be doing bulk charging, and will take you most of the way until you get to the last mile (about 80% of the charging). That last mile (20%), your (smart) charger should pull back to not damage the plates. Usually the smart chargers will regulate all this for you, so you get most of your bulk charging out of the way with as much charge as the battery will take, but nearing the end the smart charger will scale it back for you to not damage the batteries. Finally, at the end, there will be just a float charge to keep things topped off.

Maybe that solar could be used for that last 20%, but quite frankly I think it's a huge waste of money to even consider it. Solar power is just a giant joke at Burning Man in any context outside of bringing your home setup that you also use the remainder of the year. I laugh at the pitiful wattage ratings on those solar panels when compared to how much those suckers ponied up for the benefit of pitiful power. Save your money and buy a decent Honda generator and use nature's great natural battery: fossil fuels.

[Captain Goddammit]

Agree totally, with everything you just said'

[GreyCoyote]

I will echo BBadgers thoughts on the technical end. Good stuff there.

I do however want to encourage the original poster to bring the panels and play with them for one reason: Burning Man is all about tinkering, learning, exploring, pushing limits, and looking at things in a different way. Even if your panels completely fail to do what you hope, you will still have learned something. And you never know when that knowledge will come in handy.

Confession of a deep, dark secret: I view Burning Man as a test bed for things I may need after the Zombies take over the earth. If something works on the playa, even partially, then it stands a good chance of being useful after TEOTWAWKI. Or at least thats the excuse I use for about half of my playa goofings.

[Captain Goddammit]

Agree 100% with alla that too.
Look at the fucking only-good-for-one-week boat I built. There's a lot more work and money it that, and no one would call it sensible or practical.
I sure don't mean to discourage setting up the solar system if you wanna! I'm just sayin', the biggest reduction in genny running time will probably come from highest possible charging rate while it's on.
It's the guys like you doing this stuff that will eventually make it practical enough for me to do it someday!

[BBadger]

Yeah, I'll get behind that. It's not like anything purchased and used for Burning Man is that practical anyway. It's a great place and reason to experiment with any technology.

[kowtow]

I'm totally in the boat "no pun intended" of just wanting to experiment. Ya I dropped a few hundred bucks on panels, batteries and an inverter, but the stupidest thing about it.... I bought it all for one week in the desert. I know it's not practical in the slightest, but that's what makes it all that much more fun for me. There isn't anything about Burning Man that's practical and that's what drives me to the playa more than anything. It gives me a chance to prepare all year for something that is temporary and not worth a shit come the Monday-after. To me this is all about as practical as buying some lady-type a dozen roses just so they can die a week later, just about the time I'm waiting in the doctor's office to get rid of the gift "she" gave me that lasts twice as long as the roses!!!

On the solar aspect it's about me geekin' out on balancing all my power usage with all my various power generation techniques and seeing if I can calculate it down to a gnat's ass and be correct. I'm sure by Tuesday all my calculations will turn to dust and I'll be beggin' someone for gas so I can keep my genie going just long enough to mix that last pitcher of margarita's before I drift away in a fog, not to reappear until that Sunday morning.

Thanks for the great advice.

[BBadger]

Yeah, it's when people think they're going all "green" or "saving money" (sans huge subsidies) with solar panels that I really have to step in and set them straight. Good luck with your experimentation.

[tatonka]

reading his post on his bike , he got results from solar for just charging his bike , I was thinking you could put a shade stucture on it with the panels on top

[media]

[theCryptofishist]

I wonder if this could work...

[cablemonkey]

I've run solar for the past 5 years with no issues. I have a single 80w panel that I put on top of the nearest RV and then forget about for the rest of the week. Two sunlyte 100Ah batteries in parallel and a small morningstar regulator. I've got a small 450w xantrex inverter that I use mainly for my cpap and running LED lights at night.

IIRC, there's a radio station out there that's 100% solar as well. It's doable, but like most things out there, a bit harder.

[LowePro]

I'd be interested in others' thoughts, but in my research I found websites recommending the optimal angle of solar panels based on Lat, Long, and date, to maximize solar exposure.

For BRC in late August, I came up with: Tilt the panels to approx 37 degrees, aim the panel due south. If you use a compass, correct for the magnetic declination in NV by aiming the panels just slightly to the Southeast. Luckily, the hexayurt roof is about 37 degrees and made a great solar panel holder. I just used some scrap 2x4s on top of the van to make a simple frame to tilt another small panel. Wiped off the panels once a day with a damp rag. We did this and had good output from all of our panels all week.

[nixiebunny]

Solar is the sort of thing that is nice ONLY if it Just Works. To do that, you need to have more panel than load, by a factor of two at least.

I use it mostly on my bike, to charge the sound system. I found that an extra-big panel made my life much happier. A smallish panel just causes aggravation. You do not want aggravation out there.

I assume an equivalent of 6 hours of full sun per day on the panel, tilted about 45 degrees towards the south. I then figure that the solar charger is about 50% efficient overall, including all losses from panels to batteries.

The best thing that I do to make solar work for me is to just not use much electricity! I have made water-handling gizmos like showers and greywater processors, but I power them with little pumps on timers to ensure that no juice is wasted. You can buy a lot of 555 timer chips and power MOSFETs for the price of a 100W panel.

I also use the solar/charging system at home for other projects, such as an underwater robot for a competition, which wins extra points for using solar charging. Plus it's faster than connecting a real battery charger to each battery sequentially.