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Solar Tilting Logic


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I am installing 4 solar panels on our RV. They will be in 2 rows of 2, wired in parallel. I am building mounting hardware out of angle aluminum instead of using mounting hardware made for solar panels. It won't be much more cost or effort to make it so that I can tilt the panels if I need or want to. This is what I am planning at this time. I am having a hard time wrapping my head around the permutations in how I tilt them. I am trying to figure out how I will use them before I finish the design and install them. I expect that my goal should be to maximize total daily power generation when it will be most challenged.

 

Let's say hypothetically my solar energy needs are most difficult to obtain on December 21st while located in southern Arizona, or someplace with similar sun angle. Assume I will park the rig so my panels are running lengthwise east to west. I can then tilt them south toward the sun.

 

I put together the diagram attached showing the end view of the panels in three methods, for lack of a better word. The upper method has them at a more efficient angle to catch the low sun if it were not for the fact that half the panels would not put out any power because they would be shaded. So really, that method won't work at that time of year with the spacing constraints on my roof.

 

The second method, has the south panels at a low angle to minimize the part of day that they would shade the north panels. The north panels are up in a more efficient angle. The rear panels will produce more energy than the front panels. I understand that having the panels wired in parallel, I maximize the total energy output while a panel, or two, are shaded. Interpolating that logic, it seems that this method would be the best to implement when I need to maximize my solar power harvest. Is my logic correct? Or will the imbalance between the north and south panels cause inefficiencies that will require me to lower the angle of all the panels such as in the third method I illustrated?

 

Jim

 

 

 

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Looks like some great plans. When I first installed solar about 8 years ago - I had great plans about adjusting my panels for different parts of the country. Did it once the decided to just leave them alone. I have three 200 w 24v panels. To much trouble to change. My panels have served me well over the years just as they are mounted. But, then I am not as agile as I used to be.

 

Safe Travels!

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For almost EVERYONE, in almost every circumstance, they have NO BUSINESS on the roof tilting panels. Yes, you can gain some harvest. Substantially in the right circumstances. It is also a pain in the butt, and simply dangerous. ESPECIALLY dangerous in the desert when that 40+mph windstorm comes up and you watch your panels move around and decide to lower them to protect the panels and your roof. Are you going on your roof in 40mph wind?

 

My answer is at add enough panels so you don't have to worry about power "lost" because they are not tilted.

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I very rarely disagree with Jack, but in this case I might to some degree. If you're in the southern states and have 40+ mph winds, then absolutely not. Tilting will only lead to disaster.

 

However, if that is not the situation you find yourself then tilting may prove to be a massive advantage. I did look at the the picture you attached. That's not a very workable situation. For tilting to be effective you would need to build a multi panel framework where both panels are being tilted at the same degree in unison.. one over the other. Does that make sense?

 

The easiest is to construct a 2 part mounting system. One part mounted to the panel frame, one part mounted to your roof, and preferably for conveniences sake, a hand tighten type bolt to connect the lower and upper mounts. That would allow you to add a graduated member between the two mounts that would allow you to adjust the tilt of your panels.

 

I think it all boils down to two schools of thought.. install inexpensive panels everywhere and wherever you can to make up any difference in production of a single panel to another, or spend twice the price for more efficent panels and make them as effective as possible. In the end the result is probably about the same. I really don't know which is more cost effective.

 

I DO know however how many panels I have to squeegee from time to time and less is more. :P

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post-48662-0-22888700-1435962566_thumb.jpgAgree totally with Jack. Tilting systems add weight, tilted systems can get ripped off in high winds, and getting on a roof when it has snow is rather risky. I tried doing this once to scrape off very wet snow and started to slide off just sitting down. Got out the 12' ladder and swept off the snow. Panels seen behind 5th wheel are part of older son's solar farm. He has about 3 kW total and is totally off grid with own well and cell/wifi tower at 7800' in Sangre de Cristo mountains of northern NM. It was time to head south

 

OP has 340 square feet of roof. A 200 W panel is 15 square feet. He has potential for 22 panels or 4500 W. Or simply put them in two rows of 6 down each side to eliminate crowding/shading by a/c etc. He can easily install 2400 W. He could have three parallel series of 4 (96 V) or 96 V to controller. We have two parallel series of 3 (235 W at 30 V) for 90 V to controller

Reed and Elaine

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at 7800' in Sangre de Cristo mountains of northern NM.

 

Totally off topic, but if you want to see "amazing" hit the Sangre de Cristo's! Un @%$(*^ gorgeous!! Wildlife on your doorstep, clean crisp updrafts and sunsets that will make a grown man blubber. :D:P

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If you tilt them to the side and you have them side by side your row closest to the sun will be shading the back row. I am at 100% by 10 am. You should just mount them and then decide if you need to add a tilt mechanism.I don't think you will.

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I agree I do NOT want to be up on any RV roof at my age adjusting panel tilt THATS JUST OUT OF THE QUESTION.

 

HOWEVER of course tilting can GREATLY increase energy capture.

 

That sort of leaves you with a choice of NOT going up on the roof orrrrrrrrrrrr oversize your array so you meet your energy needs without ever tilting.

 

THEREFORE I didn't do it but am considering in the future, a method to tilt my panels WITHOUT climbing up on the roof. Believe it or not in our local Amish Community there is a gent who sells panels and frames and mounting hardware, much of which is made up of fiberglass that resembles channel iron and angle iron. Its lightweight, no rust, yet strong.

 

My plan is to have a flat on the roof frame that can hinge on either side (street or curb) of the RV and then lift poles or rods so I could lift up either side allowing them to hinge on the opposite side. ORRRRRRR just have them tilt to one side only which means you must always park in one direction. If they could tilt either direction you could park facing East or West.

 

Of course that takes time and materials and engineering and fabrication and dollars, but I'm retired and have the time, money, energy, and know how plus would enjoy such a project as a labor of love. However if you had to hire all that done it may well be cost prohibitive.....

 

Soooooooooo do your homework and decide if you need or want to climb on your RV roof and if you don't want to climb or mess with tilting, SIMPLY OVERSIZE YOUR ARRAY SO YOU MEET YOUR ENERGY NEEDS WITH A FLAT ON THE ROOF MOUNT LIKE SO MANY USE AND NEVER HAVE A PROBLEM. Its sure easier and cheaper that way to mount even if you need more panels to meet your needs.

 

PS I dont see any all right or all wrong answers here. No harm in agreement or disagreement with another's method. Its your choice NOT ours or what we may like or dislike. Tilting can increase energy yet its much more complicated to mount, while flat mount is cheap and easy but yields less energy. EITHER can work fine if properly engineered and constructed.

 

Go for it, let us know how it turns out

 

John T

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Well, just for the record, I don't disagree with any of the points raised by Jack or Reed. Is it possible? Yes.Can it be of some benefit? Yes. On that note... my panels have 2 part mount assemblies that are perfectly capable of adding in a tilt bar, but I have never utilized them for that purpose. My energy requirements are modest and flat suits me just fine 19 years and running. ;)

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Yarome, another for the record. Like you my current flat mounting satisfies all my modest energy needs, but tilting is just another possible option if I ever needed more energy. Its just fun for me to consider the design and fabrication and toss out options to others who are getting started. I don't see flat mount OR tilt as right or wrong, keep all options on the table and open is my preferred method when designing.

 

Love sparky chat, thanks yall, this is fun.

 

John T

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I have tilt rods for my solar panels. I use them to raise the panels so I can clean under them.

 

Ok. Call me guilty. :P:lol: Done that...

 

If a person wanted to eek out a few watts, it's certainly doable and potentially worthwhile at certain times of the year, but I've never used my mounts other than the aforementioned for cleaning purposes.

 

When it's fairly hot out, like it is now, and my battery bank starts pushing below 85% or so, I'll just plug my portable ice maker into John's 110vac exterior outlet (he sleeps like a rock) and call it 'good'. :lol::D:lol:

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As far as keeping the panels "straight up" (no tilting) getting the best average solar impact morning to night, my own personal experience was DIFFERENT.

 

NOTE: Just because that was my experience don't mean another cant have a different experience in a different location, I'm ONLY reporting what MY experience was in MY location at a certain time of year, yours may be different!!!

 

When playing around with a 100 Watt portable folding panel with an onboard ammeter and tilting it versus having it lay flat WHEN RAISED UP AND TILTED TOWARD THE SUN THE OUTPUT INCREASED DRAMATICALLY (subject of course to suns location in the sky WELL DUH)

 

In other experiments if I kept the panel basically facing the southern sky morning to night and wasn't moving it during the day and had it somewhat tilted (angle depends on your geographical location and time of year) ITS OUTPUT WAS GREATER IF TILTED THEN IF I KEPT IT LAYING FLAT MORNING TO NIGHT.

 

THEREFORE, my experiments showed and its my opinion proper tilting (yes, I know, it depends on angle and where sun is and location and season) can increase output versus if the panels are always kept flat. In our area I have seen several large residential solar arrays that are fix rigid mounted and they are tilted around 30 to 50 degrees (depends on location) and facing the southern sky. If a person had the means and budget then you can get into all that auto sun tracking EXPENSIVE !!!!

 

Of course, however, on an RV Roof tilting gets more complicated and as we all discussed above, climbing up on a roof isn't for everyone and could get dangerous. If such is the case you simply keep them flat mounted and capture what energy you can even though its less then what tilting can achieve. Mine are flat mounted but I have enough capacity to capture my energy requirements. FOR MOST PEOPLE FLAT MOUNTING IS FINE (for sure easier and cheaper and safer)

 

I have seen in person plus plenty of pictures of rooftop tilt methods and the majority are where the RV is kept parked in one position for extended periods facing East or West such that the panels are tilted towards the southern sky and the tilt angle depends on your geographical location. Its my opinion in certain locations in certain seasons such captures more energy in a morning to night time period versus if they were kept flat the entire time. If not we can horse laugh those people for going to all that work and expense NOTTTTTTTTTTTTTTTTTTTT.

 

Summary, flat mounting (what I have but may change in the future) is simple, cheap n easy and fine and works for most people no problem THATS CERTAINLY THEIR CHOICE. However, if you have the means and ability and can stand a few more pounds for fiberglass or aluminum mounts and racks and have the need to capture more energy and can do it safely SAFE PROPER TILTING IS CERTAINLY ANOTHER OPTION AND CHOICE. Neither method is right or wrong, neither method is good or bad, it depends on the individuals needs and means. Flat mount if you like or tilt if you like and others can do the same, I'm NOT here to decide how others do it, ONLY to answer questions and help whenever I can.

 

PS My preference, if I designed a method to tilt my panels, would be to use lightweight fiberglass or aluminum such that I could accomplish it WITHOUT GETTING UP ON THE ROOF. Much much safer even though it takes some engineering and construction to accomplish such.

 

HAPPY FOURTH OF JULY ALL AND GOD BLESS AMERICA Yarome is welcome to plug into my outlet anytime he wishes !!!!

 

John T

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Alternate plan 22 (or 28, your choice) Throw a couple of plug in panels on the ground and tilt them to your hearts content.

 

No roof, gather them in the wind, align them to the moon, all kinds of options.

 

Besides, tilting is a 360 degree option really, as opposed to a side to side. What do you do when your parked north to south? Raise the front of the trailer to 45 degree's? Kathy would have you by the ...belay that, and your frig level would be off, (yeah I knew if I thought long enough that another reason would come up) I can see all the coffee cups on gimbals in the trailer just so they don't spill. And trying to chock the tires. Oh boy!!

 

In Michigan, my 4-100 watt flat mounted, 12 year old panels with poor wiring (paralleled wiring 10 gage) were putting out 25 amps the other day. About 75% of rated cap. We had a number of bad heavy overcast days and this was the first bright and sunny. I was down 230 AH (35%) and the boys were cranking. I got back about 80% of that the first day and topped up the second day. I was almost thinking of turning on the charger.

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Hey Bill, you "raise" (pun intended) a good point "Besides, tilting is a 360 degree option really, as opposed to a side to side. What do you do when your parked north to south"

 

The tilt assemblies I've seen and used limit you, of course, to park your rig East or West (to allow for tilt to the southern sky) NOT North or South. Oh the hardships and sacrifices we must make when camping lol. I've seen a lot of tilt set ups, but NEVER a 360, don't give me any ideas though !!!!

 

Happy Fourth

 

John T

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For curiosity sake at what point in the daily charge cycle does the solar controller output begin to exceed the battery bank amperage acceptance capacity? (Assuming full sun)

 

It would seem to me solar efficiency is moot at that point unless there is a solar dissipating load brought in to absorb the excess amperage that would go lacking with the better effieiency. I would want to at least want to understand this contemplating the OP's OP.

 

As I recall from my submarining days, time is the governing factor once the finishing rate is reached. Especially if gassing is to be avoided.

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Tilting - in the old days, when panels were VERY expensive, you really needed to optimize them. So based on your latitude, you would set the angle of declination ~ 4 times per year, once per quarter. Then, you would face the sun and rotate through the sun's arc during the day, east in the morning to west in the evening and back to the east at rest (ready for the next day). And it could be a quite substantial gain, at the expense of simplicity. (moving parts, motors, electronic monitors / positioners) and these items had to be fairly robust!! Wind, rain, snow, all the elements could throw at them. And, again your trying to optimize your ROI (return on investment).

 

Now, with much cheaper panels, and the increases in efficiency vs. the upkeep of the mechanical systems.... for our use and traveling style, a couple of set out panels are a LOT LESS hassle.

 

Panel tilt - http://www.solarpaneltilt.com/

 

Clock . My flat panels are usually done about 1 PM - you design for 5 - 7 hours of full output, Then you have sun, haze, partly cloudy, overcast and green sky. When you get to green, blank the panels and head for the shelter and hope that withstands the tornado. If I recall, 1000 w/m^2 (1000 watt solar per square meter and efficiency is 20% ---- 200 watt per sq meter of usable power) - https://en.wikipedia.org/wiki/Solar_cell_efficiency - so with all that, not every day is perfect and not every day is bad. Even on bad overcast days, I get a couple of amps per hour. One of the reasons that I carry a Honda. Pure boondocking, get up in the morning, run the Honda for an hour while I make coffee / breakfast and dump into the batteries. Charge during the day and run for a bit while doing supper.

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SC Clock, wow a great and very technical question WHICH I CANT ANSWER. Seems to me to answer that question a person would need to know 1) Battery banks Amp Hour energy storage capacity.............. 2) The state of charge of the battery bank................3) The total net energy the solar array is producing and how much and how long (now that's hard to predict as it depends on sun and angle etc)....................4) How the Solar Charge Controller functions.

 

That being said, I have woke up in the AM and say my batteries were 25% discharged and the sun starts shining and I begin to notice how many charging amps are flowing into my batteries and watch their voltage rise. It eventually goes up to over 14 volts and as the day goes on subject to sunlight it later drops to 13.6 volts and maybe later (depends on sun and use) it may drop to 13.2 Float level, and as the sun falls down finally to 12.6.

 

What my Solar Charge Controller is doing and what it does when my batteries are fully charged and what becomes of excess energy (wasted?? It cant be created or destroyed per the laws of physics) I cant say, sorry.

 

I sort of see your question and its answer having to do with if you have enough solar capacity and battery bank energy storage to replenish all the energy you use when there's no sunshine YOU DONT NEED MORE PANELS OR TILTING ETC as once you're fully charged where's the energy going????? Since it cant be created or destroyed I would assume the Solar Charge Controller is dissipating it as heat energy and/or shutting off or reducing the solar energy flowing into the controller?? With no load on the panels their voltage rises within limits and the controller no longer uses/converts energy as the electron battery bank is full.

 

Problem is, its hard to predict the sun and your daily energy use, so if you usually have enough solar and battery capacity even if its cloudy and rainy you probably have enough right???????????? and if enough with flat mount panels THERES NO NEED TO CONCERN YOURSELF WITH TILTING TO GET MORE ENERGY.

 

What's that saying. Any solar is good and more is better????????? I don't see much of a problem of too much solar, as its the Solar Charge Controllers job to charge the batteries but NOT overcharge them.

 

Sorry I cant answer your question, maybe some of the fine more solar experienced gents here can.

 

John T

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Something else to consider if tilting in windy locations, how well is your roof attached to your RV? You may have the panel mounts glued to the roof to the point they will never come off but if the roof peels off the RV you have got problems. Different RVs have different roof construction so your situation will have to be looked into. If your RV was like mine 1/8 luan glued to blue foam then you don't have a lot of strength there to work with.

 

I built mine to tilt, tried it once and never again due to wind issues. It did make checking the screw tightness in the junction box easier as well as roof cleaning so I'd do it again.

 

Sandia Labs used to have a solar power center that had a bunch of good solar planning books, everything from wiring to tilting and pointing, couldn't find them this morning though. What I do recall is that active pointing is much more important in summer than winter since the sun makes a much larger arc. Tilting does depend a bit on the off-axis performance of your panel, how much power it drops per degree that the sun is not directly in line with it, that varies by panel. They had nice charts that gave the sun elevation for different months and locations (north to south) and a recommended angle for maximum power production, again most of the change was in the winter.

 

Making a powered tilting array could be great fun, there are a lot of surplus high-power linear actuators out there so cost shouldn't be prohibitive. You could probably even do a two axis pointing array without breaking the bank.

 

I saw one interesting manual setup that did tilt and pointing, the panels were on a lazy-susan type arrangement with hardware coming through the roof to rotate the array and crank it up and down. It looked interesting but I didn't think it was practical as it didn't have a solid mount for the panels, just gravity and casters aside form the pivot mount in the center.

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I'm a tilter. Now that I've said it I feel better.

 

Here's my situation. In a perfect world I would never tilt panels on the roof. As has been pointed out, climbing on the roof is dangerous and dealing with wind is a hassle. But I don't live in a perfect world. Although I have a 43' fifth wheel, I only have room on my roof for the 5 panels mounted there now. They are 24v 160 watters (800 total) that have been up there for 8 1/2 years. I have tried every way possible to figure out how to put additional panels up there, but it just isn't going to happen. With 2 air conditioners, 3 vents, a TV antenna and a satellite internet/TV antenna in place, there just isn't room for any more. So short of replacing the existing panels themselves with some that put out a little bit more power, it is what it is.

 

We replaced our RV style refrigerator with a household model a couple years ago. This increased our daily AH usage from around 200 to around 300. Before installing the refrigerator we were able to create all the power we needed from the solar panels, but now have to run the generator for a while each day, usually in the morning when I can slam 120 amps into the 8 golf cart batteries.

 

Most of the year, from April to November or so, the panels are never tilted. That's because the days are long enough and the solar angle is high enough that we get a good charge. However, in the dead of winter when days are the shortest and we need power the most, flat panels just don't provide enough. I end up running the generator a lot to make up the difference.

 

We have spent the winter months boondocking in the Arizona desert for the past 9 years so I do have some experience with how it works. If I don't tilt the panels I get maybe half the amount of power I get with them tilted. I know the formulas say you should get more but it doesn't work that way in real life. In the dead of winter flat panels do practically nothing until 10 am or so, and quit being of any use after about 3 pm. That means you only get about 5 hours of decent charge time, and during that time you only get about 70 percent of what you would get if the panels were tilted.

 

My panels are mounted so that they tilt to the right side of the rig. I park with the nose of the trailer pointed at about 80 degrees, or just a little north of due east. Parking at any angle you prefer is not an issue in the Arizona desert. This also positions the door and major windows on the south side so as to avoid north winds and soak up as much solar heat gain as possible.

 

I park at this slightly north of east angle so that I get the morning sun on the panels earlier, and get as much charge as possible during the morning hours. This is important because the batteries are lowest in the morning and will take all the power the panels can produce. By sometime around noon or 1 pm the batteries have reached their absorb voltage. The rest of the day the voltage is held constant but the amps slowly drop as the batteries become fully charged. The batteries don't need all the power the panels can create during absorb. It's during this time that we often do things like laundry so as to use that extra power. Our Whirlpool front loader runs off the Magnum PSW inverter just fine.

 

As I said, I wouldn't tilt if it were not the only way to avoid hours of generator time. And no, I'm not going to carry around some additional panels to mount on the ground. I already have way too much stuff to haul around as a full timer (16 years now). I only go through the hassle of tilting if we are going to be in one place for a week or more. I have looked for motorized tilting systems without success. I did run into a fellow at the Imperial Dam LTVA last year who had built his own. They worked great but he figured they cost more than the panels themselves. He had considered marketing them but soon realized that he couldn't make a decent profit given the manufacture cost and the market. If someone could come up with a powered tilting mount that would sell for $100 or so, I think he could sell a lot of them. I'd buy 5. I'd even built my own if I could find some decent plans.

 

So, that's my story and I'm sticking to it. I would encourage everyone to install a system that does not require tilting. Tilting panels is a bad idea. That said, sometimes you gotta do what you gotta do.

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Let me be a little clearer about my previous statement. Tilting is definitely of benefit technically. However, other factors come into play - as brought out in the discussion above. There are some people and some times where tilting may be an option. Rif is a perfect example. But for MOST people tilting should not be considered as a solution to power generation during the design stage. Simply design the system for non tilting conditions and see if you can generate the needed power in the dead of winter for your anticipated use. THEN, and only then, decide if the additional genset time with non-tilting panels is a compromise you are willing to make.

 

Again, for MOST people tilting is not a viable power boosting mechanism when all factors are considered. But there are certainly exceptions.....

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