RV Solar Part IV – Panel Tilting & Winter Solar Optimization
It’s been almost a year since we made the leap to solar on “the beast”. For those of you who missed the chair-gripping series I’ve got the whole exciting detail of how we decided what to buy and install in Part I (discovery), Part II (equipment) and Part III (installation). Since that time we’ve been geeking out and enjoying our panels through extensive dry-camping travels from FL to CA. I’m happy to say our panels have served us perfectly. On good sunny days we’re usually fully recharged on the batteries by noon plus the panels easily keep-up with our daytime power usage even if we’re on the internet all day. There’s honestly not much we’d change.
But there’s always an opportunity to geek out a little more. As days grow long and the sun sits lower in the sky we’ve started to think about winter solar optimization. Now solar panels actually like cooler temps (their output increases at lower temps), but they have a problem with angle which opens up all kinds of fun thoughts and experiments on tilting. And opportunities to blog, of course. So, here we go:
1/ Why Tilt Your Panels?
If you remember my lessons from last year, getting the best out of your solar system is all about minimizing loss. The same lesson applies to tilting too. The power density of a solar panel is always at its’ maximum when the solar panel is exactly perpendicular (at 90-degrees) to the sun. The further you get away from perpendicular the more power you lose and so the less power output you get. Since sun angle varies by both latitude and time of day that means your power output is varying all the time. So, how do you know what to do?
Well, in summer the sun will get pretty high in the sky and stays there for quite a few hours (as an example, here in Palm Springs it gets to ~70-degrees elevation) so your panel output will be pretty darn good even if they’re flat. However in winter everything changes -> the sun stays closer to the horizon (here it only rises to ~30-degrees) and your power output plummets. Sunearthtools.com has a really geeky cool page that’ll give you the exact angle of the sun any time of year for any direction and spot (just plug in your location):
How much of a deal is this, power-wise? In Palm Springs in summer you really don’t lose anything by keeping the panels flat whereas in winter you’ll lose more than 50% of your power output if you keep them flat. It’s HUGE!! To demonstrate this here’s another cool tool that’ll calculate daily flux (= an approximation of the total amount of energy hitting your panels) based on location, time of year and tilt.
2/ How Do You Tilt?
The fanciest type of tilting systems are “sun trackers” that exactly track the sun all day long, but these are not exactly practical on a free-wheelin’ RV roof. Some RVers keep their panels mobile and just bring ’em out to tilt/track the sun manually whenever they need them. With 6 heavy panels to lug around that wasn’t an option we wanted on our “beast” so it made a lot more sense for us to permanently attach the panels and look for other tilting options.
Our solution was to get the AM Solar mounts (highly recommend them, even if you aren’t going w/ AM Solar for the rest of their gear), and then add-on home-made tilting bars. Some basic 1/4″ aluminum stock from Home Depot cut to whatever length you want with holes drilled in (you can even drill multiple holes to have multiple tilt options). Combine with screw/nuts and you’re good to go!
3/ What’s The Best Tilting Angle?
If you’ve made it this far and manage to remember what we talked about in #1, then you know that what we’re looking for is to get your panels as close as possible to 90-degrees to the sun. The cool sunearthtools.com link will tell you what angle the sun gets to in your area, and some simple geometry will give you the optimal tilt angle:
At our current latitude and time of year we’re talking around 60 degrees tilt at noontime for best results. Now, obviously the sun moves diagonally across the sky during the day and rises/sets somewhat southerly in winter so that number doesn’t stay constant and the real (max. total energy) formula is a rather more complicated (the cool tool shows that). But if you face your RV East-West and tilt panels facing due south more or less at the 90-degree noon-spot you’ll get pretty darn close to getting the best out of the sun.
4/ Beware the Shadow Monster
Tilting is just like everything in solar. You’ve got to make sure you avoid ALL shadows. Together with Marvin we were very particular when we installed our panels last year to make sure they had NO shadows from anything on the roof whether tilted or not, even with long winter shadows. I’ve seen shading models that show just 3% shading of a solar array can lead to a 25% decline in efficiency, with 10% shade producing up to 50% decline! The losses are dramatic and could mean the difference between a system that works and one that doesn’t. Even panels that have special “bypass diodes” (meant to help the shade problem) will suffer voltage loss for each cell shaded. Don’t be caught by the shadow monster!
5/ And Our Results Were….?
We conducted our little tilting experiment out in Owl Canyon BLM. Our tilt-bars only go to ~45-degrees so we knew we wouldn’t get optimal output, but we expected a pretty significant boost. Mid-morning with panels flat our 600W system was putting out ~20Amps. With the tilt we hit ~30 Amps, a 40% improvement. As the day wore on our boost got even better with the MPPT charger kicking up output to a stunning peak of~45 Amps at around noon (MPPT really shines with higher-voltage panels in colder temps). Coooool!
We plan to do even more detailed tracking experiments later this the winter and will undoubtedly share these exciting results with our readers, but for now this is a good start. There is also much more geekiness that can be done with solar so don’t expect to see the last of this sunny series.SPONSORED LINK:
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We LOooVE Comments, So Please Do
John B. Abela says
Thank you, thank you, thank you!!
Thank you for sharing this data. As a person planning on buying my first rig in the next year or so I have been heavily planning on buying as much solar gear as I will be able to fit on the top of my 5th wheel. Data like this is a huge help to know future power draws and demands and what I can expect from a system!
So happy it’s helpful! Nina
Lauren Brown says
Maybe you and Paul can check out our 24-panel, stationary, roof-mounted system when you swing through San Luis Obispo next spring and tell us if such a tilt system is practical for us. We produce well under 50% electricity this time of year compared to summer. Or maybe we could tilt the whole house!!!
Hehe…yeah, winter is the one time of year you really want to tilt. Personally I think a single tilting angle is probably fine. It may not give you optimal output, but it’ll increase output dramatically for relatively low cost.
Woow you guys are a whole electrical plant by now…way to go.
We DO love to geek out on the solar. It is soooo very cool.
Steve & Gari says
Awesome article! Thank you and congratulations on your system. We dream of recreating something similar and your info really helps.
If you’re planning on alot of dry-camping solar really is nice. It takes a few years to get pay-back on the system (all depending how much you dry-camp), but it sure is fun!
WOW….tons more than I ever dreamed about the panels. Great job explaining. We really never considered installing them but now I see how easy it is to reposition them…HUM! Food for thought.
My take on the whole tilting deal is that you really only need to do it in winter. The flux models show that tilting in summer really doesn’t make alot of difference. So, we plan for tilting only for winter boondocking…and those little tilting arms are super-easy.
If you could get power tilting by wireless remote control, that would be the cats meow!
Good articles on solar. They will come in handy for us down the road. Thanks.
Oh wouldn’t it just! Unfortunately the technology that is sturdy enough for an RV roof, yet also inexpensive easy enough to tilt isn’t out yet (or rather I haven’t seen anything that would come close). The sun-tracker systems are super-expensive and not appropriate. I’m thinking someone will come up w/ a system soon, likely something similar to what our RV slides run on (a simple motor-based system).
Jerry B. says
I can sure see the benefit, but I think I’ll just oversize the panels somewhat and suffer the loss, instead of climbing up on the roof to raise the angle. Plus, you have to be parked in the right direction to maximize the light which isn’t always possible. I’m shopping for a setup myself right now, so your info is timely.
Whats next for you guys, nuclear?
Over-sizing is always a good option. We over-sized our system and could probably get by fine in winter without tilting, but I have to admit it IS nice to be able to tilt at least one angle for that extra boost in winter boondocking locations (e.g. in the SW desert). In summer tilting doesn’t make alot of difference so you’re fine with being flat, but you may want to give yourself at least one option for winter especially if you’re planning to stay put and boondock winter-long.
Mark S says
What a great post….really enjoying geeking out with you on this solar thing. We are learning so much from you guys (not just about solar stuff either!). I’m afraid to ask if Paul has burned out on the Investing blog, haven’t seen a new post in a while. Maybe just busy playing with the panels on the roof, right? =)
Yeah, I fear Paul’s not blogging much anymore 🙁 He’s got alot going on w/ trading (and panels, haha) these days so not as much time for the blog. I’m going to see if I can convince him to get going again.
Deas Nealy says
Nina, Quick question. I am looking at the Tiffin 34 RED and one rig has the propane frig and the other has a residential. I was curious if you guys could sustain with a residential on your style of boondocking with all the solar or would you still prefer the standard Propane?
The unit does not have solar yet and has 2000 watt invert-er and 4 batts
No, we couldn’t sustain a residential frig with our current set-up and would still prefer the propane. You can do it with solar but you’d require minimum 2 extra panels (maybe more), 2 extra batteries and (ideally) a dedicated inverter for the frig (so that you don’t have to run your big inverter all day and night). I’m basing that off new frigs running ~5 Amps (it’s probably more with the compressor running, but I’m guesstimating that’s the average), so a total of an extra 120 AH needed in a day. At that rate even 2 extra panels wouldn’t be enough to keep up! I haven’t done all the calculations in detail so these are rough work, but it’s a lot of extra load.
Here’s another link I found for you from a blogger who’s done some “real-life” experiments w/ a residential frig. Their rig has 2 extra batteries (660 AH total) and 1000 Watts of solar, but in a recent 30-day boondocking outing they found they still needed to run their generator ~1 hour/day to keep-up. I don’t know what their other usage is (TV, internet etc.) so hard to make an accurate assesment, but it kinda lines up with what I would expect.
Deas Nealy says
Good information. I figured this set up was for people that plug in most of the time. We are interested in your type of travels and it would be annoying to have to run the generator all the time..
Nina, love your blog. Just found it yesterday. We are in the process of being able to full time – need to get the house sold!. Can’t wait. We are also looking into solar panels. We have an older 30′ Class C and the generator is loud and smelly – thus solar would be the answer. We are really looking into the portable ones either the ones that fold up or have the panels mounted. We live in BC and a lot of the campsites are covered so we thought it would be ideal to have them moveable in order to catch the sun. Would you ever consider that, if redoing. Thanks and once again love the blog . Melissa
For the solar panels specifically we really like having them attched to the roof. They’re pretty heavy & bulky, and to haul 6 of them around all the time would be a pain. I do know folks who keep them mobile (e.g. Imperfect Destiny) and I think if you have a smaller system having them mobile is totally workable, but with 6 panels such as we have we really like the freedom of having them on the roof.
Glad you enjoy the blog!
Do you actually get up on the roof to tilt each one of your panels?
We only tilt the panels in winter, but yes…when we need to tilt it requires a trip to the roof. In total it takes ~20 mins to get all 6 panels done. At some point I’m sure we’ll find a more techno-savvy way of doing this, but for now manual tilt does the job.
David & Kathy C. says
It makes sense having the solar pointed to the south and the Beast (RV) pointed east in the winter and taking in all the sun on the passenger side. You don’t need the awning right? You want the sun beating down on you. I love that…
In the future adding a couple more batteries and solar panels for the future electric refer you may be running out of roof space?
What about mounting the panels on the slide outs at the top and tilting them up. You can bracket them @ 30, 45 or 90 degrees, whatever you need. Use them as awnings.
I haven’t seen this on Google or Yahoo Images.
This is genius or horribly flawed…
Exactly the reason we generally face that direction! The entire RV acts as a “shade” on our entry door side so we don’t need to use the awning. Also we get afternoon sun on our front window which warms the rig (usually a plus in winter).
The side-mounted solar panels are actually not that crazy an idea. Boaters (cruisers) often do this on their boats -> mount panels on the sides and tilt them up. The only problem w/ RV’s is the shade issue. It would work beautifully in winter where the sun is quite low on the horizon (as long as you always park in the same direction), but the panels might get too shaded in summer. Still it’s a fun idea!!
Pat H. says
The above post by David and Kathy speak of pointing the “Beast” east taking all the sun on the passenger side. When you agree with her you aren’t really because to have the afternoon sun coming into the front windshield you must be pointing west!
I am installing my solar system this week and because of unfortunate roof shading considerations I will be by necessity lining up 4 panels on the passenger side end to end. Not only will this put the “sitting area” outside the entry door in the sun during the winter but will keep the windshield from being an afternoon solar furnace in the summer as the sun will be setting onto the rear of our coach. I like your situation of having the sun through the windshield to warm you in the winter but it is a configuration I am unable to employ. It seems that there are advantages and disadvantages to pointing a rig in either direction; I’ll take what I’m dealt.
Yup…you’re right. I’m often getting East and West muddled up thanks to my really bad sense of direction (I even mess up right and left :))
Like you said there’s different positives to both ways. We’re able to tilt our panels either direction (to the right or left side of the coach) so we can choose to park either way. If we park facing west we have afternoon sun in the windshield, our “sitting area” is shaded by the coach (sometimes nice to have), but our fridge is on the sun side all day (not great). If we park facing east we get morning sun (also nice sometimes), all-day sun in our “sitting area” (sometimes nice, sometimes not) and the fridge is on the shade side (better for the fridge). Hopefully I got those directions right this time!
There’s no real “right” way and I think you’ll be fine with either one.
Pat H. says
Were you able to take advantage of the 30% federal tax credit available for solar installations? If you did this would make an excellent blog subject.
Yup, we DID actually take the 30% tax credit and I wrote about it here:
Definitely worth taking advantage of when you do the installation!
Pat H. says
Thanks, Missed that post!
Bill M says
Want to start by saying I love your blog. But I do have questions about Solar and RVing. How much can you use your TV and satellite at night with your setup? I’m looking to go full timing in a few years and need to decide if I need both solar and a generator.
At night we rely entirely on our batteries (no solar at night obviously) so it comes down to how much battery capacity you have. We have 440 amp hours (220 usable) and typically watch a few hours of TV each night without much impact at all. Our satellite + LED TV only draws ~3 amps DC (add ontop of that phantom plus inverter of around 5 amps DC) so we have plenty of juice to spare.
The switch to LED TV was one we made specifically for boondocking. If you’re interested I did a 2-part series with calculations here:
Perhaps the better question to ask regarding the generator versus solar question is what will you do if you have several cloudy days?
When we have full sun (i.e. Most of winter) our 600 watts of solar (plus 440 amp hours of battery) completely covers our needs and that includes running Internet and TV all day and most of the night if we so wish. Where we run into shortages is if we go through several cloudy/rainy days in a row (where we can’t fully charge our batteries) or we camp in shade (which we often seek in summer). That’s when we either gotta conserve power or use a generator to make up the difference.
If you’re ok with being flexible on your power needs then solar alone will do you fine, but if you need your evening TV fix regardless of the weather, then a generator is a nice backup. We run pretty much 100% solar all winter and spring, but will use the generator if dry camping in the heat of summer or during inclement weather.
Hope that helps!
Have you thought about an automatic sun tracking device like they use on telescopes to track the night sky? (I don’t know if it is even possible) just a thought that crossed my mind.
We didn’t actually consider this just coz we wanted a very simple, light and secure mechanical support system for the panels on our roof. Our roof can take weight, but we wanted to keep the support as light as possible. Also we like that the panels can be bolted/secured down for bumpy roads and high winds.
That said, the tracking devices are becoming lighter and we just had a neighbor who had one mounted one on their 5th wheel roof. It obviously takes up a lot more space so you can’t have as many panels on the roof, but I’m sure you gain back somewhat in total output. Plus I have to admit it looks pretty cool. I haven’t looked closely enough at the calculations to see if it is worthwhile, but it’s certainly interesting.
For those of you who asked about automatic tilting I’m pleased to add this excellent self-made tilting mechanism from one of our readers “Doug”. We have not implemented this ourselves so I’ll let his words tell the story:
Two of the pix are from my third and latest prototype, and the other pic is a first prototype which had many issues but is kinda cool to look at, anyway.
As you can see the basic machine is really quite simple, just some 4″ wide aluminum U-channel from Amazon, a 12-volt linear actuator from eBay, and some 3/8″ bolts, nuts, and washers. The devil is in the details though, as the math to figure out exactly where to drill the holes would likely fluster most mere mortals—but not us engineers!
When the actuator is retracted, the two pieces of U-channel are parallel to one another, so the panel is “flat” relative to the roof. The actuator itself is at a slight angle though, in this case about 4.3°. This gives it a mechanical disadvantage of 1/sin(4.3) = 13.2, which means the 18lb panel effectively “weighs” 18×13.2 = 238lb. In other words, it requires that much force from the actuator to budge it from full retraction. But this particular bargain actuator is only rated for 225lb—so we offset a bit of weight by cantilevering part of the panel beyond the hinge, so it acts like a seesaw. And of course when the actuator is fully extended, the panel is at the desired ~50° tilt.
Reed Cundiff says
We had thought about tilting capabilities; however, our son who is in the solar business did like the idea of our climbing about on roof at age 74 (Jerry noted this on his post of three years ago)and said to just put on more flat panels. . They cost him about 50 cents a watt as a contractor. We have 1.4 kW and we have room for another .7 kW if we so choose. The power drops off as the cosine from normal and we really only need full power (up to 1330 W to controller) in summer when we use the Dometic power hog air conditioner.
We have six x 235 W panels which are 30 V panels. These are ganged in two series of three each so the voltage from each series is 90 V. The two series are then joined (paralle) to go to MPPT at 90 V. 1300 W at 90 V is only 14 amps so the TriStar MPPT-45 is only handling 14 amps.
The power is then stored in a battery bank of four LFP batteries (each battery is 4 x 180 amp-h LFP cells) in series to provide 180 amp-hr at 48 nominal volts (720 amp0hr at 12 V nominal). This is 9+ kW-hr of storage or about 7.2 kW-hr of usable energy since LFP should provide several thousand cycles down to 80% DOD.
We have likewise changed entirely to LED. The outside lamps required 10 amps at 12 V and not use only 1 amp.
We are full timers and primarily boondock (currently mootchdocking at younger son’s place to help out with 2-year old and 4-week old grandsons). Planning to head back to Yucatan for fourth winter.
Reed and Elaine
1,400 watts is alot of nice solar 🙂 And yes, at that level you have enough extra that you don’t really need to tilt. Maybe one day we’ll get there ourselves.
Gary Doty says
We just started full time 2 years ago and right off the bat you inspired us to go solar. We had 600w on the roof and 600Ah bats in the basement and have been using all solar most of the time. We’ve just traded in the 5er & ford 550 for a 40 ft. “beast” (Tiffin Phaeton) and we’re putting the 5er solar system on the new unit. I’m a little concerned because now we have a residential refrig and if I’m not mistaken, the 10 amp label on 120 ac turns into 100 amps on DC. I know the fridg is not on all the time but do you think this is going to be a problem in that the auto start gen will be running off & on all day to keep the bats up? I asked Tiffin if they would swap it out with a gas/elect but I have a feeling that isn’t going to be an option. So, we may not be boondocking as much as we use to…
It’s possible to do solar with a residential fridge, but you do need MORE. Friends of ours who have a residential have measured 180 DC amp hours real usage (in 24 hour period). So, you’d need to power 180 extra amp hours which means at least 2 extra batteries and 200-400 extra watts of solar panels (depending on conditions). So, that’s what I’d add to your base. That means instead of 600 watts, you’d be looking at closer to 800-1000 watts.
These are just off-the-scruff calculations. Conditions would alter your actual usage of course (and you can never go wrong with more solar).
Gary Doty says
Thanks for the reply. It’s basically what I figured. Might have to figure in several smaller solar units in addition to the three large ones we now have. Always a challenge to figure where to put extra batteries. Keep up the great blog. We enjoy following your travels. We’re headed south in another month down towards Why BLM land thanks to blog. Was there any place in particular that a 40′ MH would work best? Keep up the good boondocking information. We LOVE IT.
The area we stayed last year would work fine (reviewed on the blog). Just unhook at the entrance and scout around before you take in the big rig since there are some rutted roads in there.
Thanks for your post as we recently added 640 watts of solar to our MH. I have been using a few of the web sites you recommended in calculating the “optimal” tilt. I used a little trigonometry to figure out how long the tilting bar should be for 45 to 60 degrees tilt in 5 degree steps…Law of Cosines made it pretty easy…especially with this handy online calculator….in Google search for Law of Cosines Calculator…just plug in your numbers and drill your holes for each implementation.
For example…we have (4) of the 160w panels from AmSolar and the mounting holes are 24″ apart…so solving for C (tilt bar) use 24 for sides A and B and plug in the angle you want to achieve. If you plug in 45 for the angle your result is 18.37. The 45 degree tilt bars that AM Solar sells for these panels are 18.5″ between the mounting holes…so they must have used the same calculator 😉
Gary Doty says
Good info, since I’m changing our panels over from our 5er to our new MH and want to put tilting brackets on them. Would those brackets fit on a 37×65″ panel? And would they be strong enough to hold them in the 70 mph breeze?
They’d be strong enough to hold the panel for sure, but in 70 mph breeze? We don’t even tilt our slim panels in those kinds of winds. We’ve kept our panels tilted up to 40 mph, but I don’t like to push it beyond that. We even put in our slides at higher than those wind levels.
Gary Doty says
Sorry. I should have been more specific. I meant 70 mph not tilted. We had 60 mph winds at Palo Duro canyon and everything came in/down – slides, sat. dish, etc. Only time I’d been in anything like that was when hurricane Andrew blew by us.
Well we just managed a 90 mph storm at Cape Blanco last month. Can’t say I want to experience that again, but our panels stayed on the roof.
Happy New Year. Thanks for all the data over the years. Now a procedure question, hope you can help….
Backgroud info: We have a gas/electric refrig that is a power pig. (Norcold 8cf). We have 810W solar, 6 lifeline 6V 220AH batteries and the Magnum 2812 inverter. We travel with the inverter on and the refig on electric and keep it on electric during the day light hours but have to run back to the M/H and switch to gas before dark. Does that seem normal or am I missing something?
Also it looks like the inverter has a lot of overhead. Do you switch the inverter off when you’re not using your 110V appliances or keep it on all the time?
Any guidance is appreciated.
Yes, the inverter has some overhead. We typically leave the inverter off and only switch it on when we need to run our 110V stuff (computers, TV, satellite, microwave, blenders etc). Since your fridge is gas/electric I’d just run it on propane all the time unless you’re plugged in. That’s what we do. The fridge runs a tad warmer on propane, but it’s very efficient and functions perfectly. It only ever runs electric when we’re plugged in to hookups.
Excellent. Thanks again.
Gary Doty says
We have 1,140w on the roof and 910 ah in the basement. We have the same inverter and only turn it on when we need to. However, we also have a residential refrig on a separate smaller inverter that we leave on all day long to run the refrig. The solar keeps up with everything during the day. In the eve we’ll turn on the coach inverter (2,000 w pure sine) to watch tv, etc. I also have a small 180w inverter that I run during the day to keep the computers, cell phones, head sets, etc. charged up. Takes about a half an amp to run. At night I turn off the frig and small inverter before we hit the sack and only loose about 4 degrees until am when I turn on the frig inverter. We also do a lot of boondocking in our 40′ Phaeton. By the way, the batteries are Sun Extender PVX-3050’s. 2 in series are 12v at 305ah. Their footprint is almost exactly the same as a normal battery but they are about 3″ higher and about 40lb more than a regular battery.
Gary & Joanne
Having a smaller, separate inverter is a great option for a residential fridge. That’s what we would do if we end up with a residential. Also having a separate inverter for your laptops is a nice little mod and will save the overhead of running the bigger, main inverter. We’ve thought about it, but just have never gotten round to doing it.
Lifeline also has taller batteries with the same base footprint as our current ones. We could fit them directly into our existing space and gain some amp hours, but we do add more weight. They’re bleeding heavy things!
Nicholas Bluhm says
I also started with the AM Solar bars….
And then modified them to give me several additional tilting angles…..it’s quite an easy fix
Buy aluminum knots of the same size…(.Fastenal sells aluminum nuts if you cannot find them); drill holes evenly spaced along the length of the bar; take it to your favorite aluminum welding shop and have them tack weld the nuts on the same side as they were originally supplied by AM….
Nice little mod on welding the nuts to the bar. We actually made our own tilt bars from aluminum stock. It was cheap and easy.