The Art Of Solar Parking

Solar panels have to be aimed at the sun to work. I’m serious. They really do. When they are bolted to a vehicle, that doesn’t change...but the location and orientation of the rig certainly does! Combine that with the fact that the sun itself follows a varying path through the sky, depending on time of year and latitude, and you have a lot of variables to consider if your rig relies on solar for power. So where – and how – you park your RV has a big impact on how happy you’ll be with your solar panels’ performance.

When folks put solar arrays on their house, there is generally some kind of site survey done to determine the best location and orientation for the array. There are professionals who specialize in this, and that’s because solar panel performance is hugely dependent on their orientation to the sun, and being free from shadows. On a house, once the panels are installed, everybody can just forget everything they know about site surveys (except the surveyor guy, he should probably try and keep remembering). When you operate a solar-powered RV though, you basically do a site survey every time you park. Each time, you have an opportunity to either wring every last drop of performance out of your system, or completely wreck its output.

Might as well learn how it’s done, eh? This post is going to talk about the factors you should consider when parking your RV for solar, and what you can do about each of them. I was just going to write a simple post with only the basic, easy tips. But then I thought, “Nah, I’ll do another massive snooze-fest. People love those!” There are three major topics to pay attention to, and some bonus tips at the end:

Site Selection
Orientation
Shadows
Advanced Tips

SITE SELECTION

RVers consider many factors when parking their rigs: The view, proximity to town and recreation sites, how hard it is to level. If you have solar panels, the solar exposure of a site is on that list. For us, “solar suitability” is usually our first priority, though sometimes we get cocky and just park however we like.

The Most Important Thing*

If you remember only one thing, it should be this: Aim your panels South. I would love to go into depth about why this works but Ching told me that would put everybody to sleep. The sun doesn’t pass directly overhead as it passes through the sky from East to West; it swings closer to the Southern horizon. The intensity of the sunshine (as felt here on the ground) is also much stronger at midday. You collect more total energy by taking advantage of this midday peak, even though it means lower energy production in the morning and evening. There are a few exceptions to this rule, but they are rare. Just point ‘em South.

*This applies to locations in the non-equatorial Northern Hemisphere (like the US). If you’re between the tropics of Cancer and Capricorn (ie. near the equator), this rule kinda doesn’t matter. And if you’re in the Southern hemisphere (Australia, Chile), the direction to aim is North, not South!

So if you’re in search of a parking spot with good solar power prospects, you’ll want to find one that has a clear view of the Southern sky. To do this, we use the same tool that most RVers use when hunting for wild camping sites: Google Maps. We just ask ourselves a few extra questions:

  • Terrain view: Is the spot positioned where it won’t get southern sun, such as a north-facing slope, behind a mountain, or in the bottom of a steep-sided valley?
  • Satellite view: Is there anything obviously tall to the south of the spot? Radio towers, hoodoos, and buildings are common issues.
  • Satellite view: What’s the vegetation like? Is it a small pull-out hemmed in with overhanging trees, or a wide open meadow? This can be hard in the desert or thick forest where you lose a sense of scale. If you’re lucky, the satellite has caught a car (or even an RV in popular boondocking areas) in the image, providing a reference.

If you want to take things to the next level, try using SunEarthTools or SunCalc. These free websites will draw a miniature arc describing the sun’s path, for any date, and centered on your chosen location on a Google Map. At first glance it seems like an intimidating amount of information, but once you’re comfortable with the display, they can be quite helpful in selecting a future campsite.

SunCalc

SunCalc

SunEarthTools

SunEarthTools

Until we actually turn up at a site though, we don’t really know. Sometimes we get there and it’s just a disaster – that might mean moving on to a backup choice, or just sticking it out. Once we decide to stay, we move on to the next phase of parking: choosing where exactly to put the rig.

ORIENTING YOUR RIG

In most wild camping spots, you have several choices of where exactly to park and which way your rig will face. To get it right, you’re going to need a special tool…but the good news is you’re probably already holding it:

The Humble Compass

Nope.

Nope.

Any compass will do, if used correctly. Except the one built into the rearview mirror of your truck – those are kind of a joke. Any modern smartphone has one built in. There is no complicated orienteering to do: You just hold the thing out as level as possible, and see which direction it says is South. It’s pretty simple, but there are two details to know about: interference and declination.

            Interference happens when nearby conductive objects throw off the reading. So: Stay away from metal stuff. This includes your vehicle! GET OUT and walk several paces away from your truck to get a proper reading. This applies to the one in your smartphone, too. We learned this the hard way after parking in the dark once, and learning that we had aimed our panels due North because we stayed in the truck to read the compass. That is literally as wrong as it’s possible to be. We had to re-park the whole rig in the morning.

            Declination is the difference between true north and magnetic north. Compasses point at magnetic north, but the sun’s position in the sky is related to true north, so we have to compensate for this difference. Here in the lower 48, the error caused by declination is rarely more than 12 degrees, and while that is a major problem if you’re navigating, it makes very little practical difference when you’re parking your RV. If you’re heading to Alaska, the difference gets larger – you may want to look into it.

If your panels are flat-mounted, you may be able to park your rig in any orientation without trouble, but first consider the items on your roof (antennas, vents, A/C shrouds). RV roofs are crowded spaces, and in nearly every install, there is at least one thing that will throw a shadow onto your panels if it’s turned wrong. Even short things (like open vent covers) can shade a panel if the panel is mounted right up next to them. This effect is more pronounced in winter months, when the sun doesn’t get as high in the sky (so shadows are longer). You want these items to be North of your panels, so the shadows go away from them. Tape a note to your dashboard, if it’s hard to remember what goes where!

If Your Panels Tilt

You’ll want to park so that the “hinge” of the tilting mechanism runs East-to-West…meaning that the panels will tilt up to face South. On most rigs this means parking with the long axis of the rig running East-West.

Our array doesn’t tilt, but is also not horizontal because of the shape of our roof. It’s as if they are “permanently tilted” to the rear. So our “hinge” is effectively across the width of the trailer, thus we aim our rear bumper South.

Ground Deploy

If your panels live on your bed while driving and then come out to play on the ground when you park, you have some options: Firstly, if the cord is long enough, you can park the rig in the shade, and put the panels in the sun, you lucky dog. Secondly: You can “track” the sun. Automatic tracking devices don’t improve performance enough to offset the extra energy they consume, except on large installations. But you have a bitchin’ human-powered tracker (either yourself or your kids), and it’s definitely worthwhile to use that. Point the panels Southeast before bed, turn them due South around 11:00AM, then point them Southwest in the afternoon. But don’t forget!

Shadows

People, you can’t have shadows on your solar panels! Have I said that enough times? You just can’t. Unless you don’t care about making free electricity…then I guess it’s fine. This means self-shading from objects on your own roof (as mentioned above), but also shadows cast by nearby objects.

When you’re parking your rig in constantly-unfamiliar spots, this can be quite tricky. I have definitely forgotten about a light pole, or tree, or misjudged how long a building’s shadow would be. One time I misjudged a whole fucking mountain (it seemed so far away)! It’s hard to do with only judgement and intuition, but thankfully there is a magic bullet for this one. It’s just a question of getting the right tool:

There is an app for that: Professional site surveyors use specialty iOS and Android apps to conveniently get everything they need for their work. The really useful ones use augmented reality to draw the path of the sun over a live view via the phone’s camera. You hold up your phone, and you see whatever’s around you – with the arc of the sun’s path overlaid. This is quite possibly the best mobile application for AR that I’ve ever seen (yes, even better than Pokemon Go). So. Freaking. COOL!

The path of the sun through the sky, as visualized by SunSurveyor.

I recently got one of those apps –  Sun Surveyor ($10 on iOS, $8 on Android) – and have been using it almost every time we park. It’s especially useful up here in the Pacific Northwest (LOTS of TALL trees!). Anybody can do solar in a desert, but since we like to venture into all types of terrain, this app has really paid off. With it, the problem of identifying shadow-casting objects goes completely away. Spotting trees, buildings, even mountaintops that may get in the way becomes intuitive and fast. When you have to do a site survey basically every time you park, a tool like this is wonderful!

Here’s a great example of how it works: While we visit friends and family in Seattle, the Toaster will be in a storage lot for about a month. We didn’t clean out the freezer; just going to let the solar panels keep everything running. That’s a non-issue, so long as the rig gets decent sun. Since we won’t be in it, we needed to know for sure that when we parked it (late in the afternoon), the spot we chose would get unbroken sun throughout the day. But we had no idea what the lot would look like until we got there. When we arrived, there was a single tall tree due south of our spot – oh no. I normally would have erred on the cautious side and abandoned the site. We’d have to look for another place to store the rig. But instead, I stood in the parking spot and whipped out SunSurveyor. Here’s what I saw:

Relief! It’s still early enough in the year that the sun will clear the top of that tree. That means a good 7 hours of sun each (non-rainy) day. That’s exactly what we needed to know!

Brief demo of the interface and some 3D compass features.

The app can also display the arc of the sun (or moon) on a google map (like the two websites mentioned above), and there is a “street view” mode, which does the same thing except from street level. So you can legitimately tell if Big Ben is going to shade your RV at 3pm on the fourth of July, 2025. This is limited, of course, to things which can be seen from a Google-mapped street…so remote desert wild-camping sites won’t be in there…until Google extends its grasp a little further.

SunSurveyor does some other cool stuff, like give times for sunrise and sunset, twilight, dawn and dusk, plus “golden hour” and “blue hour” (photography stuff that Ching can use). There’s also location-tracking for the moon and milky way (interesting), and a tool for calculating the length of an object’s shadow based on its height (useful for settling bets?). All this info can be given for any date, past or future. I already had apps that did some of that, but I’m happy to have it all in one place now.

Disclosure: We got a discount on our copy of Sun Surveyor in exchange for providing a review and mention here, but the comments and opinions are my own.

If you don’t want to pay for an app – or if you’re just a techno-grouch (as I normally am) –  here’s some less-techy tips to help keep you in the sun:

  • If you drove through low-hanging vegetation getting to your remote little campsite, check for debris that got knocked down onto your roof. Panels covered in pine needles or leaves will be shaded no matter how clear your parking spot is! We are repeat offenders on this one.
  • Your head is lower than your roof, and higher than the ground – so as you walk around a site, remember that shadows falling across your face will land shorter relative to roof panels, but reach further over ground deploy panels.
  • You can ignore anything shorter than your rig: I know that sounds stupid now, but I have agonized over a 10-foot tall bush for too long before realizing it didn’t matter!
  • Wet puddles on one edge of a field and dry puddles on the other edge probably mean the wet side gets a lot of shade.
  • Vegetation. Some plants love sun; others don’t. Brambles, most berries (especially raspberries and blackberries), and kudzu love it. Rhododendron, ivy (both poison and regular), and mosses want shade. If “shady” plants abound at your parking spot…reconsider. Yes, I know this is a crazy tip…but just think how mountain-man-badass you’ll feel if you actually get to use it!
  • Yeah, that SunSurveyor app is looking a lot better now, isn’t it?

ADVANCED TIPS FOR SOLAR NINJAS

Here's some bonus tips for those who want to play around a little bit or test your skills. None of them are likely to make a huge difference in your system's performance, but might eke out a few more amp-hours here and there.

Predicting Shadows With 3D View

Apple and Google both have “3D view” options available in certain cities, which display their otherwise-flat maps with a height element. The feature seems to extend quite a long way away from the main city center though, often working in wooded areas nearby. Finding a good solar spot in cities can be hard, so it’s worth turning this feature on to help gauge the height of nearby buildings and foliage. It even works on trees! Sooo creepy! Just don’t get thrown off by the shadows you see in the satellite imagery – those depend on the time of day (and year) the images were captured, and probably don’t line up with the time you’ll actually be parked there.

Aim to Cover Your High Demand Times

Deep-cycle batteries like to be discharged slowly. When you suck a lot of current out of them, they have a reduced effective capacity (this is the Peukert effect). So if you have high power usage in the morning or evening rather than at midday, it may be worthwhile to aim your panels for peak energy production to occur at that time instead. The extra current coming from the panels will reduce (or possibly eliminate) the current which must be drawn from the batteries. This is primarily useful if your battery bank is undersized compared to your panels – a common issue in RV installations. If you try this, do the math and watch your instruments to see if it really is helping – this should not be a common occurrence.

Align Your Array to (the Disappointment of) Reality

We have intentionally oriented our panels due East, because we expected afternoon rain. Or we had a terrible spot with only Western exposure, so we just aimed the rig that direction, to get as much as we could out of the few hours of direct light available. There is no point aiming South if the panels will be shaded throughout midday. Shadows turn off solar panels. Period. This is a micro-managing technique, suited only for very short stays (one or maybe two days)…but once you’re confident in your battery capacity, it can be fun to try, especially if it means being able to use a convenient (or beautiful) campsite instead of hunting for a sunnier one.

Okay, so that’s how to park your panels! As usual, I’ve tried to be as thorough as possible, but please let me know if I’ve overlooked anything.


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