RV Solar Part IV – Panel Tilting & Winter Solar Optimization

Paul and Alex go a-panel tilting

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?

In winter the sun stays closer to the horizon

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):

Solar Diagram for Palm Springs, CA from Sunearthtools.com. The top line shows the sun angle in mid-summer, the bottom line for mid-winter.

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?

Our home-made tilt bars

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

See ma...NO panel shadows!

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.

RV Solar Part III – The Installation

Marvelous Marvin

So, we come at last to the final installment of our story, and appropriately so on the last day of the year. It’s the last hurrah, the chocolate treat, the final ray of sunshine on the panels…you get the drift. Having decided on our equipment and specs we needed to make the very critical choice of whether to do it ourselves or get help. We’re relatively handy, but not exactly overly-confident and the idea of drilling a hole in our RV roof was enough to send me into a mild panic. So, for our personal sanity we decided help was needed and as it so happens AM Solar knew a good installer (himself a full-timer) who was travelling through Florida while we were here.

And that’s how we met Marvin.

Now, I’m not one to beat about the bush so I’ll just come right out and say it -> Marvin was marvelous. Not only is he a very nice and down-to-earth guy, but he knows solar and the final workmanship was beautiful. So, I’m very happy he came along and am equally happy to recommend him to others (his website and blog is here: http://precisionrvmobile.com/ and he’s travelling West from FL through TX and onto Yuma, where he’ll land sometime in March 2011).

Marvin spent around a day and a half doing the installation itself and a few extra hours chatting and going over questions with us.  Since we didn’t do the install ourselves, I won’t go into all the nitty gritty, but I’ll point out some key points that made the installation work:

• Careful Placement of the Panels:
  

  Marvin and Paul placing the solar panels on the roof

  The panels were placed on the roof so as to ensure there were *no* shadows from any of the existing structures up there (e.g. aircon, antennas). Also, they were placed so that they can be tilted with *no* shadows. Both these things are critical to make sure you get all the power you can out of those babies. Remember even a teeny amount of shadow can kill your power by huge amounts.

• Short, Efficient Wiring: 
  

  General Overview of our Installation. We were able to get nicely short wire runs.

  Marvin did a lovely job of running lines from panels to the combiner box at the back of our roof. From that point it was a direct shot through the roof, down along our our back closet and into the floor to our back left storage bin where he installed the solar controller. The short & direct wiring job was the very reason we were able to stay within our voltage drop goals. Remember that the longer the wire, the more your loss and minimizing loss is what it’s all about

• Controller Located Close to the Batteries:
  

  Marvin installs the solar controller in the bin right next to our battery bank.

  Our solar controller is in the bin directly adjacent to our batteries which is as close as you can get without being in the same room. This very close placement was what allowed us to meet less than 1% voltage drop between the charger and the batteries….another critical loss point. Marvin routed all the wires through the bin wall and sealed the hole to make sure the battery compartment was kept isolated.  

• Attention to Details: Marvin did a very nice job of routing wires carefully, sheathing everything, sealing holes, tying up loose ends and so forth. The final job was very clean and workmanship nicely done.

The final panel placement. The slight shadow on the left is mine and the ones in the back from the trees.

To finish off our install project, the day after Marvin was gone and for a few days after we diligently measured voltage loss across the system. So far, so good. Everything indicates that we’re meeting our goals of 2% voltage drop from our panels to our controller and 1% drop from controller to batteries. 

Did we do everything perfectly? Probably not. Does our system rock? We certainly think so! We’ve been in partially shaded sites (for part of the day) so we haven’t pushed the system to it’s max yet or run the full amperage through the wires so there’s always room for more measurement and improvements. That’ll be a project for 2011 and we’ll let you know how it goes.

In the meantime I wish everyone a Happy New Year and a fulfilling and joyfull start to 2011. See ya’ all next year!

RV Solar Part II – The Equipment

So, following on from my gripping introduction to solar yesterday it’s time, with fanfare and fireworks (it IS almost New Year’s Eve after all), to reveal our choice of equipment. Every RV is different, so what we chose may not be right for your rig or your needs. Always, always take the time to figure out what’s right for you (true in life, love and general happiness, is it not?). So,  feel free to take our example as input, but definitely not as gospel

Going With 24V Panels

Our 100 Watt 24V Panels

I should start by saying that we decided to go with higher-voltage panels up-front and this, in turn, affected all our other equipment choices. The benefits of 24V panels are less loss through the system (using the water-hose analogy it’s like starting with a higher-pressure hose up-front) plus we liked the easier wiring and the current boosting capabilities it gave us (see below). It’s a slightly unusual choice and it is more costly. Most RVers choose 12V panels which require thicker wiring, but also give more open choice in controllers and panels. It’s a cost-benefit analysis and I would say you can get a solid solar system either way. In our case we’re geeks, and hubby had a decent year in the market so 24V was the way we decided to go…

Once we decided on 24V that immediately narrowed down our choice of vendors since not too many people offer a 24V panel that’ll fit comfortably on an RV roof. After much research we ended up going with a set of products from AM Solar, with an upgrade on wire-size and batteries. These guys only do RV solar (nothing else), have a good reputation, are all RVers themselves, are nice folks and above all were able to answer all our nit-picky questions. The final installation met our loss goals so we’re happy with the results. Here’s the full list:

1. 600Watts of 24Volt Solar Panels - We decided we wanted a pretty liberal power supply with 600 Watts of 24V panels, which led us in turn to 6 of the AM Solar RV100 series panels. We like the specs, warranty and format.
(Oct 2012 Update -> AM Solar has updated their line-up and now offer a  100W panel which is slightly shorter than the old RV100, plus some newer/niftier larger sizes. They no longer offer our exact 24V system, but all their panels are still “high voltage” so you’ll get the benefits. Check out their website for more info)

The Tristar Controller

2. Tristar MPPT 45 Controller (TS-MPPT-45) - Given our up-front choice for higher voltage panels, we needed a good controller that could handle the higher voltage input. MPPT controllers fit the bill and the Tristar 45 has good specs. It has all the charging profiles, including a custom setting, does temperature control and will actually sense and charge to the right voltage at the battery terminals using an external voltage sensor. This last feature is rather nifty since it makes sure you really get the right voltage exactly where you need it (= at the batteries) -> good stuff. Another nice feature of this controller is that if you generate more voltage than you need, it’ll convert that extra power into additional current going into your batteries (= a little boost for faster charging). Since we’re using higher voltage panels we should (hopefully) be able to take advantage of the boosting feature on a fairly regular basis.
(Oct 2012 Update – This is still one of the best controllers out there and has worked perfectly for our 600 Watt system. However, if we were to do it over we would probably choose the bigger Tristar 60 so we have space to expand our system size in the future)

3. AM Solar Tilt Mounts – We went ahead and chose the tilt mounts from AM Solar. We like the fact that they provide space under the panels and allow us to tilt when we need to.
(Oct 2012 Update – We love these mounts and would recommend them even if you decide to use a different company/installer. They make tilting super-easy)

4. Combiner Box – We decided to use a combiner box on the roof. So, each panel is wired individually on the roof, then they’re combined together in the box and a bigger wire goes from there to the controller. The bonus of this set-up is that you can use smaller wires on the roof, the wiring is easier/cleaner, plus you can easily add another panel down the line (if you ever need it).

Marine-grade wiring for the roof

4. Wire Upgrade - The standard system from AM Solar for the 24V panels use #10 marine-grade 90˚C wiring on the roof  and #8 wiring internally. Now, that may seem waaay too thin given what I wrote yesterday, but remember that 24V can run twice as long as 12V on the same wire for the same loss, plus we’re using a combiner box. We wanted to target ~2% voltage drop from panels to controller and ~1% drop from controller to batteries. So, we crunched the numbers using the wire tables I gave you yesterday and decided #10 was OK on the roof, but we needed to upgrade to the #6 wiring internally. That combo ended up working for the amount of wire we used in our install. For a home needing more wire you might need #8 externally and #4 internally and for a 12V system wired in series you might decide to use #4 everywhere -> it all depends on voltage, current and how far you’re running the wire. If I were doing this over for someone else I’d crunch the numbers specifically for their home.
(Oct 2012 Update -> AM Solar now offers #6,#4 and even #2 wiring for their systems and if we were to do it over we’d go with one of the bigger wire sizes, simply for the extra leeway. Bottom line is you can never go wrong w/ thicker wiring)

5. Lifeline AGM Batteries - We decided to upgrade our batteries to a bank of 4 Lifeline AGM 6V 220AH batteries (GPL-4CT). The AGMs will charge faster, and since they’re sealed there’s the bonus of no more maintenance. Lastly, since AGMs have really low internal resistance you can pile a lot more current into them -> that meshes nicely with the current boosting feature of our controller.
(Oct 2012 Update – Fabulous batteries! These have served us perfectly and we’d choose the same again)

Xantrex battery monitor

6. Xantrex LinkLIKTE Battery Monitor - This monitor hooks onto the batteries and tells you exactly how much power is either going either in or out of your battery bank. It’s definitely a geek-device and allows us to monitor exact usage from the batteries, something none of the other monitors we already have will do. If you’re just starting out on your solar quest and are looking for a device to tell you how much you’re using out in the boonies, this is the device that will do it for you.
(Oct 2012 Update – This is a great battery monitor and has served us well. We’d choose the same again)

Looking for another panel supplier? Here are some good, additional links on panel costs and suppliers around the US:

• Solar Panel Comparison Shopping – http://www.solardesigntool.com/compare-solar-panels-modules.html
• Solar Panel Prices – http://www.ecobusinesslinks.com/solar_panels.htm

The final installation and measurement info comes next…..don’t go away…

RV Solar Part I – The Discovery Process

Harnessing the sun is a beautiful thing

It’s a cold winter day here in S.FL we’re generating power from the sun. As a self-confessed geek I find this outstandingly cool and for the past 5 days we’ve been glued like little kids in front of the solar charger display, oohing and aahing over the power coming in. We’re now ready to hit the road and live “off the grid” in the best of ways, but it took us a fair few months to get to this point. So, these next few days I’m going to take you aspiring solar RVers on our journey so that you too may one day enjoy the fruits of the sun. We’ll start with the discovery process, then the equipment and end in grand style with the installation. So, here we go…..

Why Go Solar?
First things first, solar (for most people) is not exactly a cost-saver. Everyone likes to think it is, but given the price tag (anywhere from $1500 to $6000, depending on number of panels, equipment and installation) the return can take a good few years to make sense financially. If you use mainly private campgrounds or just do the rare day of dry-camping, the good ‘ol generator will do just fine. If, however, you like to go “off the beaten track” on a regular basis solar can be a definite bonus. We like a lot of spots that don’t offer electricity, and we love the idea of being self-sufficient and not having to run the generator. And, of course…it’s just so very cool….

How Many Panels Do I Need?
The first question most people start with, is how many panels do I need? Panels are expensive and you can’t expect to generate enough solar power cover everything (e.g. aircon’s are too big a power draw for regular solar use). The best way to estimate how many to get is to calculate your average usage (in amp hours) versus the average power you can expect to get from your panels (in amp hours). A very approximate rule of thumb is to target ~1oo Watts of solar for every 100 amp hours of battery capacity, but it’s best to do an individual assesment. Most RVers want to be able to use their computers, lights, appliances and maybe TV/satellite, but individual needs vary (by alot). Also, panels are usually rated for sun hitting directly on the panel at 25˚C, so actual power output will almost always be lower than their “optimum” rating. .  I won’t go through the individual calculations, but I’ll let you know (later) what we decided to do and I can direct you to Jack Mayer’s page for good examples on how to calculate your own needs.

The Basics of Solar = Minimizing Loss
Solar is basically about trying to convert sun power into real power. All this sounds good and dandy, but very basic problem with this whole idea is that it’s an inefficient process….in fact a really inefficient process….and everything you do along the way (adding wires, routing through machines etc.) causes you to lose some of the original power you generated. Just to give you an example, solar panels themselves are only about 15% efficient (so, of the power coming in from the sun, only ~15% gets converted, even less if the sun isn’t directly on the panels or it gets too hot or bits of shade are present etc. etc.). Then you add a wire onto that panel and you lose a bit more (wires have resistance and the longer and thinner the wire the more resistance it has == more power loss). Then you put that wire into a charger (== more loss) , then more wires, then finally into your battery. So, every step of the way you’re losing power, kind of like trying to put water through a hose with a bunch of holes in it. It’s a fact of life with solar so in order to do it right you’ve got to do everything you can to **minimize** loss. If you start off by understanding that basic concept you’ll save yourself a lot of tears and head-banging later on.

So, How Do I Minimize Loss?
Once you start reading up about solar you’ll find a lot of info (much of it conflicting) on how to do it. I’m not going to go through all the details, but what I am going to do is give you a few key basics and route you to a couple of sites that will teach you the rest. Here’s the top tips we gleamed from all our research:

1. Buy Good Quality Panels & Go Higher Voltage if You Can - You want quality panels that have a long-term warranty, and if you can go with a higher voltage. The reason is to minimize loss. You can run 24V two times longer than 12V on the same wire for the same loss. It’s the very reason industrial power-lines run at such high voltages (often 110kV or above) = higher voltage means less loss over distance.
2. Beware of Shade - You might not think you need to worry about a little bit of shade on your panels. After all, the rest of it is getting sun, right? As it turns out even a teeny bit of shade can cut power output by huge amounts, and putting one square of your panel in shade can sometimes lock out power altogether. So, beware of any shade from roof elements (aircon, antennas etc.) when you install.
3. Use Thick Wires - One of the most important decisions you can make in your solar installation is using the right size wires. Wires are the pipes that route whatever power you get from your panels to your batteries. They’re often the single biggest loss point in any solar system and they’re often the single biggest mistake people make. Thicker wires will carry more power for longer distance with less loss, while thin wires can cause you to lose so much voltage that your batteries never get fully charged. The “standard” size wire (usually #10) that you get with a 12V solar system will typically be too small. You want to minimize loss to 2% or ideally 1% which means thicker wires (e.g. #6 or #4), especially for the parts of your system carrying the largest current. Higher voltage panels give you extra leeway, but you still need to think about proper size. Use tables or calculators or graphs to help calculate what size wire you need.
4. Get a Good Controller - The controller’s job is to convert whatever power you’re getting from your panels to usable power for your batteries. Typical deep-cycle RV batteries have 3-stage charging profiles, and they are sensitive to temperature. So, you want a controller that allows adjustable multi-stage, temperature-controlled charging. If you’re using higher-voltage panels you will also need a controller that can handle the higher incoming voltage.
5. Locate the Controller Close to the Batteries - The further your charger is away from your batteries, the more voltage you loose. You want it as close as possible (but not in the same bin) as your batteries.
6. Use the Right Charging Profile for your Batteries - When setting your controller, look at the battery manufacturer’s specs to determine the right charging profile for your batteries. Many flooded cell batteries require a higher charging voltage (typically 14.8V) than what the controller manufacturer recommends (often 14.4V). Go with the battery specs.
7. Consider AGM Batteries - If you can afford the switch AGM batteries have a much lower internal resistence than flooded cell batteries which means less loss getting power into the cells and a much faster charge time.

Those are the big basics. There is a lot more, as well as details pertaining to mounts, wire connections and such, but for those I’ll direct you to the experts:

• Jack Mayers Site – Lots of good, detailed info here on Solar including using higher-voltage panels.
• Handybob’s Site - He’s very opinionated (no doubt), but there’s lots of good info hiding here. Take time to look through the text and pictures.
• AltE Site - This is a commercial site, but they have plenty of detailed articles written in plain English explaining how solar power works.
• AM Solar – Another commercial site with some easy education articles.

Next, we’ll reveal our choice in equipment….stay tuned….