sailboat solar testing

Sailboat Solar – Series vs Parallel & Shading

We’re trying to decide on the right solar set up for our new-to-us catamaran. We’ve been told our sailboat solar install will cost a small fortune, so there is no room for errors.  Which means it’s time for some informal Wynn testing!

When we conducted our solar panel tilt test in the deserts of California, we noticed the power didn’t change much until we tilted the last of our 6 panels. We thought: What the Heck?!? Shouldn’t we get more power with the tilt of each solar panel?  Which lead us to thinking a lot more about how shading affected our solar performance.

Now fast forward six months.  Here we are trying to decide on the right solar set up for our sailboat.  What worked best for our RV (that can be parked at a specific angle to align perfectly with the sun) might not be the best for our cruising sailboat (that will float and shift around at anchorage depending on the wind and currents).  Which poses two questions we need to figure out before we begin our solar planning:

  • how to best orient the solar panels because of shading
  • decide between parallel or series wiring for our solar install

Series would allow us to run thinner gauge wires which means smaller holes in our boat and less potential for leaks. Less leaking would be a huge plus but that tilt test still sticks in my head and makes me nervous.  We know shading could be an issue, but just how much of an issue?

With all my questions back and forth with GoPower! (the maker of our solar panels) and Just Catamarans (the place installing our solar) we decided the best way to wrap our heads around it and be certain, is to test it all!  There’s nothing more convincing than seeing it with our own eyes and let me tell you, the results are quite surprising!

We are blown away with the test results. It’s crazy how much shading a single cell diminishes the power output.  We’ve always known shading on a solar panel is bad but didn’t understand just how bad it truly is.  We also didn’t realize how much more shading affects panel performance in series than it does in parallel.  After seeing the results, you might be asking yourself, “why would anyone install solar panels in series”?

The Benefit of Series Wiring

Panels are combined and create higher voltage. Because of the higher voltage, the wires to the charge controller can be a smaller gauge (thinner) and the run can be longer. This is great for going through walls and tight spaces (for example a tiny house or RV).

The Benefit of Parallel Wiring

Each panel works independently. If one panel is shaded, it will not affect the entire solar array. This is great for a sailboat with lots of shadows (from lines, mast, boom, etc.) or a cabin in the woods with varying shadows throughout the day.

What we learned about Shading

Shade is our enemy! If a shadow covers a single cell of a panel we can pretty much kiss that entire solar panel goodbye. This info provides us with an idea of the power we can generate from our solar install on our sailboat. With the unavoidable shading on a sailboat we’ll be lucky if we ever see our solar reach its maximum power potential (which we had no problem achieving with our tiny home on wheels).

Panel Direction Matters

After seeing the results of this test we’ll make sure the solar panels are aligned parallel with the boom and NOT perpendicular. With the shade from the boom, it’s better to have it over one panel and not two. Depending on the size of the shadow the boom casts, it could knock out each panel it covers. Our boom sticks out so far it will likely cover two panels if they were installed perpendicular.

The Solar Solution For Us

Now we know we will wire the panels in parallel and mount them parallel with the boom.  This means we will be able to fit five of the six panels we removed off of the RV across the stern of the boat.  That will give us a whopping 1400 watts of solar!

I’ve researched stackable MPPT controllers and I think that would be our best solution. “Stacking” the controllers allows us to put fewer panels on each solar controller. Which would help reduce the power loss from shading. But, that is all a little ways out and may not be necessary so, we’ll cross that solar bridge when we get to it.

This test was a real eye-opener and learning experience for us, as I’m sure you could see in the video. Until solar panels become more technically advanced to better deal with shading, we will rarely see the maximum performance out of them on our sailboat, which really is a bummer.

If you have your own shading, wiring, or solar install story please share it in the comments below.  We can all learn from each other’s discoveries, tests, and experience.

Want more details on the solar products we use?

Equipment used to film this video:


Disclaimer – This test is not perfect and we are not solar experts.  We share our experiences and what we learn from them. This is not sponsored nor have we been compensated in any way to share this information.

Famous for my "how-not-to" videos, and typically the man behind the camera, sometimes I’m forced to be here in the “spotlight”. When you see my face you’re probably reading something more technical than adventurous, but either way I do my best to tell it like it is and infuse my opinions into the commentary…after all this is a blog and not MSN.

Comments (117)

  • Katherine Williams

    Your latest solar upgrade seemed to put the panels in series. I might be wrong, but if so, why? Notice more of an effect with shading?

    Or maybe you don’t care as the boat is going away soon anyway?

  • James

    So have you thought about upping your batteries just a little more and go with electric drive on your props and remove the diesel motors and tanls

  • Senol

    Very informative video, thanks.
    When you compare parallel and series connections don’t you have to consider the voltage together with the current?
    Since the voltage will be multiplied by 2, series connection shall be better.
    Am I missing something?


    Good testing but you missed a key point. The shading results also depends on how many by-pass diodes the panels have, if any. When you shade an individual solar cell it turns off, partially or completely, and won’t allow current to flow as easily or at all, depending on how much shading is happening. Obviously, this is a bigger problem when the panels are in series rather than when in parallel. Only way around it is to have a bypass diode around the shaded area however that means the mfr has to have added it INSIDE the panel. Canadian Solar uses half-cut cells and has more columns and they put a by-pass diode on each column. Allegedly, Sunpower has a by-pass diode integrated in across each cell and thus would be the most shade tolerant. Canadian Solar says that their panels have “Better shading tolerance.” Sunpower has a video comparing their panel to “others” under various shading conditions. I can not find an actual test, like you did, on either. I don’t know about other panels… damn hard to find that info.

  • Geoff

    Hi Guys, great videos. Have you guys looked at any DC2DC chargers for charging a trailer while driving? The once I’ve come accross are also MPPT solar controllers, but they have all been from Australia. I’m looking for advice on functionality and perhaps something local.

  • Jesse Orchard

    Hey there guys. Not sure if this is the right place to place this as we’re just starting to follow you a few years down the track now…
    Me and my wife are building towards getting into cruising, still 5-10 years away at this financial point.
    I noticed you mentioned the shading being a bit problem with the solar. Did you consider any of the ‘Shadow-protected’ solar technologies, or was there nothing available when you set out?
    I’ve observed that along with other techniques companies are putting a diode between each string or cell so that shade doesn’t almost completely cut out that panel. Check out the Solbian SXp series for example. I’m sure there are other brands out there doing similar things too.

    Look forward to continuing to catch up on the backlog of videos you’ve put out while we wait for our opportunity to join this lifestyle 🙂

    • Both sets of panels are ‘shadow protected’ and the same tech as the Soliban. Those diodes don’t work as well as one would wish.

      • Sailing Cyclops

        A blocking diode will prevent current from going in reverse through the cells that aren’t producing enough voltage. Up to 24 cells are behind each diode, and on rectangular panels, the cells of each group are usually oriented along the longer dimension of the rectangle. If you shade multiple cells, and they’re all in the same group, you’ll see a lot less of a power decrease than if you shade across multiple groups. Also, diodes can go bad. They’re easy to access for testing in the junction box on the back of the panel. A common failure is caused by nearby lighting, causing a diode to not block reverse current as efficiently as it should, and sometimes not block it at all. This means shading the cells protected by that diode would cause a much larger degradation in power.

  • Philip Copeland


    I am setting up a new cruising cat and was interested to hear how your batteries have been going. 1200AH seems like a lot – what have you found you have been using and how far down have you drained the batteries?

    Also – are you happy with the way the wiring from the solar panels has worked out?

  • fred ancora

    hello guys…
    Jason, you mentioned in one of your more current videos that you had a extra good way for wiring the solar panels on your sailboat. Can you please elaborate?
    thanks, fred

  • daniel Dupont

    I love you guys

  • Hi Guys,
    It might be pleasant to set up a little wind turbine while at grapple to help energize the batteries. Thanks for the post.

  • Hey Guys,

    Take a look at solar optimizers for each of your panels. They help tremendously with shading. You will be able to run parallel 48 volt lines. I’ve used them before. Ask your guy about it.


  • Allan E. Gaines {"RocKiteman" on YouTube}

    I was curious if you two were considering adding some type of wind turbine to Curiosity to generate more electricity, or if you already determined that to be impractical?

    FWIW: A while back I saw something online about a company that manufactures vertical axis wind turbine systems that attach high up on your mast to get better airflow and avoid having horizontal axis blades close to the deck {and you}. This might be OLD NEWS for you, but I thought I’d mention it.

    SAIL SAFE!!!

  • kat

    we love your testing videos. we are in the process of installing a 5kw solar power plant in our yard we asked our installers to bring us one 320kw panel to experiment with for our rv this summer.your shading test lead us to change our orientation of the plant slightly because we watch you two i feel more prepared not only for our home and rv but for our future boat. i wish you were experimenting with wind too. where did you get that cool blue and white large ice cube maker?

  • Alex Todd

    I’m curious if the two of you have explored wind and/or water generators to supplement your solar. It seems solar is meeting your needs, but I’d be interested in hearing your thoughts on the other two.

    Plus, I always enjoy your testing videos!

  • Evil Genius

    Solar Edge is not a micro-inverter system. It uses MPPT units on each PV module and feeds the optimized DC from those to a central inverter. It is a string inverter system.

    Emphase is a micro-inverter system which inverts DC to AC at the PV module.

    Both are grid-tie systems. Neither is usable off grid.

    If they don’t sense a grid to sync their output AC sine wave to, they don’t put out power. That way they don’t backfeed a grid that is shut down and cause utility linemen any undue excitement.

  • Ross

    So I was watching some random YouTube videos and saw one sailor mounted a wind generator on their boat. It may be nice to put up a small wind turbine while at anchor to help charge up the batteries. I am about useless when it comes to electricity so I don’t even know if it would be possible to tie the two systems together like that but its a thought.

  • Bruce

    Our TC700 was purchased 8 years ago with two 68 W Uni-Solar flexible amorphous silicon panels. 136 W is not adequate for us in the tropics, so we plan to install more. One really nice feature of the Uni-Solar panels is that every solar cell in each panel has a bypass diode fitted, mitigating the effect of shading. We often park in partial shade, and still manage to harvest quite a lot of solar energy. The bad news is that I believe Uni-Solar is not making this type of panel any more.
    We shall take your advice for our upgrade and install a greater number of smaller panels (in parallel) to reduce the effects of shading.

  • Allan

    Have you considered or investigated microinverters to deal with the varying output from each panel? Solar Edge is one recommended manufacturer of microinverters.

    • Rossinonte

      Re ALLAN’s suggestion. Microinverters like Enphase would convert solar DC to AC at the panel. Various panels with various shading and angles to the sun would generate power at different levels piped through a thinner AC cable and I can see the benefits. However once this goes down below, it would have to be re converted back to DC to charge the batteries right? This double inversion/conversion process seems inefficient doesn’t it?

  • Jim Norman

    I sent you some information on solar panels after watching you discover that solar panels left to themselves will almost quit working when shaded. This can be solved by using one of three methods to bring the power to your charge controller and inverter. The DC converter or the Micro inverter will allow a panel to be shaded without destroying the effectiveness of the entire string. Here is a link that will help you decided how best to modify your installation.

  • Scott Crawford

    We use an appropriate size wind generator in conjunction with the solar. The wind generator can be brought on line as necessary because it is capable of continuous power day and night.

  • John Schroeder

    Check out handybobsolar. He’s done a lot of research as to why mostt solar installations are very ineficient. Battery manufacturers spec 14.8 volts or more to correctly charge your batteries. Most controllers will only give you 14.3 volts and with varying degrees of efficiency. Most wiring is undersized and puts the controller to far from the batteries. He’s well worth a read and isn’t selling anything.

  • Serhiy

    “…But, if we add that extra power there’s a good chance we’ll need to upgrade our MPPT charge controller…”

    This is mistake if you want to use one controller. It can break down usually in the most inopportune moment, for example in the middle of the Atlantic. Right to have multiple controllers with excess of power. In this case, you can rewire solar panels to working controllers. Safety at sea is very important.

  • Pat & Susan

    Hello Wynns,

    We are full time RVers and have been following and learning from y’all for a long time.

    We are going to be adding a big solar system to our new Class A RV in the next couple of months.

    I assumed I would be going with the latest and greatest including lithium batteries and was very surprised when two very reputable solar designers/installers that we talked with discouraged us from going with lithium batteries and would only install AGM batteries.

    When questioned as to why they would not install lithium batteries they stated that they had safety/fire concerns and felt that the technology was not there yet.

    Have you investigated the safety aspect of lithium batteries and are satisfied there is little/no risk of fires?

    Thanks for sharing all you knowledge and experience with us over the years,

    Pat & Susan

  • GHetrick

    I have been reading what everyone is posting on here and it hit me, what if you do solar when anchored and set up a water generator? It would slow down your boat when sailing, but it could charge your batteries when the sail is blocking the panels. I googled it and found a company in Germany called Torqeedo. You already have a lot of components and just need a few more to maybe make it work. Someone somewhere has probably set something up for their boat.

  • David J. Wohlfeil

    Jason and Sweetheart

    Would there be any way of place a three or four square unit on top of your mast. By having someone design a carrier for them? Would they be too heavy for your mast, especially in the wind? Just a couple ideeers there. Automate and have them fold in and out and twist as needed like a satellite. Better call NASA tell them to work on that. Tell them that you will believe they made it to the moon through the Van Allen Belts if they build a system for you without charge.

    I wish you were still RVing but understand the need for change. Oh Yeah and Sweetheart please watch them ropes from now on. Keep hand and feet clear of them at all times. Jason you can not sail without a clew.

    Have fun kids


  • Van

    Time! All of your tests in the video were instantaneous measurements. As bypass diodes clamp down for shading, I’m told it takes time (measured in minutes not seconds) for an MPPT charge controller to compensate for the reduced input voltage. That effect is magnified when panels are wired in series. Perhaps not something you want to hear for that swinging boom, but workable as an RV antenna shadow slowly creeps across the corner of one panel.

  • Mike

    Hi Kids. Shading a problem ??? Check out the Solar Stick.
    Disclaimer — I don’t have one, I just think they are a real possibility.

    Mike in KC

  • Dick Epler

    Jason & Nikki, I can understand why you would want to install your excellent RV solar system on your cat. After all, you’ve invested several thousand dollars on superior components (solar panels, solar controller, and inverter) however, I would argue that it makes little sense for most other sailors to go to the expense to develop and maintain either solar or wind renewable power systems. The problem is your environment. Both solar and wind make sense where you have control of your environment; that’s certainly not the case for sailors … especially blue-water sailors.

    Regarding solar, I think many are confused by the rating of a solar array to its daily output. The main reason to have a large solar array (1000 W) is to replenish the energy drawn from a battery bank used to operate modern appliances such as a microwave, air conditioner and possibly a residential refrigerator. Consider that a typical 120 Vac residential microwave rated at 1.4 kW, will draw around 117 Adc when running at maximum power. That’s intermittent power, but a residential refer and/or A/C is a more continuous draw especially when in the tropics. With such usage, it won’t take long to reduce the capacity of the batteries to 50% requiring a recharge. As you discovered with your motorhome, that’s no problem for solar … for stable environments … big problem for constantly changing environments.

    I’m sure you know this, but it’s rare to ever get the rated power from any solar array. Consider that a 1000W array should be able to deliver a continuous 67 Amps to a 12V battery bank under ideal conditions: while possible that’s rarely the case. But if achievable, the time required to recharge a 600 Amp-hour battery bank, depleted by 50%, would be about 5 hours. That assumes your array is perpendicular (assumes tilting) to the rays of a cloudless sun at all times (assumes a sun-tracker) … and no shading … as we’ve seen, shading just a single cell can knock out the whole panel.

    On a sailboat, where you can’t control your environment, an optimally configured 900W array (6-150 Watt Panels) will be lucky to produce 500 Ahr/day … and that’s when sailing in the tropics. The amount of sun power (aka solar insolation) is much less north of the tropic of Cancer) and south of the tropic of Capricorn.

    For example, at 44 degN, in Portland, OR, the average insolation for June is 6 kWhr/sq.meter/day. Thus, the daily power expected in June from a 900W array in Portland, OR, is 5.4kWhrs or 450 Ahrs) … again that assumes the panels are perpendicular to the sun for the full 6 hours. If that’s not the case … if it’s a cloudy day, or if it’s winter, or one or more panels drop out due to shading … the output can drop to less than 10% of maximum available solar energy. Again, control of the environment is the key which is a big problem for sailors.

    Now, regarding wind, and the use of wind generators, understand that the energy in wind is directly proportional to the square of the velocity. Said another way, the energy in a 70 knot wind is four times the energy in a 35 knot wind (X2^2 = X4) which is why you see the big waves, right?

    During high winds, anything on a boat not securely bolted to the keel (or hull of the boat) is subject to disappearing. It’s not unusual for a blue-water sailor to get surprised by a sudden gale force wind of 75 – 88 kph (a 9 Beaufort wind force) with the sails up. If the winds progress to a force 10, they’ll be no time for the winch, best to use an axe to bring the sails down quickly by chopping the lines. Even when the mast is bolted to the keel, it often snaps to take it and the rigging over the side (more need for an axe). Given that solar panels (and wind generators) are necessarily exposed to the elements, they will likely be the first to go.

    If you really want to operate residential appliences on a sailboat, it’s probably best to use a small auxiliary generator complete with an additional fuel tank (required when in the doldrums 800 miles from land). Most blue-water sailors like large fuel tanks.

    • Lawrence Kingery

      I have to say, you know your stuff. Makes me curious what your background is.

      I was contemplating this question if I had a catermarine. I would like your thoughts. I would entertain buying a Curtis marine motor and replacing one of the two motors. While under sail power or anchored, Regen mode could be enabled. This would obviously provide asymmetry on the boat and reduce the speed because of conversion to electricity. Have to go sailing to Regen.

      It may be better to somehow mount the unit down the centerpiece to eliminate the asymmetric forces. To avoid the structural problem, a tow behind drop unit would be interesting. The nice part is, shut it off and their would be little drag. If actually mounted to the boat, it could be used as a motor in emergency situations for brief pushes. This is just a solution to a thought problem that I seem to think will work.

      Before I sent this, I just looked it up since it is a patent idea. Looks like someone though of the same thing. Check this out Dick, Jason and Nikki.

      • Dick Epler

        Lawrence, like you I’ve considered other possibilities for generating marine electricity. Predictably, of the two you suggested, I like the shaft driven Curtis regen motor best (more flexible operation). My guess is that Jason would like the water-power tow solution best (I hope he reads the article you referenced).

        Of course, when trying something new, implementation (how you do something) is most important often requiring a systems approach to reveal the tradeoffs involved. You seem to have done that on an intuitive level, but a more rigorous approach may be of value if significant money and time is a factor. My guess is that you have more practical experience in this area than I.

        Of course, as Jason likes to point out, everything is a tradeoff, often requiring testing in multiple environments. For Jason, however, the opportunity to video-tape a reasonable implementation/test for the education of others is often the deciding factor … where simplicity is key. Too complicated and he loses his audience, right?

        Lawrence, you asked about my background and I think my resume reveals that, by nature I’m a physicist; by training, an electrical engineer (electronics not power); and by avocation, a problem solver. I have experience with many things on different levels (designer, builder, user), but now that I’m in my ninth decade (82 years young), I’m my wife’s 24/7 caregiver (married 61 years – like Jason and Nikki, we’ve done everything together) … and so now I tend to live vicariously through the adventures of others.

  • Lawrence Kingery

    If you want to know why you are getting the results with the solar panels in series or parallel, feel free to give me a shout. Mr. Epler above explains it very well in technical terms, I can bring it down to earth. It may actually be worth doing a combination of series and parallel if you have multiples of two solar panels.

    Either way, I appreciate your videos as both instructional and fun to watch. Keep up the good work!

  • L42 SV At Ease

    Thermal runaway. One very important fact that I learned the hard way is that battery cell temperature controls the charging rate of your batteries. If your batteries are hot and not well ventilated, then your charge controller will keep sending more current into your bank until the charge voltage is reached. As you know, more current and higher cell voltage further raises the temperature and the cycle continues until the batteries catch fire. Outback has a battery sensor that I added and thought I was all set. Everything worked perfect while we were living aboard and sailing full time. The problem occurred when we left the boat dockside, on shore power, and left it for a week without the air conditioning running. The Xantrex ac battery charger did not have a temperature sensor and all three of my me Lifeline AGM batteries were boiling when we got back down to the boat. The smoke/CO2 detectors were alarming when we approached, so thankfully we secured power and ventilated the space before entering. I am sure that our Leopard would have caught fire if we would have arrived even a day later.

  • Charlie

    Actually more of a question than a comment – have you – or anyone else – used Zamp solar panels and if so how did their panels compare to other brands?

  • illya

    When you do run your DC cables from the battery to the inverter, controller, i would suggest KnuKonceptz OFC (oxygen free copper) wires from amazon, I’ve gotten them 2 times now and they are fantastic. Extremely flexible and the copper is very fine stranded and wont corrode like non OFC wire will. I have 3 panels in parallel total 300 watts, I’m going to try the same kind of tests you guys did with mine and see what type of losses i have. I expect about the same. I have room for plenty more panels if i want but for my uses i don’t really need more.
    Great test and very informative, i wouldn’t have guessed the losses of covering one square in parallel are so great, Thank you :),

      • illya

        i finally got around to testing mine, 3×100 watt panels in parallel. I covered one square on one panel and it went from 18 amps to 10, so very close to the same results you had in parallel. I did a few others like 2 squares and it was pretty much identical to yours. I have renogy panels and equipment, I have been happy with them though as they keep my batteries at full charge all the time. Even on cloudy days i might still get 2 amps so it’s better than nothing at all.

  • Lew

    A very good resource for things nautically solar is Bruce Schwab

    these people specialise in solar energy for marine considerations, including weight.

    Speaking of weight, it doesn’t appear that anyone is telling y’all, but it’s really important to keep weight out of catamarans if you want to maintain any sailing ability to speak of….

  • Dick Epler

    Jason & Nikki, I think if you would have included two other measurements in your test (voltage into and out of the MPPT), you would have seen the relative contribution of a compromised panel array and the MPPT to reduced charging currents into the battery for series and parallel configurations.

    If your panels are connected in series, then losing one panel will drop the voltage into the MPPT by almost 18 volts. I don’t know enough about your controller to predict the effect. However, if connected in parallel it will simply reduce the charging current by one panel’s contribution (about 8 amps), while the voltage output remains at 18 volts (less wiring losses) resulting in a more predictable MPPT operation.

    I know you don’t like technical stuff, Jason, but once you know something about solar cells and how they’re connected and used with by-pass diodes to build a solar panel, you’ll better understand the results experienced.

    Your panels use mono-crystalline photovoltaic silicon cells. Since each cell will produce about 0.5 volts, you need 36 cells (a 4 X 9 matrix) connected in series to get 18 volts from a panel. The physical area of the cell is what determines the current output of the cell/panel (typically 30 to 38 mA per square centimeter depending on cell efficiency). The larger the cell the higher the current output. Thus for an effective cell area of 225 sq. cm. (typical), the cell current might be 8 Adc (max, for sun directly overhead). Since the panel’s 36 cells are connected in series, 8 Adc is also the current output of the entire panel.

    A little background: photovoltaic cells turns sunlight into electrical current by using a silicon P-N junction (which is what determines the cell’s voltage). As long as the P-N junction is working the cell will produce 0.5 volts, perhaps at a reduced current if the cell is partially shaded.

    However, once a cell is completely shaded, the P-N junction reverses current to absorb power from the other cells in the array. That causes the cell’s voltage to rise until the reverse breakdown voltage of the junction is reached (in the range of 10 – 30 volts). Thus, rather than contributing 0.5 volts to the matrix, it will reduce the voltage of the whole matrix by 8 volts or more which may not be enough to effectively drive the MPPT … effectively removing the panel from the array (whether series or parallel configured). Recall that MPPT controllers can only function properly if the voltage from a solar array is greater than that of the battery bank.

    Solar panels that are advertised to be tolerant of shading use by-pass diodes to shunt the panel’s current around the shaded cell thus averting the reverse breakdown voltage problem. Of course, without the use of a by-pass diode, it’s also true that the cell junction would be permanently destroyed due to excessive heat buildup.

    Ideally, you would use one by-pass diode per cell, but due to cost, most panel manufactures use only one by-pass diode for a group of cells, reducing not only the available current but also the panel’s voltage output into the charge controller possibly compromising operation.

    Your Outback MPPT is a smart (computerized) charge controller that uses a proprietary algorithm to receive voltage from a solar array (up to 150Vdc) to charge a battery bank arranged in one of the standard 12V/24V/30V or 60V configurations. The purpose is to provide maximum battery charging without overcharging, as signified by significant gassing (hydrogen & oxygen), which occurs at 2.46 Vdc per cell (14.8 Vdc for a 12V bank, or 29.6 Vdc for a 24V bank, etc.). I don’t know enough about the Outback MPPT controller to know how it will respond to shaded-cell, series/parallel solar array configurations, but if you would have also monitored the voltages in and out of the controller, you would have the information necessary to better understand and to explore other options.

    Note: The Kyocera panels may use silicon cells that are more efficient than the GoPower. All cells aren’t the same. Typically, silicon cell efficiency has been between 16 – 17%, but recent technologies are producing efficiences closer to the theoretical maximum of 27% … the current record is 25%. That may also account for the differences in power you experienced.

    BTW, folks, I’m the other guy with a 2011 Monaco Vesta motorhome like the one you had (different color). I think I wrote you once before (years ago) about solar stuff but since I didn’t receive a response, I’m guessing it was too technical for your liking.

    • John S.

      Looks like the Wynns are too busy learning the ropes (and lines and sheets) of sailing to reply but I just wanted to say that this is a very informative thread.

      Thanks to everyone who added information to what Jason and Nikki posted.

  • Heather Scott

    George(the cat) and I really enjoyed the video and learnt a lot about solar power and found it all pretty fascinating….

  • HyOnLyph

    I’ve been following you guys for quite a while. My wife and I just purchased our first Motor Home. I was shocked by your video and the amount of voltage drop when covering one cell. How can that be. I would have figured it would be proportional to the number of cells on the panel. But no, it almost cuts out the production of the whole panel. Why is this? I see in one of the other comments that there is a difference in cells being wired in series or parallel. Is this what causes the cut-off? I would have never been aware of this if not for your videos. I hope someone dives into this issue and gives us some more info on the technology.
    Thanks again for all of your amazing videos and info.

  • Nik

    I’m really curious how you’re going to wire all of those panels in parallel. That is just an astronomical amount of copper wiring for that wattage. Lets say you only need to do a 20 ft run from the panels through the controller to the batteries, for that many panels you’re going to be looking at like 80 Amps at 12V. At 80 amps, you’d need to use 2/0 gauge wire to keep your voltage drop to around 2%. That wire is so absolutely massive (not to mention expensive). Are you going to keep things at 12V or do a few series parallel pairs to increase your voltage any?

  • Rod Reichardt

    Great test! I found some of the assumptions I had about solar were wrong. I did not expect such dramatic results from minor shading either. Parallel versus series results make sense though. What kind of power does your onboard ge set have? Do catamarans typically have things like auto gen start like RVs? Are you going to use your lithium ion bank from your motorhome? So many questions…..

  • David

    Hello, me again.
    I did a bit of detective work having been a bit inspired by your video, and I looked up the manual for the Outback Flexmax 80 Solar power controller. On page 99, it states that the maximum power voltage of your solar array should be around 12 – 24 volts higher than the nominal battery voltage for optimum performance. I believe that you are intending to use Go Power CTI 160 solar panels from your RV. These seem to be the ones that you mention in your Resurrecting Dinosaurs blog post. Looking at the Go Power website, the CTI 160 panels have a maximum power voltage of 18.42V.
    What this means is that you shouldn’t really connect those panels to that power controller in parallel as you suggest in your latest video. You will have an input voltage that is lower than the ’12 – 24 volts above nominal battery voltage’, range that is recommended. It is likely that the best way to meet this requirement is to pair panels together and wire panels within the pair in series and then all the pairs together in parallel. This will leave you with three pairs where each pair generates 36.84V at maximum power and is hence your solar controller input voltage. This is just at the upper range of the ’12 – 24 volts above nominal battery voltage’, and so would be more efficient than wiring all the panels in parallel, according to the Outback manual.

  • John Egan-Wyer

    Hi. I’ve watched most of your RV videos and all your sailing videos. Basically I’m a fan. Regarding your RV video and panel tilting, I remember saying to myself ” what shading?” As your 6 panels were mostly facing the sun, each threw a shadow behind itself ( I’ll watch it again when I get home and probably find I was mistaken) anyhow, I think (and I’m no expert) that the last panel to be tilted was producing less power than the other 5 ( because it hadn’t been tilted yet) and as such might have actually been acting as a resistor to the current flowing from the other 5. I liken it to a 12V car battery (which is actually 6x2volt cells wired in series). When one cell goes bad. The whole battery is prevented from producing its full current. If I’m correct, your problem is not strictly shading , but one or more panels blocking the flow of current from the other cells. This would happen mostly from shading in your case, but in the tilting test, was not shading per se, but acute angle to the sun of panel 6. Again, im no expert. But if my thoughts help you reach a greater understanding of the problem, either directly or indirectly, then we have all gained.

    Keep living your dream

  • Jason Heinz

    Loved the video and great Wynn Curiosity at it’s finest!
    Of course this answers my questions of I was hoping the panels from the R/V would be used on the Lagoon.
    I have seen a lot of panels installed over the dinghy boom. Which provides sun protection on it as well. So a double benefit. I figure you will be looking into wind generation also. I wish there was a helical model that the public can purchase, as this will spin more with less knots of wind. However the ones suggested above, I have read a really good.
    For another option of power generation, and I know you budget isn’t ready for this yet. Especially now that Jason has intimate knowledge of the engines. But have you ever thought of Electric Motors for propulsion.
    This would provide you power generation while you are under sail only. I don’t think you have the battery bank sufficient for this yet. But in a couple of years, who knows.
    At least it makes servicing engines MUCH easier!

    Keep up the amazing work. And thanks for letting me follow you guys.

  • Alan Bosch

    LOTS to think about! We certainly appreciate y’all sharing your trials and tribulations.

    I did not see distinction made between the two basic types of solar panels and suspect yours are the crystalline tye (produce higher output per sq inch) vs the amorphous panels that are cheaper but less output per sq inch. The biggest advantage to the amorphous is the fact that they do NOT require 100% direct sunlight to produce power. Might want to consider the option. They are ALSO less prone to damage as they are flexible.

  • Sat Amagai

    It you want to install your panels in series, you would want to add a bypass diode in parallel with each panel. That way, if one panel is shaded, current can still flow through the bypass and not kill the whole system. You can then still take advantage of the higher voltage. In a shade-rich environment, you might want to consider using a greater number of smaller panels rather than fewer larger panels, so that you can minimize the % of panels that are down due to shades. Smaller panels may mean taking a hit on overall capacity and efficiency, and adding complexity to the circuit. On the other hand it also means you can replace damaged panels easier, which might be an important consideration in blue-water passages. Ideally, each cell in your panel has a bypass diode, but I don’t know if they make such a panel.

    • Sat Amagai

      If your panels have integrated bypass diodes, you shouldn’t have to add an external diode, but your data made it look like they were either not there, or faulty. I found someone else who did a similar experiment,

        • Sat Amafai

          Then it just doesn’t make sense. Blocking one cell should have dropped that panel down to a little less than 2/3. Instead, it looked like you lost that whole panel. Your outputs should have been close to 5/6 in parallel, or 2/3 in series. Instead it looked like you got 1/2 and 0 respectively. I’ll be very interested in what you hear back from go solar folks.

  • David

    Hello again.
    The other thing I wanted to ask was, have you seen “Sailing Zatara” on youtube?
    The reason that I ask is twofold, firstly, they just installed 680w of solar on their boat and installed it on a frame at the back of the boat behind the boom, so that it is not shaded by the boom and secondly, they are based in Ft Lauderdale, Florida, so they’re not far from where you are.
    They are newbies who have just purchased a boat to become liveaboards and learned to sail, and they have recently started their Youtube channel. Their boat is a Beneteau Oceanis 55 monohull.

  • David

    Looking at your video, you seem to have the existing panels underneath the boom on the roof of the main living area. You know that these panels will usually be shaded so they won’t produce 390 watts under normal conditions, it will usually be less.
    If you look at SV Delos as an example, she has a frame constructed over the back of the boat, for her panels. This means that they are behind the boom and won’t be shaded by it. What I am wondering is, since you are going to be spending, it would seem, thousands of dollars on Lithium batteries, why not spend some money on having a frame made to go across the back of your boat, that was big enough to mount all six of your RV panels above where you store your tender / dinghy? This would give you 960 watts, unobstructed by the boom, assuming that you dispose of the existing panels. (I’m not sure if it is good practice to put different panel types into a single solar power controller, so I’m assuming that your current panels on the boat are different to your RV panels and that this would be bad practice, so therefore just getting rid of the existing boat panels.)
    Also, with respect to series vs parallel, I have read that MPPT power controllers are most efficient when they have an input voltage that is a good deal higher than the desired output voltage. This is an additional argument for series. So, what you could consider with six panels, is a combination of series and parallel. With six panels, there are two obvious choices, 1) pairs of panels linked in series, and those three pairs linked in parallel, and 2) sets of three panels linked in series, and those two sets linked in parallel.
    If you mounted all six panels on a frame over the back of the boat behind the boom, the amount of shading would be minimal, so the advantages of parallel over series would diminish, however, if you chose series, you would become vulnerable to a mechanical failure of one cell of one panel stopping current from all six panels. Hence one of the mixed series / parallel could well be best. They would increase the input voltage to your solar power controller hence boosting efficiency over parallel, reduce the amount of wires / thickness of wires required over parallel, but also give you some resilience so that if you had a cell / panel failure, then you would only be losing half or a third of your power input.
    Just some thoughts after watching your latest video.

    • David

      One additional thought. If 960w isn’t enough for you, you could purchase two extra panels identical to your RV panels, and then have a frame big enough for eight panels attached to the back of your boat. These could be wired as four pairs or two fours, to get some of the benefits of both series and parallel. You would ensure that the frame was large enough for the eight panels when it was ordered, so that all eight panels would be mounted behind the boom and not obstructed by it. You would then ditch the existing panels, (assuming that it’s not a good idea to feed different panel types into the solar power controller, and that they are different) leaving you with 1280w system.
      It might be worth trying to measure what your current 390w system actually generates mounted under the boom. You latest tests suggest it will be much less than 390w…

  • David Kenny

    Hi Guys,
    you might want to look at what Sailing Trio Travels did on their catamaran they had an Solar Arch created on the transom to overcome the shadow problem and have 980 watts of solar combined with lithium batteries and have not needed a generator.!saltair-3-befores/c196y


  • Patrick Hayes

    We have had good luck with Aurinco panels, panels with cells in parallel to reduce shading impact. So even if some shade hits the panel, it does not shut it down completely. Flat, flexible and served us for 17K miles across the south pacific last year. You might consider If you eventually upgrade some of yours.

  • David Hanus

    In my part of Oregon many of the remotely located radio relay sites are adding small wind turbines to supplement current installed PV systems. More systems yes but each system can be smaller since it doesn’t have to carry the full charge load. Both compliment each other. Many of these sites have also gone to 2 small 125VAC generators (redundant) and use high output (80 Amp 12VDC) multi stage switching power supply (smaller and lighter) battery charger/maintainers for shorter generator run times than charging at 35-40 amps 12VDC off the motor alternators.

  • Bill Beckham

    Hi Guys, all the full time sailors with good solar supplement their systems with a wind generator. Looks like it makes all the difference in the world.

  • marchal peck

    Well have you thought about a wind generator shade would not be a problem and its good day amd night no matter the weather

    • mrkoje

      I was thinking the same thing! I was considering it for my FW but haven’t yet decided to go forward because the prop needs to be quite a distance in the air for efficiency. I’m thinking on a sail boat with a mast that it might be possible to mount something like a wind generator on the top.

  • From your experiment, I make the following conclusions:
    In series mode, Shutting down one panel, nearly shuts down the circuit. This would indicate that a panel not producing energy, becomes highly resistant to electrical current. This shuts down current flow even from the producing panel. The same is true in the individual panels when a single section is covered. This would indicate that the individual sections are connected in series in the panel. But covering only part of the section still gives current so the individual electricity producing cells in the section are in parallel. It seems to me that parallel connections would be better on any mobile that could be subjected to shadows. This would also be true for the design of the panels. Are any panels made that connect the sections in parallel rather than series? If so, they could be wired in parallel before going to the charger to reduce wire size. It would be like combining many smaller panels in parallel.

  • To avoid shading problems, you either need Enphase micro inverters on each panel which changes each panel to AC instead of running DC to one single inverter. This way, if one panel is shaded, it won’t bring down the whole array. Each mico-inverters take the place of one single inverter.

    Another good, maybe even better is a SolarEdge inverter with a Solar Edge Optimizer on each panel. But to do these you will have to change out your inverter.
    Shading is a problem with all solar panels, but the above methods will help with the shading problems.

  • Deborah Kerr

    Very thorough testing-some great information-thank you to the Wynn’s curiosity once again (lol, no pun intended??)!!

  • Nik

    All of those numbers made sense. Per series string, take the percentage un-shaded of the single cell that is most shaded and that is the percentage of max power you’ll see. So when you did everything series and covered 1 cell so it was in 0% sun, you got effectively 0% power. When you moved the cardboard to cover 2 cells, each was 50% shaded so you got 50% power, then you covered 4 cells so 75% of each was sun, you got 75% power.

  • Bill

    Check out how they rigged the solar panels on Off the stern, above your dingy? Completely behind the boom. Of course, main mast may still influence at some angles but you’d be out from under the boom.But you must have already thought of this.


  • Simon Baker

    Have you thought about mounting the panels else where? I’ve seen some yachts with special platforms built behind the boom (usually above the dinghy) to mount them. Others have also mounted them on the side of the yacht.. Could you mount them upfront maybe? Just ideas to think about.. Also as someone else already suggested also use a wind power turbine.

    Here’s a link to (supposedly) the quietest wind generator on the market which also links up with solar powers.. Good luck!

  • Brian

    What about wind generators??

  • I absolutely agree with a previous comment. Definitely look into wind as well as a complimentary power generation to your solar. After living on the boat for two years, I can definitely tell you there are times where the wind generator kicks in (especially at night) and will keep your batteries VERY happy. We have the D400 which is quiet and well known but there are many others out there as well.

    Highly recommend it since there are many days that are cloud cover and without the wind generator you are going to rely on your generator or engines to recharge your batteries.

  • Nikki, it’s a shame you can’t deploy the amorphous-silicon solar panels such as the ones made by Unisolar. I run these on my motorhome, and they’re AMAZINGLY shade-tolerant. You can literally get half the output while the other half is in shade, because they don’t have the blocking effect of crystalline panels.

    You can also walk on these panels, they adhere to the mounting surface with a butyl adhesive. But unfortunately, they are only about 70% as space-efficient as crystal technology. You need about 50% more mounting area for the same power. Too bad.

  • For all things cat-related, may I recommend a wonderful blog by Marce and Jack Schulz? Formerly of Pittsburgh, they’re now citizens of the world, living aboard their catamaran Escape Velocity. They crossed the Pacific in that dinghy, and are now, I believe, in Fiji. What an adventure! Here’s a link:

    They’re also wonderful writers, and the blog is fun and exciting to read.

  • Roy Birkeland

    Just to throw something else in,, knowing that residential solar has the option of ‘mini converters’ that turn each panels output into 120v AC, would that possibly be a solution to the increased wire gauge of a parallel DC setup. Each panel produces 120v AC, and feeds that into the boat to be used as is, or sent to a controller for 12 v DC for the storage batteries. Just a thought.


    Hi. Why in the world are you using polycrystalline panels? When you shade part of a polycrystalline panel you essentially lose the whole panel. When you share a mono crystalline panel, you only lose the shaded squares. They are much more efficient. Are you able to mount the panels astern of the boom?

  • Scott Harrington

    Agree with Al above, would love to hear your thoughts on wind, as it would work at night as well to add a bit more power to your battery bank. Also how many amp hours will your new battery bank be on-board?

  • James Cook

    What kind of adaptor did you use to switch your solar panels from Parallel to Series? or to word it differently how did you connect multiple panels in series to a single charge controller?

    • Nik

      Many controllers can handle a variety of voltages so in series they ran the controller at 24v and in parallel the controller saw 12v. No adaptor necessary, just wired differently.

  • Al Lipscomb

    You need to give some thought to adding wind power as well. It is a very different animal than solar, but in some cases they complement each other well. Sailboats are one of the best use cases for wind power in a mobile environment (they are horrible for RVs). A modest wind turbine can produce a reasonable amount of power in conditions that normally are not favorable to solar. They also have additional applications (like being used to heat water) that are not done well with solar.


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