Outfitting Our Catamaran with Solar Panels


Last Updated on September 4, 2019 by Amy

In this post, we tackle a big project for our outfitting – solar panels.  Solar panels are the most popular method of gaining power for a cruising boat and on a catamaran, there’s tons of room for solar panels.

First of all, massive thanks go out to another Helia owner, Tad on Bisou, who pioneered the solar approach that we’ve taken on Starry Horizons and was incredibly generous about sharing the details of his set up and answering lots of questions.  Thanks Tad!

Determine How Much Solar You Want

This is actually fairly easy. After nearly five years onboard, we’ve learned that the answer is “as much as you can get”.

Solar panels are the most efficient way cruising boats can get power, and walkable solar panels are not intrusive to sailing and cruising life, and they look good on the boat. Put on as many solar panels as you can.

Even with an optimum set up, it’s unlikely that we would be able to run our navigation equipment and autopilot on solar panels. Which means that on passages with good sailing conditions, we end up needing to run our generator or engines for power.

Power Usage Spreadsheet

I found a generic form online and modified it for what I assumed would be our usage.  You can download a copy of the spreadsheet to customize for your own usage here: Power Usage Calc.xlsx.  I’ve got another post planned where I’ll detail out exactly how to use that spreadsheet, but the remainder of this post will focus on our solar setup.

Placing the Solar Panels

Next, we needed to figure out how many panels we could actually fit on Starry Horizons. Based on a suggestion from Pat, we targeted Solara solar panels, and thanks to Tad, I had a basic layout of solar panels that would work on the Helia.  Since I was doing all this research before we had actually seen Starry Horizons and needed to figure out exactly how many Solara panels would fit, I did a bit of graphical wizardry.  Using a graphics program, I traced a to-scale outline of the Helia and created to-scale panels that I could move around and see where they would fit.

Graphical Set Up
Graphical Set Up

This was immensely helpful and allowed me to mix and match all different sizes of panels, both from several manufacturers as well as the different size Solara panels.  

Solar Panels We Installed

We installed 10 panels in total, eight 120W panels and two 50W panels for a total of 1,060W of capacity.  

Purchasing Solar Panels

While we were in Miami, we were lucky to meet Rob Warren from Coastal Climate Control at the Miami boat show who distributes the Solara panels we were looking for.  He was very helpful answering questions about the panels and helping us flesh out our set up.  The Solara panels are classified as marine grade, “semi-flexible” panels and have a non-skid walkable surface on them.  This was important to me as I was worried about how a “regular” panel would hold up in the marine environment and with the amount of real estate the panels would take up the boat, I needed to be able to walk on them.

Meeting Rob Warren
Meeting Rob Warren

Solar Controllers

Since the solar panels are set up to output at a higher voltage than ideal to charge the batteries, we also wanted to get solar controllers.  There are two options, PMT controllers, which are the older generation and don’t do a good job of maximizing panel efficiency and Maximum Power Point Tracking (MPPT) controllers, which use an algorithm to find the best combination of voltage and current to deliver power to the batteries.  As Rob explained to us, an MPPT controller can result in 10-20% more output from the same panel.  That’s a lot!

Another concern we have is shading.  If panels covered up by shade, their output drops.  And if several panels are wired in series together, the output from all of those panels can drop even if only one is covered with shade!  In order to maximize the efficiency of each individual panel, we elected to go with individual Genasun MPPT controllers for each panel.

Wiring Solar Panels

We ordered the panels and Pat was nice enough to let us ship them to him so they’d be ready for us once we got over to Palmetto.  One of the first things we did when the boat arrived in Palmetto was put a plan in place for running all the wiring for the solar panels.  This is one of those areas where it would have been great if FP had put a bit of extra thought into making this easier for aftermarket installation.  They only have very small access points into the vertical supports in the cockpit (not nearly big enough to run all the wires we needed)  and the headliner panels in the cockpit are glued in place so if we wanted to hide wires behind them, we’d need to tear them out and likely replace the panels.

So instead, we decided to do something pretty custom and once again Rian at Mondo Marine came to the rescue.  For all the panels at the aft end of the boat, we either ran the wires into the traveller, or straight down into the cockpit.  Rian and Aaron from Mondo then came up with a fiberglass conduit running from the traveller into the salon.  And then from where the wires enter into the salon, they made up another fiberglass cover to hide the wires as they run back behind the oven.  It turned out pretty slick and unless you’re really looking, you can’t even tell that these additions weren’t part of the boat from the factory.

For the panels on the forward part of the boat, we hid the wires in the “gutters” in the hardtop and dropped them through the salon ceiling behind the oven.  We’ve kept a really close eye out for leaks and had to rebed things a few times to make sure we got it completely secure, but everything looks good (at the moment at least!).  The wire for the solar panel on the hardtop gets run through the conduits in the hardtop, down the forward starboard leg in the frame and down into the boat that way.

All of the wires come together in the closet for the port aft berth where our electrician George wired in by-pass diodes (hot spot preventers) and then all of the Genasun controllers.  Well, he did the first 9 and then I did the last one, thanks to all he taught me!  George also wired in a kill switch for us just in case we need to isolate the solar panels and work on the system.

Solar Panel Monitoring

Now, all that detail and you probably think this saga is over, don’t you?  Well, think again my friend.  We needed some way to monitor how well the panels were performing, as well as more detailed monitoring of our batteries.  Once again, I shamelessly stole Tad’s idea for a monitoring system and looked into a company out of Germany called Philippi.  Their PSM monitor has the capability to monitor solar, batteries, tanks and a host of other features should we decide to expand the system someday.  Tank monitoring was something I was interested in as FP does not provide any holding tank monitoring, even as an option.  I was getting really tired of removing a panel to check the black water level!

Fortunately, Rob Warren and Coastal Climate Control also distribute Philippi systems.  He and I spent quite a while discussing our setup and what components we would need.  We set up the system so that we could have detailed monitoring of our house battery bank, the voltages of our port and starboard engine start batteries, solar output, and holding tank sensors.  The detailed monitoring of the house battery bank also shows us the net charging input whenever the batteries are being charged by the battery charger (generator/shore power) or engine alternators, but we don’t currently have it set up to show the output from those sources.

For those of you who are interested, I put together a very basic schematic of the components that we’re using and the Philippi literature does a pretty good job of detailing out exactly which components are necessary.

Philippi System Schematic
Philippi System Schematic

The touchscreen monitor is a pretty cool display and I like the graphical representations it shows for the different options.  

Solar Panel Performance

Most of our days since installation have been spent on shore power or under cloudy skies at anchor.  During sunny periods, I’ve regularly seen 40amps being pumped out by the solar panels, all the way up to a max of 64amps!  Even hazy clouds have cut this down quite a bit, but even on those days, we’re putting about 12-15amps into the batteries during sunlight hours.  This doesn’t seem to be quite enough to have full independence, but as we have to run our Cruise RO watermaker every 3-5 days, and thus the generator, it should be fine for our purposes.

What We Would Do Differently

Three of the panels we installed are the semi-flexible walkable panels that are just aft of the traveller. If there is any place on the boat to put rigid solar panels, with higher efficiency, that’s it. We’ve also seen a lot of catamarans with solar panels in this position and extending off over the back of the boat.

Hypothetically, we could take off the three semi-flexible walkable solar panels (360 W total) and put on at least five rigid 150W Solara panels (750 W total).

Additionally, we could add a whole other 120 W semi-flexible walkable solar panel on our hardtop. It’s that big!

This would up our total solar capacity to 1,570W.

2018 Update

In 2018 we changed our batteries to lithium ion.  Our solar controllers were not compatible, so we had to switch them too.


  1. Sorry to bring a post back from the dead, but I just wanted to say I really appreciate y’alls documenting your journey. We are in the preparation phase and I’m reading as much as I can about the different systems of these awesome catamarans.
    It looked like you were able to secure the wires from the solar as best you could but I still saw some free-floating wires behind the oven cabinet and was wondering if you’ve noticed any chafe or problems because of not being able to fix the wires. I was reading that ideally they should be attached every 18 inches. It seems like most of these cats don’t meet that standard from the factory but seem to do alright with the electrical wiring. If you have time I’d love to know how the overall wiring set up and the things you have installed have held up to the pounding of ocean crossings.
    Thanks for your blog posts and videos again.


  2. Thanks for posting this, from what I read on various forums….solar power is one of the hottest topics in our ever hungry power consuming lifestyle so the more real world posts the better.

    I agree with you about your wire hiding skills…..at least in the photos those mods look factory and probably wouldn’t notice.

  3. Hi David, I have downloaded your Excel sheet, I was surprised auf the powerconsuption from your fridges, is it possible you have forgotten that the compresor ist not running all time? If it runs 20% you have to dived ist bei 5.

    Cheers Tim

  4. I’ve just started playing catch up on your blogs and others lately as my wife and I are seriously contemplating our retirement on a FP Lucia or Helia. We are unfortunately a few years away still from living the dream but I’m doing the research I can now. Beyond a doubt your blog has provided more insight into the process than most other resources so thanks for all the effort you guys put into it. This article in particular was really well done and has given me a few ideas for my current boat power requirements. Have fun and safe travels!

    1. Hi Jason,

      So glad you’re finding the blog helpful! Best of luck as you get started and let us know if we can help answer any questions!



  5. Great write up, all of your articles are.
    I’m taking delivery of a lagoon 450s next month and wanted to know if you still like your solar system? Would you change anything? It’s been more than a year, how are the panels holding up?
    Thanks for any info.


    1. Congrats on the new boat Steve! The new 450s looks very nice.

      To be honest, I go a bit back and forth on the solar system. The unobtrusiveness, ability to walk on the panels, controller for each panel, clean look are all really nice and on peak days I’ve seen outputs of over 60 amps. However, most days we get somewhere between high 20’s-40amps of output, and when considering the normal electrical usage, it nets out in the 20amp range usually. My guess is that if we had the same wattage of standard hard panels raised a bit off the deck, we’d have more efficient output.

      That being said, the solar does pretty well keeping up with our electrical needs and we can use the genset to top things off when we run the watermaker. So I’m definitely not in any hurry to tear things out and start over! If I were to add one more thing, it’d be a hydrogenerator to help meet the increased draw of the autopilot/chart plotter/radar etc… Hope that helps and let me know if we can answer any more questions.

      1. Hello David,

        “if we had the same wattage of standard hard panels raised a bit off the deck, we’d have more efficient output”

        Is this because raising the panels would get more sunlight to them, or because traditional hard panels produce power more closely rated to the rated power?

        We also have flexible panels and it seems we get somewhat less power than what other people report they get with traditional hard panels.


        1. I don’t think raising the panels would get them more sunlight but I do think raising them up off the deck a bit would help keep them cooler. In these hot climates we’re in, the extra heat decreases efficiency a bit.

          1. Hi David
            It’s nice to hear how your solar system is operating, but you’d be better off logging the daily, weekly, or monthly amp/hour per day accumulative yield on your Philippi PSM. Instantaneous amp output is good for bragging rights, and I’d say 60 amps from your panels is mighty impressive, but it all depends on the available irradiance and whether there is a full or partial load. If the batteries are full and the fridge isn’t running, then there will only be a small load and so only a low current output from the panels, no matter how much available irradience there is.
            The panel wattage rating is a very misleading number, as this is what the panel theoretically may possibly produce under perfectly ideal conditions, and will rarely if ever produce that much power. In normal usage you’ll see a lot less output than the panel rating, but with your panels that contain SunPower cells, you should be seeing around 1/3 of the total panel wattage in amp/hours per day on a good solar day with a full-time load and no shading; i.e. a 140 watt panel with SunPower cells should yield around 47 amp/hours per day, whether a glass or a walk-on panel.
            Glass panels also operate with high cell temperatures, even when raised and ventilated. The Solara Power M panels are built to withstand excessive heat and radiate most of the heat back out of the front of the panel when mounted on a solid surface. It is primarilly voltage that gets reduced with elevated cell temperatures, and on all types of panels it will be by 2 or 3 volts from the voltage measured at the 25C cell temperature that is used when the panel is rated.
            Thanks for your input. Keep having fun out there!
            Rob Warren – Coastal Climate Control, Inc.

          2. Rob, again I bow down and am grateful for your expertise! Thanks for chiming in!

            So I’m curious, with our setup (8 x 120W panels + 2 x 50W panels) how many amp/hours per day would you say we should be seeing in total? Assuming lets say that the batteries are at 50% charge and can accept max input. I’ll work on seeing if I can pull the yields from the Philippi but last time I tried the excel document had formatting issues.


  6. This is a great write-up David, and congratulations on a great installation. It would be nice to know at some point what the 24hr yield is from the panels. I would estimate somewhere in the region of 350 amp/hrs per day on a good solar day with a full-time load.
    There is always some misunderstanding regarding Blocking Diodes and By-Pass Diodes, but the golden rule to remember is that a silicon solar cell will consume power as well as producing it. And if the power it consumes is large enough, it can cause the cell to heat up to such a high temperature that it can burn through the panel and destroy it. A Blocking Diode would be required if a solar panel were connected directly to a battery, to prevent the battery being drained overnight when the sun had gone down. Without a blocking diode (or a solar controller, which acts just like a blocking diode), you’d wake up to a dead battery and a nice, warm solar panel!
    Blocking Diodes are required to be installed in the positive output lead of each panel if two or more panels are connected in parallel to one solar controller. This is required in order to prevent one panel back-feeding into the other if one or more cells became covered by an opaque object like canvas, towels, etc. This is an important safety feature and should not be omitted, alhough the diodes in this application will reduce the voltage output of each panel by around 0.7 volt.
    By-Pass Diodes, which are identical to Blocking Diodes, are used to prevent one or a group of heavily shaded cells from receiving excessive back-feeding current from unshaded cells, within the panel itself. All well made solar panels of over 50 watts will have By-Pass Diodes, also known as Hot-Spot Preventers, either incorporated into the panel or in an external connection box, and these do not consume any power or reduce panel voltage during normal operation.
    Interestingly, the cells are seemingly more vulnerable to hot-spots and overheating when the batteries are fully charged and there are no other loads for the solar panels to supply power to. In this “dormant” state, each cell happily feeds back into itself without harm, but if any cells were to get hard shaded, latent power from unshaded cells could feed into the shaded cells unless prevented from doing so by Blocking and/or By-Pass Diodes. From this it can be deduced that it is not in the best interest from a safety angle to install cut-off switches for the solar panel outputs. The Genasun controllers only draw less than 1/10 of a milliamp on night-time standby, that’s less than 0.01 amp/hour overnight draw on your solar array, so that should not be a concern.

    All the best,
    Rob Warren

    1. Thank you so much for that write up Rob! Hopefully, that will help me explain things more clearly in the future, and if not, I’ll refer them to this comment!

      Once we get back to the Caribbean and have an opportunity to put more consistent loads on the batteries (the fridge and freezer compressors don’t have to run all the time up in the colder weather in Canada!) we’ll do some more 24 hour type testing and will write up a follow up solar post.

  7. Hello David,

    Awesome writeup on an uncommonly large solar installation. We have a modest 4 panels and 4 Genasuns setup.

    Could you please expand on the by-pass diodes. I know these are mandatory when people connect more than one panel to one charger, but you have one per.

    Alternatively, how does a hot spot happen in your 1 to 1 setup, that it needs be prevented?

    Thanks in advance,

    1. Glad you enjoyed the write up and thanks for reaching out to us! The by-pass diodes were the large topic of a lot of conversation among the people we had working on the boat. The general consensus was that they would most likely not be required for our 1 to 1 setup, but that it wouldn’t harm anything to have them installed. Also, for our panels the by-pass diodes converted the 3 wires coming out of the panels down to the two wires that then got wired into the Genasun controller so there was that benefit as well.

      And I will admit that my knowledge of hot spot issues is a bit lacking, but I was told that it is unlikely we’d have any issues with a 1 to 1 setup, but if a blanket or something got left on top of a panel, it may cause an issue. Sorry I can’t be a lot of help with that question, but if you’re interested in trying to learn more, I can direct you to the guy who helped us set up the basics of our system.

      1. Great! It is said that one ounce of prevention is worth a pound of cure.

        I very much like the kill switch. I wanted one as well, but there was a question on whether this kill switch should be installed after the Genasuns (1 switch for all) or before the Genasuns (4 switches, at least in our case). The issue, you see, is that the Genasuns are powered by the boat’s batteries, at least at night, and there was a question of whether the Genasuns would be OK just getting cut-off, perhaps as the panels were under the mid-day Sun. I actually called up Genasun technical service to ask, and was told no-one had ever asked such a question before, and they did not know.

        We then ran out of time and we therefore have no switch yet –but for now at least each Genasun has its own fuse that can be pulled out. Your write up seems to answer the question of where can the switch be safely located: after the Genasuns.

        The Philippi looks quite cool. You have a photo where it displays 44A coming out of the panels and 30A going into the battery. I suppose other devices on Starry Horizons were consuming 14A at the time? Or does that screen mean something else?


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