Tag Archives: Flexible solar panels on a sailboat

Solar Breakdown

With several trips planned over the summer, and due to the fact that it’s really too darned hot to use the boat much in July and August anyway, we thought it would be prudent to strip the solar panels off our bimini. That way, if some tropical weather developed while we were off elsewhere, it would be one less thing to worry about.

(If you haven’t been around long enough too have read the original post from back when we designed and installed our solar charging system, here it is:  Our Vision Realized)

One advantage of flexible solar panels is that it’s not a major task to remove them and pack them away. Disconnect the wiring connections and release the fasteners holding them to the bimini, and you can just slide them off and store them below. It doesn’t even require any tools. But when I started taking things apart, I discovered a very unpleasant fact. The system I’d designed used several rigid MC4 adapters to electrically combine the panels. And almost every one of them had failed in some way.

Here’s a 3-to-1 combiner I removed. You can clearly see that the left leg is cracked and failing, the center one is more or less OK, but the right one has broken off completely.

This was typical of all the combiners I removed. Nothing was holding a lot of these wiring connections together except friction.

Once I pulled everything apart, I made a small pile of everything in the system that had failed in some way.  Amazingly, the system was still working fine, but a good tug on many of the panel leads would have pulled them completely loose from these broken combiners.

The majority of these parts were tucked into pockets in the bimini, so I know UV exposure wasn’t the problem. Either they got brittle and delicate in their four years of use, or some sort of stress, possibly caused by the bimini flexing in the wind, was breaking them.

I scratched my head a bit and thought about a solution. The system I designed needs these combiners to tie our six solar panels together in the series/parallel circuit I’d layed out. They’re pretty important parts. But I didn’t want to just replace them with more of the same now that I saw such a high failure rate.

Fortunately, some research turned up a solution. Rather than rigid combiners, I found that they also make these MC4 pigtails. The piece on the right is a direct replacement for the old one on the left below.

I’m thinking these pigtail-type combiners will be a lot more forgiving of twists and torques than the old ones were. I ordered enough to replace all the existing connectors.

We don’t have a lot of travel planned between now and the end of hurricane season, and it’s finally cooling down enough to start spending some time out on the water again , so we recently re-assembled our solar system using these new parts. Everything snapped together fine, and seems to be working well. Check back in a few years for an update on how these new parts hold up!

In the meantime, if you happen to be designing and installing your own solar charging system, you might want to consider the type of MC4 combiner to use. I just can’t recommend the rigid ones for marine use.

Sunshine And The Fine Art Of Boom Management

Last Monday at 0900, I turned off the breaker to our onboard battery charger. Since then, our refrigerator and freezer, lights, water, stereo, fans, indeed our entire DC electrical system, has been running solely on solar energy that we’ve captured and stored. In the days between then and now, we’ve seen a mix of sun, clouds and rain. I’ve followed the system’s operation closely. The day’s first trickle of power starts flowing into our battery bank a little before 0730, and the panels don’t shut down and go to sleep until about 5 PM. So far the peak power generation I’ve seen in bright sun at midday is just a touch shy of 20 amps. I designed our solar array to put out over 30 amps, but since it’s only mid-February and the sun is pretty low in the sky (and the panels are often being shadowed by the masts of surrounding boats), I’m confident we’ll get closer to and maybe even exceed our design goal once we head further south.Solar2

It’s now exactly one week later, and after seven days unplugged, our bank reads 87.2% full. The charging day is just beginning, so even though it’s supposed to remain cloudy today, I expect our bank to be above 95% full by dinnertime. My goal was to create a system that would eliminate the need to run our generator or engine to charge our batteries. I believe we’ve succeeded. 🙂

Also, on Monday afternoon a strong front blew through with 40+ knot winds. The method we worked out to mount our flexible solar panels to our fabric Bimini survived the gusts with no hint of lifting or flapping.Bimini5

One thing I didn’t sufficiently appreciate though until we actually activated our array is just how sensitive solar panels are to shadowing. I found that the shadow cast on the panels by the boom could drop the system’s total output by up to 60%.  Getting the most out of our system means that in the morning, I have to pull the boom to its starboard-most position to get its shadow off the panels. In early afternoon, it has to be pulled all the way to port as the sun moves west in the sky. So we’ve learned that proper boom (shadow) management is now going to be a part of our daily routine if we want to keep the solar juice flowing and the bank topped off.Solar3

I’ll soon do another post in our More Power, Scotty! series to give some of the technical details of how we integrated solar charging into our onboard electrical system.

Our Vision Realized

We knew from the beginning that we were going to need a lot of power. For instance, our freezer was able to keep gelato frozen and the refrigerator kept the beer chilled all through the long hot summer, but at a cost of 100 amp hours a day. Our total daily electrical consumption when sitting at anchor is close to 150 amp hours. But we did not want to have to run our generator (or even worse, our engine) for hours every day to keep our batteries charged. And I don’t like wind generators. I just don’t. No, I knew our solution was going to be solar. And the best way to do it appeared to be flexible panels mounted to our bimini. We had space for 500 watts of panels, and using the lighter flexible panels mounted to the fabric bimini eliminated the need for a complicated and expensive support framework. So I set to work and drafted a design.

It took three months and the bimini had to make three separate trips back to the canvas shop for tweaks and adjustments, but we finally tightened the last screw yesterday. And I have to say, I’m in love with the results.

Bimini1 Bimini2 Bimini3

Here were our design criteria:

We didn’t want to put a couple of boat bucks worth of solar panels and wiring on a worn out bimini. So we retired the one Eagle Too came to us with and had a new one made.

We used Sunbrella Supreme rather than regular Sunbrella, because we wanted a truly waterproof bimini. The old one would only slow the rain down rather than stop it, and Sunbrella depends on a coating for its water resistance, which eventually washes out. While the top layer of Supreme appears the same as regular Sunbrella, its softly flocked underside makes it truly waterproof.

We wanted the panels to be mounted securely enough to hold up to pop-up thunderstorms and their brief 50 knot winds, but easily removable in case a severe or tropical storm is predicted. I didn’t want to depend on Velcro, because I didn’t trust that the adhesive holding it to the panel would survive the tropical sun. Do you have any idea how hot a black panel gets in full sun? Plenty hot enough to melt adhesive.

Six panels meant a lot of wiring, and we wanted the bimini to organize it in a way that made everything look neat and orderly rather than like an explosion at a spaghetti factory.

Tony Renbarger of Coastal Canvas of Pensacola took on the challenge, and met every one of our requirements. i think his solution to our mounting problem was quite elegant. His research led him to a fastener from Australia we’d never seen before called a Stayput. The moment he showed it to me, I knew it was exactly what we were looking for. The post on the fastener fits the grommets in our panels perfectly, and once you flip down the key, they lock the panels in place by jamming against the grommets if the panel tries to lift. For extra security, I purchased some stainless steel E-clips from McMaster Carr and used them to lock the keys in place.

Bimini4 Bimini5

The hardest part of using these fasteners is that you have to get the placement exactly right. The smaller 50 watt panels we used on the aft end of the bimini only had four grommets, one in each corner. But the larger 100 watt panels have eight, four down each long side. Tony wasn’t sure he could get that many to line up precisely, so we only used the Stayputs on the four corners. I then had him sew some fabric loops into the top, and we used black parachute cord to secure the center grommets. This securely holds the center of the panels down, but will be very easy to remove if necessary.


Some strategically placed Velcro tabs and two boots on the bimini trailing edge manage all the wiring.

Bimini7 bimini8 Bimini9

Even though the panels are only a few pounds apiece, their combined weight was causing the bimini to sag just a bit in the center. So we added a spreader bar between the center bows to keep the top taunt.


And Tony found some nylon standoffs to keep the bimini frame from rattling against the new siderails we had installed when the wind blows.

Bimini12 Bimini13

Using two smaller 50 watt panels on the aft end of the bimini left us plenty of room for a larger viewing window to let the helmsperson keep an eye on the sails.


A word about the panels we used. They’re from King Solar, and we purchased them on Amazon. Since we have Prime, they shipped for free, which is pretty amazing when you consider that they came all the way from China. We bought four of the 100 watt panels, and two of the 50 watts. The 120 watt panel they offer was actually a bit too long to fit our bimini, while the dimensions on the 100 watt fit our top exactly. There were two things I liked best about the King Solar panels (besides the incredible price). First, they radiused the corners, making them friendlier to fabric biminis. Some other models have square corners, and are wicked sharp and will tear or poke a hole in fabric if given the chance. Second, they mount their diode boxes on the underside of the panels rather than on top, which offers them a little more protection from the weather. We had Tony add some squares of extra fabric under where the diode boxes would sit to eliminate chafe.

So after probably six months of research and planning, and another three of construction and alteration, we finally have the top we’ve been wanting.  In full sun, we should get from 30 to 35 amps of DC power from this design, which means it should only take four to five hours of sunlight a day to make all the electricity we need. And you know what’s really amusing about all this? SInce our boat is our primary (and only) residence, then due to our crazy tax laws, the American taxpayer will be providing us with a hefty tax credit to pay for the cost of our new bimini and installing solar panels on our yacht. Is this a great country or what? 🙂

We’ll have another post in the near future that details the specifics on the controller we’re using and how we’re wiring into our existing charging system. It will be the next installment of our More Power, Scotty! series. Till then…