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Case Study: Time to Go Solar by Ed Eisen

Time to Go Solar

by Ed Eisen

It's midsummer. We're at our favorite anchorage, and it's another perfect day on the water. What makes it even better, is waking to the smell of coffee my wife started a few minutes ago. I crawl out of bed and slither up to the cockpit, cup in hand. What a view. We can see the mainland and a few boats throwing spray on a glassy blue ocean. Just as I raise my cup I think, “Damn, I forgot to start the generator.” The ole Honda 2000 is fairly quiet, but it is still not my favorite sound as I enjoy the morning. The other time I have to hear the generator is when the sun has transited to the other side of the boat, and I'm ready for happy hour. We bought the Honda when they were all the rage, and it has been a wonderful alternative to charging with the boat's diesel for the last ten years. Lately, I have felt a growing envy of my fellow boaters with solar power. So, after our typical family debate on cost versus benefits, my wife and I decided to add solar and more silence to our 2005, 43 foot Jeanneau.

We started from scratch and spent many hours studying the concepts and equipment necessary. We are far from solar experts, rather just retired boat owners who wanted a quiet way to charge batteries. If you are a first time, solar-do-it-yourselfer like us, I hope this short story of our installation will be of interest.

Sizing the system

While at the San Diego Boat Show, we visited the Sun Powered Yachts booth. We learned about their panels and reviewed a list of possible power requirements on our boat to determine how much solar wattage we needed. For us, the big items are the refrigerator and freezer. We use the freezer more as a beverage cooler, still two refrigeration units are the biggest draw on our boat. All lights are LED's so not much draw there. The other considerations were that we had easy space for two panels on our bimini and two were all we had budgeted for. With little more thought to sizing, we purchased 2x SunPower 110 Watt panels that we were optimistic would satisfy our needs.

Acquiring parts and a plan

The panels were our major single purchase, but we soon realized much more is needed to complete an installation.

1. How will the panels fasten to the bimini?

2. How to position the panels?

3. Will they connect in series or in parallel?

4. What size wire do I use

5. Where do I run the wires?

6. How do the wires enter the boat?

7. How do I switch the system on and off?

8. What kind of charge controller is best and where should it be mounted?

9. How do I protect the system from overload?

The picture shows most of the additional parts I purchased. It turned out I did not need a few.

1. Fastening the panels to the bimini

There are six grommets on each solar panel used for holding it to a surface. With two panels, I had 12 grommets. They have an inner diameter of 5/8 inch which meant I needed a ¼ inch diameter fastener. I discussed fasteners with both Sun Powered Yachts and my canvas guy, Tom Anderson (Custom Marine Canvas by Tom). Lyall at Sun Powered Yachts suggested using LOXX fasteners which appeared to be a quality and elegant solution. However, it was going to cost $75 for the 12 fasteners I needed.

Canvas Tom suggested an elegant and economical solution, a nylon bolt with rubber washers to sandwich the canvas and stainless steel washers to sandwich the panel. I liked this approach.

I bought twelve ¼ inch nylon bolts and nuts, 24 stainless steel washers (nylon was too flimsy), 24 stainless fender washers, 12 stainless locking nuts and 24 rubber washers for a total of about $20.

Any fastener will require a hole in the canvas, in this case ¼ inch diameter. Canvas Tom suggested purchasing a hobby style soldering iron for $3.99 at Harbor Freight Tools. The soldering iron is exactly ¼ inch in diameter. When heated it passes through the canvas (Sunbrella in my case) like butter and leaves the threads melted so they will not unravel. The soldering iron turned out to be a great way to achieve our holes and without removing the canvas.

The hardware goes together in the order shown in the picture above, bolt, ss washer, two rubber washers, ss washer, nylon nut, two fender washers and the lock nut. The canvas is sandwiched between the two rubber washers and bolted tight. The rubber avoids chafing on the fabric and gives additional protection to the holes to avoid fraying. The panels are sandwiched between the fender washers and held tight with the lock nut.

This picture shows two bolts fastened to the canvas and ready for a panel. (Hint: I found the rubber washers in the plumbing department of the hardware store. They are actually replacement faucet washers. I enlarged the hole to ¼ inch.)

Viewing the bolts from under the bimini, my wife and I were very pleased that they blended in well and were not obvious. In fact, only one row is visible as the others are inside a zipper channel that holds the bimini support.

With the panels mounted, you can barely see them. I took this picture holding the camera as high as I could. At normal height, you might not even notice them.

2. Positioning the Panels

We were aware that shading affects solar performance, so before mounting the panels we experimented with placement. Using a multi-meter to measure volts and amps, we shaded the panels with our double back stays, the boom, the mast and radar and a big piece of cardboard. We had watched a YouTube video showing the effects of shading being about a 40% decrease in performance Our testing (not to be confused with scientific testing) showed a decrease of only about 5 to 10%. At this point we were glad we bought SunPower solar panels because they are obviously the evolved generation. We decided that the shading effect was so small, that we would mount our two panels simply based on where we thought was the most convenient and aesthetic location.

3. Connect in Series or Parallel

We decided to connect the panels in parallel because shading has less affect this way. Potentially there is more current loss in parallel, but our wire run was short enough we didn’t think the loss was significant.

4. Wire Sizing

There are online charts we used to help calculate wire size based on various factors including length of run. Our run was short. It’s all in the back third of a boat! We used 10 gauge wire which is larger than needed, but over sizing would help eliminate current loss. It’s better to go too big than too small.

5. Running the Wires

Next the issue was how to get the wires from the panels to the boat. With two panels there are four wires, a positive and a negative from each panel. I bought a pair of “MC4 Branch Parallel Adapter Cables” from Amazon. These take the like poled wires from each panel and combine them with a single wire resulting. Picture a “Y” with two wires on the top and one on the bottom. In the picture you see both adapter cables connected to the four solar panel cables and only two wires, a positive and a negative, running into the canvas.

I was reminded that real electricity is coming through the wires from the panels, so I didn't connect to the panels until I was ready to activate the completed system. “MC4” refers to the connector on the cables. I found these are standard and are on all the solar products I bought. They are the same ones used on our SunPower panels. Notice in the picture left that the cables disappear into a hole in the bimini. I made that with the soldering iron, and it’s just large enough to fit a MC4 connector through. It goes into a zipper sleeve, so you can’t see it from below in the cockpit. Also notice the cables lay over the bimini window. We will fix that later. Next the cables needed to run down to where they will enter the boat.

In our case, it was best to run them down the back stay. I wanted to use true outdoor solar cable rated for outdoor use. On Amazon I bought two 20 foot pieces of “10AWG Solar Extension Cable with MC4 male and fema