Mounting Solar Panels/Modules:
The solar modules (the correct term for what most people call solar panels) will be mounted by attaching the long sides of the frames to the mounting structure. The long sides of the frame have a flat surface on the bottom, which need to be against the surface of the mounting structure. A typical diagram of the frame sides and mounting holes for the KD 140 modules is at:
I’ve found the diagrams to be very accurate. If you are having a mounting structure made up (as in an arch), I’d have the welder make the holes in the mounting structure 5/16 inch, as the solar frame holes are 8 MM (about 5/16 inch). If the mounting structure is going to support the long sides of the frames by a length of much less than 1/3 the length, I’d recommend that something be used to reinforce the frames. I’ve used 1/4 X 2 inch aluminum “L”, which is available in “bright finish” which looks like polished stainless steel. There are two kinds of “L”; Architectural and Structural. Architectural has a 90 angle on the inside corner, so that it can go again the bottom and outside edge of a panel. Structural has a “fillet” on the inside corner, and is stronger, but cannot be install against the outside bottom of the panel. “Square tube” of 1 – 1 1/2 inch could also be used. The long sides of the frame have a flat surface on the bottom, which need to be against the surface of the mounting structure. We use 2″ X 1/4″ aluminum extrusion to go across the bottom of the panel on most installations.
Types of solar panels and how that effects the mounting location
There are three types of solar modules typically used on cruising sailboats:
(1) Monocrystal, best represented by Solar World (formerly Shell, formerly Siemens, formerly Arco) see
SolarWorld AG – Solarmodule, Solarstrom, Photovoltaik. Monocrystal cells (the individual little elements of a solar module) are dark gray to nearly black, sometimes a little blue. They do not have any crystal patterns in the cells. Mono are the most efficient, and will make the most power per square inch. They are typically the most expensive per watt. Each cell makes a relatively small amount of voltage, and putting all the cells in series adds the voltage together so that they can charge batteries. Some modules have less than 36 cells, and will not do a good job of charging batteries unless the ambient temperature is very low.
(2) Polycrystal, best represented by Kyocera. These will have gray to blue cells with a pronounced crystal pattern evident in the cells. Poly cells are made by pouring melted silicon that is less pure than mono type cells into a mold. The brick of silicon then is sliced into very thin sections (called wafers). This can result in cells that are nearly square or rectangular. The mono cells are made by a process in which a single crystal of silicon is placed into a melted pool of very pure silicon, and withdrawn extremely slowly so that a single crystal structure (called a boule) about 6 inches round emerges. The mono cells are then trimmed so that the edges are cut off, so that they can be placed close together. The poly cells do not need to be trimmed, and when placed in the module end up with less background showing. Therefore, the polycrystal modules can have about the same overall efficiency as the mono but at a lower price. We have the very popular Kyocera 85, and 140 watt modules in stock.
(3) Amorphous (or thin-film) modules are mode by taking a surface (like a sheet of glass or plastic) and then vapor depositing the silicon (and then the other materials) onto it. This could be less expensive, and is where a lot of research is going on. They are less than 1/2 as efficient, so they need at least twice the surface area. These are the only modules that can withstand significant shading without loosing significant output. If you shade 10 % of a thin film modules, you will lose 10 % of the output. If you shade one cell of the crystalline modules, you lose at least 50% of the output, and shading one row of mono- or poly-crystalline module cells can reduce the output to near zero. So, if you are mounting the modules on an arch under a wind generator or directly under the boom, thin film may be the best modules to use.
If you will be making a mounting structure that can pivot the solar modules, it is possible to gather about 10 – 20 percent more power (more in the northern latitudes). If it is easy to do, then I figure it is worthwhile, like on a rail mount. However, it is likely that the increased complexity and cost for a bimini or arch mount will not make it worthwhile. There are automatic tracking devices that could be used, but the added expense and complexity makes them not cost-effective and less reliable.
I like arches as they give a place to mount all the stuff you need on a cruising sailboat. Ours incorporates solar modules, wind generator, fishing rod holders, throwable PFD, propane tanks, extra fuel and water jugs, stern anchor, antennas, and more. The best place for solar modules is high and aft, assuming you don’t have a wind generator and/or radar dome directly over the modules. Stainless is generally heavier and more expensive than aluminum. I’ve had two customers very unhappy with the “bargain” stainless arches they had custom built. Both had rust “blushes” that could not be permanently removed. Aluminum can look almost as good as stainless – see my notes of this elsewhere.
If you are going to put the modules over the bimini;
If they will be shaded by the boom, then what I said about thin-film being best applies. That is, thin film will make more power when partially shaded than the mono, and poly crystalline modules, but
takes more room to make the same amount of power.
If you have a hardtop, then the modules can be mounted using aluminum angle, cut into 3 – 4 inch long pieces, with one piece on the long side of the frame of the module, flat against the bottom, and another angle mounted to the flat surface of the hardtop. Then a bolt through each of the vertical portions of each piece of angle. Two inch angle works well. Eighth inch thickness is usually sufficient. This allows for some curvature of the mounting surface. The modules must be at least one inch from the surface in order for air to flow under them. High temperatures cause the modules to make less power. If the boom is over the modules, consider making a “roll bar” that would protect the modules in case the topping lift were to break.
If you have a soft bimini; the slickest setup I’ve seen uses additional bows that go over the top of the bimini, more or less paralleling the original bows. These will need to have fore and aft bracing to prevent them flexing in that direction. The modules can be attached to the bows using “Helm” clamps; plastic clam-shell clamps that attach to a flat surface on one side and to a one inch tube on the other. I’ve also welded up a stainless frame with tabs that allow bolting to the holes in the long side of the frames. This is then attaches to whatever you have to work with. One inch stainless “U” bolts can also work well for mounting situations where you are attaching to one inch (or for that matter, other sized) stainless tube. I’d avoid putting bolts through the fabric of the bimini. Besides increasing the chance of water leaks, you are likely to see chafing on the fabric and it becomes much more difficult to take the fabric down.
If you are mounting the solar modules onto the rails, or atop lifelines, then I have brackets that
mount a one inch stainless tube between stanchions, on which the solar module mounts with Helm clamps or Doohickies and a 1/4 X 2 inch brace across the short dimension of the modules. This works much better on center cockpit boats, where the modules can be mounted aft, so that they don’t interfere with the walkway. A complete kit for rail mounting is $99 and includes 8) stainless U bolts, 2) brackets, 6.5 feet of one inch stainless tubing, 2) Doohikie clamps, and 2) cross braces. An article about mounting a small solar panel is at: http://www.captaincurran.com/2015/09/how-much-solar-power-do-i-need-for-my-boat.html
Wiring the modules
If you use panels that have a terminal strip inside a junction box, you’ll probably want to use 1/2 inch (trade size) strain reliefs at the holes in the junction box on the back of the modules ($3 each). Also use Corrosion X or a similar product on all the wire terminals (also to be used at every electrical connection). Most of the panels are available with what are called “MC4” connectors. These are waterproof and sunlight resistant connectors designed for use on roofs, but work well
on boats. We have the materials and tooling to make up wires in 12g to 8g with the MC4s. The size of the wires will depend on how far the wire run is to the batteries (or wherever you will be attaching the wires to the boat’s electrical system). I’d use Nigel Calder’s “Boat Owner’s Electrical and Mechanical Handbook” or a similar source to find the chart to calculate the voltage drop. BTW, you should have this book on board if you are going cruising. I’d use the 3 percent table to calculate wire size, but if that wire size is too large to work with, 10 percent is acceptable, unless you are using MPPT . The charge controllers we recommended have Maximum Power Point Tracking (MPPT), which increases the efficiency of the system, but will not do as well if there is too much voltage drop. More on MPPT at: Blue Sky Energy Inc. and in “Charge Controllers”. Unless you are using MC4 connectors, I’d recommend not putting wire connectors above deck – it dramatically increases the chance of corrosion problems. If the modules are mounted such that they can be removed for hurricanes or theft protection, then use waterproof butt connectors with heat shrink and hot melt glue on the inside. Also, leave enough extra wire so that you can cut the connectors off and then reinstall new ones later. For the through-deck fitting, I like mini-clamshell vents. Properly installed, they clamp the wire in place so that it cannot move around and cause leaks, and they’re cheap ($2 – $3).
Like I always say sometimes, compromises must be made. Bulwinckle