Installing a solar panel
When living aboard our Tartan 34, our electrical needs under sail and at anchor are primarily determined by the Adler Barbour refrigeration system. Our 13 5-amp alternator provides plenty of power when motoring and quickly charges the three 90 amp-hour batteries. All other electrical requirements, lights, stereo, etc., are small when compared with refrigeration.
We chose to install a solar panel to add some charging capability. Third-generation solar panels are reasonably efficient, and it was possible to "hide" the panel on top of the companionway dodger.
We studied solar installations on other boats and read the literature. There were several types of installations we wanted to avoid. We wanted a fixed setup and didn't want to continually move the panels at right angles to the sun. We also didn't want another post on the stern or the panels hanging on the lifelines interfering with boat operation.
We found a 64-watt, third-generation panel from Uni-Solar that measured 49 inches by 29 inches, just about the size of the top of our dodger. I chose not to purchase flexible panels or older, second-generation panels because output per square foot is less and any shading significantly decreases power output.
When we had the dodger made we had several small straps sewn into the top to tie down a solar panel, so naturally I tried to tie the large, awkward, rigid panel in place using the tie-downs. However, the tie-downs would not properly hold the solar panel in place. They also put stress on the dodger and caused water to puddle and leak.
Because the sewn-in dodger tie-downs didn't work I initially gave up on the idea of using the top of the dodger and reluctantly created a tripod on the stern about six feet off the deck. The tripod consisted of two three-foot pieces of 1-inch aluminum angle iron, a one-inch stainless steel tube post, and several U clamps. The tripod supported the panel at three places and worked fine, except our windvane blade kept hitting the edge of the panel under sail. It also added to an already cluttered stern. Worst of all, I didn't like the looks of it.
I kept thinking about the dodger knowing that the top area was large enough to carry the panel, the orientation was acceptable, and we could work the boat under sail. The problem was how to support the panel adequately without degrading the purpose of the dodger. When the dodger was made I had a large grommet sewn into the center of the after edge of the dodger so the solar panel wire could run up under the edge out of the way along the inside of the dodger next to the tube frame. I decided to try to support the panel front and back using the -inch aluminum dodger tube frame only touching the dodger at the edges.
The after deck tripod was quickly dissembled. (Fortunately, I had not drilled any new holes in the deck.) Once again I laid the panel on the dodger. I bought six feet of one-inch-by--inch flat aluminum bar stock at the hardware store. I cut the aluminum stock in half and laid the two three-foot pieces fore and aft on top of the dodger frame and placed the solar panel on top of the aluminum supports to see how it would fit. Satisfied that it would work, the aluminum bar stock was drilled and bolted to the bottom of the solar panel using the four mounting holes provided on the bottom of the solar panel. After laying out the assembly on top of the dodger it became clear that the dodger tube frame was not made to support the weight and bulk of the solar panel. A pair of three-foot, adjustable -inch bimini support tubes were purchased to provide added support to the aft sides of the dodger. The added support made the dodger much sturdier. The dodger was stretched tight on top and the four holes to be drilled in the bar stock were located on the dodger tube frame. The bar stock/solar panel assembly was clamped in place with the dodger tight on the frames, and -inch holes were drilled through the bar stock, the dodger, and dodger frame, exiting the underside of the dodger frame. To prevent leaking and tearing, the dodger was removed from the tube frame and four grommets were inserted into the dodger where the bolts were to go through. Four 20 stainless steel bolts were passed through the bar stock, dodger grommets, and dodger frame and tightened using nylon insert nuts. The solar panel wire was run from the electrical box on the underside of the panel through the large grommet on the aft edge of the dodger down next to the frame tube and into an external two-wire plug and socket in the cabin top. The wires are fed to the solar charge controller located in the electrical terminal area under the nav station. A 10-amp DC charge meter is located in the charging circuit below at the nav station.
I like the installation. It's neat, tidy; it doesn't interfere with sailing the boat; and the solar panel is unobtrusive and even provides some support for the dodger. The only drawback is removing or lowering the dodger requires unbolting the solar panel. To date we have removed the dodger two times in clearing the decks for a hurricane. Electrically it works as well as the tripod, except the mainsail shades the panel on certain tacks; at anchor it works fine. The panel provides a full output of 4.1 amps when the sun is overhead and less than 4.1 amps when the sun is at an angle. It provides approximately 27 amp hours per day but can't keep up with the refrigeration and other electrical needs all by itself. It provides about half our needs in warm, sunny climates.
Is it cost-effective? I have about $450 invested in the panel, solar controller, and meter. I also spent about $50 on the aluminum bar stock, wire, connections, and bolts, not counting my labor and the money spent on the aborted tripod effort. The solar panel saves about gallon of diesel per day, or 75 cents, not counting engine and alternator wear and tear. At a savings of 75 cents/day compared with an investment of $500, the solar panel will pay for itself in about two years.