To the editor: Like many voyaging sailors who spend a good deal of time on the hook, we need all the “free” energy input we can get. Since we cruise in southern waters, below 25° north latitude, we can rely on 10 to 12 hours of solar energy each day, even in the winter. Solar panels today are much more efficient than even five years ago. A 125-watt panel is actually 25 by 56 inches, slightly smaller than our 29-by-54-inch 64-watt panel. Since a new 125-watt panel can fit in roughly the same space as our existing 64-watt panel, I plan to replace our panel with a 125-watt unit.
I agonized for days over where to mount the 64-watt panel. I tried a tower structure aft, but it looked unstable and unsightly. Also, we do spend some time at sea, and I didn’t want the solar panel to be a problem in strong winds in a seaway. The panel was too big to mount on the rail, so I settled on the top of the dodger as the best place. The dodger position was secure, and the panel mounted flat and was out of the way when we sailed the boat.
It turned out that the top of the dodger was the ideal place for one panel, since we could easily access the panel while standing in the cockpit and on deck in front of the dodger, and a raised panel cleared the boom when the boom was tied off. Boats with larger dodger areas could mount two or more adjustable panels. The problem with several panels is that the crew could spend a good part of the day adjusting them.
We soon discovered that the efficiency of solar panels is highly dependent on their angle to the sun. With the panel lying flat on the dodger, we missed an estimated 35 percent of the available solar energy. Orienting the panel perpendicular to the sun all day would be ideal, but it’s usually not practical. Adjusting the angle of the panel occasionally throughout the day makes it possible to present as much panel area as possible to the sun, as it moves from east to west.
The boat’s heading makes a difference in how we raise the panel for maximum solar energy input but not as much as we first thought. It appears our two-dimensional adjustment system works well enough. The farther south we are, of course, the more sunshine. With the boat facing north, we simply tip the pane up from the front to catch the sun’s rays all day over the stern. To be able to orient the solar panel side to side as well as fore and aft would require a much more complicated mechanism, and it likely would make it difficult to fold the panel flat and out of the way when sailing. Some boats have solar panel supports and adjustment mechanisms hung off the stern. We believe stern-mounted panels would be unwieldy, interfere with our self-steering wind vane and could be a problem when sailing in a seaway.
With the boat facing east in the morning, we tip the panel up about 30° to catch the morning sun. When the sun is abaft the beam and nearly overhead to the south, we lay the panel flat. Once the sun has moved to the southwest we begin adjusting the panel to the west. As the sun is setting, the panel is elevated about 60° and angled to the west.
We have a DC amp panel meter that shows the effects of adjusting the panel angle. This way we determined the best panel angle for various times of the day. The panel-angle adjustment braces have screws to set the panel various angles to the sun. It turns out only four adjustment points are necessary to capture most of the sun’s rays throughout the day.
– Dick de Grasse is a U.S. Coast Guard veteran, professional engineer, commodore in the Seven Seas Cruising Association and freelance writer. He and his wife, Kathy, live in Maine when not cruising in southern waters.