Free docks often do not provide electric hookups and neighbors don't like one running engines to charge batteries. So I finally broke down and bought an 80W solar panel for the boat.
After doing some research, I found that there is not a lot between different brands of solar panels and all panels of a particular size put out the same current. The 80 Watt panel measures 47.3" x 20.8" x 1.3" (1200 x 527 x 56 mm) and puts out about 4.5 amps maximum in direct sunlight.
It is interesting that many of the panels are branded by fuel oil companies such as Shell, BP, Total or Mobil; I suppose doing their bit for a greener planet.
I mounted the panel on top of my bimini top, putting a few screws through the stainless steel bows and through the fabric into the aluminum frame.
When installing a panel, the most important thing to watch for is that the whole panel is in sunlight with no shadows. The shadow of just a halyard over the corner of the panel will cause the output to drop considerably (like from 4.5 down to 1.0 amps).
While it helps to angle the panel to face the sun, it does not make a huge difference, as long as the whole panel is in sunlight, so you probably don't need to have the panels hinged and adjustable, as this compromises the strength of the installation, especially in foul weather( there is a lot of windage on those panels). So I mounted mine flat on top of the bimini on the starboard side. I hope to buy a second panel soon for the port side.
Many people have the panels attached to the top rails outside the cockpit, and then hinge them up like wings to face the sun, and fold them down when they are sailing, or when it it is not practical to have them up. Some installations have a specially constructed stainless steel arch with the panels secured flat on the top (see photo below).
There are a couple of options for regulating the output of the panels. The cheaper option cuts the panel off when the battery reaches a certain level, and the more expensive model electronically regulates the flow to the batteries. I considered going without any regulation, since I had 600 AH of batteries and 4.5 amps of charge is not ever going to do them any harm, especially when I am drawing some current. But in the end I got cold feet and bought a very sophisticated regulator for about €150.
The installation was easy, as I simply tied it in with the wind generator and shared the same breaker.
The panel cost €450 and I now wish that I had bought two of them. I would hardly ever need to run my engine with 7 or 8 amps trickling into my batteries all day long.
The cost is not that bad when you consider the cost of the gallon or more of diesel (€4) one would use every day to charge batteries when you are sitting idle at anchor for extended periods.
I have seen some boats with 5 panels and even they wish they had more. Some minimalist, purist yachties will balk at so much power usage, but when your yacht is your full time home, there is no need to skimp on the comforts and technologies like refrigeration, computers, TV, microwaves and proper lighting that can quickly eat away at your battery levels. Refrigeration current is the main killer on most yachts.
A funny side effect of having free solar energy and no need to run the engine at anchor is that your hot water does not get heated when you don't run the engine for a while. Of course, the solution might be to go totally green and use a sun shower.
When not connected to the batteries or a load, the voltage on the terminals of a single panel should read 21 volts on a voltmeter.
You can hook two panels in series for 24 Volt systems, but it is equally important that no shadow falls on either of the panels.
See the wiring diagram
Howard [ Just Imagine ] 09-Feb-2008