Our Seawind 1160 with two solar panels mounted above the dinghy davits (standard installation), and with one each mounted above the retractable cockpit shades.
For a 2008 Seawind 1160, two 140 watt solar panels installed above the dinghy davits were an option, but they weren’t installed on our boat. The upside of that is that we didn’t inherit already degrading, older kit. As well, that amount of solar couldn’t even keep up with the standard refrigerator and freezer installation on the boat.
Kyocera panels seem to be very commonly installed on boats, and they do come with a good warranty and are quite robust. However, they’re not terribly efficient, and there is a rare amount of surface area for solar installation where panel shading won’t seriously degrade power output. My research indicated that Sunpower cells were the most efficient for commercially available panels. Solara marine panels manufactured in Germany using Sunpower cells were present at the Annapolis sailboat show, but wow were they expensive.
Marine type solar panels don’t seem to be more robust for a salt air environment than the residential type Sunpower panels. What they do seem to be designed for is an output around 17 volts, something closer to the charge requirement for marine house batteries. The Sunpower residential panels have an output of closer to 40 volts, so they won’t work with the MPPT controllers commonly found at boat shows.
Sunpower doesn’t sell to RV or boat people in the US; it seems their business model is large installations on private homes or commercial properties, and finding a way to purchase just four panels was challenging. Eventually Craigslist came to the rescue, and 4 E series 230 watt panels with suitable dimensions for the boat were located and purchased. Each panel is about 31.5″ by 61.5″ and nearly 2″ thick. The newest flavor (X series) of these panels (250 watts at the same form factor) would have cost us $680 apiece retail (we finally found a guy who could get them for us). We got the slightly less efficient E series panels for $150 apiece. Wow, Craigslist is our friend!
Installing two panels on the dinghy davit structure was pretty straightforward, using simple aluminum bar stock purchased from a scrap metal dealer, all attached with stainless steel U-bolt hardware. Installing the panels above the cockpit’s retractable fabric shades required some custom fabricated stainless steel tubing. We got Alejandro, the best guy in Ensenada, Mexico to work with us during a slow spell, and we ended up with the stainless steel mounts installed for under $300 US. I’d hate to think what that might have cost in the US.
Each panel weighs about 33 pounds. Mounting provisions for each stern panel is around 8 pounds. Mounting provisions for each cockpit top panel is probably more like 20 pounds. Then there’s wiring and weather proof junctions required to create a series, series/parallel, or parallel electrical output – more about that later. Then there’s a MPPT solar controller required to take the maximum output voltage at the maximum output amps output and convert it to the most appropriate voltage to charge the batteries. That puppy is another 16 pounds or so. We purchased the pre-built wiring, combiner connectors, and the Schneider Electric XW-MPPT solar controller from the good people at Northern Arizona Wind and Sun. They have great prices and technical support – something definitely worth paying for.
The Schneider Electric / Xantrex XW MPPT 60 solar controller.
So there you have it; 132 pounds for panels, 56 pounds for mounting provisions, perhaps 6 pounds for electrical wiring, and 16 pounds for the solar controller. All told, maybe 210 pounds for what on a perfect day might provide up to 920 watts peak power for a couple of hours, and much less average output over the course of the day, what with sun angles, panel shading, wire losses, and such.
After messing around with wiring each pair of panels in series/parallel to produce double the voltage at half the current (leads to lower wire losses), then trying all panels wired in parallel, we concluded that the parallel scheme led to the lowest output losses due to shading. Shading is the bugger of solar on a sailboat. Trying to avoid creating shade makers in addition to rigging, mast and boom, etc. leads one to abandon aft mounted wind generators and antenna systems. That doesn’t leave a lot of options – especially for wind generators.
Our observations so far:
We had to leave JollyDogs at Marina Cortez in La Paz for 2 months. We left the freezer and galley refrigerator turned on. We didn’t have shore power access and had to rely on solar to keep our 800 amp hours of LiFeP04 batteries charged. Turned out it wasn’t a problem; a friend kept an eye on things and noted that the batteries generally maintained a full charge. We did tie the boom to one side, and JollyDogs was facing North, so with the Wintertime sun to the South we got pretty good solar input.