Marine Solar Panels For Sailboats, Power Boats and Yachts for Keeping The Batteries Charged


(updated 3/2018)

Keeping our batteries charged was a never-ending problem while cruising on our Catalina 34 sailboat. The electrical requirement for lighting, VHF, and refrigeration to keep a few drinks cold would drain our batteries. Our only way to charge the batteries was to run the engine and we had to run our diesel at least 30 minutes twice a day just to keep the batteries charged.

While cruising in a remote area, a problem with a raw water pump on our diesel engine left us with no way to charge the batteries for a couple of days. We turned off the refrigeration, and all unnecessary electrical devices. We were even reluctant to burn an anchor light, for fear of draining the batteries. We really needed an alternate way to charge the batteries.

We decided to get a solar panel, but, at the start, we knew very little about solar panels. We had a vague idea of how they worked - you know, the sun shines on the panel and it puts out electricity to charge the batteries - sounds great. After doing a little research, we found there are several different types and sizes. Which solar panel type is best for our application? We also had to decide where and how to mount the panel. Do we need a regulator (Charge Controller)? Its not difficult, but there are several things one needs to consider before running out to the nearest marine store and plopping down cash for a solar panel.

Which type panel is best?

There are three common types of solar cells used in solar panels sold today, each with their own advantages. This may be boring stuff but if someone is going to buy a solar panel - they need to know the types available and the advantages of each.

Solar modules (solar panels) are very sensitive to shading. Once a solar cell or a portion of a cell is shaded it becomes less effective. The design of some solar modules offers protection from partial shading by including a diode between every string or cell.

Monocrystalline are single silicon cells grown into larger crystals, then cross-section cut into small wafers to form individual cells that are later joined together to form a solar panel. This cell type has a very high conversion efficiency which means it takes up less space on deck.

Multicrystalline (Polycrystalline) cells are also single silicon cells constructed by utilizing multiple amounts of smaller crystals to form a cell. This cell type has high conversion efficiency.

Amorphous silicon, the most inexpensive to manufacture, is produced by depositing an active silicon material on various substrates like stainless steel sheet. The conversion efficiency is not as good as the single crystal type but work better in shaded situations. Shadow protected means that a panel continues to charge when part of the cells are in a shadow, like a stay, which is a great advantage on a sailboat.

Flexible panels are also available for battery charging applications. Same technology as the hard panels, just light weight and flexible. Also, kits are available to allow mounting flexible solar panels on canvas such as a bimini top.

The chart below depicts a sampling of some manufacturers offerings:

Brand Type Form Sizes Space Required Shadow Protected Warranty (Yrs)
Manufacturing
Warranty (Yrs)
Output Protection
Solarland
M/P Fixed Frame
10 - 160w 9.8sq. in/W Yes 2 25
Solartech Universal M Fixed Frame 285-360W 8.6sq in/W Yes 12 30
Gioco M/P Flexible 65-170W 11sq. in./W Yes 2 25
Solbian M/P Flexible 40 - 145W 9.4sq. in./W Yes 5 5

Type: M = monocrystalline, P = multicrystalline, A = amorphous

What size of solar panel do I need?

To be absolutely self sufficient, the solar panels should exceed the basic requirements by 20%. That may be hard to do giving space or budget or your goal may be only to reduce engine/generator -running time.

At the very least, you need to add up your estimated daily ampere-hours (A-Hrs) of DC energy consumed. Include everything that consumes DC current: instruments, VHF, lights, refrigeration, pumps, etc. (see our easy to use energy estimator calculator located on the e Marine homepage bottom left corner) After figuring your estimated energy consumption, you can begin to shop for solar panels that fit your needs.

We went through the basic exercise and came up with these figures for current drain (amps) over a 24 hour day:

Amps Hours/used A-Hrs W-Hrs
Cabin lights (led) .50 A 3 1.5 19.2
Refrigeration 5 A 10 50 640
Anchor light .25 A 8 2 25.6
Electronics/VHF .75 A 6 3 38.4
Totals 56.5 723

56.5A-Hrs x 12.8 V = 723 W-Hr *1.2 divided by 4 hours sun a day = 216W of solar required.

After reviewing sizes and types - we decided on two Solarland 150W panels. We had the available space on board and the costs were in our budget. It was more energy than calculated but it gave us extra sould we add more equipment latter on.

We purchased the two Solarland 150-watt solar panels and a 25A charge controller on the Internet. The prices on the Internet are much better than those found at local marine stores. Several sources are available; all you have to do is search for "solar panels" on any search engine. We had to wait about 10 days to get the panel, but the savings were worth the wait.

Mounting and Wiring

It may be no easy task deciding where to mount a solar panel. The best areas for mounting a panel are usually aft: on an arch, on top of dingy davits, on top of the bimini, between two stanchions, or on a pole on the rail. Available with the flexible panels are kits that attach the panels to your canvas top. Keep in mind that flexible panels must have a firm backer board for they wil fail in a short period of time.Take your time and think it through. The best place depends on the configuration of your boat. The size of the solar panel(s) may determine the best mounting. Be sure that you follow instructions from the manufacturer and do not do anything that will violate the terms of their warranty.

We have dinghy davits and decided to mount the panels on a bar above the davits. The bar helps stabilize the davits as a side benefit. This worked out very well; the solar panels are about the same height as the bimini top. We had a bar fashioned in the right shape at a local shop that makes arches and bought hardware to form a triangle brace for the bar. The solar panels were attached to a mounting kit that could attach to the bar. The cost of the bar and attaching hardware was over $200, but the installation looks good and is very strong and is out of the way.

The wires from the solar panels to the batteries should be tinned marine grade. Ordinary automotive wire may look similar to marine grade wire, but after a few months in the marine environment it can suffer a loss of conductivity. A quality charge controller with settings for AGM or wet cell (flooded) batteries is a must to keep from overcharging the batteries. The positive lead from the solar panel charge controller must be fused to protect from over-current. If a battery monitor is not on board, give thought to installing one or purchase a solar charge controller with a meter.

Was it worth the cost?

After one cruise to the Abacos, the answer is a resounding yes. On sunny days, the batteries are charged by early afternoon. We only have to run the diesel engine to charge the batteries on cloudy days. The solar panel starts charging when the sun comes up. By 10:00 A.M. the batteries are well on the way to recovery from the previous night's use. Solar panels are the cleanest and quietest way to charge the batteries. We are very happy with the results.

Weekend cruisers and even day-sailors may profit from a backup way to charge the batteries. Outboard powered boats surely need an alternative way to charge their batteries. Boats on moorings could benefit greatly from a solar panel. It is a safety thing: VHF radios, anchor lights, bilge pumps all depend on a well-charged battery. Solar panels are sure to become more popular when sailors find out about their durability and efficiency in light of their declining cost.