Solar Update - Some Real-World Benefits of Installing Solar

This has been a very exciting year for solar in the marine industry. Many boaters have embraced the technology and, now, have had an entire boating season or two to discover the real benefits of installing flexible solar panels.  In this article, we are going to look at what is involved in a typical installation and then share some feedback from boaters who are using solar panels.

Installing Solar.  If you are thinking about installing a solar array on your boat, the first thing you have to do is figure out how much power you use in a typical day. Then you can decide whether you want the solar panels to provide all the power or to simply offset your daily requirements. The largest DC load is refrigeration, which can draw 50–125 amp-hours per day. Many boaters install enough panels to offset the fridge or stay at anchor an extra day. Once you have determined the daily amp-hours required, you can calculate the size of the solar array. The conservative rule is 20 percent of wattage equals the daily Ah output. For example, a 250 watt solar array x 20 percent = 50 Ah. If you are more optimistic, you can use 33%, a 250 watt solar array x 33 percent = 83 Ah. 

Installing on Canvas. One of the big benefits of flexible solar panels is that they can be installed on canvas. You can choose to install them permanently or temporarily. The two most popular mounting options are sewing zippers onto the solar panel and canvas, or gluing velcro on the panel and the canvas. Flexible solar panels, unlike their predecessors, do not require any space between the actual panel and the surface so they can even be affixed directly to canvas or a hardtop. Some boat builders glue them directly to the hardtop, but we prefer snaps so they can be removed in the off-season.Solar panels come with a short pigtail lead, terminated with an MC-4 connector. These connectors provide a good connection and have a weatherproof seal.

How Many Panels do You Need? The next step is to decide where you want to place the panels on your boat. Luckily, flexible solar panels come in a number of different sizes and shapes, both square and rectangular. This allows you to maximize the wattage based on the space you have available. For boaters who have limited space, be creative in the arrangement of the panels to get as much wattage (i.e. potential amp-hours) as possible. For boaters with a large bimini, power boaters with a flybridge or modern sailboats with a wide beam, getting the wattage you need isn’t too hard. We commonly see 400 to 500 watts of flexible panels installed.

The price for a 100W solar panel can range from $300–$1,500 and, in this case, you really do get what you pay for. Many off-shore panels use inexpensive PVC for the backing which can yellow and crack with our seasonal climate. As well, the output of the less expensive panel may be close to 100W in the first year but may drop significantly the following year. Unlike these mass-produced panels, the high-end panels are each made by hand and individually tested before they leave the manufacturing plant. In most cases, they ship with a five-year replacement warranty.

Look For A Bypass Diode. Also, double-check that the panel you choose has a bypass diode, which will prevent a shaded cell from de-powering the entire panel. These diodes effectively split the panel into two independent power sources. Without a bypass diode, one shaded cell can prevent the entire panel from producing any power.

The final step is wiring. When choosing the right size of wire, make sure to consider both voltage drop and amps. For most installs, the panels should be interconnected with gauge 10 wiring to ensure that you harness close to 100 percent of the solar output. The solar panel comes with a short pigtail lead, terminated with an MC-4 connector. These connectors provide a good connection and have a weatherproof seal to withstand the outside elements. We recommend that each panel has its own controller and that you choose the controller based on your battery type (flooded, AGM, gel, etc.) Fuse each panel directly at the battery. Solar panels are like battery chargers and should NOT be connected at a DC panel.

Monitoring.  In order to appreciate the output of the solar array, you should also install a solar monitoring device to measure not only the output current of the array at any time but also the daily amp-hour production. Even though many boats are equipped with a battery monitor, a battery monitor only provides you with the net effect at the batteries. This net effect, is the difference between the charge going into the battery (e.g. alternator, battery charger, solar array, etc.) and the draw going out of the battery (e.g. lights, inverter, water pump, fans, stereo, etc.) A good solar monitor will tell you how much current is going into the batteries at any given moment plus the daily cumulative benefit from the solar array. 

Feedback - This year we had the opportunity to speak to a number of boaters, who had installed solar, and would like to share their feedback with you:

Grand Banks 36 – (3) 125W Panel - “Our boat did not come with a generator, we had been discussing solar for some time but the expense was a huge barrier. We often boat at a remote, powerless outstation and would end up plugging into our neighbour’s boat. We are not winter boaters so solar was a perfect solution for us. For the first time, we stayed at the outstation for two weeks with no concerns, the solar panels kept up with our consumption.”

Beneteau 51 – (4) 100W Panels - “We have a total array of 425W, with each panel wired to its own controller and then along a dedicated line to the battery bank. The panels are then monitored by a metre and we have seen up to 20 amps being generated by mid-day sun. It’s fun to watch the energy rolling in. The panels have provided a quiet and automatic means to ensure our house batteries remain charged especially when we are off the grid for several days at a time. We don’t miss our diesel generator at all.”

Cruiser 28 – (1) 140W Panel - “Our fridge would often run on low and then shut down during the night. The boat does not have enough space to add additional batteries and there is no generator. Installing just one solar panel kept the batteries charged and the fridge running.”

Hunter 45 – (3) 125W Panels - “Solar hasn’t changed the way we boat, but it has made it a lot quieter. We always liked to anchor, but before solar we had to run the generator daily to sustain battery levels. In the last two years we ran the generator about 30 hours per year, this year it was only 7 hours. The longest we were at anchor without running the generator was four days. The batteries were draining a little bit more every day progressively. We did find that when we moved the boom to minimize shading on the solar panel, the rate of charge increased dramatically. It was also amazing how long the charging day was even on overcast days.  I would definitely recommend solar panels on a boat. If there was only some way to use the excess solar energy to heat water, that would be very beneficial.

Sail 33 – (1) 125W Panel - “We were able to use our fridge throughout the day without having to motor. We ordered the solar panel with the black backing (instead of the white or clear) and installed it on top of our dark blue dodger so it virtually disappears. More than once, when we mentioned to guests that we have solar, they asked “where?” The solar cells are black so placing them on a black flexible panel seems to reduce the checkerboard effect. This summer we did not have to plug into shore power which removed the hassle of pulling out cords and connectors.”

Sail 37 – (1) 100W Panel - “Installing solar has allowed us to go a long weekend without running the batteries down below 70 percent and we did not need to plug into shore power. We installed the flexible panel on top of the dodger so it is out of sight and out of the way. However, it is subject to shadows from the mast and boom. It was important to us to choose a panel that would keep working even when a few cells where in the shade.”

Solar is a great solution for boating in the Pacific Northwest as the summer cruising months often produce sunshine from 6:00 a.m. to 8:00 p.m. It’s refreshing not have to worry about power anymore. If you are a power-boater, solar will either replace a generator or reduce the time you have to run your generator. For sailors, solar will allow you to just sail with no need to motor or motor-sail to your next destination in order to recharge your batteries. 

About the author: Jeff Cote is the owner of Pacific Yacht Systems, a full service shop delivering marine electrical and navigation solutions for recreational boats. Visit their website and blog for info and articles on marine electrical systems, projects and more: