You may have heard stories from wizened sailors of rusted or cracked first-gen solar panels that couldn’t even keep a light bulb on for an hour. However, over the past decade, solar panel technology and manufacturing has improved by leaps and bounds.
Additional, solar panels are much cheaper and more powerful. Best of all, they are both sturdy and flexible, allowing them to survive all the pitches and rolls that come with a life on the high seas. Because of these improvements, more and more sailors are inviting solar on board.
The way we like to use photovoltaics on a sailing boat is to recharge the batteries, phones, and tablet, keep the drinks chilled in the fridge, and enjoy lights at night without having to turn on the noisy engine. Your neighbors in a peaceful cove where we’ve dropped anchor will appreciate the extra peace and quiet.
Where to start? First, buy seawater resistant panels. The market is swamped by solar panels which promise you suitable for Boating or Yachting. Some panels offered in illustrated catalogs by the usual ship-chandlers are not suitable for open oceans. A label like ‘Yachting’ doesn’t mean it resists salt-water. If in doubt, ask the manufacturer!
We bought flexible Solar panels for two reasons. First, they are light, at least half the weight of a framed panel. Second, they are only 4 mm thick, compared to an inch or more to the framed ones.
One of the biggest challenges of incorporating solar panels on a boat is finding the space to install them. While solar panels got more powerful per face over the past decade, they still take up space.
The best option will depend on the dimensions and layout of a boat. Obviously, the smaller the boat, the more difficult it will be to find a spot for panels. Some sailors have solved this problem by crafting overhead structures or racks on which to place panels. Others have fixed solar panels on the sides of the boat, embedded them in the deck, or purchased foldable panels they can take out and reposition around the ship.
We considered an overhead structure at the stern of the Yacht as well. In our opinion it’s everything but easy on the eyes. They say, there’s no arguing about taste. A rack at the stern with a solar panel reminds me of a big spoiler mounted on a car by a bully of the village.
Anything that blocks the sun’s photons from hitting the panels can dramatically lower the energy the panels produce. Between mast, sail, spreaders, boom, and the radome, solar panels get hit with energy-dampening shadows. To make things even more complicated, the shadows will change depending on the heading and location of the boat. Last but not least, consider the heat that the black panels develop in full sunshine. To be sure overheating does not damage them before time, conduct away the thermal energy.
We installed the panels in a way that avoids the most drastic shadows. If necessary, we consider purchasing more solar panels to offset any restrictions that may come from unavoidable shadows.
For a start, I installed two panels on the deck-house, and two more on the spray hood fixed by Velcro tape. The ones on the steel decks-house remain even in pure sunshine at a moderate temperature, because of the steel underneath. The others on the spray hood get rid of the heat through the canvas. In both cases, the panels are well above the water and will not submerge in seawater.
According to the manufacturer, the daily solar power in Amps as a rough estimate is dividing panel wattage by 3 (Mediterranean), by 4 (Baltic- or North-Sea) and 5 in spring or fall in the northern hemisphere.
Those numbers assume a “good” solar day with a full-time load. Fully charged batteries – no solar output!
At the end of the season 2018, I fully confirm these data. Between May and late September, on average Amps per day equal total panel wattage divided by 4 was easy to achieve. On the Baltic, power output increased, when we moored the Yacht west-east or vice versa and fixed the boom to the north. Less shadow more power.
As a matter of principle, solar energy does not always work so well. There are days of pure sunshine, but heading south, the shadow of the foresail blocks most of the photons. Instead of full power, only three or four charge the batteries.
I like to mention one more important point. Technology has improved, and it deems the installation of a charge controller essential. The keyword is MPPT technology that makes the maximum use of energy.
MPPT stands for Maximum Power Point Tracking. The central problem addressed by MPPT is that the efficiency of power transfer from the solar cell depends on both the amount of sunlight falling on the solar panels and the electrical characteristics of the load. As the amount of sunlight varies, the load characteristic that gives the highest power transfer efficiency changes. MPP optimizes the system when the load characteristic changes to keep the power transfer at the highest efficiency. MPP is the process of finding this point and keeping the load to suit the system.
We installed two Victron MPPT 75/15 controllers, added a VE.Direct Bluetooth Smart dongle to set the parameters via mobile or tablet and to monitor readings like power, voltage, and amps. The Victron provides information of voltage and amps on the solar side and the state of charge of batteries. It constantly optimizes the current-voltage characteristic or I–V curve.
I am delighted to say the system works very well. Even on a dull day, there is a constant charge going to the batteries, and when the sun shines, albeit that is occasionally in the Baltic, the charge level increases remarkably. The benefit of the MPPT technology in the charge controller is to make the best use of whatever available current is produced by the solar panels.
Even on the dullest of days, the batteries were receiving a healthy charge, and with never during the whole four months did they fall below an 80% state of charge. It was fascinating to watch the daily output on the tablet as the batteries went from their partially discharged state in the early morning to a full charge later on.