Solar Boating 101: 5 Things to Know

Until recently, solar was not capable of severing the tie to shore power, so it was only functional for extending range, or for partial charging. But it’s now possible to produce a solar boat with reasonable speeds and accommodation that can continuously cruise without ever charging from the shore. Ever. Sustainable Energy Systems has been producing boats like this since 2012. As long as it is daylight our boats get enough energy from the sun to go, even on overcast and rainy days.

Here are 5 cool things about Solar Boats

1. All the advantages of electric boats

These include quiet, no fumes, no vibrations. This means easy conversation and the sounds of nature. It also means you arrive at your destination feeling energized and refreshed, rather than fatigued from hours of loud vibrations. Reliability is high and cost of ownership is low. How much is a season’s worth of fuel and engine maintenance? That is your savings every single year.

2. Solar boats are unlimited

Regular electric boats are inherently limited by their battery capacity and their efficiency. Their range is measured in hours, then you either have to return to your specialized charging equipment or fire up your generator. For a regular electric boat, range is the ultimate question, just like an electric car.

Solar boats are independent and off the grid. This means you don’t need to run power to your dock and/or can keep your boat on a mooring bouy. The sun will keep it charged and ready to go. It also means you can cruise literally anywhere.

3. Choose how to use the sun’s energy

Imagine for a moment you threw your batteries overboard. This means the available energy you have is real-time what the sun provides. All our boats can go 5+ knots directly from sunshine on a sunny day. On a cloudy day the boats can go 2-4 knots depending how thick the clouds are. See graph below.

When we went to Alaska on Wayward Sun in 2021 we mostly cruised this way. We adjusted the throttle to match the energy produced by the solar panels. This is called “solar sailing” and results in no net draw on the batteries. It was also during the covid pandemic and we were not allowed to go ashore in Canada, so this solar sailing cruising method suited us. We were underway all day, almost every day. The quiet motor made this a pleasant way to spend the days. We cruised 1400 miles without plugging into shore power.

Being cloudy most of the time meant out average speed was just under 4 knots. This is fine for some folks, but most of us like to go faster.

Most of us like to explore the cool places we go to. Every hour we spend exploring on land is and hour the batteries are charging. If we are underway for half the day and explore half of each day, then we can burn a whole day’s worth of sunshine in half a day, thus increasing average speed while still maintaining net zero draw on the batteries. Similarly we can be underway for a day then explore for a day. This solar sailing plus cruising method is sustainable forever and results in a reasonable average speed.

4. Batteries increase speed

Now imagine we put on our scuba gear and retrieve our batteries from the bottom of the sea. But oops, we just dropped our solar panels overboard. Our solar boat just became a regular electric boat. This means is has limited range, but we can go anytime, night or day, rain or shine. We just have to plan ahead to stop to charge. If you drive an electric car, you know you can greatly extend your range by slowing down. Same for an electric boat.

Most of our seamanship skills are sufficient to keep both batteries and solar panels on board, so we can utilize the advantages of both sunshine and battery power. And when we cruise most of us stop every few days for provisions and fresh cinnamon rolls. If we plug in to top off our batteries during the times we already at a marina anyway, then we can use that energy over the next few days to maintain a very reasonable cruising speed.

5. What about back up power?

You may have noticed that we have not mentioned a generator or a “range extender” of any kind. With a solar boat that is not necessary. The sun rises every day. You may have also noticed that most, if not all, electric cruising boats do rely on a range extender for any practical range. While that is an efficient way to burn diesel, we don’t think it qualifies as electric cruising. Our Townsend 34. Is the first, and perhaps only, electric cruiser that has comparable speed and range of a diesel trawler.

Summary

Solar boats do cost more up front. However, if you factor in the savings in fuel and maintenance costs, and the superior experience of electric power, the value is self-evident.