Is solar the future of boating? This engineer turned boat-builder says yes

KINGSTON, New York — Behind the diesel-powered Rip Van Winkle party boat, across from Mathilda, the decommissioned 19^th-century tugboat, and about 1,000 yards upriver from the rusted husk of a retired New York City hospital barge named the Lila Acheson Wallace, you will find the Solaris, pitching softly on the placid Rondout Creek, a tributary of the Hudson River.

It’s an elegant boat, white and cream-colored with wooden accents, its spotless 45-foot hull a stark contrast to some of the older vessels surrounding it at the Hudson River Maritime Museum, where it was built and has been docked since 2018. But the Solaris stands out for another reason, too: the shimmering solar panels that adorn its roof.

Unlike most boats, the Solaris does not have a gas-powered engine. Nor does it have the ability to plug into a charging station and replenish its batteries. Instead, it gets all of its energy from a 6-kilowatt array of solar panels and 32 lead-acid batteries, a combination powerful enough to propel the boat 100 miles downriver to New York City without a second thought.

The Solaris is the first Coast Guard–approved solar-electric boat in the nation, and that approval means that it is allowed to operate commercially. Dozens of times each week between May and October, it carries up to 24 people at a time on historical and environmental tours of the Hudson River and the Rondout Creek tributary.

But David Borton, the boat’s creator, has a much more ambitious vision for solar-powered boats.

“My goal…is to replace every fossil boat with a solar-electric boat,” Borton said with a laugh. ​“Now that’s a ridiculous goal because that’s not going to happen, but that’s the direction that we are moving in.”

It’s certainly an unconventional view.

Ships, boats and other marine vessels are a major source of air pollution and planet-warming carbon dioxide emissions. Thanks to prodding from policymakers, the private sector is starting to take steps to limit both. Larger ships, like those that haul 90 percent of the world’s goods and account for most maritime CO₂ emissions, are expected to switch out their bunker fuel for alternatives like green ammonia, methanol or biofuels. Meanwhile, many electric boat startups are vying to replace smaller fossil-fueled boats with what are essentially aquatic electric vehicles — powered by lithium-ion batteries and fueled up at charging stations.

But the idea of running boats on solar energy has gotten a lot less attention. In Borton’s view, that’s a mistake. He thinks solar is an underappreciated power source for boats — one that can play a meaningful role in transitioning the entire maritime sector away from fossil fuels.

Making the Solaris

Borton has spent nearly two decades designing, building and captaining vessels that run on the power of the sun.

He built his first solar boat back in 2005 and has since built or designed nine more. In 2013, he retired from his decades-long career as a professor of solar engineering at the Rensselaer Polytechnic Institute to focus full-time on the endeavor. He founded his company, Solar Sal Boats, the following year.

After a few successful demonstrations of the technology, including a solar-powered cargo run up the Erie Canal, Borton realized that for his company to scale up, he’d have to get the blessing of an outside source.

“I really needed Solaris as a Coast Guard–inspected boat so that if anyone says, ​‘Solar boats aren’t serious,’ I can say, well — ask the Coast Guard,” he said.

Not only does the approval lend Solaris some gravitas, but it also legally allows it to carry more than six paying passengers, Borton said, making the vessel a viable replacement for things like commercial tour boats.

But Borton is not a Coast Guard–recognized boat-builder, so he needed help to carry out his plan. That brought him to the Hudson River Maritime Museum, which has a wooden-boat-building program helmed by renowned local woodworker and boatwright Jim Kricker.

“David approached us, and he knew about Jim and…his incredible experience and expertise. And he said, ​“Would you like to bid on the building of my Solar Sal?” Lisa Cline, the museum’s executive director, told me. ​“And we said, ​‘Of course we’d like to bid on it.’”

After several years of Kricker and team toiling away on the Solaris in a barn on the museum’s campus, the staff grew attached. In 2018, as the project wound down, Cline recalled asking the museum’s board of directors what felt like an increasingly obvious question: ​“Shouldn’t we keep this boat?”

So Cline pulled together a business plan, ran it by the board and then brought the idea to Borton. He was enthusiastic. More people than he could have imagined would be exposed to solar boats this way, and Kingston is just over an hour south of his home in Troy, New York, meaning he could easily show off his handiwork to potential customers for future Solar Sal boats. Plus, as a former professor, Borton appreciated that the vessel would serve as a ​“floating classroom,” helping educate the public about local history, ecology and, of course, the merits of solar power.

Borton and the museum hammered out a deal, and as the summer of 2018 came to a close, the Solaris hit the water for the first time. Since then, the boat has been a huge success for the museum, Cline said, estimating that somewhere between 25,000 and 30,000 passengers have been on board over the years. (Kingston’s population is just under 24,000.)

“She is very popular,” Cline said. ​“She’s like a little ambassador for us.”

Solar sailing

One of the first things passengers hear upon boarding the Solaris is a primer on how its solar-and-battery system works. It’s an attempt to preempt one of the most common questions about the boat: What happens if the sun doesn’t shine?

“To me, that’s a non-question,” Borton said. But perhaps it’s more accurate to say it’s a settled question, or at least one for which he has a compelling answer. In 2021, Borton and his son Alex took a different Solar Sal boat — the Wayward Sun — on the first-ever solar-powered journey through the cloud-shrouded waters of the Pacific Northwest’s Inside Passage. The 1,400-mile voyage took 20 days and is Borton’s strongest evidence yet that solar boats work just fine when it’s overcast.

Decades of technological progress have made it such that solar photovoltaic systems, whether they’re used to generate electricity for the grid or power a boat like the Solaris or the Wayward Sun, can still produce practical amounts of energy on cloudy days. Those same technological forces have also made solar far cheaper than when Borton first became interested in the technology five decades ago, during the 1970s oil shock. Then, the price per watt of a solar panel was around $100, compared to an average of just 27 cents today — but Borton believed in the technology nonetheless.

“In 1974, I couldn’t buy gasoline, and I looked around at all the sources of energy for the planet, and solar is the only one that makes sense.”

Today, solar is the fastest-growing source of energy in the U.S., with photovoltaic panels dotting rooftops and blanketing fields around the country. But the boating world has yet to embrace the technology as enthusiastically. To date, Solar Sal has sold just four boats — including Solaris.

One hurdle is that solar boats remain more expensive upfront than comparable gas-powered models, though Borton says that the initial investment is offset by low maintenance costs and free fuel.

Across their ​“life-cycle, they are less expensive,” Borton said. ​“A main contributor to that is fossil needs to have oil changes. And if you bring it out of the water [for maintenance], you have to drain the water out of it. You’ve got to change the gear oil. You’ve got to keep putting gasoline in it.”

He’s also made some progress on lowering the sticker price of a Solar Sal boat. Most of Borton’s creations have been handcrafted wooden vessels, but the latest Solar Sal model is fiberglass. That allows the company to use molds to produce the boats — a much less labor-intensive process, and an important step toward raising production volumes and reducing costs. On the Solar Sal website, the Wayward Sun, a wooden boat, is listed for nearly $300,000; the new fiberglass Solar Sal 24 is listed at $135,000. The company is about to finish up its third fiberglass boat.

Right now, the hulls of the fiberglass boats are made in Florida, and then the boats are completed by a Maine company called Belmont Boatworks, but Borton says the plan is to eventually move all production to New York. Ideally, he’d build a facility that is capable of producing hundreds of boats per year — Borton is trying to lock down both customers and potential manufacturing partners to make that vision a reality.

Besides the upfront cost, another barrier to the widespread adoption of solar boats is speed. They’re much slower than most gas-powered vessels: Borton’s boats top out at around 7 knots. That’s not fast enough to, for instance, tow a wakeboarder — or keep up with a seafaring container ship. This presents some limitations on what solar is practical for, though you won’t hear Borton ruling out any use cases; he told me he’s working on a design for a 100-ton cargo vessel for a potential customer.

But for certain applications, like moving smaller cargo loads in canals, which typically have lower speed limits, the gentle speed offered by solar boats is sufficient. And for taking people on serene tours of local waterways — like the Rondout Creek and the Hudson River — it’s just right.