Solar Boating: Exploring the Proven Viability of Renewable Energy on Water

Solar boating uniquely blends the comforts of powerboating and the adventurous spirit of sailing, particularly when the wind is favorable. While powerboats often focus on speed, solar boats operate at speeds similar to sailing vessels. This is great news for those familiar with sailing, as both solar and sailboat enthusiasts optimize their journeys based on natural elements like tides and winds. Solar boating offers a fantastic way to harness free energy from the sun while enjoying a peaceful and exhaust-free experience on the water. Importantly, when the sun sets, a solar boat transitions to functioning like an electric boat; however, during daylight hours, even overcast ones, solar boats provide a reliable cruising experience without the risk of running out of energy.

In recent years, local innovators have designed and built numerous custom solar boats, pushing the boundaries of sustainable boating technology. Although innovation comes with risks—some ideas may not pan out—these pioneers are instrumental in discerning what works effectively, offering valuable insights for the boating community. Based on current performance reports, solar boating caters especially well to long-distance coastal cruising, particularly in the idyllic landscapes of the Pacific Northwest.

With a background in electronic product development, I installed my first electric marine motor nearly two decades ago, inspired to protect my young daughter from harmful carbon monoxide fumes. This experience ignited a passion that led me to establish a manufacturer of small electric outboard motors in the Pacific Northwest.

In 2014, I began supplying specialized electric racing motors to high school solar boat racing teams in California. One of these teams participated in the inaugural offshore solar regatta in Monaco, where I witnessed firsthand the elegance and performance of advanced solar racing boats. My initial impression was that while these racing vessels are stunning, they don’t compete with their high-speed combustion counterparts in terms of speed. While solar racing boats provide a safe and accessible racing experience, they are unlikely to participate in high-octane hydro races anytime soon.

Solar power does present certain advantages for lake boats lacking dockside recharging infrastructure and is ideal for activities like salmon trolling. That said, the most exciting application for solar boats lies in coastal cruising.

Sailors exploring the waters of the Pacific Northwest in the summer months often find auxiliary engines more useful than sails. If you’re someone who enjoys the warm sun on your skin during a cruise, you may well have noticed the high fuel prices at remote gas docks and the anxiety of fuel shortages. Conversely, solar boating offers a quiet, clean, and impressively reliable experience, featuring fewer moving parts for maintenance and a solid-state system. With solar power, you can refuel literally anywhere each day, and the cruising speeds remain reasonable even in less-than-ideal weather conditions.

In 2018, I developed my first solar performance modeling spreadsheet utilizing NOAA’s solar incidence models. This tool predicts all-day cruising speeds and daily ranges for any location worldwide, under different sky conditions, and with various combinations of boat hull design, battery sizes, motors, and solar arrays. My findings reveal that an optimally designed solar propulsion system can deliver performance equivalent to combustion propulsion for long-distance cruising on boats measuring less than 45 feet in length.

Using this data, I configured Swe Pea, an I-14 sailboat hull repurposed as a solar sailing craft. Swe Pea was ready just in time to participate in the inaugural Salish 100 cruise from Olympia to Port Townsend in 2019. The setup included a standard EP Carry outboard with a lightweight lithium battery, two 100-watt solar panels, and a solar charge controller. Without solar energy, Swe Pea would only have a range of 6 nautical miles; however, with solar power, she completed the full course while keeping pace with other wind- and gas-powered boats of a similar size, never once needing to recharge from the grid.

In fact, Swe Pea had even more endurance than expected. Midway through, we took a detour from the main group for a 28-mile trip starting at Blake Island. Navigating Rich Passage and Sinclair Inlet to lunch at Port Orchard dock and then passing Bainbridge Island through Agate Pass towards Kingston. That day’s conditions included intermittent sun and clouds early on, with thunderstorms, headwinds, and opposing tides from Agate Pass northward. While I felt some apprehension about lightning while out at sea, I never worried about running out of power. It was a delight to revisit the Port Orchard dock, despite its disrepair—nostalgia swept over me as memories of fishing here as a child came flooding back. Cruising under solar power offered me a peaceful journey (aside from the thunderstorm). I enjoyed listening to the ferry’s prop cavitating beneath me in Rich Passage and noticed seals and dolphins thanks to their breaths. The sound of leaping salmon signaled their activity, and a friendly seagull came to greet me without leaving any mess. I was thrilled to confirm that a balanced solar propulsion system indeed alleviates the range anxiety typically associated with pure electric vessels.

Throughout my adventures, I’ve gathered data on numerous small and larger solar boats, including my own Sunnyside, a 14-foot, 1,000-pound camp cruiser originally a C-Lark sailboat. Sunnyside boasts a proven daily range of up to 40 nautical miles on sunny days and approximately 30 miles under overcast conditions. It’s worth noting that cloudy skies can reduce solar generation potential to about 25% compared to sunny days; however, even with reduced solar power, Sunnyside can maintain a speed of 3 knots, only slightly down from 4.2 knots on fully charged days.

Two more local solar boats, Wayward Sun and Electric Philosophy, were designed by Devlin and built with impressive performance specifications by their owners. Wayward Sun is a 27-foot monohull originally intended as a day boat but became the first solar-powered vessel to traverse the entire Inside Passage—an extraordinary feat considering the pandemic’s travel restrictions. Wayward Sun achieves comparable performance to smaller combustion-powered displacement boats, reaching a top speed of 6.5 knots while cruising at 4.5 to 5 knots with solar energy, even under overcast skies.

Electric Philosophy, highlighted in the November 2021 issue of 48° North, is a 40-foot catamaran capable of recharging more quickly from her expansive solar array than from shore power. She maintains a leisurely cruise speed of 6 knots, but can increase her pace if desired. Since her launch in 2021, she has covered thousands of nautical miles, including a round trip to Alaska. Notably, during an excursion featured in the magazine, the owners had sailed for three months without needing to connect to shore power for charging—illustrating the independence that solar cruising can offer.

Wayward Sun and Sunnyside were both designed with minimal battery capacity, encouraging their skippers to make real-time use of solar power during daylight hours. This budget-conscious design approach minimizes costs, as batteries can be a significant expense. I relish the challenge of adjusting my power flow to the motor depending on the solar output—ramping up to 100% throttle at midday, then tapering off in the evening. This method isn’t for everyone, but it allows me to maintain a 100% state of charge in my battery. On average, Sunnyside can cruise at 3.7 knots on sunny days, which is commendable for a boat of her size.

In contrast, Electric Philosophy has a larger battery bank to support higher speeds, allowing for longer cruising intervals before needing to recharge. These examples—14-foot, 27-foot, and 40-foot vessels—demonstrate the practical capabilities of solar boats across various sizes and hull types.

Here’s a concise summary of key insights about modern solar-powered cruising boats:

• It’s evident that solar technology matches the performance of many combustion-powered boats for displacement cruising speeds. Daily range, typically estimated by multiplying cruising speed by roughly 10 hours, favors combustion-powered boats. However, in terms of upper range limits defined by fuel capacity and consumption, solar boats excel with an essentially infinite range.
• While consulting an expert is beneficial when designing your own solar system, mature components are now available in various sizes, making it feasible for anyone to take on this exciting venture.
• Onboard solar panels cost significantly less than an equivalent battery bank, making solar boats more economically viable than pure electric vessels. For instance, Sunnyside’s full system—including motor, battery, solar panels, charge controller, monitoring tools, and remote controls—comes to around $2,750 at retail prices. In contrast, constructing a functionally comparable electric boat without solar assistance would nearly triple the cost, necessitating a greater battery capacity and a robust dock charger. My calculations indicate that well-designed solar boats can be built at costs similar to those of combustion-powered vessels.
• Solar boats operate with an electric drivetrain, which modern solid-state systems require less maintenance and are more dependable than traditional combustion engines. Lithium battery banks, designed for solar-powered systems, often last well over a decade and are affordable when replacements become necessary due to their lower capacity requirements. Furthermore, solar energy eliminates fuel expenses while cruising.

So, is solar-powered cruising the right choice for you? The benefits of solar boating are particularly appealing to those who enjoy displacement speeds and often embark on long, remote journeys where refueling can be costly, inconvenient, or even impossible. Moreover, solar day boats attract those who moor at buoys or private docks without access to electric power for maintaining battery levels. If you’re an aging sailor, you might miss the thrill of a fast sail but will appreciate the simplicity and ease that come with solar-powered journeys.

If you’re intrigued about switching to solar propulsion, consider the following: the timeline largely depends on your willingness to be a trendsetter. Presently, well-designed solar boats are still custom-built, featuring long design-build times and associated costs. In essence, you can’t simply purchase one and set sail the next day. However, if you’re enthusiastic about the technology right now and have the resources, the components for solar boating are readily available. For those preferring a stock design with most challenges resolved by seasoned builders, expect to find options in a few years as an early adopter. If you’re not tech-savvy but appreciate the benefits of solar energy, waiting a few years will allow you to witness the development of proven mass-produced models, likely within the next 6-8 years. Those who value sustainable energy and are cautious with finances can find the first used solar boats in 10-12 years.

Having embraced solar-powered cruising alongside countless other small vessels over the years, I confidently assert that this mode of propulsion offers rewarding and independent experiences. Notably, the advancements demonstrated in this article showcase the extensive potential of solar boating. The freedom offered by solar-powered cruising is comparable to traditional sailing, with the significant advantage of more predictable performance, even in variable weather conditions.

To explore long-distance remote solar cruising further, consider attending seminars at events like the Port Townsend Wooden Boat Festival or the Seattle Boat Show. Sam Devlin Designs has matured several solar boat concepts, while David Borton at Solar Sal offers solar day boats on the East Coast. My company, dedicated to small electric motors, is enthusiastic about sharing knowledge on solar boating and I am excited to discuss possibilities with interested customers using my solar performance model.

The path for any new technology is often riddled with challenges, but long-distance solar cruising has successfully navigated these early stages. Keep your sights set on the future of solar boating—now is the time to embrace this innovative form of maritime adventure.

Recently, a friend and I boarded Sunnyside, my 14-foot solar-electric converted sailboat, for a day-long journey to circumnavigate Vashon and Murray islands—a total of 38 nautical miles. While Sunnyside can cruise at an average of 4 knots for ten hours on a sunny day, this projection leaves little room for error. Thus, we strategically planned our trip, accounting for an additional 5-mile reserve by utilizing the tides, and I packed extra fully-charged batteries, just in case.

Setting off at 8:00 a.m. from Point Defiance boat ramp, we navigated up Colvos Passage on the outgoing tide and crossed the northern end of the island at slack tide. Our goal was to ride the incoming tide south and return to Point Defiance by 6:00 p.m. However, our day did not unfold as planned. Smoke from wildfires diminished our solar output by about 10%, and we couldn’t resist taking a fishing break that delayed us past Point Robinson Lighthouse.

Though we could have anchored for the night at Portage Bay, we opted to press on despite accumulating risks. In retrospect, that might not have been the best decision; I wouldn’t hesitate to anchor if given the chance to do it again. Regardless, we continued our journey and arrived at Point Defiance right at dusk, significantly later than we originally intended.

It was an exhilarating adventure, but it underscored several important lessons. First, when deviating from your plan—such as stopping to fish—it’s crucial to consider your options and potential changes, like reaching port before darkness. Although we had sufficient charge for our return, unexpected weather hindered our journey. Better preparation for the evening winds would have informed our decisions throughout the day. Moreover, as wildfires become increasingly common in the summer, tracking air quality should become part of our planning as well.

Ultimately, maintaining safety can occasionally conflict with intentions; I was influenced by a desire to complete the circumnavigation, but knowledge prompted self-assurance regarding our choices. My main takeaway remains simple: prioritize the experience—this adventure was truly worthwhile and resulted in lasting memories.

Joe Grez brings nearly 40 years of experience in product innovation and holds 47 patents. His company, PropEle Electric Boat Motors, manufactures the ultralight EP Carry electric outboard in Washington State. For more information, visit www.electricpaddle.com. By the time you read this, he will have solar sailed another Salish 100.