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

Solar boating uniquely combines aspects of powerboating and sailing, but it bears a stronger resemblance to sailing, particularly when there’s wind. Much like powerboating, solar boats offer comfort and ease of use, yet their “fuel” comes from the sun, refueling daily for free. Power boaters often seek higher speeds, while solar boaters typically achieve speeds comparable to sailboats. This similarity means that just as sailors plan their journeys around tides and winds, solar sailors should also consider these factors when setting out. By utilizing natural, free energy in real-time, solar boating provides the added benefits of a quiet, exhaust-free experience—one that’s not only enjoyable but also environmentally friendly. A crucial point to note is that when daylight fades, a solar boat might function like an electric boat with certain range restrictions. However, as long as there’s daylight—rain or shine—stranding is not a concern for solar boaters.

Over the past decade, numerous custom solar boats have been designed and built by innovative minds. Innovators play a vital role in testing new technologies and sharing their results, contributing to the collective knowledge and progress of solar boating. This process, while risky, helps distinguish effective solutions from unproven concepts. Current performance data indicates that solar boating appeals to certain boating segments, particularly in the Pacific Northwest, where long-distance coastal cruising is prevalent.

Having dedicated my career to electronic product development, I installed my first electric marine motor nearly twenty years ago to protect my young daughter from carbon monoxide fumes. This decision sparked my passion for electric boating, and I now lead a company in the Pacific Northwest that manufactures small electric outboard motors.

Thanks to this background, in 2014, I began supplying custom electric racing motors to high school solar boat racing teams in California. One team participated in the inaugural international offshore solar regatta in Monaco, allowing me to witness the performance of advanced foil-borne solar racing boats firsthand. My initial observation was that, despite their beauty and elegance, solar racing boats lack the speed of their high-octane counterparts. Solar boat racing presents a safe and accessible class event, yet solar boats are unlikely to compete in unlimited hydro races anytime soon.

There are certain advantages for solar lake boats where dockside recharging infrastructure is absent, and a solar kicker motor is ideal for salmon trolling. However, the most exhilarating application for solar boating lies in coastal cruising.

Anyone familiar with cruising a sailboat in the Pacific Northwest during July and August knows that the auxiliary often sees more action than the spinnaker. Those cruising with displacement power boats understand the extra costs associated with fuel at the gas dock, and when venturing into remote areas, gas docks can be scarce. Fuel filters can clog, engines may develop issues, and the unpleasant plume of diesel smoke can dull the morning sun while you sip your coffee. In contrast, solar boating offers a clean, quiet, and highly reliable means of electric boating, with fewer moving parts and a solid-state system that minimizes maintenance and lubrication concerns. Moreover, solar boats refuel daily, literally anywhere on Earth, making them incredibly efficient. Even in less-than-ideal weather, cruising speeds remain reasonable in summer months with solar power.

In 2018, I developed my first solar performance modeling spreadsheet utilizing NOAA’s solar incidence model. This tool can predict cruising speeds and daily ranges based on factors like location, weather conditions, hull resistance, battery capacity, motor size, and solar array specifications. It has become evident that a well-engineered solar propulsion system can match the performance of combustion propulsion for long-distance displacement cruising on boats under 45 feet in length.

I utilized this modeling tool to configure Swe Pea, which is based on a hot-molded I-14 sailboat hull with a previously damaged transom, transforming it into a solar sailing vessel. Swe Pea was ready just in time for the inaugural 100-mile Salish 100 cruise from Olympia to Port Townsend in 2019. The system was straightforward, employing a standard EP Carry outboard motor with a lightweight 6-pound lithium battery, two 100-watt solar panels, and a solar charge controller. Without solar assistance, Swe Pea’s battery provides a range of only 6 nautical miles. With solar, however, Swe Pea successfully completed the entire journey while keeping pace with other wind and gas-powered boats of a similar size, never requiring a recharge from the grid.

In fact, Swe Pea had more potential. Mid-way through the trip, Swe Pea and I diverged from the group for a 28-mile adventure that started from Blake Island, traversing Rich Passage and Sinclair Inlet to the Port Orchard public dock for lunch, then continued behind Bainbridge Island through Agate Pass and up to Kingston. The day’s conditions were variable—intermittent sun and clouds early on, followed by thunderstorms, headwinds, and opposing tides as we approached Agate Pass. Despite my concerns about potential lightning on the water, I remained unconcerned about range. The joy of docking at Port Orchard brought back fond memories of childhood fishing trips. Solar power ensured a peaceful experience (barring the thunderstorm), allowing me to hear the ferry’s prop cavitation through my hull and marvel at the sounds of seals, dolphins, and jumping salmon. A seagull even landed on the bow to greet me, without leaving any evidence of its visit. On this trip, I was pleased to confirm that a balanced solar propulsion system can effectively eliminate the range anxiety often experienced by pure electric boats.

To date, I have gathered data from various small and larger solar boats, including my own Sunnyside, a 14-foot, 1,000-pound camp cruiser built from a C-Lark sailboat hull. Sunnyside boasts a proven daily range of up to 40 nautical miles in sunny conditions and around 30 nautical miles on overcast days. Note that cloudy skies can reduce solar generation to approximately 25% of sunny potential. However, on Sunnyside, decreasing solar output from full capacity to a quarter of power consumption only drops actual speed from 4.2 knots to 3 knots.

Two other local solar boats—Wayward Sun and Electric Philosophy—each showcase impressive performance as designed by their owners. Wayward Sun, a 27-foot monohull originally constructed as a day boat, became the first solar boat to navigate the entire Inside Passage. This achievement is noteworthy considering that pandemic restrictions prevented her crew from stepping onto Canadian land. Her performance rivals that of many combustion-powered displacement vessels, especially smaller cruising sailboats, achieving a top speed of 6.5 knots and a solar cruising speed of 4.5-5 knots, despite facing overcast weather during her journey.

Electric Philosophy, featured in the November 2021 issue of 48° North, is a 40-foot catamaran capable of recharging more quickly from her extensive solar array compared to mains at the dock. She can cruise leisurely at 6 knots, with the capacity to increase speed based on her crew’s preferences. Since her launch in 2021, Electric Philosophy has covered thousands of nautical miles, including a round trip to Alaska. During a three-month cruise, she never required shore power, demonstrating her independence from traditional fueling methods.

Both Wayward Sun and Sunnyside were designed with minimal battery capacity, challenging their operators to use real-time solar power effectively throughout the day. This approach is cost-effective, as batteries can be expensive. I personally enjoy the process of adjusting the power flow to the motor to align with solar power throughout the day—starting at 100% throttle in the morning, reaching midday levels, then tapering off at dusk. This method may not suit everyone, but it allows me to maintain a constant state of charge in the battery. Alternatively, I sometimes allow a little battery usage in the morning to continue charging throughout the day, aiming to end the day with the same charge level as I began. With this strategy, Sunnyside averages an impressive speed of 3.7 knots on sunny days for a 14-foot displacement hull.

In comparison, Electric Philosophy features a larger battery bank, providing the ability to cruise at higher speeds with necessary breaks for recharging. These examples, representing various sizes and hull types (14 feet, 27 feet, and 40 feet), illustrate the practical capabilities of solar boats.

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

• With instances like these, it’s evident that solar performance is comparable to many combustion-powered vessels in terms of displacement cruising speeds. Range can be defined in two ways: daily range—which can typically be estimated in the summer by multiplying speed by approximately 10 hours of run time—and overall range, derived from a boat’s fuel capacity, consumption, and mileage. By this broader definition, solar boats take the lead due to their almost infinite range.
• While it’s advisable to consult with experts when designing a solar boat system, numerous mature components are available in various sizes, enabling almost anyone to build a well-founded solar vessel.
• Onboard solar panels are far more affordable than an equivalent battery bank. Consequently, solar boats often save on upfront costs. For example, the comprehensive system for Sunnyside, including the motor, battery, solar panels, charge controller, monitoring tech, house bank, remote steering, and throttle, costs approximately $2,750 at retail. This investment is just slightly higher than that of a comparable combustion setup. If Sunnyside were a purely electric boat with no solar capability, the expense could nearly triple due to the necessity for enhanced battery capacity and a powerful dockside charger. My calculations indicate that well-designed solar boats can be constructed at costs equivalent to those of traditional combustion-powered boats, especially when accounting for economies of scale.
• A solar boat operates on an electric drivetrain, which modern solid-state electric systems require less maintenance compared to combustion setups. Additionally, lithium battery banks used in solar systems typically last over a decade, and their smaller capacity can make replacements more economical. Not to mention, solar technology allows for elimination of fuel costs during cruises.

So, is solar-powered cruising right for you? The appeal of solar-powered cruising is particularly strong among those who prefer cruising at displacement speeds and those often undertaking long, remote passages where the need for refueling can be inconvenient, costly, and at times even impossible. It is ideal for individuals disinclined towards the breakdowns and maintenance associated with traditional combustion engines. Solar day boats are also appealing to boaters who anchor on buoys or at private docks without access to power, ensuring they can maintain a full charge. For sailors who find themselves aging, the thrill of a brisk reach in the wind may diminish, but the joy of not having to navigate a bustling foredeck to hoist sails can provide a newfound freedom.

If this concept intrigues you, the next question is how soon you can switch to solar propulsion. Currently, well-designed solar boats are often custom-built, which translates into long design and build times, along with associated costs. In simpler terms, you can’t just walk into a store and buy one to take home. If you’re keen to be an early adopter and have the budget to do so, solar technology and components are readily available. For those who appreciate tech innovations but prefer a stock design with previously resolved issues, reputable builders will likely offer options in the coming few years. If technology isn’t your forte, you might want to let some history unfold before you make a move. Now that solar boating has been effectively demonstrated across various boat sizes, mass-produced options should start emerging in 6-8 years. Those who value the benefits of natural-energy cruising but lack the budget for a new vessel will likely find used solar boats entering the market in about 10-12 years.

Having camp cruised alongside various small vessels over the years, I can confidently affirm that solar propulsion presents a viable and rewarding approach. However, the examples discussed here indicate that the possibilities extend far beyond that. The independence afforded by solar-powered cruising is unique—akin to sailing, but more consistent and predictable land-based performance remains crucial, especially when weather conditions are less than favorable.

For further information on long-distance solar cruising, consider attending seminars at the Port Townsend Wooden Boat Festival or the Seattle Boat Show. Sam Devlin Designs has introduced several solar boat designs, while David Borton at Solar Sal develops solar day boats on the East Coast. While I can’t speak for other electric motor companies, the organization I’m involved with is excited about sharing insights on solar boating for smaller vessels, and I welcome the opportunity to run predictions from my solar performance model for interested individuals.

The journey of any new technology is challenging, especially during its initial, innovative phase, but long-distance solar cruising has successfully entered this realm. Keep your eyes peeled for the rise of solar sailing, as this new era in boating has begun.

A friend and I embarked on a journey aboard Sunnyside, my 14-foot solar-electric converted sailboat, to circumnavigate Vashon and Murray Islands in a single day—a total of 38 nautical miles. Despite Sunnyside’s maximum speed of 4 knots sustained over 10 hours on a sunny day, our planning accounted for tidal assistance for an additional 5 miles, accompanied by extra fully charged batteries just in case.

The adventure commenced at 8:00 a.m. from the Point Defiance boat ramp. Our route took us through Colvos Passage on an outgoing tide, with plans to cross the north end of the island at slack tide and ride the incoming tide south back to Point Defiance by 6:00 p.m. Although our journey didn’t precisely follow the plan—smoke from wildfires inhibited solar power by about 10%—we couldn’t resist stopping to fish for a few hours, putting us behind schedule at the Point Robinson Lighthouse.

Ultimately, we chose to continue despite the challenging conditions of a 15 to 20 knot breeze and corresponding seas from the south. An overnight anchorage at Portage Bay was an option, but our determination to complete the circumnavigation drove us forward. This choice represents the most significant risk we took during the trip. In hindsight, anchoring for the night could have proven wiser, as we reached Point Defiance right at dusk, much later than planned.

It was an excellent trip, but the experience underscored vital lessons pertinent to solar sailing: plan and track options intelligently when changes occur, like fishing stops, always considering nighttime landing. We adequately charged for the remaining distance at reduced speeds, but unforeseen weather conditions impacted our predictions. If we had been more aware of the evening winds, we could’ve made more informed decisions during the day. Additionally, keeping track of prevailing summer weather conditions—like smoke—has become increasingly important.

Ultimately, safe navigation should sometimes take priority over speed and objectives. While I was eager to finish the circumnavigation, next time I will exercise caution. My chief takeaway? Simply get out there. This trip was filled with memories worth cherishing.

Joe Grez boasts nearly 40 years of experience in product innovation, with 47 patents to his name. He operates PropEle Electric Boat Motors, which manufactures the ultralight EP Carry electric outboard in Washington State. For more details, visit www.electricpaddle.com. By the time this article is published, he will have solar-sailed another Salish 100.