Is the future bright for solar-powered superyachts?

From shipyard roof-top installations to the Monaco Energy Boat Challenge, solar power is having something of a moment, yet it is rarely found on superyachts. What is the current status of solar tech and will it ever increase traction as an onboard renewable on big boats?

While solar power is increasingly a key source of renewable energy for national grids, industrial manufacturers – including shipyards – and homeowners, it hasn’t made much impact on the design and operation of superyachts. Aesthetics, practicalities, cost and low energy yield are all blamed to varying degrees, but that hasn’t put off some corners of the yachting industry.

No one visiting a boat show in the past few years could have failed to notice the Eco line of catamarans from Sunreef Yachts, for example. The Polish brand has made a point not only of using solar power in its hybrid projects, but has developed its own patented, toughened solar panels that are built into every square metre of hull and superstructure. Similarly, Silent Yachts set out specifically to develop a range of operationally eco-friendly power cats that draw on solar as the dominant power source and couple that to a complete electric drivetrain.

“The solar panels are limited by the space on board, which is why historically we picked a catamaran, and also why we didn’t pick a sailing cat where the mast and sails would impede the sunlight,” says Steve Bell, Vice Chairman of the board of Silent Yachts since the company changed ownership in early 2024. “We store as much energy as we can in batteries, which on our Silent 62 is around 300 kilowatt-hours in total. Cruising at six knots uses 20 kilowatts per motor, or 40 kilowatts total, so a simple maths calculation [300 divided by 40] suggests an eight-hour range.”

The 62 carries a total of 16.8 kilowatts-peak (kWp) of solar panels, meaning in an ideal scenario the panels would produce 16.8 kilowatts of power. This is never the case, however, as losses through efficiency, angle of sun, dirt on the cells, or any number of factors, always impedes energy generation. It is one of the details that sometimes gets lost in the marketing about the capabilities for generating power from the sun. 

“On a really good day our 16.8 kilowatts peak of panels will pull around 12 kilowatts,” confirms Bell. “There’s a misconception that kilowatts-peak equals actual kilowatts produced, but that doesn’t happen with any solar panel.”

Hotelerie

There is also the hotel load to consider. On the Silent 62, this typically equates to around 10 kilowatts when using energy-hungry systems like the air conditioning, which means the solar panels are serving the hotel load while the stored energy is powering the drivetrain. It starts to make more sense if you consider a typical operational profile, the Med cruising around the Balearic or the Greek islands, for example. This may involve two or three hours of motoring to reach a bay, then spending the rest of the day at anchor.

“What we’re also trying to do is manage the hotel load to keep that energy burn to a minimum, including educating our customers about things like turning stuff off when it’s not needed,” Bell says. “That means you effectively get to run the yacht off solar and only need to charge the batteries with the generator every four or five days.”

Bell adds that cruising at 3.5 knots reduces drivetrain power draw to around 8 kilowatts. If you minimise hotel load, this could mean free, continuous daylight cruising. But you still wouldn’t be sailing around the world using only solar power: “You could do that, but only if you want to do it at two knots – which people don’t,” adds Bell.

For Silent Yachts, whose largest planned model is the 36.74-metre Silent 120 Explorer, scaling up is relatively straightforward for models like the 80, which uses the same propulsion drives as the 62 and has more space for solar panels to handle the increased hotel load. The challenge is transferring the tech to bigger superyachts, where the hotel and propulsion energy demands on energy are exponentially higher. This may suggest there’s a limit to the usefulness of solar as a renewable energy source on superyachts, although that is somewhat missing the point.

Substance over style

The idea of covering every surface of your superyacht with solar cells creates another obstacle centred on aesthetics. Styling is a key driver of owner interest, but one way to integrate solar energy more comprehensively – and less obtrusively – is solar glass. Glass that integrates solar cells to draw power has been around for a long time, and not just in land-based architectural contexts, where the technology is increasingly popular for large public buildings, electric charging stations and even private car ports and domestic terraces. For Italian builder Arcadia it has been a trademark feature in several of its models since the first 25.9-metre A85 model in 2009.

Arcadia yachts show how solar tech can be transformed into something that is architecturally pleasing – especially from the inside – while meeting the twin demands of sustainability and practicality. The glass superstructure of the A85 contains more than 40 square metres of solar panels, producing up to 4.5 kilowatts of energy – not enough to power the yacht, but sufficient to make a contribution to the hotel load, particularly when combined with other energy-saving design elements. The glass used by Arcadia was developed by Austrian company Ertex Solar, which produces glass that can be specified with different levels of transparency and solar cell density, as well as patterns and designs. Arcadia says improvements in solar tech have led to a 30 percent increase in energy yield since its first launch.

The same year the Arcadia A85 was launched, Feadship came out with its Aeon Future Concept, which had not 40 but 400 square metres of solar panels. The Dutch builder has since taken steps to include solar cells on one of its latest launches, the 59.5-metre Project 713 (now named B), which underwent initial sea trials last July. The first Feadship to carry solar panels for auxiliary power generation, over 87 square metres of high-efficiency solar cells are recessed into the curved superstructure surfaces of the upper decks. Feadship claims that the laser-cut, walkable, saltwater-resistant panels are able to counteract the effects of partial shading and can generate a total power of approximately 16.8 kilowatts, equivalent to about 100 kilowatt-hours on sunny days.

Other superyacht builders are considering how solar might form part of the future energy mix. Heesen Yachts, for example, is looking into adding thin-film photovoltaic panels on the mast and integrating cells into the fabric of sun awnings for free, sustainable power.

“In our case we looked at putting 25 square metres of flexible Solbian SP panels on the mast of a 50 or 55-metre yacht,” says Erik van Mourik, Manager Cost & Accounting D&D at Heesen. “This would save approximately one percent of the hotel load on a 24-hour cycle. This is not much on its own, but if you combine it with other measures such as waste heat recovery and smart air-con zoning, you can create a more substantial package of energy savings.”

Baglietto uses solar energy to run its Bzero fuel cell technology. Sized to fit on a yacht, the array of solar panels at its one-to-one-scale test installation at the shipyard in La Spezia powers a hydrogen production module, which filters and de-ionises seawater through AEM-type electrolysers to produce green hydrogen with 5.0 purity grade at a maximum pressure of 35 bar. The PEM-type fuel cell then uses the hydrogen as fuel to produce clean electricity. The prototype plant is now producing hydrogen and space has been allocated for the Bzero technology aboard Baglietto’s second 60-metre T60 hybrid in build.

Another example of solar being harnessed as part of wider energy strategy on board is the Project Zero sailing yacht featured in the last issue of How to Build It, which is aiming to reduce onboard energy consumption from 90 kilowatts to less than 30 kilowatts. In this case, a key part of the energy production comes from hybrid photovoltaic-thermal (pv-T) panels developed from existing land-based building tech.

In general, however, the pace of development of solar tech has been relatively slow, despite next-gen technologies such as perovskite structures that promise to improve the efficiency of panels at lower cost than traditional silicon cells, and allow for novel uses such as the creation of solar paint, or solar fabrics for awnings and sails. But perovskites are still a way off commercialisation and it doesn’t alter the fact that their placement and orientation will remain critical.

Painting with light

The idea of a paint that can capture energy from the sun has been mooted for several years, but so far no such paint has emerged on the market. In fact, there are three possible solar paint technologies currently being explored – even if they are still years away from commercial production or availability.

The first is a product developed by a team at the Royal Melbourne Institute of Technology that absorbs moisture from the air and uses solar energy to break the water down into hydrogen and oxygen, with the hydrogen being used for clean energy.

The second, developed by the University of Toronto, uses colloidal quantum dot photovoltaics – essentially nanoscale semiconductors – to capture light and convert it into electricity more efficiently than conventional solar cells. The dots can be tuned to different light spectrums by changing their size.

Finally, there are perovskites. Named after a Russian mineralogist, perovskites are a type of crystal structure and have been a topic of discussion for a while now. Perovskites offer properties that allow for higher power conversion efficiency (similar to what are known as multi-junction solar cells) and can take liquid form – ideal for solar paint. A team at the University of Sheffield in the UK developed the first spray-on solar cells back in 2014, but more recently scientists at Oxford University have produced a micro-thin perovskite coating with the potential to generate up to nearly twice the amount of energy of current solar panels and can be applied to almost any surface. The researchers believe that over time, perovskites will be able to deliver efficiency exceeding 44 percent, pointing to the increase in yield they were able to achieve during just five years of experimentation, from 6 to 27 percent.

Product placement

“The difference in efficiency between having a panel flat or tilting is around 25 percent,” says Bell. “That means if you have panels mounted vertically in the hull topsides, or even on sails, then in the midday sun in the tropics you’re not going to get any photovoltaic energy. For example, at 0900 on a beautiful sunny morning in Venice we looked at what the panels on our 62 were producing, and the high-voltage panels – which are around 13 kilowatt peak and typically produce nine to 10 kilowatts – were producing just 1.8 kilowatts.”

While the solar industry is constantly talking about new solutions and innovative products, Bell suggests the fact that manufacturers are selling huge numbers of conventional panels means there is less incentive to invest in new tech and new production methods with potentially high start-up costs.

“For our new models we’re looking at how to optimise the space for panels based on retaining aesthetics,” he continues. “We are looking at solar panel tech, but I think that isn’t going to change much for the foreseeable future – technology development at the moment is really in batteries and energy management. Indeed, while there have been some improvements in panel efficiency over recent years, by contrast we’ve gained 15 percent capacity for the same physical size of battery over the same period.”

It may well be that the sweet spot for yachts that draw on solar power as a key provider of sustainable energy will remain in the 20 to 40-metre bracket, but there’s still no reason why larger yachts should not include solar as part of their power mix. For one, it’s essentially free and it’s green – at least in the operational phase – and anything that reduces the need for fossil fuel power generation is a positive.

Moreover, by its very nature it drives a conversation about how to mitigate energy consumption on board, whether through smart zoning, developing new technologies in air conditioning, insulation and lighting, or just more efficient energy management. As solar tech improves with more efficient cells and more innovative materials able to harvest more energy, it’s only going to get more interesting for yachts of any size.