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Solar-Powered Catamaran Begins Transatlantic Voyage

The solar panels are mounted above the decks. Click to enlarge.

Sun21, a solar-powered catamaran developed and sponsored by the Swiss Transatlantic21 Association, departed the European mainland on 3 December on the first transatlantic crossing in a vessel powered solely by the sun.

The boat uses two 5kW solar modules (about 65 m2) to power twin 520 Ah 48V lead-acid battery packs (one in each hull) and two 8-kilowatt electric motors, allowing a constant speed of 5 to 6 knots. Approximately half of the energy produced during the day will be stored in batteries for powering the motors at night.

Sun21 is following Christopher Columbus’ historic route to the Americas, including the departure from the Spanish port of Chipiona. The next port of call for Sun21 will be the Canary Islands. The solar catamaran is scheduled to arrive at Puerto Calero on Lanzarote by the end of this week.

A stop-over in Tenerife is planned for mid-December before the boat heads for the Cape Verde Islands. After that, the catamaran will be out in the Atlantic for at least three weeks non-stop. Its final destination will be New York City with a scheduled arrival for May of 2007.



Rafael Seidl

Interesting, but perhaps more useful for a pleasure boat or research vessel plying coastal waters than for crossing the open ocean. 5-6 knots is not a whole lot but very low noise and chemical pollution is valuable in some contexts.

We have an ecologically sensitive shallow lake on the border between Austria and Hungary, where only the emergency services and a few fishermen are permitted to use ICE-powered craft. recreational users must make do with battery-powered electric boats, rowing/pedaling or sailing. Solar-powered houseboats would be permitted, though I expect you'd need some sort of permit for a semi-permanent GPS-based anchorage even if it's far from shore, where rustic huts on stilts are nestled in the reeds. The occasional hailstorms might pose a problem for the panels, though.

Bob Bastard

Great! Its powered completely by renewable energy. What will they think of next? A wind powered sea vessel? :)

Bob Bastard

In all seriousness, the solar power would be quite useful for powering batteries and on board electronics, as well as motors for when wind conditions are unfavorable. I wonder if it would be feasible to design a solar array of comparable power that could dual as an auxiliary sail, or be deployed/stowed depending on conditions?



My horse does 500 miles per m² of renewable biomass. Sadly it can't swim across the Atlantic. Not yet.



The newer photo-dye deposited in matrix on watertight fabric substrates would make a nice "solar sail." But the relatively low I/M2 and obvious high costs might kill it on the drawing board. This is an area that Mike Gratzel's cell licensee(s) are working in on smaller scale fabric applications.

I like sailing and wouldn't hesitate to get behind a prototype - initially as proof of concept.

Bob Bastard

gr, thanks! I had read the gcc article already, but hadn't heard about his work with photo-dye. That tech sounds like it could have quite a number of interesting applications. The ability to cheaply manufacture conformal, integrated, or even flexible cells could really expand the market for solar energy.


Thre are competing technologies from large steered propulsion kites, and chutes akin to those for paragliding. Depending on conditions, one can obtain 30+knot, though 15-20 knot is more normal.

Roger Pham

Motive power for a boat can come from concentrated solar thermal energy driving Sterling engine or Rankine cycle engine capable of upto 30% efficiency. Either solar trough collector, or solar tower using Freshnel lenses can do it. The excess energy can still be stored by battery for night time use.

In contrast, flat solar panels are capable of only ~15% efficiency. However, flat airfoiled-shaped sails may be outfitted with solar panels and can also be used to catch the wind to speed up the vessel. At favorable winds, sail boat can go as fast as 20 knots. With good weather prediction as to wind speed at night, all the day time electrical energy can be use to increase the boat's speed. Or, the solar panels can be mounted tiltable in different directions to both enhance the solar efficiency as well as catching the wind at the same time, which ever most favorable.

These will require more work, but hey, this is just a show case of technology and nothing practical, so it's all play and no work, to be philosophical about it!

Roger Pham

Also, if solar tower is used, it can also serve as a mast for the sail, thus doubling the propulsion power.

Roger Pham

Sorry, please scratch out the use of concentrated solar power. The rocking boat in turbulent sea will make sun light focusing in one small spot a challenge. Plus, flat solar PV can produce electricity even in cloudy days, whereas concentrated solar PV cannot. Still, adding a mast for adding a sail to this boat will make the voyage much faster.

P Schager

As the sponsors have noted on their site, the purpose of this is to "generate confidence in a key technology for the future." We should be proud of them, and set the jokes off to the side.

Once it is established that you can navigate well on just PV, the hybrid sailing/PV vessel becomes an obvious thing to pursue subsequently. The amount of time you have neither wind nor much sun is low and would greatly increase the number of people willing to dispense with ICE engines, fuel, pollution and racket. (Especially with the advent of parafoil kite tow, which can work with lower winds.)

Rather than a PV fabric, I would look to several other solutions. Film PV that can be flexed in one dimension, like Unisolar's or CIGS, with a rogallo-type sail. Conventional panels on a rigid wing such as the one used in San Diego in 1988 to defend the America's Cup. A sail covered with small cells affixed to a sail like sequins. Fanfolding panels. Fresnel lenses or other concentrators etc. Or just make a boat exactly like transatlantic 21 and fit it with a parafoil tow (hey, why stop with the Atlantic?).

And these boats will help launch the PV industry's next stage, guaranteeing a strong market whatever governments may do on subsidies, until technology outgrows the need.

PS: sorry about the overlap; I wrote this earlier and had trouble posting. Concentrator, BTW, would probably be only for windless sunny days but that might be good enough for many sailors.


I was about to froth at the mouth over this one, but Bob has said most of it already.
Wind power is much better for this kind of thing. The main problem being the large crews needed to handle the sails, unless this has been dealt with by now.
The amount of power you get from solar is so small that it is just a token. You might be able to run ship's electrics off it if the requirements were small but you wouldn't want to run too many toasters or kettles.
A big panel like this looks very dangerous to me in high winds. What were they thinking of.
I would use sail + diesel if required. Most of the high seas can take a few diesel fumes, unlike most cities.
It looks like they are spending a lot of money to get a corporate brochure shot rather than a contribution to maritime transport.


5 kW from 65 m2 of solar panels means they really didn't spend very much on good quality efficient panels. The current ones appear to be around 7.7% efficient.

If they had gone for SunPower A300 panels, they could have had 21% efficiency, and peak power of 13.5 kW. Would have made it a lot faster.


@Bob Bastartd, mahoni:

Congratulations for missing the point completely.


Perhaps a more practical use of solar and PHEV on a boat ->

Jay Tee

I would add a few small windturbines, perhaps one at each corner of the vessel.
That would help keep the batteries charged....
Some of you mentioned that 5-6 knots is slow...... but actually it's not bad for an ordinary sailboat.


Roger, the solar concentrator is not completely off base. KVH and SeaTel manufacture consumer grade gyro-controlled gimbaled parabolas for satphone/TV comms. Polish the mirror, aim it at the sun and PV/thermocouple concentrator...

The above design appears extremely hazardous in any wind above 20kts - the Atlantic ocean can be a hostile place - which is why I like sails.

My thought is to create a wind-powered vessel with auxiliary electric drive. There are some nice demos using regenerative power from props spinning while under sail. Add some experimental PV, compact wind turbines, Li-Ion house bank, and a B99 mini-diesel genset - we get a nifty renewable vessel that promotes sustainability.

Find a big green sponsor, take it on a world tour and hey, maybe the recreational boating industry would get a few ideas.


What is the point ?


Jay Tee, 5-6 knots may not be slow for a sail boat, but it is slow for crossing the atlantic ocean, it's kind of huge and will probably take a while.

Roger Pham

Oh, and another idea: How about with a big enough boat, you can drag along an algae farm (marine algae) on the water, grow the algae and harvest oil for propelling the ship's diesel engine. Waste heat can be used to distill water for consumption. Algae biomass can also be processed into human food as well. With a solar efficiency of ~10%, oil algae can produce a lot of fuel given the large surface area that can be dragged above the water.
So, fuel for the ship, water and food for human occupants...what more can one ask for?


Roger, you have an idea for a movie...we can call it Water World! :-))

spankyn anjelz

Eh, sounds like a bunch o' wanna be do-gooders tryin to win the "Save the Planetz" sim. Get real.

Roger Pham

spankyn [no] anjelz,
u deserve a spankin', dude! Whap! Whap! Oh yeah? Hurt so good?

That's right, Water World II!. The previous Water World movie starring Kevin Costner was a flop! Hopin' Water World II would fare better!

But seriously, if eventually, with more "nucular" weapon proliferation and eventual exchanges happen in a wide-spread scale in the continents, then your only good bet for survival is to drag in the middle of the ocean your own life-supporting algae farm and a diesel boat which should be fast enough to outrun any hurricane that you can see in the horizon. The beauty of solar-powered algae farm is the built-in long-term fuel storage and higher speed potential to outrun the hurricanes, unlike PV and lead-acid boat with very limited energy storage and slow speed that can be dangerous if a storm appears in the horizon. By then, the CO2 level world-wide would be much higher, thus would allow for even faster algae growth than now.

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