Solar catamaran

I assume this must have been discussed before but I can't find a specific thread.

There is much discussion about on solar/electric boats. On another forum second hand solar panels were discussed so I had a look. Seems here in Australia second hand 180w panels can be had for $10-$20 each.

If you built a cat say 10m (32') by 4.3m (14') and pit a flat roof over the whole thing you could put enough panels up there to run a pair of (for example):

Electric Outboard / 48v / 2200w / 160LB thrust https://www.emppl.com.au/collections/complete-system-solutions/products/electric-outboard-48v-2200w-160lb-thrust

Output is just under 1.5kW each. Normally a pair of 4hp would be inadequate but you can run the electric motors at 100% provided adequate cooling. You'd get hull speed and wire it to use any surplus charging to top up batteries, then ultimately to run a water maker.

Might just be viable and affordable.

 

If only it were that simple....

There’s a lot more to a solar electric boat than the motor and the panels like the charge controllers and batteries, which are of equal importance.

And those motors really wouldn’t be adequate for that size vessel once you factor the displacement with heavy panels and added windage with that large of a hardtop.

Would they move the boat? Yes.

Would you have control over the boat and be able to maneuver in current, wind, etc..? No.

For something that large, I think you’d want a minimum of 3kw motors with larger props.

 

It does sound very marginal at best, but....what if you have stored power, as well as that being generated in real time ?

 

I've been considering various designs for solar liveaboard cruiser for a while now and I keep going back and forth. I believe a ILAN type power trimaran would be best. Make it 15m instead of 10m for less weight, a little less space. A catamaran should work fine too but might have less range / more costs. Or a solar harryproa might be more flexible, then you would have the option to put sails on one side and have most of the cabin and solar roof to the other side. I've also considered a LDL trawler (low displacement length ratio) but you'd get less roof, more resistance and need a bigger battery.

Ultimately it's a game of putting as much roof surface on an as lightweight and long boat as you can build. And accepting the compromises of such a solar boat. The upside for me would be lots of off grid power for water and appliances, low maintenance and solar panels are incredibly cheap now. If hydrogen fuel cells became cheaper that would change the game and allow you to generate and bunker a lot of fuel for long range.

A 10m x 4.3m catamaran has maybe a flat roof area of 6.8m x 4m so you could fit 4x4 340W solar panels (1.7m x 1m, 22kg. They are not quite as cheap but you can still find offers for new ones with <500€ / kWh. So that would be 27.2m² or 5.4kW weighing 326kg on the roof.

"All Sky Insolation Incident on a Horizontal Surface" is about (average)
4.75 kWh/m²/d in North Sea Summer,
2.72 in North Sea Spring,
7.01 Meditaranian Summer and
4.63 Spring / Fall and
2.27 in Med Winter

So multiplied by the surface area that gives you how much you can generate while driving in good weather plus whatever large battery you add. I'd prefer more solar and relatively small 10kWh battery plus a small backup generator.

I've attached a list of solar boats I've found. And my range calculations I've made a while back based on the prelimina results that a 15m trimaran could achieve 6 knots with ~3kW. Possibly optimistic. Maximum daily range is really at 5 knots (90 miles) and it depends on where and what season you travel. I've also attached my early sketch for a 15m trimaran with 50m² of solar roof. It's naive and needs improvement but after considering other options I think it's still the best configuration. I'd build the hulls cheap out of solid fiberglass like the cargo ferry prototype and only use for storage.

I've added Cs or "solar coefficient" to the solar boat list which is solar area multiplied by length divided by displacement. The planetsolar reaches 186 and energy observer 140, my trimaran sketch with 4t would be 187.

 

Are these panels affected by salt ?

 

Presumably not, at least not the (heavy) glass panels. They are encapsulated in EVA film and glass and a backing sheet so I don't see how salt could enter. The connections could corrode and need some kind of protection. I'd be weary about cheap flexible panels though.

PS: I've also considered if you could remove the aluminium frames and put the glass panels directly on top of a foam core roof to make them walkable. That might be useful for some designs but might also lead to scratches, plus heat issues.

 

I guess if the wind is on or abaft beam, these things could work OK, but otherwise rather tested. I really think the wind direction becomes the main obstacle.

 

Yeah I've wondered about wind impact too especially for low power designs. Alscal mentions here that his 8 hp outboard that can drive his 20m trimaran Carabao at 6 knots in calm water struggles in big wind and sea. This is why I have been considering a harry proa again for a more hybrid approach.

Trying to maximize the roof surface leads to not very aerodynamic and blocky designs with overhangs. Then the overhang you'd want above your head so you still have a side deck to be able to access all areas of the boat. The trimaran I sketched could have the the overhangs be able to flip up or down to more solar gain or to reduce windage.
Flexible solar panels would also better for more aerodynamic shapes. And they would be light enough to change by hand, compared to the pretty heavy overhang.
A larger catamaran might also be better for windage, allowing a more sloped design to the sides.

 

It has to be considered as something that can extend range, rather than be a reliable motive power for all circumstances.

 

Or a backup generator for less than ideal circumstances.

 

That's another way of approaching it I guess, but the distances involved better be modest, and the tides and currents friendly, you do need some speed over the ground at times. But I certainly have pondered having a displacement cat with panels plastered all over the cabin roof for the purpose you envisage, just not as the main power, more as a back up where range could be a problem.

 

I don't have the experience to really judge this so I'd be curious about guzzis or others opinion how viable or limited this use scenario is. Weigh the downsides with the benefits. And compare it more to a slower monohull sailboat cruiser where you'd also plan around the weather.

Upside is that you have ample of power for daily life and rather cheap costs. No fuels and also relatively low maintenance and complexity. Despite needing chargers and controllers like solgato says, most motorsailer have those anyways, plus rigging and engine and fuel. In that way a solar boat is simpler.

And distance, I imagine skippering around the mediterranian sea from town or anchorage to the next. Maybe also have a 40hp outboard motor to be able to get out of dodge.

With cheap hydrogen fuel cells this would totally change. You'd maybe be at anchor for 2 weeks and all the time generating hydrogen which gives you a big buffer. Maybe in 5-10 years one could upgrade.

Or an alternative to solar could be a kite powered electric cruiser that uses crosswind kite power for sailing as well as for power generation at anchor. Wind power is more steady and crosswind kite power has a high power density. But for that you need automated kite control units.

 

It's not like it has not been done before. SolarWave (46ft, 10t catamaran) is operating since 2010, mainly in the greek islands. They say 15-35nm usual autonomy, 60nm under ideal conditions, lots of trip planing required. 8,5kWp panels, 2x 200A/48V LiFePo4, 2x 10kW motors. "Wie weit kann man denn mit der SolarWave so fahren?" https://www.solarboot-projekte.de/wie-weit-kann-man-denn-mit-der-solarwave-so-fahren/

If you have money, good solar instalations can be done even on small sailboats without compromising sailing ability. Check out this Pogo 30 with 978Wp that can still sail as designed: Pogo 30 electric sailing yacht - 978Wp SP & SX series - SOLBIAN Solar https://solbian.solar/en/pogo-30-en/

 

Thanks, some interesting info. And I hadn't realized the SolarWave 46 was actually a separate prototype from the Silent Yacht 55.

I believe a solar boat designed for low power could be much lighter and have larger solar area. Small living space for size of boat should be a compromise. The experiments, showboats and luxury hybrids are cool, but do not demonstrate a very good value proposition yet.

I think the FlatCat solar 39' comes closest to what Guzzi is asking (no plans available though). But still a bit heavy with 4.5t lightship - if you look at something like the Outcut 29.5 weighing 1.45t or the harry proas. The 80' cargo ferry prototype weighs 4t. There has to be a better sweet spot for length, performance and cost.

 

Good example of a hybrid (electric/solar/generator) here.
Herley Boats - Electric Hybrid Power Catamaran - Powercat 3400 https://herleyboats.com/catamaran-powercat-3400/