# Can solar energy power a catamaran?

Discussion in 'Multihulls' started by EscapeArtist, Sep 4, 2016.

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### EscapeArtistJunior Member

I've been kicking around the idea of using solar power to drive a catamaran, and I'm interested in more of a coastal cruiser that would sail a few hours a day, and not something that would be a blue ocean yacht. I started with Terho Halme's Catamaran Design Formulas (http://www.catamaransite.com/catamaran_hull_design_formulas.html
) and got some basic parameters - draft, displacement, engine power and hull speed. I made some assumptions about the amount of available solar energy from a NASA website (https://eosweb.larc.nasa.gov/sse/global/text/global_radiation) which gives average daily solar radiation by latitude. From this, I got that you might be able to expect about 4 kWh/m^2/day, and if you assume about 15% conversion efficiency then you get about 600 Wh/m^2/day. I knocked off another 20% for other losses to get 480 Wh. Then I plotted the power required from Terho Halme's equations against the available solar power, assuming I could cover 60% of the LWL x beam area. Not a chance. The required power is way above the available solar energy. But then I thought, power goes up approximately with the cube of velocity, so how fast could you go even if you aren't at hull speed? It turns out that for the boat lengths I calculated, it's pretty consistent at ~4.5 m/s (10 mph). If you didn't mind a kind of lazy day on the water, maybe that wouldn't be so bad. Obviously, I'm ignoring all kinds of things here like cost, weight, batteries and getting home before dark, but I thought I'd throw this out for discussion.

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2. Joined: May 2009
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### Doug LordFlight Ready

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### EscapeArtistJunior Member

I knew about Planet Solar, but I hadn't seen that video. Thanks!

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### Steve WSenior Member

l encountered a power trimaran of about 40 ft back in the summer of 2013 on the Trent Severn waterway that was doing the loop powered by a torqueedo and solar only. It was slow and couldn't travel every day but it had made it from Florida.

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### EscapeArtistJunior Member

That's kind of what I was thinking about. Just go when the sun shines, and not too fast so you can enjoy the scenery.

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### StumbleSenior Member

It is technically possible but grotesquely expensive and impractical.

Figure a 40' cat needs about 20kw/hour at cruising speed. And 1m^2 of covered space generates about 1kwh/day in solar power. To run on batteries you can also figure that every 100lbs of lead buys you 1kwh of usable power.

When you do the numbers you have at best a couple of hours a day operating at low speed before needing to stop for a couple of days to recharge. All at a price that will dwarf the expense of installing a mast and rigging. Or really just buying a small Diesel engine and fuel.

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### EscapeArtistJunior Member

For a 40' (12 m) boat, you need 28 kW to maintain hull speed which I agree is out of reach for solar power. At that length, the width is 5.5 m and I assumed 60% of the total area would be covered by solar panels, or about 40 m^2. You can actually get at least 4 kWh/m^2 per day between +/- latitude 40 deg, and in many places quite a bit more. That's enough to get 4.3 m/s or 9.5 mph. I forgot to say in the initial post that I assumed 5 hours a day of motoring, so you'd get ~50 miles per day if it was sunny.

Yeah, I've completely ignored batteries, so that's something to look into. The batteries would smooth out variances due to scattered clouds. I've been assuming that if there's no sun, you stay home.

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### redreubenredreuben

Solar power is ultimately what powers all internal combustion engines, it's just a veeeeery long process to transform the fuel !

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### mydauphinSenior Member

Sailboats are solar powered.

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### StumbleSenior Member

Not you can actually get about 1kw/m^2/day not 4.

The theoretical maximum amount of power available in 1m^2 at noon on the equator is 1kw. Solar panels run about 20% efficient. So a realistic 'best case' is about 200w/hour, over a six hour production day works out to a max of 1.2kw. But then you have to take into account the frame size, mounting efficencies, and any shading.

So your 40m^2 will realistically produce about 40kwh/day. If you ran during day light and used the power as you produced it that's about 6.5kw/kr. Or probably 2-3kn at best. So figure a days run in the 18nm range.

Batteries are easy too. Assuming you stick with FLA you get a usable capacity of about 1kw/100lbs of batteries. It varies a bit with the specific battery used, but that's a workable number +\- Pukerts efficency.

Like I said, it's technically possible, but grotesquely inefficient. Solar Planet, the custome built \$15 million 150' (whatever length I don't remember) ship set the Trans Atlantic speed record for an electric vessel at an average speed of about 5kn (if I remember correctly). Or about the passage speed of 30' heavily loaded cruising boat.

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### zimbodaveJunior Member

I'm also interested in this idea. You know. Everyone says it'll be too slow....it won't work....don't waste your time. But. Just google solar wave by nedship. They're building them right now. And they work. Youtube search to see video of sea trials of the first production boat. It's on the sea. Doing 10kn on solar alone and 15 combined with the generator. If they can make it work now. I'm in with a good chance when I'm ready to build mine in a few years time. I'm realistic enough to realise I'll still need big gensets for crossing oceans but I'll be diesel smoke free in the islands and when on the hook. Won't know what to do with all the power when anchored. Which for a cruising boat is a large percentage of the time.

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### zimbodaveJunior Member

And sun21, the first solar transatlantic boat. About 42' I think. Also the solarwave 46 which was the predecessor to the solarwave production boats. So they're out there. And as electric cars become more prevalent. The tech will come down in price and spill over in to the marine world. Keep at it.

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### StumbleSenior Member

There is no tech in the world that will allow solar panels to generate more power than the sun puts out, and there isn't enough power in the sun's output to power a boat.

The only way to run a boat from solar is with a big battery array. Right now the best batteries in the world store about 1/50 the power as a gallon of diesel. When that gets closer to 1/10th it will be realistic. But even the best storage device on drawing boards isn't even close to that, it likely won't occur in the next 50 years.

So the only way to have an electric boat is with a diesel generator, or accept a massive reduction in capability.

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### Richard WoodsWoods Designs

Agreed, solar power smacks of perpetual motion. Energy cannot be created!

The only reason electric cars are cheap to run is because power stations pay so little for fuel compared to what we pay in gas/petrol stations.

RW

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### mydauphinSenior Member

I have 4 large solar panels on my boat. They power the bilge pumps, the led lights, the radio. Gps and even my laptop. But even after a day charging they could not power my dingy for even 1 hour. Sail power works, and it is eco friendly.

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