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lemur

solar sailing

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I've been reading about solar sailing projects and they seem to mostly focus on using solar panels to charge batteries that are used to run propellors. The problem is that the batteries are heavy and cumbersome. I am wondering why the batteries couldn't be replaced with some kind of sea-water hydrolysis system since, as I recall, salt water electrolyzes more easily into hydrogen and oxygen anyway. I also haven't seen any that combine wind (sails) with solar panels. Could solar panels be used to make hydrogen and the hydrogen used as fuel for propellors when their is no wind on a sailboat?

Edited by lemur

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You assume that a hydrogen and oxygen storage is lighter than a battery pack. That assumption is not necessarily true.

 

Also, on a boat, the weight is not much of a problem. If you have a typical sailboat (I am not an expert, I just googled some for their weight), you will find that a 10 meter boat can easily be 3-4 tons. The addition of a battery pack is relatively harmless then. Also, boats often just go in a straight line, so "handling" and "acceleration" which are typical problems with heavy cars are no problem at all. Finally, boats often actually have added weight at the keel, for stability. The manufacturers deliberately use extra heavy materials...

 

Sailboats can get so much more power from their sails than from solar panels that I guess they don't bother to use solar panels for propulsion... However, there are plenty of sailboats which use solar panels for other systems (like the lights and power in the cabin).

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Sailboats can get so much more power from their sails than from solar panels that I guess they don't bother to use solar panels for propulsion... However, there are plenty of sailboats which use solar panels for other systems (like the lights and power in the cabin).

 

I think the issue is for propulsion when there is no wind, or in tight spaces where sailing limits maneuverability, e.g. pulling in to the marina. Solar electric runs a motor.

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I think the issue is for propulsion when there is no wind, or in tight spaces where sailing limits maneuverability, e.g. pulling in to the marina. Solar electric runs a motor.

Fair point. It can be used to run a motor for just a little while. Let's see how far we can get...

 

A quick Google search tells me that 10 meter sailboats have engines of minimum 10 hp (or 7.5 kW).

 

On a bright sunny summer's day, you can get 1 kW/m2 of power from the sun. A solar panel can get you 15% efficiency... so about 150 W/m2.

Therefore, to run continuously on solar power, the meter sailboat needs 50 m2 of solar panels.

If it is to run only 10% of the time on solar power, it still needs 5 m2 of solar panels... which is the absolute max. on such a small boat.

 

Perhaps that's an indication why it's not used. Surface area is not in plentiful supply... and the sails are often blocking the sun anyway.

Edited by CaptainPanic

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Fair point. It can be used to run a motor for just a little while. Let's see how far we can get...

 

A quick Google search tells me that 10 meter sailboats have engines of minimum 10 hp (or 7.5 kW).

 

On a bright sunny summer's day, you can get 1 kW/m2 of power from the sun. A solar panel can get you 15% efficiency... so about 150 W/m2.

Therefore, to run continuously on solar power, the meter sailboat needs 50 m2 of solar panels.

If it is to run only 10% of the time on solar power, it still needs 5 m2 of solar panels... which is the absolute max. on such a small boat.

 

Perhaps that's an indication why it's not used. Surface area is not in plentiful supply... and the sails are often blocking the sun anyway.

 

Which is why you would need batteries to have any hope of making it work.

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Which is why you would need batteries to have any hope of making it work.

Indeed... and thus we can return to the question of the OP: assuming that we can fit 5 m2 of solar panel on our 10 meter long yacht, what do we choose to store the equivalent of 30 minutes of sailing at 7.5 hp?

 

You'd need to store about 10 MJ of energy, or about 3 kWh (that's 30 minutes at 7.5 hp). We can do that with hydrogen (and oxygen, but we'll just release that into the air), or with a battery pack.

 

Battery

Using technology from the Tesla Roadster electric car (wikipedia info), we can see that a battery pack can store 53 kWh. So, our battery needs to be 6% of the car's system, and would have a weight of 26 kilograms.

 

A battery system furthermore is a relatively easy system with a number of wires, a generator (which may simply be the electric engine) and the battery pack.

 

Hydrogen

Assuming 100% efficient combustion (which isn't realistic), and using the Lower Heating Value (wikipedia info) we would need 82 grams of Hydrogen. In gas form, at atmospheric pressure and room temperature, that is almost exactly 1 m3 of gas. Therefore, compression is probably needed. And that means that you have a gas tank with compressed hydrogen and a combustion engine. This could well be more complicated, certainly more explosive (more dangerous), and less efficient than the battery pack.

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Hydrogen engine may much heavier than a battery pack and single DC electric motor. In addition, we need a gas tank & compressor if we use hydrogen engine. But i'm confuse, solar sailing??? isn't it a propellant system for space craft program?? :-(

Edited by Newbies_Kid

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Just a thought. With the sail boat scenario the largest issue is the needed surface area and cost of the solar panels. The weight of the batteries is trivial ( the expense is not ) .. Well maybe it is trivial compared to the cost of a 10 meter sail boat :) With the weight being less a concern maybe cheaper/heavier batteries would make sense.

 

What if the solar panels were ditched completely. What if the batteries were charged by a small turbine/prop in the water. Normally if the vessel was providing its own locomotion that would just be counterproductive. But lets say the ship allowed a small percentage of the usable wind energy its getting to instead counteract the added drag of a small submerged turbine. When the boat is moving through the water it can be keeping the battery topped off. Of course if you have no wind for an extended period of time, but plenty of sunshine, those on board would surely be wishing they had went for the solar panel array.

 

Preemptively apologizing if this is considered a thread-jack.

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What if the solar panels were ditched completely. What if the batteries were charged by a small turbine/prop in the water. Normally if the vessel was providing its own locomotion that would just be counterproductive. But lets say the ship allowed a small percentage of the usable wind energy its getting to instead counteract the added drag of a small submerged turbine. When the boat is moving through the water it can be keeping the battery topped off. Of course if you have no wind for an extended period of time, but plenty of sunshine, those on board would surely be wishing they had went for the solar panel array.

 

Alternatively, I've often thought about putting a wind spire or five on a boat in place of sails. You could then use the output to drive an electric motor or charge a battery or whatever. I'm sure the propulsive efficiency would be lower than for sails, but you could also go directly into the wind. The ability to go directly into the wind *might* make up for the loss of efficiency as you could set your desired course directly rather than have to tack. Also, navigation would be much easier and the need for seamanship skills would be reduced.

 

No worries about charging batteries though. You could definitely do that!

Edited by InigoMontoya

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Interesting.

 

I also thought about using spire on a boat, but not feeling alone. I would suspect there will be/are attempts with some interesting outcomes. Battery technology has come a long way in the past decade, so has alternate energy engineering. To combine modern lightweight materials for a hull, with solar infused spires and massive efficient steeper batteries for ballast, along with flow through salt water chambers (improved McCabe) all a in corrosion free environment may one day exceed the efficiency of traditional sail boat.

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Hydrogen engine may much heavier than a battery pack and single DC electric motor. In addition, we need a gas tank & compressor if we use hydrogen engine. But i'm confuse, solar sailing??? isn't it a propellant system for space craft program?? :-(

Many people have said that hydrogen storage and engine could be heavier than batteries and electric motor, but how is that possible when hydrogen could be electrolyzed directly into a tank that would compress the resultant gas? Furthermore, no one seems to have understood the concept of using solar-cell fabric in the sails themselves so that they could be collecting solar energy while functioning as wind-collectors. As for the issue of wind being more effective than a motor, why can't they run simultaneously? Doesn't the wind blow faster than the top-speed of a sailing ship? If so, I would think any motorized propulsion would only add to the wind-driven speed, although I am not an expert in sailing.

 

Another question is whether the electrolyzed hydrogen could be stored in a balloon whose buoyancy could be used to reduce the weight of the ship? If the wind is blowing in the right direction, wouldn't such a balloon just add to the sailing thrust while reducing water-drag by counteracting weight? I've never heard of a "blimp-boat" but wouldn't such a construction be advantageous in comparison with a pure sailboat with no air buoyancy?

 

 

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Many people have said that hydrogen storage and engine could be heavier than batteries and electric motor, but how is that possible when hydrogen could be electrolyzed directly into a tank that would compress the resultant gas?

Hydrogen is a very light gas. If you want reasonable energy densities, that means it must be stored under high pressures. High pressures mean heavy pumps and pressure vessels. If you want it light weight... OK, but now you either have negligible energy storage or 90% of your boat is hydrogen storage. Neither of those are desirable options.

 

Furthermore, no one seems to have understood the concept of using solar-cell fabric in the sails themselves so that they could be collecting solar energy while functioning as wind-collectors.

Does any such technology exist? A solar cell that is robust enough to be whipped in the wind and such like sails are? If such technology exists, I've certainly never heard of it or anything like it.

 

As for the issue of wind being more effective than a motor, why can't they run simultaneously?

They certainly could, but baring the invention of your tough-as-nails-flexible-solar-cells-used-as-sails gizmos, there wouldn't be much point.

 

Doesn't the wind blow faster than the top-speed of a sailing ship?

No, it doesn't. That boats can travel faster than the wind pushing them has always been one of the true marvels of sailing, IMO.

 

Another question is whether the electrolyzed hydrogen could be stored in a balloon whose buoyancy could be used to reduce the weight of the ship? If the wind is blowing in the right direction, wouldn't such a balloon just add to the sailing thrust while reducing water-drag by counteracting weight?

Sure, but now imagine that system in a storm. I see two interesting possibilities...

 

1) It'll get shredded.

2) It'll destabilize the boat causing the boat to capsize.

 

 

I've never heard of a "blimp-boat" but wouldn't such a construction be advantageous in comparison with a pure sailboat with no air buoyancy?

I highly doubt it.

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Hydrogen is a very light gas. If you want reasonable energy densities, that means it must be stored under high pressures. High pressures mean heavy pumps and pressure vessels. If you want it light weight... OK, but now you either have negligible energy storage or 90% of your boat is hydrogen storage. Neither of those are desirable options.

How much do you really need to store it if you can burn it immediately in the motor? Ok, it's nice to have reserve power when the wind is calm but if there's no disadvantage to running the motor while the sails are up, why not run full speed and park when the wind dies? I suppose there are water friction issues that make it more efficient to go continuously slow than intermittently sprint and stop. I don't sail, btw, so this is all hypothetical for me.

 

Does any such technology exist? A solar cell that is robust enough to be whipped in the wind and such like sails are? If such technology exists, I've certainly never heard of it or anything like it.

There's some stuff online about solar fabric and even some concept stuff about such solar-cell sails (I'm not the first to think of this). What you are saying makes sense, though, considering the electrical connections and the fragility of the photovoltaic material. Still, maybe you could do something like figure out a way to use the parabolic shape of the active (white) sail to reflect and somewhat focus light onto a solar collector that can be moved around to position it in the focus of the sail-reflection. I don't know if the sail would whip around and wave too much to maintain a consistent concentration of reflected sunlight on the collector though.

 

No, it doesn't. That boats can travel faster than the wind pushing them has always been one of the true marvels of sailing, IMO.

I've heard that but I still don't understand how it is possible. Maybe the energy could be used to somehow improve the hydrodynamics of the hull instead of power a motor. Well, that's probably just grasping at straws. I guess the big issue would be how to store the solar energy to make some time with the wind is low.

 

Sure, but now imagine that system in a storm. I see two interesting possibilities...

 

1) It'll get shredded.

2) It'll destabilize the boat causing the boat to capsize.

I believe there's one concept boat online with rigid solar sail that is supposed to be able to go down and basically cover the deck.

 

I highly doubt it.

Thanks for your lucid realism - too bad your insight doesn't also include more promising ideas. Surely there must be some way to improve sailing as transoceanic transit. It is basically totally sustainable assuming people would avoid having wars, piracy, etc. at sea as seems to have been common during high colonialism.

 

 

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How much do you really need to store it if you can burn it immediately in the motor?

If you're not going to store the hydrogen, you'd be a fool to create it in the first place. Just feed that solar energy directly into an electric motor.

 

Thanks for your lucid realism - too bad your insight doesn't also include more promising ideas. Surely there must be some way to improve sailing as transoceanic transit. It is basically totally sustainable assuming people would avoid having wars, piracy, etc. at sea as seems to have been common during high colonialism.

One thing to keep in mind.... Sailing is quite possibly the oldest form of transportation still in common use(*). Over the *thousands* of years many, many people much smarter than you or I have done everything they could to improve upon the state of the art. Thus, I imagine sailing as one of the most mature arts out there. As such, making dramatic improvements is not likely to be easy.

 

 

 

 

(*) The only form that I can imagine that compares is horseback riding, but how often is it still used as actual transportation rather than mere recreation anymore? A debatable point, I concede. Thus, this footnote.

Edited by InigoMontoya

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If you're not going to store the hydrogen, you'd be a fool to create it in the first place. Just feed that solar energy directly into an electric motor.

That's true. I guess I am just fixated on utilizing the abundant water in some way.

 

One thing to keep in mind.... Sailing is quite possibly the oldest form of transportation still in common use(*). Over the *thousands* of years many, many people much smarter than you or I have done everything they could to improve upon the state of the art. Thus, I imagine sailing as one of the most mature arts out there. As such, making dramatic improvements is not likely to be easy.

True, but beware of thoughts like this deterring hope of innovation. Just because some aspect of a technology has been optimized in numerous ways for centuries doesn't mean it can't be improved upon. Especially once you start dealing with combining new technologies with older ones, you face the challenge of optimizing an essentially new hybrid. Also, it's a trap to think in terms of people being smarter than other people when they attempt to innovate. It has less to do with being smarter than it does with generating an idea and passing it to someone who can carry it further in some way.

 

(*) The only form that I can imagine that compares is horseback riding, but how often is it still used as actual transportation rather than mere recreation anymore? A debatable point, I concede. Thus, this footnote.

Bicycles are the most efficient technology for converting energy into surface transit, I think. Bicycle designers always seem to be messing around with different alloys and designs to maximize performance for the most competitive cyclists, but the basic bicycle is about as efficient as you can get. There are some human-powered-vehicle competitions that deal with wind-drag and add various forms of power to increase overall speed and range, though. There are also infrastructural innovations that would improve commuting by bicycle (or horseback, why not?). And, of course, the holy grail of bicycle modernization, imo, would be a good rain-canopy system that didn't blow you away like a sailboat in a storm-gust. But I think the bicycle was basically perfected in the 19th century.

Edited by lemur

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True about the sailing histoy toya. Most of the brightest minds spent a lot of time improving travel, like today. However, the technological curve for development did increase recently in sight of all history. Flight is an example. Imagine if the Roaman’s or other succeeded in industrialization. I here they came close.

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What up with the guns you all? Do I have to dispaly my Daisy?

It's relevant to my day job. Suffice to say that pic was taken in my office.

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And, of course, the holy grail of bicycle modernization, imo, would be a good rain-canopy system that didn't blow you away like a sailboat in a storm-gust. But I think the bicycle was basically perfected in the 19th century.

 

That's easy. Just dress for the weather and wrap your stuff in plastic. There's no need for a canopy.

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That's easy. Just dress for the weather and wrap your stuff in plastic. There's no need for a canopy.

True. That works pretty well but it's still not quite as inviting as stepping into an enclosed vehicle. It would be a lot easier to encourage people to bike for local commutes if there was a simple but highly effective canopy that would make cycling in the rain almost as dry as driving.

Edited by lemur

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True. That works pretty well but it's still not quite as inviting as stepping into an enclosed vehicle. It would be a lot easier to encourage people to bike for local commutes if there was a simple but highly effective canopy that would make cycling in the rain almost as dry as driving.

 

How about making covered tunnels designated for bicycles and pedestrians?

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How about making covered tunnels designated for bicycles and pedestrians?

A few years ago, I heard of plans for a tunnel near Amsterdam somewhere that involved having a tunnel whose air flow could be controlled to have tailwind in both directions. I don't know how this would work, since it seems like the pressure differential between the two ends of the tunnel would depend on the weather of the moment, but the idea sounded good. Maybe some kind of fans were involved. I've tried googling this with no success, though. Such tunnels would be handy for connecting cities with their surrounding residential areas for CO2-less commuting.

 

 

 

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And today I stumbled across a link the OP might appreciate....

I've seen that one before, but thanks. I think that was the reason I first wondered about combining sails with solar.

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