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Dual Underwater Parachute Tidal Power Generator

One opens, gets pulled by the tidal flow pulling a cable turning a generator while the other closes and retracts.
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That's pretty much it. Advantage is it would be very light and cheap. One opens, pulls the cable turning generator, then closes while the one now closest to the generator opens and in turn pulls the generator in the opposite direction. (The generator obviously geared to turn in only one direction from the alternating input shaft.)

This has to have been thought of before, gonna assume it has but put it up anyway.

Inspired by Paul's idea in the link.

doctorremulac3, Jan 26 2023

Inspired by Paulo's idea. Weight-towing_20oce...current_20generator
[doctorremulac3, Jan 26 2023, last modified Jan 27 2023]

Old technology they looked into 20 years ago. https://www.nbcnews.com/id/wbna3339905
[doctorremulac3, Jan 28 2023]

Someone else trying out an idea. https://www.youtube...watch?v=Eo4Yr4H7_Uo
Similar to mine except it's not one catching element and it resets differenty. [doctorremulac3, Jan 28 2023]

Venetian Turbine Venetian_20Turbine
Very similar to the above link; by [Vernon] in 2005. [neutrinos_shadow, Jan 30 2023]

https://www.usni.or...placed-paddle-wheel [pocmloc, Feb 02 2023]

Cool place to try out a model of this idea. https://www.tripadv...nty_California.html
[doctorremulac3, Feb 02 2023]


       Lighter and cheaper than a rotary turbine?
pocmloc, Jan 26 2023

       Yea, not sure what I'm gaining here. The idea would be to have a really big water catching thing, but dunno is it's worth it.   

       Okay Poc, how about if these "parachutes" are really big? We're talking like a football field? Yes? No?   

       Sure it's a moot point, somebody has to have thought of this.
doctorremulac3, Jan 26 2023

       Thinking about this more than I should, I came up with a football field size dual underwater parachute resetting concept.   

       One football field sized parachute is getting pulled by the water, just picture a big square parachute all bulging with water.   

       Then picture the alternating parachute returning to the generator shaft, it's totally flat.   

       The way one turns to the other it it simply rotates from a water catching position to a flat non water catching position. Likewise the flat chute rotates into a water catching position why the force of the water catching chute before it gets flattened and the cycle repeats.   

       So theoretically you can have all the water at the mouth of a particular river or bay tapped without having to build the big earthen or concrete dam.   

       Hmm. Could probably use this for a wind farm as well.
doctorremulac3, Jan 26 2023

       At any given time, the tide is pulling in one direction. Is the change-over between these two parachutes supposed to coincide with the turning of the tide?
pertinax, Jan 26 2023

       No, just pulls about 100 yards or so, might take a minute or two depending on the speed of the water flow, gets unrolled for its catching position into a flat lesser resistance position and pulled back and forth with the other one doing the opposite.   

       Boy, talk about needing a picture. I don't even think a picture would do it, I think it needs an animation.
doctorremulac3, Jan 26 2023

       This is related to "it's more efficient/faster to sail across the wind than with it". This idea will never be as good as a turbine.
neutrinos_shadow, Jan 27 2023

       I agree, but I’m making up lack of efficiency with sheer volume. Also I didn’t mention that this will work equally well whether the tide is going in or out. I know turbines do that too, but this is a big bag that catches MOST of the water flowing in a particular direction without having to squeeze it through penstocks to power a turbine. Doesn’t have to be just to water catching elements either, could have multiple and series theoretically a mile long or so.   

       I also realize that me description sucks, I would have no idea what this was if I read it, itctrakly needs an animation.
doctorremulac3, Jan 27 2023

Voice, Jan 27 2023

       Dual umbrellas might be better.   

       Oh there's no doubt that a parachute winch generator the sizer of a football field will produce more power than a turbine the size of a bicycle.   

       So I don't think efficiency (in terms of energy in the water vs. energy out) matters very much here. What matters is exactly what you put your finger on, //very light and cheap// - in fact I don't even think the weight matters, just the cheapness.   

       The question is like for like, to generate x gigawatts of power, your parachute rig will be cheaper or more expensive than a turbine.   

       Yeah its just string and fabric but scale it up and you start having to factor in wear and tear = ask any sailing boat maintenance person about how much wear and tear there is on fabric sheets and attached ropes.   

       And the generator has to output the same amount of power whether its driven by parachute winches or turbine blades. So the drive shaft torque will be the same. So no cost savings there. Maybe even more expense because the turbine has longitudinal thrust whereas the parachute pulley has lateral thrust. Plus the reversing gearbox of course.
pocmloc, Jan 27 2023

       Couple of comments:
- My original idea was to locate these solutions in ocean currents and not on tidal areas. This way the thing doesn't have to keep doing 180 degrees turns.
- I'm not sure the "parachutes" need to be football field sized. Is the goal to stop any sailing in the area? Plus the maintenance would make it unfeasible.
- Instead of a flexible parachute which will tear with time, use a solid, light-weight, cone-shaped, neutrally-buoyant structure with a lid at the end of it. The lid opens or closes depending on the cycle.
- And on a more personal note, my name ends with an "o": Paulo.
PauloSargaco, Jan 27 2023

       Sorry Paulo, my bad.   

       What I'd like to see is how big this thing would have to be to turn a Hoover Dam size turbine.   

       Questions of wear and tear are certainly core to this. The idea is to have the only hard structural elements be two long oval cables. The huge "water sails" for lack of a better term would be made out of whatever's cheapest to get the job done because this is a study in budgeting. "How big would this have to be to replace 100 turbines? Okay, how much cheaper is that than the 100 turbines?"   

       As far as tearing, the water movement here is very slow and predictable. These things are located in areas where you have highest ocean movement, but the areas where that's worth doing are going to be entrances to bays. They'd be 15 to 20 feet under water so as to not impede shipping or marine life transit.
doctorremulac3, Jan 27 2023

       //This is related to "it's more efficient/faster to sail across the wind than with it". This idea will never be as good as a turbine.//   

       You can't make a turbine that can extract meaningful energy from water moving at ocean current speeds. A fast current is 0.5-1mph. Hydroelectric dam turbines, of some designs, do work more like a sail vs a spinnaker. That is they are foil designs, but they benefit from high velocity for energy density and high pressure to prevent any cavitation - which is sort of analogous to stalled airflow on the low pressure side of a spinnaker, but with extra phase change complications. Ultimately an ocean current turbine would end up looking like an axial flow wind turbine, it would have to be extremely large to extract meaningful energy out of slow flow. In being large it would have end up being delicate, and the ocean doesn't tolerate delicate things. Because it would be large and spinning you run into problems with the speed of the tips, water really doesn't tolerate things moving quickly. So your turbine needs to scale up to have a cross-sectional area large enough for a meaningful amount of energy, but can't scale up because all the parasitic losses scale non-linearly.   

       This is where a massive underwater spinnaker/parachute makes sense. Nothing about it gets less efficient with scale. In order to extract energy from the flow, the parachute will have to be traveling slower than the current, which means you will have water "spilling" over the edges, at massive scales that could be an issue, but it's trivial to engineer in a few holes like real parachutes.   

       //As far as tearing, the water movement here is very slow and predictable.// Most of the time, sometimes it gets very angry. One of the best currents for this would be the gulf stream right up the US east coast. Right in the way of hurricanes.   

       //They'd be 15 to 20 feet under water so as to not impede shipping or marine life transit.//   

       As deep as that? That's basically the surface, right in the zone of big swells and you'll be catching a lot of whales. The first challenge will be anchoring the device. Take the Blake plateau off florida, you want to be in the zone that's around 1km deep. Offshore oil drilling does this, almost 4x this nowadays actually, but it's not cheap. The next challenge is extracting energy out of something moving S L O W L Y. Do we do this anywhere? Lets run some numbers.   

       Work done is force x distance. A good sized wind turbine for comparison is say, 1MW, so 1.0x10^6 J per second. The distance being say 0.5m gives 2 million N, or 200,000 kg so a 200 ton cable, viable. I don't know how big the parachute will have to be for that amount of force, but let's say it's reasonable. Say your cable is payed out from a ~30m circumference drum, you'll get something like 1 rpm. You'll need to gear that up 100-1000x for an efficient generator.   

       A river might be a better bet, the amazon is 2-4x faster than ocean currents.
bs0u0155, Jan 27 2023

       Yea, this could certainly be put on a river as well, but I like that this particular design (I'll get a drawing going) works in both directions which lends itself to tidal flow tapping. I know current systems do as well, but looking at the amount of water flowing through my local bay for instance under the Golden Gate Bridge, 390 billion gallons moving that weighing three trillion four hundred seventy-one billion pounds moving at 3 to 7 knots.   

       So the concept is grab this slow moving water with the biggest catching thingy you can do, which needs to be cheap and light, so like a big pillow case. Fills up when the opening is facing the flow, flips around, moves to the reset position flat, then when the water is flowing in the opposite direction, the pillow case opening that's aimed the other direction opens up and fills.   

       I'll get a drawing going.   

       Hey B, if I got the numbers on this with regards to weight, speed of the movement of that weight etc, would you be able to determine the kilowatt hours potential of this thing? I'd have to do a lot of web clicking, I'm thinking you already have that in your skillset yes?
doctorremulac3, Jan 27 2023

       Possibly. The tricky part is calculations on how much power you can extract from flow with devices like this. There should be some way of extrapolating from water wheels etc. Should be simple enough.   

       Taking energy from tides (vs currents which are mostly thermally driven) does technically slow the Earth's rotation however. Go too far and you'll upset the calendar industry.
bs0u0155, Jan 28 2023

       I'm seeing problems with catching and harming things, like whales, dolphins, submarines...
RayfordSteele, Jan 28 2023

       The scoops are moving with the flow of water then ejecting that water at the end of the cycle. Nothing could stay in it. Nets could be put in place but I don't think that would be necessary. Theoretically. Although nets might serve a dual purpose of holding the scoops in shape AND keeping things out.   

       Okay, so let's say with a scoop apparatus the size of say ten football fields, getting maybe 20% of all that water, maybe a trillion pounds over 24 hours. The water flow is from 2 to 7 miles per hour about. So maybe, 40 billion pounds per hour moving at, call it, 4 miles per hour average? 40 billion pound moving 4 miles, would that be the equation to look at? Where's the resistance factor? You're pushing water out of the way, how to you compute that load? Looking at it in reverse, how much energy would you need to move 40 billion pounds 4 miles? Not really sure how to set up the model.   

       With current technology they're estimating 2,000 megawatts, more than twice the city's peak demand, but that's taking a little sip of that water. This idea is to take a significant amount and just pull massive Hoover Dam sized turbines.   

       And by the way, my idea (if it were feasible) doesn't hurt any marine animals like turbines would.   

       They looked into this 20 years ago and bailed for some reason. (link)
doctorremulac3, Jan 28 2023

       [bs0u0155]; you make a good argument. Experiments must be done!
[doctorremulac3]; that linked idea is reminiscent of [Vernon]'s "Venetian Turbine" from 2005.
neutrinos_shadow, Jan 30 2023

       Very cool!   

       Vernon you clever son of a gun! Get back here and take a victory lap!
doctorremulac3, Jan 30 2023

       Occurs to me, you could also to an angled attack to get more speed out of it. The main idea is those football field sized collection, tarps I guess you'd call it.
doctorremulac3, Jan 31 2023

       Wonder if there's a design out that that's just one huge aileron that just cycles up and down.
doctorremulac3, Feb 01 2023

       // one huge aileron that just cycles up and down.//   

       That could work. Although "aileron" isn't particularly accurate, servo-tab? Anyway, a foil section that can vary the angle of attack and therefore direction of force. It's a fairly simple mechanism to automatically modulate the angle of attack vs the power transfer arm and flow. Again, a river would be better.   

       Even better would be to make it continuous. You could do a wheel. Front vanes generating upward force, rear generating downward force, net rotation. Top and bottom would have 0 angle of attack and therefore cancel out.
bs0u0155, Feb 01 2023

       Yea, that would be optimum, but trying to think of a shape that fits best in a relatively flat very wide space.   

       But the aileron couldn't be flexible, that adds to the weight and expense. The main thing about the huge curtains, pockets or whatever is they'd be conceivably cheaper and lighter.
doctorremulac3, Feb 01 2023

       Tidal power generation can tear turbines apart. I can't imagine what sort of material a chute can be made from, that wouldn't get destroyed. This is no doubt at least partly why previous research was stopped.
tatterdemalion, Feb 02 2023

       //I can't imagine//   

doctorremulac3, Feb 02 2023

       OK my question is still, what is the benefit? Compare this thing to a standard tidal turbine. Each of them generating a certain number of MW.   

       Both this thing and the tidal turbine require a generator or dynamo, with watertight bearings, sitting on a strong mounting point fixed firmly to foundations, and with cables and switch-gear to connect their electrical power output to the grid.   

       Both these things require the end of the generator shaft to be turned.   

       This thing has a big reel and the string and the parachute. The turbine has a couple of propellor blades or vanes. That is the only significant difference.
pocmloc, Feb 02 2023

       Well the main difference is volume of water tapped for energy.   

       The idea of catching all of it with this big sheet is you get all that mass. I guess you could call it a moving dam. The turbines, for all their efficiency, are tapping the movement of a body of water only equal to the area of their blades, (albeit more effectively) and the area of contact with the water isn't very large.   

       This area of incidence, impact or whatever, with a turbine is perhaps a few yards, where the area of contact between water and this water catching thing is several acres.   

       So say that 40 billion pounds per hour is moving at up to 7 knots, you're telling it "Hold it there water, before you move anywhere you're gonna have to push this sheet out of the way." (That in turn turns the turbines through the cables attached to it.)   

       Then theoretically you've got a cheaper material than steel being used to catch that water.   

       I'd say another possible advantage of this is the actual generators could be put up on dry land, needing only cables running on pulleys leading to them to transfer the tapped motion of the incoming and outgoing tidal current or river flow.   

       So short answer, volume of moving water tapped for energy would be more with this. Would it be better than turbines once the logistics of getting everything in place set up? Dunno. Maybe, but might be a lot better, like one of these in place under the Golden Gate Bridge powering San Francisco and Oakland.   

       Certainly might be worth exploring.
doctorremulac3, Feb 02 2023

       But for a given size of generator there is an optimal amount of water energy that the generator can handle.   

       I'm thinking that the generator itself is the main cost here.   

       However big you make the parachute I can make turbine blades big enough to extract the same amount of energy from the water. Plus a little bit bigger just to prove some kind of petty point.   

       And yes you are right theoretically the generator could be on land. Well so could the turbine generator, just have a driveshaft running down into the water.   

       At the end of the day isn't this the reverse of the argument about screw vs paddle drive for ships? See: Rattler vs. Alecto
pocmloc, Feb 02 2023

       I'm mainly looking at the area of the flow space that's tapped.   

       So for a turbine, you've got several circular areas, the paths of the turbine blades. That's the moving mass of water you're tapping.   

       I'm talking about trying to basically tap ALL that water moving in. You've got a roughly rectangular shaped moving body of water, you're blocking the whole thing, (or as much as feasible anyway)   

       You can't make those turbine blades as big as the rectangular area blocked because you're using a bunch of circles rather than one massive dam.   

       I guess that's the best way to describe this, it's basically a shifting dam.   

       And yes, this would be the paddle wheel vs propeller, and it loses on that account, but the idea is to make up for in by having several thousand times more mass being tapped and with a much cheaper cost per square yard of water blocked. For one thing you could basically have one generator instead of dozens. That would be a significant cost savings in that area alone.   

       Theoretically anyway.
doctorremulac3, Feb 02 2023

       Poc, check out the link. This would be a cool place to try this idea out.
doctorremulac3, Feb 02 2023

       //So for a turbine, you've got several circular areas, the paths of the turbine blades.//   

       The issue with turbines and other similar devices is the rotational component and how that scales. If you want to capture more flow, you need a bigger circle. But when you scale up the radius, you scale up the circumference Pi-fold, and with it tip speed. This is why WW2 fighters didn't just keep growing, supersonic propeller tips are an efficiency nightmare. Water is much worse at 10-fold lower speeds, which you run into fast because you want huge flow capture area. The genius of jet engines is that it side steps the problems by compressing the air and eliminating a lot of relative speed difference between the blades and gas flow. Hydroelectric dam turbines do a similar thing with pressure.
bs0u0155, Feb 02 2023

       Hey b, you're the one to evaluate this with your knowledge of hydrodynamics & such. Do you think this is worthy of taking it to the next level whatever that is? Making a model or something?   

       Theoretically there's somebody who could even make a computer model. Know anybody?
doctorremulac3, Feb 02 2023


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