Carl-Pålsson | - I´m sure a submarine would be able to pick up a giant under-water balloon on its sonar. I am also sure that the seastead would publish a navigational hazard such as this to the relevant shipping organizations to avoid accidents.
- Nevertheless I would love to see this collision. Do you think the submarine would bounce on or puncture the balloon? What would happen if it punctured? Would the sub fall through the air bubble to its death on the ocean floor?
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Carl-Pålsson | The forum software is evil. |
Carl-Pålsson | - Interesting point. Hanging all the ballast in a cable probably wouldn´t be very prudent, if the line snapped. Thus to keep the spar upright in this event the GB mass could only be a fraction of the regular ballast, which would reduce storage capacity.
- And the big question is whether there actually are any advantages over established, reliable energy storage systems like electrical batteries.
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Carl-Pålsson | - Height by weight is capacity. Thus every reduction in height would need to be countered with an equal increase in weight.
- If we assume 1000m for the cable weight version and 100m for the water tower version, we´d need ten times the weight of the cable weight in water to end up with the same capacity.
- In addition to extra ballast required you would also need extra flotation to make up for the increased weight of the whole platform including seawater, added ballast etc. you´d have to do the math on this but it doesn´t feel economical to me.
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Jesrad | The Brent Spar probably had gas turbine generators that dwarfed the “couple tons of ballast water” in terms of power and charge. One would have to calculate the power requirements per surface of seastead, and compare the mass of ballast needed according to power required, with the expected mass corresponding to the surface. That’s a complicated calculation and I don’t think I could do it. |
Sundiver | The relative sizes would matter as would speed/inertia. A big nuke at more than a few knots would tear right through I think, with a major “glub”. It probably would have some sort of fall but I think the upwelling from the bubble would tip the tail up and nose down and it would plow into the bottom. At lower speed it might very well just bump the balloon aside with maybe some small rips. The balloon would be quite visible on sonar and would most likely also have an acoustic beacon.
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Sundiver | A couple of tons wouldn’t be a problem. For fire suppression and domestic water pressure though, there’s not much value in using a water tower. You don’t save energy because you have to pump the water up to start with (unless you use a hurricane tower or mist lift otec to generate it). Domestic systems work pretty well and are OTS (off the shelf). A large amount of fresh water (for a colony) would weigh alot though and for stability, lower is better.
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vincecate | - So a 10 ton weight (after displacement) lowered 1000m would store 27 kWh. Enough to supply a single family home for a full day.
From http://www.webriggingsupply.com/pages/catalog/rope/braided_cable_pulling.html it looks like 25,000 lbs rope is a bit over $1/foot.. So 3,000 feet would be around $3,000. The 10 ton weight might cost $2,000. So call it $5,000 for 27 kwh. This is $185/kwh. This is more expensive than batteries, but should last longer than existing batteries. The weight should last a very long time. Probably could get a better price on the rope or the weight. If you already had an external ballast, the weight could be free. In that case it is $3,000 for 27 kwh or $111/kwh. You can also use 1/5th the weight (2 ton) and 5 time the length (15,000 feet) at 1/5th the strength. Then the weight is cheap and the rope is about the same. So it also gets close to the $111/kwh. Given the life expectancy and that there are probably cheaper sources of rope, I think this idea has potential. The electric motor/generator from a hybrid should work for this. It is also a kind of fun idea that only people floating in the deep ocean can play with.  |
thebastidge | I’ve lived in several places where ther was no municipal water system (right now, in fact). It is trucked in, stored in tanks, and pumped by your grid or generator electricity to where you need it. I have seen where these tanks were at ground level, and where they were on the roof. The roof is always better. - the problem is that you need bigger pumps to get decent water pressure when the tank is low and the need is elevated. Bigger pumps are more expensive to buy and replace.
- They also have to work harder when water is being used.
- A smaller pump that doesn’t start and stop as often, moves smaller amounts of water over longer periods of time, is more efficient and lasts longer.
- It works no harder when water is flowing out of the storage tank than when it is simply topping it off.
- Smallr pumps are also able to be powered by more intermittant or weaker input sources, because they don’t draw as much current at any one point in time.
- the heavy work of getting good water pressure is done by gravity feed.
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Sundiver | Stability means weight down low, not high. There are ten million boats out there, almost none of them use gravity systems. Neither do oil field platforms. The reason is is that you have to pump the water up there anyway, so just pump it into a pressure tank (like a zillion homes) and it’s done. Domestic water pressure (for a good shower) is 40psi. You need about 80′ of head for that. So if you want 40psi on the upper level, your storage needs to be 80′ above that.
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thebastidge | A water tank less than 2 meters diameter, less than two meters in height, one floor above you gives a perfectly nice shower for a family home. Empirical experience in at least 3 different countries. The only pump involved lifts the water to the tank. Feild expedient solar showers are suspended just above your head, and depending on how your spigot is set up and how fast you want your showerbag to run out of water, give perfectly fine water pressure. You can even simply dump a bucket over yourself. The only constraint is ho wmuch water is available. |
Arthur-B. | Since we’re discussing mechanical storage of energy, here’s a crazy way that probably doesn’t work, make the ballast out of large disks or iron rotating in opposite directions with two long axles (one inside another) going to the top deck. You can also use it to maintain the orientation of the seastead. The principal advantage of flywheels is that it can produce a lot of power… I don’t think it’s very useful on a seastead. The cost is also probably prohibitive, not to mention the friction losses on the bearings. |
Jesrad | Flywheels are indeed good in terms of power-rating, they can convert lots of energy quickly – but they are not so good at storing it. The power density is low compared to batteries. Also, iron is a very poor material for flywheels, spin-wound carbon fiber is prefered as it does not fragment upon failure, unwinding and burning instead. Magnetic or aerodynamic bearing can be used to reduce friction losses greatly, but even then you can’t expect them to resist any kind of movement: the precession stresses would simply deform the device and the vacuum seal could fail – or the rotor could come into contact with the stator and burn. That makes them a poor choice for a moving structure. If you’ve got two rotors spinning in opposite directions, you get no precession from the whole thing, so it’s not useful for stability anyway – but there will still be torsion efforts between the rotors and stators proportional with the moment. |
StCredZero | Another way in which water and power storage could be combined: make an out-sized Solar-Thermal water heating system with a well insulated tank and run a Stirling engine off of the heat. Thermomax heat pipe tubes work very well, and may have a better service life than photovoltaics. In a well insulated system, the combined efficiency with a Stirling engine might be higher than the photovoltaics as well. http://www.thermomax.com/tech.html Also, water tanks and insulation are cheap and don’t wear out as quickly as batteries. Apparently, this family’s single set of Thermax tubes always provided them with hot water, and generated enough excess heat to boil the hot water and burst their Pex radiant heat system. http://www.solarhaven.org/Hydronic.htm I recall seeing an account of a 3 kilowatt Stirling engine being designed and fabricated in India in the 70′s. (Operated using the heat from decaying grain husks.) So this also has the potential for being very repairable. |
i_is_j_smith | You would probably be better off just purchasing a commercial flywheel system. like the 300kW VDC-XE system from Vycon Energy or the 25kWh Smart Energy system from Beacon Power. No info on price, but the efficiency of these systems would be much higher than something homegrown like weights on a rope or pumping water into a tower and letting it fall through a waterwheel. Here’s a link to a Beacon Power presentation on using their flywheel systems for storage of wind power: PDF LINK BTW, any reason for the increase in spam lately on the boards…or is that just because TSI is so popular lately?  |
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