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Whole-Ocean Gravity Battery

Home Forums Archive Infrastructure Whole-Ocean Gravity Battery

This topic contains 26 replies, has 6 voices, and was last updated by Profile photo of cbthiess cbthiess 6 years, 6 months ago.

Viewing 12 posts - 16 through 27 (of 27 total)
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  • #2522
    Profile photo of thebastidge
    thebastidge
    Participant

    500 PSI is barely enought to power an impact wrench for a few minutes. Completely impractical for a storage battery, considering the cost, the possibility of failure requiring replacement of the system, when easier, cheapr, more maintainable solutions exist.

    #2560
    Profile photo of
    Anonymous
    • The pressure doesn´t say how long you can power stuff. You need to know the size of the pressure vessel for that.
    • Pressure-wise i´m sure you can drive power tools just fine on just 100psi or so. Forever, if your compressor tank is large enough and the tool doesn´t break.
    #2508
    Profile photo of
    Anonymous
    • A dome, ok gotcha.
    • What would you need in terms of dimensions of the dome, depth etc to equal the storage of for instance X numbers of lead acid (car) batteries for instance?
    • What do you do when you need to move the seastead? Leave the dome?
    • I´m not grasping the heat loss discussion but it seems to me like there would be massive losses of heat to the ocean. Ambient air gets compressed – heats up – gets sent down where it directly touches very cold water.
    • edit: Nevermind the last question. I guess you just suck the heat out of the air after you compress it.
    #2570
    Profile photo of Jesrad
    Jesrad
    Participant

    The pressure may not define how long you can power things, but it places a hard limit on the power you can get. Pull too high a power from a given pressure, and your efficiency drops + the gas starts liquifying because you cannot heat it enough and cannot get the gas to move through the hose fast enough. It is a limit quickly attained, if I read my history of technology right. In fact this is a MAJOR issue in supersonic and hypersonic wind tunnels, see this website about NASA’s wind tunnels.

    #2577
    Profile photo of Sundiver
    Sundiver
    Participant
    • Thebastidge, I don’t mean to flame but you seem to be speaking with authority and knowledge on this subject. Impact wrenchs run on 80-120psi. Most of the seals would be damaged in a few minutes at 500psi. You’re confusing pressure with volume. It’s like voltage and amperage.
    • Having spent some number of decades living and working in the oceans, depending on compressed air for my life and using it everyday in my work, I’m confident at this point that I can speak with authority on the subject. In this particular application (that of an exisitng, anchored platform in deep water), there is no easier, cheaper, more maintainable solution than deepwater air storage.
    • You hit on one of the most important factors for ocean operations- maintainability. It’s a tough one. This concept uses off the shelf, extremely simple, industry standard equipment. It’s scaleable and expandable. We may be talking about different ideas- I’m referring to my post “Subsea surplus energy storage, air based”.
    • I’m not sure what Jesrad is talking about. I am sure it doesn’t apply here.
    • It’s likely that airmotor gensets would operate on 200-300psi. The air would be stored near the bottom to avoid too much stress on equipment. The deeper the storage bags, the more air they will hold (because of compression). If stored at 2000ft, the working pressure would be 890psi. It would be regulated down to the operating pressure of the airmotor genset.
    • “It is a mistake to think you can solve any major problems just with potatoes.” -Douglas Adams

    #2579
    Profile photo of thebastidge
    thebastidge
    Participant

    ” Impact wrenchs run on 80-120psi. Most of the seals would be damaged in a few minutes at 500psi. You’re confusing pressure with volume.”

    • However, Jesrad’s point stands. You quickly reach a point where the power stored isn’t sufficient to do some things.

    As an example, the Mars and Jupitr explorer probes have very efficient, super low thrust engines. they have to plan any vector changes far enough in advance to make a little push correct itself over a long distance. You simply cannot make a sharp vector change. sometimes you need a brute force approach even if it is not the most efficient. That’s what I meant by my screed on efficiency, effectiveness, elegance, etc.

    • I still say, that for less cost, you can store more pressure, and probably larger volumes of compressed air on the surface, and maintain them better and recycle the materials later.
    #2581
    Profile photo of Sundiver
    Sundiver
    Participant
    • I don’t know how much it would cost on a practical scale. It’s not a problem to price out but too much of a time requirement for this forum. For one cubic meter? $300.
    • Suction piles are extremely elegant. The concept is a bit counterintuitive but it’s a common anchor system for large floating items like tension leg platforms. Here’s a link- http://www.sptoffshore.com
    • A recent variation is SEA anchor, a Suction [pile] Embedded Anchor. see the video on the spt site.
    • Here’s the really cool thing, the same anchors that anchor the seastead can be used to anchor the storage bags. The anchor lines can be composite (like kevlar) and hollow and double as the vertical risers (air hoses). The bags themselves are simple, think of the design of a high altitude balloon, with no need to consider weight (you can use stronger materials). That’s why I say “almost incidental”.
    • Heat exchange is not really an issue. What you say about the heat of compression and expansion is true but can be ignored. But the heating and cooling are energy sources that should be conserved. Like for domestic water heating and air-conditioning and refrigeration.
    • “It is a mistake to think you can solve any major problems just with potatoes.” -Douglas Adams

    #2635
    Profile photo of thebastidge
    thebastidge
    Participant

    Well, this idea doesn’t need fullly developed Seateads to test. Just a buoy big enough to hold the equipment and an anchor heavy enough to hold the bag, and a means to put it in place. Maybe space could be rented or borrowed from an existing platform.

    • Anyone got grant-writing experience and/or a university or oil company contact that might under-write such a study?
    #2650
    Profile photo of cbthiess
    cbthiess
    Participant
    • That’s a good price – about $120/kWh at 1000 meters. But concrete goes for $85/yard, 1 yard is enough to anchor 1 cubic meter of air, and turning it into a dome requires just a few 2×4’s and plywood for a form. So that’s about $35/kWh. It also doesn’t require additional pile capacity. Of course, concrete might cost more on the ocean, and it is less portable if you plan to move around a lot.
    • And you may be able to find do-it-yourself materials for lift bags that are a lot cheaper than $300.
    • I hadn’t thought of using the heat/cool directly – good point. But it would depend on whether you have need for hot and cold. If your goal is high total system efficiency for electrical storage, or cheapest electrical storage, you would have to address the issue.
    #3023
    Profile photo of Sundiver
    Sundiver
    Participant

    You asked how much for one cubic yard. That’s how much a piece of pipe, some hose, and a 500lb lift bag costs. It doesn’t scale.

    You may be able to find cheaper materials but isn’t serviability more important?

    Right on the heating cooling thing. It’s not a problem, it’s a source of heating/cooling energy.

    Concrete may go for $85/yard but an undersea concrete dome does not. That’s like saying AL goes for $1.32 a pound and that relates to a 757. Concrete is not very heavy underwater. never mind.

    #3024
    Profile photo of Sundiver
    Sundiver
    Participant

    because there is ongoing research into using subterrain vaults for the same thing. The physics are the same, the bags, hoses, anchors are all normal industry stuff.

    It could be done but would be mostly academic in nature.

    #3054
    Profile photo of cbthiess
    cbthiess
    Participant
    • It is a scalable cost because one hose could service any number of 1 cubic meter compressed air stores.
    • Servicibility is only important if it reduces expected lifetime cost. If moving around a lot, a lift bag would certainly be cheaper. If staying in the same spot, a fixed dome would probably be cheaper. Wouldn’t take much or any maintenance, either, since it has no moving/flexing parts.
    • Making a concrete dome is actually very simple. All you need to turn a yard of concrete into an air-tight dome is a reusable form made of about $50 of plywood and 2×4’s. The final product doesn’t have to be pretty. It just has contain slightly less than its submerged weight in air. Concrete having a density of 2.4x that of water, using 1 yard of concrete for every yard of air would give you a nice safety margin.
Viewing 12 posts - 16 through 27 (of 27 total)

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