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mechanical energy storage  RSS feed

 
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Been thinking about energy storage, so here's something to kick around some.
These days we're getting ever better at harvesting the energy that's all around in the wind, sun, water and even tides (although more work needs doing in the latter) but they all have one massive problem, they don't always happen when we want to turn on the kettle for a cuppa.
So, what we need is a good way to store the spare power for when we want to use it and it's a still dry night and the tide is inconveniently not flowing for another 3 hours.
But I hear you cry we can do that, we put in a battery bank and an inverter.  Sure, that works, especially small scale - and with modern LED lighting, for example, you can remove the inverter and use low voltage DC, thereby removing one of the losses.  But batteries are expensive to make and can be tricky to keep working long term, and 'most all of them degrade over time, even with good charging systems.
Large scale is harder - and we need large scale, if it's gonna save the planet.  So I got to thinking -  we already have, in some places, pumped storage hydro - and that has a lot of merit; when there's surplus power at any time you pump the water uphill, then when you need power you can generate with it.  However, it needs the right geography and takes a lot of space to do it on any scale, and when it's hot and dry your water evaporates, also the pumps, pipework and turbines and stuff are costly to install and need a fair amount of maintenance
So here's my idea, starting from the pumped storage, which I hope to build a small scale prototype of sometime.  Rather than water, I propose to lift a mass. The mass can be anything that's handy and cheap - if it's in a desert, you'd use sand.  If you have rocks, you can use rocks, if you can afford it, make 'em into concrete.  When you have spare power, a motor winds the weight up, when you need power, you let the weight down, driving a generator.  It's all simple and mechanical and thus cheap and easy to build and maintain.  It's also readily scale-able - you can double the capacity by making the weight twice as big or lifting it twice as far or just by making 2 of them - and where the terrain is suitable it can go underground - in the basement of your house, say - so needn't be visually obtrusive.  You can of course also do mechanical energy storage with a big flywheel - but that involves either crazy speeds or a lot of mass spinning or both, because you're using the speed to store the energy.  It is more effective physically if you make the mass move faster, because energy is proportional to speed squared, but high speed has it's own issues.  Gravitational potential energy though is given by mgh:  so a 1 tonne weight (1000kg) lifted by only 1m has a potential energy of somewhere around 9.8KJ. (sorry, not going to make it into BTUs for you!) If you make it 5m high instead of 1, then you get 5x the capacity, and obviously, you can make the mass bigger (although making it too big will increase the cost for whatever holds it up.
It could be fully mechanical, with a cable hanging the weight; or hydraulic, with a ram underneath or maybe some other method I've not thought of yet.  It's not going to be super-efficient, but then every system is inefficient somewhere and they key point is if it's cheap enough to build, and uses power which would otherwise be wasted, it doesn't matter if it's not so efficient.
 
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It is already being done.

https://qz.com/1355672/stacking-concrete-blocks-is-a-surprisingly-efficient-way-to-store-energy/
 
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A simple calculation will show that gravitational potential energy (GPE) is a poor store of power unless you have access to enormous amounts of storage - i.e. a lake.

Austin Shackles wrote:Gravitational potential energy though is given by mgh:  so a 1 tonne weight (1000kg) lifted by only 1m has a potential energy of somewhere around 9.8KJ


Take a look at this cordless drill battery.

It's 18v 9ah. This converts to 162 Watt-hours, which converts to approx 0.58 megajoules.

So that hand-held battery has approx 60x more energy than a 1 tonne weight raised to 1 metre.

Storing energy as GPE just isn't practical unless you can do it on a massive scale.
 
Austin Shackles
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That's the same basic idea but I can't help feeling he's over-complicated it - although it's easy to scale like that - taller tower, more blocks, same crane.  I'd have thought one big block moving slower would also work, though.  The same crane motor that lifts (say) 500kg in (say) 100s would lift 5000kg in 1000s, or would lift 5000kg a tenth of the height; since it's a linear relationship, within reason 5000kg lifted 1m is as good as 500kg and 10m.   The other variable in that tower is that per block,  more energy is needed to lift them the higher they are going - and thus, the top layer stores more energy than the bottom layer.  That might not be an issue, though, in use.

With a single crane, the output is going to be intermittent, as well, although having multiple cranes would solve that issue, as one could generate while another is winding back up to hook another  block from the top.
 
Austin Shackles
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Matt Coston wrote:A simple calculation will show that gravitational potential energy (GPE) is a poor store of power unless you have access to enormous amounts of storage - i.e. a lake.

Austin Shackles wrote:Gravitational potential energy though is given by mgh:  so a 1 tonne weight (1000kg) lifted by only 1m has a potential energy of somewhere around 9.8KJ


Take a look at this cordless drill battery.

It's 18v 9ah. This converts to 162 Watt-hours, which converts to approx 0.58 megajoules.

So that hand-held battery has approx 60x more energy than a 1 tonne weight raised to 1 metre.

Storing energy as GPE just isn't practical unless you can do it on a massive scale.



but 5000kg and 5m height would give you  25x the energy, say, and wouldn't be hard to build.  Obviously, you can't carry it around like a drill, but many things don't need so much power as a drill.  Take lighting, for example, if you use LEDs 10W will light a room.  That guy in the other link is planning 35t blocks and a 120m tall crane.  It might be that for small scale, batteries are still the way to go - but town-sized, they are still way too expensive.
 
gardener
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Have you ever cast your eyes on the workings of a good eight-day clock, or evrn a cheap one? As a kid I had a plastic german coocoo clock that you “wound” by pulling chains to raise hanging iron weights the size and shape of pine cones. They would “fall” (on pullies and gearing) over a week to power the clock and its whirring and flapping and coocooing and doors opening and closing and such.  You can’t convince me that with different gearing you couldn’t get a useful amount of LED light out of a system at that scale. The comparable battery Big Bird alarm clock I owned at the time ate “AA” batteries like they were chicken feed, and all it did was play a liitle internal voicebox record player.

I’ll bet that there is developed tech in weight-driven energy storage at the scale of hundreds of pounds to tons in some functional clock tower in Europe right now that you could go and take photos of. Recharged daily by the human labor of someone pulling on chains for an hour or two.

To me the natural upscale is with wind. Put it in the same tower as your windmill, and you’ve got the 21st-century version of the Dutch pumping tower, only yours can pump or irrigate or heat/cool a greenhouse or, within reason and depending on scale, be the power core for your whole homestead or small community.
 
pollinator
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Hydro electric can be a type of 'mechanical energy storage'.
Just wind/spin the motor up and the water goes up the hill/mountain and then you can drop it down the mountain at night for electrical power.
 
Dan Boone
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That’s the “pumped storage hydo” in the first post in the thread. My understanding of the OP is that this thread is exploring alternatives to that.
 
Mother Tree
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The video in that link was rather interesting.  I've embedded it here.

 
Matt Coston
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Austin Shackles wrote:but 5000kg and 5m height would give you  25x the energy, say, and wouldn't be hard to build.  Obviously, you can't carry it around like a drill, but many things don't need so much power as a drill.  Take lighting, for example, if you use LEDs 10W will light a room.


5000kg at 5m = 245,000 J
10W LED light for 6 hours = 216,000 J
So you can basically illuminate 1 room for 1 evening. It's not even remotely economically viable - if it was, we would already be doing it everywhere.

Have you done an estimation on what your idea would cost? What $-per-kilowatt-hour do you expect?

Austin Shackles wrote:It might be that for small scale, batteries are still the way to go - but town-sized, they are still way too expensive.


I assume you're aware of Tesla’s 100MW/129MWh Powerpack project in South Australia? The reported figures show that it will pay for itself in less that 2 years.
 
pollinator
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Yeah. I like variations on the mill pond idea, right up to the scale of hydroelectric dams. It makes sense. Just dam up a mountain valley. In a tidal zone, have a lagoon with a variable inlet that would only let water out to generate power, when necessary.

I like this idea in the coastal context because you could easily stack functions with a lagoon-based mariculture operation. Also, imagine in the case of the most extreme example possible, the Bay of Fundy, if pillar-structures not unlike the shape of its own Flowerpot Rocks slowed the ocean's egress to low tide to generate electricity. Would the intertidal biosphere thrive in such a case, with less of a dry-out each tide?

I don't think mechanical energy storage will stack up well here as described, pun intended, especially anywhere with hydroelectric infrastructure to be exploited. On the homestead level, I would consider steam infrastructure before a crane and block setup, especially in climates where we need to heat our homes over half the year round.

I think heat energy storage is probably much more accessible and practical, though with a few problem issues that need care in the handling. If homesteads can make home-scale thermal power units, converting heat to electricity, in all likelihood mechanically, then all we need is a rocketstove that burns at a high enough temperature (in excess of 1100 C, I think the figure is) to crack plastics into their constituent components and burn all but the carbon dioxide and water vapour as fuel. That way, we can address the plastics issue and that of clean, free energy as one.

Honestly, I would look at what can be done with larger battery designs, ones focused more on battery life and efficiency than small size and portability.

If you're talking about a crane and block setup anyways, it's not going to be mobile. If you had the resources locally to recycle lead-acid batteries, for instance, you could use them as your base unit for a modular power station, swapping them out at need to be recycled.

-CK
 
Austin Shackles
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Matt Coston wrote:

Austin Shackles wrote:but 5000kg and 5m height would give you  25x the energy, say, and wouldn't be hard to build.  Obviously, you can't carry it around like a drill, but many things don't need so much power as a drill.  Take lighting, for example, if you use LEDs 10W will light a room.


5000kg at 5m = 245,000 J
10W LED light for 6 hours = 216,000 J
So you can basically illuminate 1 room for 1 evening. It's not even remotely economically viable - if it was, we would already be doing it everywhere.

Have you done an estimation on what your idea would cost? What $-per-kilowatt-hour do you expect?  

Austin Shackles wrote:It might be that for small scale, batteries are still the way to go - but town-sized, they are still way too expensive.


I assume you're aware of Tesla’s 100MW/129MWh Powerpack project in South Australia? The reported figures show that it will pay for itself in less that 2 years.



The Quartz guys have presumably gone into cost in much more detail - even building the pilot thing costs and they have that already.  They are looking to be about half the cost of current battery tech, according to that article that was linked.

As for Tesla, yeah, they do impressive things with what are, essentially, laptop power cells.   LOTS of 'em (check out what's inside a Tesla car battery) and while they have bigtime energy density, the cost in materials and so on could become a problem if you want to expand it to worldwide use.  The essence of using mass is that although the density is low, so are the costs.  The mass can be more or less anything heavy, if it's locally cheap or better still free (e.g. sand in the desert).  What I'm considering is making the thing as simple as possible, thus cheap to build in many possible places.  Batteries are amazing but when you look at the global scale of the power thing, especially (and drifting topic a tad here) if you look at automotive - right now, you can make batteries for Teslas and other such vehicles but you only see a tiny number of them.  The problems will show when you try to have ALL the vehicles running on batteries, or ALL the houses running on renewable.  You then need a LOT of energy storage, distributed around the place.  The Quartz crane thing is looking at 20MWh for the full sized one, and I assume they've done the math to back that up.

Yeah, you can also do pumped storage.  We have one here in Wales, been there for many years and it works well when you have a mountain and lots of water.   You can't do it without both, realistically.  
 
Burra Maluca
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I'm reminded of the gravity light





Or this home-made version



Here's the official website gravitylight.org
 
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I had a similar idea years ago for a home scale version... as I had a potential property purchase where there was sporadic but intense wind on a beach.  The idea on my part was to take a windmill and have it lift 5-gallon pails full of sand onto a raised rack that was on a slight slope (maybe on rollers or just made of crazy carpet or stainless steel.  As the pails piled up on the rack they forced each other down the slippery slight slope, and as they reached the lower part of the slope the handle (which was fixed vertically), was grabbed by a hook and lowered, rotating gears to spin for power generation.   When one got to the bottom, it landed on another slight slope and was thus shuttled to the pick-up spot, where a hook lifted it back up when excess wind power was happening in the future.  The problem with the system, I figured, would be having enough of a size of rack and volume of pails of sand to make the system worthwhile to build for the generation of power on windless days, or times in the night when power was wanted but the wind wasn't blowing.  I never bought that property and never developed a prototype.  I like Dan Boone's clock analogy.  It gives me hope that with the right gearing that such a system could be built with minimal expense.  
 
Burra Maluca
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Austin Shackles wrote:Yeah, you can also do pumped storage.  We have one here in Wales, been there for many years and it works well when you have a mountain and lots of water.   You can't do it without both, realistically.  



I remember them building that when I was at school - Dinorwig Power Station



 
pollinator
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Mass is free,but containing it is not.
Some kind of platform is needed.
But that should be the cheapest part.
So if you want to do this on a home to city scale, maximize the mass, and minimize the distance it is moved, the gearing , motor/generator and everything else.

I propose moving an entire building,the bigger the better.
hydraulic jacks under the building moving it bit by bit.
Perhaps it's a giant water tank with a flexible plastic roof weighted with  a donut float around the center hole.
Funneling rain inside until it's full, then becoming a slightly sloped cone..

At any rate, the electric car economy is nothing but good for both kinds of storage, kinetic and battery.
A derilict electric car could have batteries still good enough for small scale home use, and the regenerative breaking motor/generators might save energy in any task that involves gravity.
I imagine a sloped feild.
A huge gantry spans it.
All day long it creeps uphill, cultivating as it goes.
At night it descends, irrigating on the way.
Solar panels mounted right onboard power it,the motor/ generator drives it, a small battery saves the energy from the night time descent, making the whole process more efficient.
Could a motor/generator drive a hydraulic accumulator?
I think so.
Soil-cement could be stacked on a platform,the platform to be lifted by hydraulics.
Soil-cement means you can stack high without the soil slumping, with building containers.
Mount solar to the sides, wind on top.
The heavier it gets, the more each inch of lifting stores.
The thing is, a platform on a slope with tracks might be better.
I'm thinking railcars for example.
Or a  vehical on a bare minimum road, the electric fed and retreived via overhead wires, trolly style.
Add trailer/more railcars for weight.
Needs more room, and a slope, but no lake.
It's been done, but if we add a supply of cheap motor/generators and wheeled platforms to the mix, it might become more viable.

I wonder if excavation of a hole is cheaper than building a crane?




 
Matt Coston
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@Austin Shackles

I believe we can both agree that GPE is economically viable at large scale (I said it twice in my first post).

I also agree that batteries are made from very finite resources, which is a major drawback.

But I am convinced that GPE is not economically viable at the scale you're proposing in your OP. Let me know when you've figured out what your idea will cost you and how long it will take to pay for itself.

Another interesting calculation to think about - the Tesla battery cost $66 million and stores 129MWh. That means it costs approx $500 per kilowatt-hour. The "Energy Vault" crane in the video is projecting $150 per kilowatt-hour. If true, that would seem extremely good.
 
pollinator
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I cannot see any reason why it is not a viable way of making electricity.

I worked for the railroad for many years, and saw the concept in action, and it is hardly new, having been developed in the 1950's. In that capacity they used the weight of the train consist pushing the locomotive to generate electricity instead of the traction motors being powered by the big diesel engine. That electricity was then routed to a big rectifier that turned the electricity into heat that was dissipated by fans and cooling water. The whole system was called dynamic braking and produced phenomenal power, but that was just a byproduct. What we really wanted was the load on the drive axles to help slow the train down without applying brakes. When electric cars did this to help charge the battery it was labeled as "cutting edge", but everyone in the railroad industry scoffed as we had that for 70 years!

The ideal place for this would be in an old quarry. We have granite quarries here that are 300-400 feet deep. Instead of paying for concrete, the crane would just have to lift huge blocks of granite or marble, lifting it to the top of the quarry, and then dropping it back down during peak grid consumption. There would be a cost of pumping the water out of the quarry, but that would not be a huge cost. Once pumping starts, siphoning would take over.

 
Matt Coston
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Travis Johnson wrote:The ideal place for this would be in an old quarry.


If the crane is economically viable, thousands of them would need to be built around the world. The crane makes sense because it can be built anywhere, and also built adjacent to the power plant, saving on high voltage cabling.
 
pollinator
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I had read about an idea like this long ago, involving the use of any sloping section of railroad, preferably a little-used one.  Using whatever alternative power source, a heavy railroad car, or several, would be pulled slowly to the top and staged there on a side track.  When power was needed they would be allowed to roll back to the bottom, with generators attached to the wheels to liberate the stored energy back into electricity.
 
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Dang CK, sometimes you really get me thinking, good stuff.

This engineering stuff is often hard for me. Biology, not so much.

A tidal communities diversity will actually rise as intertidal durations increase. This is due to a wider range of conditions provided by the wider time frame and/or wider footprint. You will find hardier molluscs, more mobile crustaceans... It would be unusual, and I don't think it has occurred yet, to find an organism capable of handling the range of conditions across the intertidal zone. From saline conditions being pounded against rocks by waves, to baking in full sun, to sitting in fresh water from rain, ice, snow... the intertidal is a brutal place with so many environmental pressures - hence it is teeming with all sorts of life. Point is, finally, the biodiversity will likely drop if the intertidal duration or area are diminished.

Bio-engineers really ought to pay attention to this zone. Antifreeze, armor, desalination, filtration, rock 'eating' (look under a limpet), etc.

Displacement of a load for power storage has also been done with train carriages on a hill as Alder mentioned. This I much prefer to the crane as it doesn't look like a construction site.

A tidal fish farm. Now you're talking. Fish is only going to increase in price and if you farm fish well they're better than wild counterparts (A friend's tidal farm got 16x fatty acids in cultured eels compared to wild stock on the same farm). Unfortunately, despite brilliant design, laws prohibited (him from) the sale of eel. It is, however, a blueprint for the restoration of galaxiid ( and other anadromous) fisheries.

Tidal power need not have much down time at all when designed to generate power on both incoming and outgoing tides. The trick is to have water in storage running turbines during the intertidal duration.

Scotland's large tidal farm (which I'm meh about the design for) was $850M which sounds spendy till you consider it is supplying 175 000 households. If those households all put in $10 a week for 10 years it would be paid for.

Imagine that. Renewable power for $10 per week. Then after ten years it is free. Of course, this is not how capitalists see it. Milk it, and then... gravy! What, the poor are revolting? Give them some soap.


 
Travis Johnson
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Matt Coston wrote:

Travis Johnson wrote:The ideal place for this would be in an old quarry.


If the crane is economically viable, thousands of them would need to be built around the world. The crane makes sense because it can be built anywhere, and also built adjacent to the power plant, saving on high voltage cabling.



I disagree. Quarries are everywhere here in Maine along with generating facilities which is why Maine's biggest export in terms of money is actually electricity destined for Hartford, Providence, Boston and New York City. But the biggest savings would come in on two fronts; not having to spend money to build mass blocks since massive chunks of granite could be hefted and lowered, and having a very short crane. In this case the hole has already been dug. No need to build the crane up to 400 feet, just drop the mass blocks down.


As for tidal power, that is being done in Maine as well. The University of Maine has been getting huge grants at getting off shore tidal power stations up and going. It will never happen of course in any big way. The Maine Lobsterman have way too much of a stranglehold on this state. They are hard workers, but a very nervous lot who get nervous of any change harming the lobstering industry. If they complain at all about tidal farms going in, then the Maine people will ban tidal power in Maine as Mainer's identity is with lobster.



 
pollinator
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Interesting thread, I'll read through it all tonight.

When I was young I worked at a fuel dock for boats, in a tidal estuary. Occasionally a huge log would get caught in the slip next to the fuel dock. Sometimes we would tie a heavy rope around the log and a piling at high tide, and watch as the tide "lifted" the log onto the dock.  We're talking about logs 4 feet in diameter.

I spent a lot of time thinking about how tidal energy could be captured.  I keep coming back to one idea using floating concrete planters and pilings.  I have a writeup and sketches somewhere, which I will dig up and post here.
 
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If you have a sloping hillside, that you don't need for any other purpose, and children aren't going to be playing around it, then a short section of track and an "incline" weighted car could reasonably be used for this purpose.  I wouldn't do this simply due to the risks to human bystanders.
 
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I have considered this as well.      As has been stated you must always consider the loss of storing the power verses using the power at peak time it is coming in.     I have 3000 Watts of solar and the best time for me to store energy is to use it when the sun is high, instead of sending it to a battery that is the time to cook with the 1000 Watt Insta pot.

That said, I have heard tale of a Amish man who bought a tanker rail road car.        He took this car and then used solar to build air pressure in this huge tank,    Then he converted all of his tools to air power, this gave him an huge storage of energy to do the task he needed to get done.

I have considered doing much he same but using like 3,000 PSI tanks with military compressor.      There are cars in Europe that drive on this method.


Another option that I adore is hydrogen fuel cells.       Yes it is dangerous, but so is gasoline.     If you know what you are doing, then you can run your car and your home from solar cells.







 
Mart Hale
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Creighton Samuiels wrote:If you have a sloping hillside, that you don't need for any other purpose, and children aren't going to be playing around it, then a short section of track and an "incline" weighted car could reasonably be used for this purpose.  I wouldn't do this simply due to the risks to human bystanders.



Yep,  this works.

https://www.aresnorthamerica.com/article/4875-advanced-rail-energy-storage-using-trains-to-store-power

 
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Recently I heard of another type of "battery." Use excess energy to compress air which, when energy is needed can be released to generate electricity via a small turbine. Does anyone know about this?
 
Creighton Samuiels
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Paul Kurtz wrote:Recently I heard of another type of "battery." Use excess energy to compress air which, when energy is needed can be released to generate electricity via a small turbine. Does anyone know about this?



Yes, but this works better when you have machines that use air power.  Pneumatic well pumps, water pumps, drills, saws etc work very well; but the turnaround efficiency of electric-air-electric is awful, mostly because compressed air heats up and then dissipates that heat during storage.  If you have a use for the "waste" heat of compression, then it might work.  An old propane tank might work for this, but would likely have to be "painted" on the inside first. (propane tanks don't need anti-corrosion coatings on the inside, so they are typically unpainted inside, so to use them with compressed air requires a method of applying paint on the inside.  Basically this involves pumping liquid paint into the tank, then rolling the tank over upon itself slowly, then pumping air through it so that the paint can cure)
 
Roberto pokachinni
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Hi Paul K.  Not exactly.  What I am familiar with is energy stored as compressed air that can be later used to run pneumatic tools. I'd be interested to know about the power generation aspect.
 
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Roberto pokachinni wrote:Hi Paul K.  Not exactly.  What I am familiar with is energy stored as compressed air that can be later used to run pneumatic tools. I'd be interested to know about the power generation aspect.



Lightsail.com was developing this, plus using the excess heat and cooling.  Water droplets carry off the heat and store it, if I recall.
 
Joshua Myrvaagnes
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What ultimate functions are you wanting to serve here primarily--light? Power tools?  Cell phones?

For light, I suppose oil lamps would be interesting to look into and maybe optimize.  Lenses, mirrors? Whatve the Amish got on that front?
 
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Lightsail.com was developing this, plus using the excess heat and cooling.  Water droplets carry off the heat and store it, if I recall.

Hydrostor:  
https://www.utilitydive.com/news/hydrostor-comes-ashore-to-turn-old-coal-plants-into-compressed-air-storage/441017/
 
Nathan Allen Lewis
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Lightsail.com was developing this, plus using the excess heat and cooling.  Water droplets carry off the heat and store it, if I recall.

Google Hydrostor as well.  Compressed air energy storage can be done on smaller scales as well.
 
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Very interesting thread ! Anyone that has experimented with small 'molten salt energy storage'? To me it seems you would need a huge volume of molten salt to become efficient. Otherwise it seems to be a cheap and viable alternative.
Another idea is to use thermal storage, good in hot & sunny locations...
 
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I've seen these river turbines a while back and still daydream about them. Still, I know too little about it.
 
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This guy does some really good calculations on energy storage options for a home-scale system:

https://dothemath.ucsd.edu/2011/09/got-storage-how-hard-can-it-be/

The conclusion is that in general, batteries are probably the cheapest, most convenient, least dangerous and simplest energy storage option.

By far the best place you can spend money and effort is in reducing your energy storage requirements. The two things to think about are reducing your overall electricity usage and shifting usage patterns to take advantage of variable electricity generation availability (i.e. directly using the generated electricity instead of storing it for use later).

You can reduce electricity usage with things like buying efficient appliances, doing things manually, drying clothes on a line, having a solar hot water system, heating with wood, etc.

You can use generated electricity directly without using storage to do things like pump irrigation water from a well or creek up to a high tank/dam using solar power when the sun is shining (or wind power when the wind is blowing), and using that water supply to gravity-feed your household and/or garden so you don't need to run electric pumps on-demand. You could also run your washing machine and other appliances when solar/wind power is available, instead of running them from stored energy.
 
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Reading this thread I immediately remembered this solution of a German enigineer, but it´s only viable if you go large scale, and by this I mean very large scale.

Find an area with massive uncracked bedrock, cut a very big cylinder into that bedrock (the techniques to do that exist in other industry sectors, mainly mining and quarries) , seal it on the sides and lift it by pumping water underneath.

Most information about the concept is in German, but there´s an explanatory article in English HERE
 
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Darren Collins wrote:This guy does some really good calculations on energy storage options for a home-scale system:

https://dothemath.ucsd.edu/2011/09/got-storage-how-hard-can-it-be/

The conclusion is that in general, batteries are probably the cheapest, most convenient, least dangerous and simplest energy storage option.

By far the best place you can spend money and effort is in reducing your energy storage requirements. The two things to think about are reducing your overall electricity usage and shifting usage patterns to take advantage of variable electricity generation availability (i.e. directly using the generated electricity instead of storing it for use later).

You can reduce electricity usage with things like buying efficient appliances, doing things manually, drying clothes on a line, having a solar hot water system, heating with wood, etc.

You can use generated electricity directly without using storage to do things like pump irrigation water from a well or creek up to a high tank/dam using solar power when the sun is shining (or wind power when the wind is blowing), and using that water supply to gravity-feed your household and/or garden so you don't need to run electric pumps on-demand. You could also run your washing machine and other appliances when solar/wind power is available, instead of running them from stored energy.



I'm probably beating a dead horse here, despite my personal prediliction for Pump As Turbine for micro-hydro (or mini-hydro) pumped storage.  These folks had interesting idea about alternative way to do pumped storage with relatively simple closed system (no evaporative losses) that ought to work well with other sustainable alternative energy generation strategies. Yet another approach to affordable scalable pumped storage hydro (or micro- or mini-hydro) with no evaporative losses (nor, hopefully, losses from spills):




 
Dave Miller
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Here's a writeup that I sent to some folks in Vancouver BC a while back.  This is a sort of tidal power network which includes energy storage, to provide power for coastal communities.  I realize that this would not be the most efficient system (vs. a tidal hydro system with batteries), but I also don't think it would kill any sea life and I'm pretty sure that due to edge effects, they would actually increase the amount of life in an estuary.  And I don't think they would be very expensive to build.  The control software might be a bit tricky, but I am a software developer so I'm not too worried about that.  Also since the planters are filled with live shrubs/trees, they would just look like a series of floating islands.

I don't envision these in the open ocean, although they might work in a calm area.  Rather they would be used in estuaries that are currently used to store floating logs, or have abandoned docks, or that have large mudflats during low tide.

I will try to make some sketches soon.

One idea that I settled on was to drive a steel piling into the bay, and attach a series of octopus-like arms out from the piling.  At the end of each arm would be a concrete floating planter, similar to the concrete docks where I worked.  Each planter would be designated as either a 'marine', or 'terrestrial' planter.  The marine planters would be empty, but the terrestrial planters would be filled with soil and planted with a guild of native shrubs and trees.  From a distance, the shrubs and trees would make the whole thing look like a natural island.

Each arm would have the ability to produce electricity, via gear reduction, air pressure, hydraulic pressure, magnetic pressure (linear motor), or something like that.  The arms could be locked in place at any position (probably balanced to keep the center of gravity under control), under the control of some smart software running in a controller either on the piling or at some remote control center.

When none of the arms are locked, the planters rise and fall with the tide, producing power when the tide is rising or falling.  Somewhat useful, but kind of boring, and probably not in sync with demand.  What is more interesting is when the whole thing operates like a battery, storing energy.  e.g. at high tide, an arm could be locked, and then be allowed to produce power (i.e. drop) whenever there is demand, until the next high tide.  The weight of the planter (+arm) generates the power.  Likewise, at low tide, the marine planters could be locked in place.  When there is demand for power before the next low tide, the marine planter would be allowed to float (rise), producing power.

If the marine planter had a valve to control whether the planter held water or not, it could be allowed to fill with water after a low tide, float up to the high tide level, then be locked in place.  So it would have the weight of the planter plus the weight of the water.

It might even be possible for the marine planter to be made airtight, providing stronger upward force after a low tide.  However since the marine planter is essentially a tide pool, locking tidepool animals into an airtight environment seems like a bad idea.  Also leaving them without water for too long would kill them.  But the smart control software could account for this.

Of course one piling wouldn't produce much power, but a whole network of them would.  Also if you had a whole network, each piling could be simplified to have just one circular planter.

I don't envision filling an entire estuary with these, but I when I was in Vancouver I saw some pretty large estuary areas filled with log rafts, so you already are using a lot of estuary space for human purposes.

I imagine that many animals (especially birds) would choose to roost and perhaps even nest in the terrestrial planters.  Likewise, marine organisms would live on/in the marine planters.  It might be wise to provide a little space between planters which may not rise and fall together, to avoid pinning some creature between them.  Likewise they would need to be clearly marked "don't tie your boat here" otherwise the boater would find themselves being lifted into the air or pulled underwater.

I realize this is an unproven, fairly wacky idea, but if the controls were smart enough, I think it could really work well as a tidal power source with built-in energy storage.

 
Michael Cox
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Interesting proposal - it would be VERY location specific, dependent on high tidal ranges to generate the change in height. I also don't think it would come close to harvesting the energy that would potentially be available.

If your floating baskets are a few tonnes then the lift of a few meters won't generate very much energy. And the same effect can be achieved with a static tank that fills passively as the tide comes in, then drains the water through a turbine at low tide. And a tank can be much larger than a moving, floating planter.

On the other hand, thousands of tonnes of water would be flowing past in as the tide flows. Dropping a turbine in the stream would generate potentially hundreds of times more power, as it harvests energy from the flow rather than its own mass. I have done considerable reading about the proposed Severn Estuary tidal barrage. The proposal involves building a massive wall across the estuary with turbines that generate energy from the huge volume of flow. The proposal has substantial positive environmental implications for wetlands birds, marine life etc... as well as implications for leisure use and the like.

Compared to your proposal it has a relatively simple infrastructure - few generators located within the barrage itself, which can be easily serviced/maintained. Infrastructure is concentrated, rather than distributed - less cabling, and so on.
 
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