/ Electric Mountain - How does it work?

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Dave 88 - on 10 Sep 2013
I might be missing something, but I'm really struggling to see how this works.

Apparently the hydro electric plant under the slate quarries, works by harvesting electrical energy in the day by water flowing down-hill, driving turbines, electricity is generated, happy days.

However, I'm told, at night when demand is lower, the water is pumped back up hill to begin the process all over the next day. What I'm struggling with, is that surely the amount of energy generated by water falling a set distance, must be exactly equal to the energy required to pump it back up to it's starting point? Maybe even more-so. Therefore no net energy is produced, which is kinda the point of a power station.

Can anyone explain this to me because it's melting my brain and google hasn't come up with any ideas.
knighty - on 10 Sep 2013
In reply to Dave 88:

It's like a battery system. It releases power to the grid when it is most needed (during the day) then when energy is lower in demand (at night) they 'recharge the battery' by pumping the water back up hill.

You are right though. It's not a great system as overall it would use more electricity than it produces. It's just been proposed to cover up the horrendous inadequecies in the UK's power generation facilities...
Irk the Purist - on 10 Sep 2013
In reply to Dave 88:

It is used to produce energy at peak times. It can be started quickly to deal with short term surges (kettles at end of Eastenders).
Shani - on 10 Sep 2013
In reply to Dave 88:
> I might be missing something, but I'm really struggling to see how this works.
>
> Apparently the hydro electric plant under the slate quarries, works by harvesting electrical energy in the day by water flowing down-hill, driving turbines, electricity is generated, happy days.
>
> However, I'm told, at night when demand is lower, the water is pumped back up hill to begin the process all over the next day. What I'm struggling with, is that surely the amount of energy generated by water falling a set distance, must be exactly equal to the energy required to pump it back up to it's starting point? Maybe even more-so. Therefore no net energy is produced, which is kinda the point of a power station.
>
> Can anyone explain this to me because it's melting my brain and google hasn't come up with any ideas.

It takes DAYS to ramp up (or down) power production at coal and gas fired power stations. Also production from renewables such as wind and solar is rather erratic. Chuck in to the mix the fact that demand is erratic and you can see that there is a problem with matching demand and supply.

To smooth out this issue, the national oversupply of electricity at night is used to pump the water to the top of EM. The water is then released downhill to address spikes in demand (hydro power is much more flexible than other forms of electricity generation and production can be quickly scaled up or down).

The whole process of what goes on at Electric Mountain constitutes a net loss in electricity.
dissonance - on 10 Sep 2013
In reply to Dave 88:

My understanding is it is to handle peaks in demand, so when everyone switches on the kettle during the olympic finals it can push a lot of power into the grid. Which nuclear etc wouldnt be capable of.
So is more a storage system than an actual power station.
Parrys_apprentice - on 10 Sep 2013
In reply to Eric the Red:

It's a business model rather than a classic eco friendly hydro system.

takes far more energy to pump it back, but it's off peak and cheap rate. The electricity they sell goes out at a huge premium for the ability to switch it on in minutes.
highclimber - on 10 Sep 2013
In reply to Dave 88: They produce electricity when it is at a higher price (during the day) and buy electricity to pump the water back up to Marchlyn Mawr when it is cheap. It's not HEP in the general sense as it requires electricty from the grid to work.
IainRUK - on 10 Sep 2013
In reply to Parrys_apprentice: Its also eco friendly.. because its storage. So we can supply power through wind but only when the wind blows.. these systems can then store that power.

Its also black start, or was. This is when the grid is reduced to a skeleton and the UK is restarted from the power generated within dinorwic.. as you need a huge amount of power to restart if the grid goes down. It used to be 10-20% or something of the lake is never released as that is kept for black start.
highclimber - on 10 Sep 2013
In reply to Parrys_apprentice: And there's now going to be a similar system at the Glyn Rhonwy site.
David Riley - on 10 Sep 2013
In reply to Dave 88:

More such storage is urgently needed as we exchange constant nuclear output for unreliable wind. But there's nowhere to put one.
I've been wondering about a solid rather than water based system.
An automatic gantry crane system loading container sized weights onto a power generating rail system up and down a mountain.
Cheaper, quicker, expandable, and easier to site than a dam.
highclimber - on 10 Sep 2013
In reply to David Riley: I suspect there'd be more energy loss through friction than with a water system - i.e. less efficient.
a lakeland climber on 10 Sep 2013
In reply to Dave 88:

It's not a hydro-electric plant but a pump storage scheme. OK it happens to use water but as others have pointed out its main purpose is to help the national grid cope with sudden short duration periods of high demand.

If there weren't facilities like this then we'd either have to run extra power stations all the time just for those couple of minutes now and again or have the electric supply vary (which plays havoc with a lot of modern electronics). There are some very well paid people whose job it is to balance the production of electricity with the load.

ALC
Hat Dude on 10 Sep 2013
In reply to highclimber:

The Festiniog power station is also pumped storage; the header lake is Llyn Stwlan at the head of the tarmac road that goes past Clogwyn yr Oen in the Moelwyns
tony on 10 Sep 2013
In reply to Shani:
> (In reply to Dave 88)
> [...]
>
> It takes DAYS to ramp up (or down) power production at coal and gas fired power stations.

No it doesn't. Modern OCGT gas-fired power stations in particular have response times of 20 minutes or so, and the use of partly loaded generating sets allows for generation to be ramped up and down much more quickly than DAYS.
David Riley - on 10 Sep 2013
In reply to highclimber: I think it might be more efficient.
jkarran - on 10 Sep 2013

OP: It doesn't generate much traditional hydro power, there's very little catchment area for the top pond. It's an energy buffer, they store surplus energy by pumping up when there is surplus and the electricity price is low (demand varies more than generated supply can) then they release it when there is excess demand and prices rise. Each way up and down the mountain the gods of thermodynamics take their cut but despite the losses it's an important part of a robust grid.

knighty:

> You are right though. It's not a great system as overall it would use more electricity than it produces. It's just been proposed to cover up the horrendous inadequecies in the UK's power generation facilities...

I'm not going to argue the uk's generating capability is great but storage does not 'cover up horrendous inadequacies', it's a vital part of any robust power distribution system. If you want to generate power efficiently you do it on a large scale, big steam turbines, plants that cannot react fast to changing load so you need an energy buffer or fast reacting, less efficient generating capacity running at part load beside your base load generation. In reality we have all three (plus other variable sources like wind/solar) in parallel with a relatively small but powerful energy buffer in our pumped hydro plants.

jk
cap'nChino - on 10 Sep 2013
In reply to Dave 88: Always wondered this myself. Thanks for the explanations. Makes sense in a very warped way.
Shani - on 10 Sep 2013
In reply to tony:
> (In reply to Shani)
> [...]
>
> No it doesn't. Modern OCGT gas-fired power stations in particular have response times of 20 minutes or so, and the use of partly loaded generating sets allows for generation to be ramped up and down much more quickly than DAYS.

My bad. I wasn't accounting for modern gas fired units. I see CCGT can generally be brought online in less than an hour.

Anyway check out Gridwatch (www.gridwatch.templar.co.uk/index.php) which shows the demand for electricity in the UK at any one time, the source and how it is being generated.
tony on 10 Sep 2013
In reply to Shani:
> (In reply to tony)
> [...]
>
> My bad. I wasn't accounting for modern gas fired units. I see CCGT can generally be brought online in less than an hour.
>
Your mistake, not your bad.

> Anyway check out Gridwatch (www.gridwatch.templar.co.uk/index.php) which shows the demand for electricity in the UK at any one time, the source and how it is being generated.

You can go straight to the original source at http://www.bmreports.com/


MikeSP - on 10 Sep 2013
In reply to Dave 88: As others have stated it runs at a net power lose.
The main reason is the response rate, it can go from 0 to full power in about 6 seconds.
David, I don't think this idea will work, think about all the moving parts (therefore losses) in the system, wheel bearings, crane etc, with the hydro plant the only thing moving is the turbine and generator. Also think about what an eyesore it would be with wagons all over the hill. The only visible bits of Dinorwig are lakes and the entrance (which always reminds me of thunderbirds).
Shani - on 10 Sep 2013
In reply to tony:
> (In reply to Shani)
> [...]
> Your mistake, not your bad.
>
> [...]
>
> You can go straight to the original source at http://www.bmreports.com/

Aren't you getting any?
teflonpete - on 10 Sep 2013
In reply to Shani:

Good website, thanks for that. Interesting to see that coal is still putting as much into the grid as nuclear and CCGT combined, that really does come as a surprise.
Jimbo C - on 10 Sep 2013
In reply to Dave 88:

It's not a power station as such but a facility to deal with peak energy demand. When several million people turn on their kettle during the break in the middle of Corrie, they let the flood gates open to meet this sudden surge in demand. When most of us are asleep at night and not using energy, they use the spare capacity to pump water back up to the reservoir and repeat the next day.

So it's not green energy as such, but it sure is greener than having a bunch of rapid start gas fired turbines on standby.
BStar - on 10 Sep 2013
In reply to Dave 88:

There are lots of replies on here, which are all good. I just thought I would add a bit too.

The Dinorwig Power Station uses excess electricity (when demand is lower than what is being generated) in the grid to pump water from a bottom lake to a top lake. When there is a sudden demand for electricity the Dinorwig station will let some water through its pipes, through a turbine to generate electricity.

Dinorwig can actually generate 1.8 Giga Watts of electricity when it is on full load. This is an astonishing amount really, considering its nearby nuclear neighbour on Anglesey could generate 1 Giga Watt. The only difference being, nuclear energy (and other forms such as coal and gas) can generate this for days on end, whereas Dinorwig can only generate this for circa 6 hours.

Another interesting 'fact' is that for every 3 units of electricity that are generated at Dinorwig, it has cost them 4 units. But when the 4 units were purchased, it would have been at a time when the electricity just wasn’t needed.

If you want to look at some pretty graphs to do with energy demand throughout the day and year take a look at this website, it's actually pretty good. http://www.gridwatch.templar.co.uk/

BStar
BStar - on 10 Sep 2013
In reply to BStar:

I didn't realise http://www.gridwatch.templar.co.uk/ had already been mentioned, my bad
alanw - on 10 Sep 2013
In reply to teflonpete: Coal has been generating a lot on the GB system for a while now mainly because of shale gas in the US. The glut of cheap gas in the states pushed out their coal which then flooded the international market. As a result, coal plant here became more profitable than gas and are kept running most of the time ahead of gas. One of the strange, unexpected vagaries of global energy markets.

Coal plant are also subject to EU Directives to limit emissions of pollutants that have resulted is some closing (about 7GW so far) and more are scheduled to follow (another 4GW or so by 2015). The ones that are due to close are using the current supply of cheap coal to make as much money as possible prior to shutting.
tony on 10 Sep 2013
In reply to Shani:

I've been using BMreports since I did my MSc 10 years ago. It's just the first place I go to to get data on electricity generation. That and the National Grid SYS.
Lukem6 - on 10 Sep 2013
In reply to Dave 88: if your smart with positioning it you could even add rain water to the fill, wont add much but every little helps.
Shani - on 10 Sep 2013
In reply to BStar:
> (In reply to BStar)
>
> I didn't realise http://www.gridwatch.templar.co.uk/ had already been mentioned, my bad

Your bad? Your bad? Jesus Christ!

;)
David Riley - on 10 Sep 2013
In reply to dapoy:
> David, I don't think this idea will work, think about all the moving parts (therefore losses) in the system, wheel bearings, crane etc, with the hydro plant the only thing moving is the turbine and generator. Also think about what an eyesore it would be with wagons all over the hill.

Think about moving a ship rather than a train. Very inefficient to go fast. Water has a lot of drag. MagLev might be worthwhile and also be the generator / motor. Then there would be no bearings and no friction.
The "wagons" would just be solid blocks stacked tightly together.
jkarran - on 10 Sep 2013
In reply to David Riley:

The problem is the *huge* amount of stuff you have to move up a mountain to store any significant energy. That and the associated track and its long term maintenance in a hostile environment.

Imagine a medium sized 13kT ferry as the load, you could get that to roll on rails pretty efficiently with the right engineering. Now raise it 400m (just for illustration, this is roughly height gained linking the biggest near-continuous set of inclines in Dinorwic). How much energy does that store?

400 * 9.8 * 13,000,000 = 5.1x10^10J

That's 14 MWH Electric mountain stores 9,000 MWH

Make the 'ferry' from solid concrete and you still get only 220 MWH

Plus it'd be an awful eyesore with big fences and a huge mass trundling up and down the hill on a 50m wide motorway of rails and reinforced concrete.

Pumped hydro really is quite elegant especially when it's burried.
jk
Dave 88 - on 10 Sep 2013
In reply to Dave 88:

Wow, wasn't expecting all this when I got in from work! That all makes perfect sense, and really quite a clever system with such spikes in demand. Cheers for all the explanations, my friend and I tried to work this out for the entire way 'round Snakes and Ladders!
David Riley - on 10 Sep 2013
In reply to jkarran:
> The problem is the *huge* amount of stuff you have to move up a mountain to store any significant energy.

But that is true for solid or water.
To do it with water requires very specific natural landscape and a huge amount of tunneling and construction work.
With solid all you need is a high place and a low place.
I think it would be cheaper, flexible and more efficient.
The main reason it's not been done is because we have existing hydroelectric technology.
teflonpete - on 10 Sep 2013
In reply to David Riley:
> (In reply to jkarran)

> The main reason it's not been done is because we have existing hydroelectric technology.

Which rather suggests that liquid is a more practical solution to harnessing gravitational energy easily than solid is.
Hairy Pete on 10 Sep 2013
In reply to David Riley:
> I think it would be cheaper, flexible and more efficient.
> The main reason it's not been done is because we have existing hydroelectric technology.

Apart from all the maintenance issues that have been highlighted, you also have the problem of matching the speed of the falling solid to the speed of the generators. It would be possible to devise either mechanical or electronics means for matching, but it adds another level of complexity, potential reliability issues and energy losses.
Run_Ross_Run - on 10 Sep 2013
In reply to Dave 88:
Electricity is cheaper at night.
David Riley - on 10 Sep 2013
In reply to teflonpete: No. It suggests rain is a liquid.
David Riley - on 10 Sep 2013
In reply to Hairy Pete:

Complexity is very cheap these days. Motors and generators are approaching the efficiency and reliability of gearboxes. It's just a problem that's not been tackled before.
Neil Williams - on 10 Sep 2013
In reply to Dave 88:

It isn't supposed to. It's pumped storage - basically a big battery to smooth out the peaks and troughs.

Neil
jkarran - on 10 Sep 2013
In reply to David Riley:

> But that is true for solid or water.

But it's a lot easier to move monumental amount's of water over land than the same solid mass and the losses will be comparable. The transport structure (pipe) needed is quite modest in size and structural requirements compared to the sort of rail bed required to move even a tiny fraction of the mass of the water stored in a scheme like Dinorwic.

To extract the energy from a solid all the solid mass has to move, with a liquid then only a tiny fraction of it at any given time has to move (actually it all moves but imperceptibly).

> To do it with water requires very specific natural landscape and a huge amount of tunneling and construction work.

Landscapes we have. Many schemes use an above ground pipe and turbine house.

> With solid all you need is a high place and a low place.

And countless tons of ugly concrete/steel for your mass to roll over.

> I think it would be cheaper, flexible and more efficient.

I don't.

> The main reason it's not been done is because we have existing hydroelectric technology.

We use pumped storage because it's well suited technically and the business model works despite the losses. It's better than the alternatives, your idea is not new.

jk
Pete Cook - on 10 Sep 2013
In reply to Dave 88: It creates electricity for a peak demand within 16 seconds and then uses cheaper off peak electricity to replenish the top pond. Full details can be found at the following link.
http://www.fhc.co.uk/dinorwig.htm
David Riley - on 11 Sep 2013
In reply to jkarran:

Sorry for the delay replying. Had to go run a race.

> The transport structure (pipe) needed is quite modest in size and structural requirements compared to the sort of rail bed required to move even a tiny fraction of the mass of the water stored in a scheme like Dinorwic.
Why does it need to be bigger or stronger if the weight and volume are the same ?

> To extract the energy from a solid all the solid mass has to move, with a liquid then only a tiny fraction of it at any given time has to move (actually it all moves but imperceptibly).
I think you misunderstood me.

> Landscapes we have.
Not really. Keeping a large lake on top of a mountain is not easy, even if we had mountains. A pile of blocks does not need enclosing.

> Many schemes use an above ground pipe and turbine house.
A solid system could look very similar except there would be no turbines and there would be solid storage instead of water.

> And countless tons of ugly concrete/steel for your mass to roll over.
No more than the ugly pipe. Put it in one if you like.

> We use pumped storage because it's well suited technically and the business model works despite the losses.
Because there was developed technology and a site that suited that technology.

> It's better than the alternatives
I don't think so.

> your idea is not new.
Did I ever claim it was ?


paul__in_sheffield - on 11 Sep 2013
In reply to Dave 88: Apart from the obvious geographical driver, one of the main motivations for Electric Mountain was to act as a peak power buffer for the nuclear generation in the area, particularly Trawsfynnyd before it was decommissioned, and also the site on Anglesey which will now be gaining a new reactor.
Nuclear works best driving a semi-constant base load, which EM buffers during off-peak and peak demand. Also, the area is to a certain extent out on a spur of the grid, so the distribution following the North Wales coast sees power quality and stability problems during demand transients. EM effectively filters some of these effects.
jkarran - on 11 Sep 2013
In reply to David Riley:

> Why does it need to be bigger or stronger if the weight and volume are the same ?

Because a lake can contain a practically limitless mass of water for energy storage, the pipe needed to move that water weighs only a few tens of thousands of tons spread over a few kilometers. That same energy stored as a single solid mass moving over a landscape imposes an absurdly high pressure on the ground.

Even if you break that mass up into smaller units reducing the surface pressure you have to move a lot of stuff so instead of an earth dam and a lake at the top/bottom you have massive freight yards of overgrown trains. You also limit the output power by breaking the mass up in this way.

> Not really. Keeping a large lake on top of a mountain is not easy, even if we had mountains. A pile of blocks does not need enclosing.

Building a gravity dam in a hanging valley is pretty straightforward and unobtrusive by comparison with what you're suggesting.

> A solid system could look very similar except there would be no turbines and there would be solid storage instead of water.

Except the solid system needs much more cross sectional area for the moving mas to pass through (if we're talking in a tunnel or tube) and massive foundations. A pipeline does not require fencing and the exclusion of people/stock, it's safe as is.

> No more than the ugly pipe. Put it in one if you like.

But you'd be looking at a 10-20m dia 'pipe' rather than a ~1-2m dia one for pumped storage and the support structure would be incomparable.

Do some sums, look at the mass you need to move to store the same amount of energy as a modest hydro system, look how fast it has to move to match the hydro plant's power capability then consider the impact on the landscape of the two systems. It just doesn't stack up technically or environmentally.

I just really don't see what problem you think you're solving by proposing what is all round a worse solution?

jk
grumpyoldjanner - on 11 Sep 2013
In reply to Dave 88:

Went on the tour they run last year. Very informative and they take you inside the mountain to see the generators. Absolutely massive inside and some mind boggling numbers when it came to the engineering and building of it!
David Riley - on 11 Sep 2013
In reply to jkarran:
>
> Because a lake can contain a practically limitless mass of water
Obviously it can't. When it reaches the top of the dam that's it.
Which is why the Dinorwig system can only run for a very short time.
This is one of the main advantages of doing it with solid blocks. You would be able to have a considerably greater mass stacked much deeper to give more storage and longer working times without needing exactly the right hanging valley and a dam.

> instead of an earth dam and a lake at the top/bottom you have massive freight yards of overgrown trains.
No. The blocks would be packed together. So no more space would be used than for the water storage.

Your objections seem to be based on a concept of how it would work which differs from mine and I don't understand what you are thinking. The potential energy storage is not changed just because the mass is solid rather than liquid, so theoretically do you not think the same results could be achieved ? You appear to have a negative view of the proposal and have come up with a vision of how awful it would be. My view is optimistic and I think I can envisage an elegant solution with no disadvantages. Of course it may ultimately prove impractical. However the world is full of unlikely things that actually work very well.
GrahamD - on 11 Sep 2013
In reply to David Riley:

Has anyone made a turbine turned by boulders yet ? I'm guessing its a bit harder than one run on water ?
jkarran - on 11 Sep 2013
In reply to David Riley:

> Obviously it can't. When it reaches the top of the dam that's it.
> Which is why the Dinorwig system can only run for a very short time.

Just as you can make the pile of weights bigger you can make the lake bigger. I said *practically* limitless, not that you can exceed the design parameters by piling more water in but that it's relatively easy at design time to add storage to suit your requiredments.

It'll run ~5Hrs flat out (1.8GW, 9GWH assuming they can keep it cool). I don't think that's a short time given it won't generally run flat out.

To store 9GWH (32,400GJ) of GPE in concrete on the same site would require

32400 * 10^9 / 10 * 520 = 6,200,000 Tons

2,500,000 cubic meters of concrete, roughly 33,000 shipping containers, roughly twice what the biggest ships on the seas can carry!

Plus all the handling equipment required to move that lot around.

> This is one of the main advantages of doing it with solid blocks. You would be able to have a considerably greater mass stacked much deeper to give more storage and longer working times without needing exactly the right hanging valley and a dam.

> No. The blocks would be packed together. So no more space would be used than for the water storage.

Lakes are a pretty natural looking unobtrusive addition to the mountain landscape. A huge freight yard and gantry crane aren't.

> Your objections seem to be based on a concept of how it would work which differs from mine and I don't understand what you are thinking.

I do tend to let my negativity get in the way of big ideas but I really don't get it. Stacked, handled, released, re-stacked how? All has to be done seamlessly in a hostile environment with minimal visual impact.


Water does all of this by itself without cranes and trains and all below the surface of a a pair of placid lakes.

> The potential energy storage is not changed just because the mass is solid rather than liquid, so theoretically do you not think the same results could be achieved ?

Of course you can store release energy by raising/lowering a solid mass. I'm not disputing that.

> You appear to have a negative view of the proposal and have come up with a vision of how awful it would be. My view is optimistic and I think I can envisage an elegant solution with no disadvantages. Of course it may ultimately prove impractical.

It already has proved impractical, pumped hydro won hands down. It's likely to be the grid-scale storage of choice in one form or another for a long time to come.

jk
jkarran - on 11 Sep 2013
In reply to David Riley:

Sorry about the spelling and typos.

Just to put 33,000 shipping containers of concrete in context you'd need a yard the size of the port of Felixtowe to store/handle them. And another at the bottom.

I'd prefer a couple of lakes :)
jk
David Riley - on 11 Sep 2013
In reply to jkarran:

More like the monolith in 2001 than Felixtowe.

I'd prefer a fusion reactor :)
itsThere on 11 Sep 2013
In reply to jkarran: I think you've been trolled
David Riley - on 11 Sep 2013
In reply to GrahamD: Turbines are clearly out.
David Riley - on 11 Sep 2013
In reply to jkarran:

You agree that in theory it would produce the same power as water. But you can't see how it could work. You don't know for sure it can't be done and I don't know for sure it can. You say it has already proved impractical. Whereas you actually mean a practical system has not been developed yet.
Perhaps it never will be. But that might be because nobody tries rather than it not being the best way in the end.

You are however right that the Dinorwig storage is impressive and more than I thought.
jkarran - on 11 Sep 2013
In reply to David Riley:

> You don't know for sure it can't be done and I don't know for sure it can. You say it has already proved impractical. Whereas you actually mean a practical system has not been developed yet.
> Perhaps it never will be. But that might be because nobody tries rather than it not being the best way in the end.

People have 'tried' but it never get past the back of an envelope design stage because other solutions are so clearly superior. You don't need to actually build a massive mess to know it'll be a massive mess!

jk
jkarran - on 11 Sep 2013
In reply to David Riley:

I'm quite enjoying this no as a thought experiment :)

How much mass do you need to move and how fast to match the 1.8GW EM can supply?

If we have a 1km long 30deg incline and we're using concrete shipping containers (185T each) limited to 30mph (15m/s on the rails, falling at 7.5m/s)... Not silly seeming as a set-up.

Assuming 100% efficiency that's 14MW/unit so you need 130 of them moving at once to generate 1.8GW. As they're 12m long you actually can't quite get enough on there inline as a train but if you could you'd be un-stacking them, loading, accelerating, decelerating, unloading and re-stacking them at the rate of more than one 185T block per second!

Obviously you could use heavier blocks or parallel trains or whatever but it's clear this gets silly at the energy/power levels needed.

Water does all of this for you quietly without fuss while looking lovely. It's spectacular when you think about it!

jk
MikeSP - on 11 Sep 2013
In reply to Dave 88:
It can be done on this scale, but it's not really worth it when hydro storage has so many advantages.
Could it be used on a smaller scale?
It has given me a really odd mental image of 'Druid Punk'. Imagine blocks similar to stone henge getting carted up a hill then allowed to roll down to release the energy (or have I been reading too much Terry Pratchett).
GrahamD - on 11 Sep 2013
In reply to dapoy:

Unless you have a motor/generator (not sure this is a reasonable prospect in the GW range)you need a way of unhooking the drive from the lifting mechanism and hooking them to the generating mechanism. Its also hard to see how you can practically avoid putting the lifting and generating mechanisms at the top of the mountain rather than at the base.
Rigid Raider - on 11 Sep 2013
In reply to Dave 88:

Climb over the fence around the concrete pond and look down the surge tunnel at Dinorwic and you'll understand just how brief and short-term the demands for power can be. The water level rises and falls many feet, sometimes a couple of times a minute, as the load comes on and off the turbines beneath your feet and the weight of the rushing water is diverted up the surge tunnel. There are always a couple of turbines spinning in tickover and they can be brought up to full power in a few seconds.
David Riley - on 11 Sep 2013
In reply to jkarran:

I hadn't intended to spend time thinking up detailed solutions to this problem. I've got too many real projects on.

Maybe a large number of automatic spider cranes climbing about on the pile of blocks moving them slowly to reduce kinetic losses (yes, water does do that perfectly). The spiders would load the blocks into a 'machine gun' magazine / buffer. They would then go serially up or down the hill with some form of distributed motor / generator on the track or tube.

The aim would be to design a system that could be installed anywhere very quickly and cheaply. It would be fun to have go at a simple prototype.
Toerag - on 11 Sep 2013
In reply to Dave 88: Surely the theory that you'd need a massive volume of concrete is wrong - concrete is much more dense than water, therefore can store much more energy for the same volume? What's the volume of the Dinorwig lake?

Oh, the correct term for the use of Dinorwig is 'peak lopping', and although gas turbines can be online within 5 minutes, they drink fuel like it's going out of fashion - the ones here used for 'black start' use kerosene at 4 tonnes an hour - the big slow speed 2-stroke diesels used 24/7 run on heavy fuel oil at a much reduced rate for the same power output.
ads.ukclimbing.com
David Riley - on 11 Sep 2013
In reply to Toerag:

> concrete is much more dense than water, therefore can store much more energy for the same volume?

Probably not a radical difference.
Jimbo C - on 11 Sep 2013
In reply to David Riley:

Concrete is typically 2200 to 2800 kg/cubic m. Water is 1000 kg/cubic metre. Factor in the fact that the solid concrete needs a container, needs space between containers in order to lift them and would need a surroudning complex of buildings, roads and heavy machinery. I don't think there's any advantage.

Now, a lake filled with liquid metal - there's an idea (joking!)
Ridge - on 11 Sep 2013
In reply to Jimbo C:
> (In reply to David Riley)
>
> Concrete is typically 2200 to 2800 kg/cubic m. Water is 1000 kg/cubic metre. Factor in the fact that the solid concrete needs a container, needs space between containers in order to lift them and would need a surroudning complex of buildings, roads and heavy machinery. I don't think there's any advantage.

> Now, a lake filled with liquid metal - there's an idea (joking!)

Now you're talking. If we used molten depleted uranium, density 17,000 kg/cubic metre we'd have the best of both worlds.

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