Hydro dam energy stores for 100% renewable power

reply to post by juleol


I'm with you on the thorium from what little I have researched in that area. It's a better bet than risking thousands of lives to line a few CEO's pockets. I have a better solution though, I'm just trying to make it safe and idiot proof first.

Cheers - Dave

Originally posted by Mr Peter Dow

So long as the selling price of 75% is more than the buying price of 100% then there is a trading profit.

There's the catch IE unless there's market volatility caused by high demand, reduced plant availability, network failures and plant outages that margin is barely enough to break even let alone recover the initial investment in a reasonable time period like, say, less than 50 years. The Dinorwig scheme currently makes more providing system restart services (means they don't necessarily get dispatched very often at all) and all they need do is be ready to provide the service at short notice to get paid for it (the service IE 'black start' capability not the energy). They'd also be providing high priced FCAS (frequency control ancillary services) which is exactly what the station was designed to do although it might have had a different name back then.

Energy-wise it's a losing proposition on a flat market.

Geology of the Coire Glas site
I have been able to extract this information from the British Geological Survey (BGS) Geology of Britain viewer, from the 1:50 000 scale map.




Click to see larger image

According to this map, the bedrock at the site which would be used to build the dam on top of and to extract rock from to create the tunnels for the underground complex seems to be a rock geologists call "psammite" which I understand to mean here "a metamorphic rock whose protolith was a sandstone".

What neither the map nor the "psammite" name is telling us is how fractured the psammite rock there is and therefore how strong and also how impermeable or otherwise to water this rock is likely to prove to be, both of which would be interesting for any engineers building a pumped-storage hydro dam scheme there to know.

What does look fairly obvious to me is that the superficial deposit of what the map calls "hummocky (moundy) glacial deposits - diamicton, sand and gravel" would not be strong enough, nor impermeable enough to build any dam on top of and at least along the line of the dam, this glacial deposit ought to be removed to get down to the bedrock within which to establish the foundations of the dam, although I would think that this glacial deposit might be made into aggregate to make the concrete for the dam by the sounds of it.

Dam foundations and height of the dam above the bedrock
The top of the Dow-Dam has an elevation of 780 metres by design.




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The lowest elevation of the current ground surface of Coire Glas along the line of the proposed dam is 463 metres and subtracting 463 from 780 is how the initial value of 317 metres for the nominal height of the dam above the existing surface used in previous diagrams was arrived at.

However, the glacial deposit of as yet unknown thickness is to be removed before building the foundations of the dam within and upon the bedrock.

Although the lowest surface elevation along the line of the dam of the bedrock too is unknown a formula relating the Height of the Dam Above the Bedrock (HDAB) to the Glacial Deposit Depth (GDD) can be easily stated.

HDAB = 317 + GDD

Examples.

If the GDD turns out to be 13 metres then the dam will be 330 metres tall.
If the GDD turns out ot be 83 metres then the dam will be 400 metres tall.




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I propose that the height of the Dow-Dam be as tall above the bedrock as it needs to be to keep the top of the dam at an elevation of 780 metres no matter how deep the removed glacial deposit layer turns out to be.

My approach may well differ from the SSE's approach. The SSE have said that their dam will be "92 metres" high and they may stick to that without having any goal for the elevation of the top of their dam.

As the diagram indicates, I propose to secure the Dow-Dam to the bedrock by massive piles inserted and secured into shafts which would be drilled into the bedrock.

Video which illustrates the principle of using wind turbines and pumped storage hydro dam schemes together.

"Dow" equation for the power and energy output of a wind farm.

"The power and energy of a wind farm is proportional to (the square root of the wind farm area) times the rotor diameter".

In his book which was mentioned to me on another forum and so I had a look, David MacKay wrote that the power / energy of a wind farm was independent of rotor size which didn't seem right to me considering the trend to increasing wind turbine size.

Now I think the commercial wind-turbine manufacturing companies know better and very possibly someone else has derived this equation independently of me and long ago - in which case by all means step in and tell me whose equation this is.

Or if you've not see this wind farm power/energy equation before, then see if you can figure out my derivation!

the only advantage i can see in ` pumped energy ` schemes is thier " instant delivery "

I live in Summersville West Virginia and we have a Hydro electrical plant just a few miles from where i live. You can see this plant here HydroElectrical Plant . Sad part is they use this electric for Ohio and not West Virginia. We also have a huge Wind Turbine Farm about 30 - 40 minutes from where I live. My wife and I visited them one year and it was truly amazing.

The problem with wind generation is it's not a dependable source of energy IE you only get maximum production when the wind blows at over 20m/sec steadily. Granted that spreading your windfarms on the network over a very wide geographical area reduces the possibility of overall output dropping right off in a short period of time like 30 minutes or less, it still is a possibility that needs to taken into account when planning how much thermal/hydro spare generation capacity needs to be online to cover off that very credible contingency. Wind speed/direction forecasts are fairly accurate allowing fair estimates of output days in advance but just a change in wind direction requires the whole farm being re-oriented (automatic) but output does plummet during that before picking up again.

We have over 1500MW (and growing) of wind farms here with a typical duty cycle approaching 50% so the biggest contingency event for us is already the wind dropping off in all regions and it does happen even with the diversity of being spread over 1000's of km on a common network.

Originally posted by Mr Peter Dow
"Dow" equation for the power and energy output of a wind farm.

"The power and energy of a wind farm is proportional to (the square root of the wind farm area) times the rotor diameter".

In his book which was mentioned to me on another forum and so I had a look, David MacKay wrote that the power / energy of a wind farm was independent of rotor size which didn't seem right to me considering the trend to increasing wind turbine size.

Now I think the commercial wind-turbine manufacturing companies know better and very possibly someone else has derived this equation independently of me and long ago - in which case by all means step in and tell me whose equation this is.

Or if you've not see this wind farm power/energy equation before, then see if you can figure out my derivation!

No takers for the derivation challenge huh? OK then.

Derivation

Assume various simplifications like all turbine rotors are the same size and height, flat ground and a rotationally symmetrical wind turbine formation so that it doesn't matter what direction the wind is coming from.

Consider that an efficient wind farm will have taken a significant proportion of the theoretically usable power (at most the Betz Limit, 59.3%, apparently, but anyway assume a certain percent) of all the wind flowing at rotor height out by the time the wind passes the last turbine.

So assume the wind farm is efficient or at least that the power extracted is proportional to the energy of all the wind flowing through the wind farm at rotor height.

This defines a horizontal layer of wind which passes through the wind farm of depth the same as the rotor diameter. The width of this layer which flows through the wind farm is simply the width of the wind farm which is proportional to the square root of the wind farm area.

Wind farm turbine formations

Therefore the width or diameter of a rotationally symmetrical wind farm is a critically important factor and arranging the formation of wind turbines to maximise the diameter of the wind farm is important.

Consider two different rotationally symmetrical wind turbine formations, I have called the "Ring formation" and the "Compact formation".

Let n be the number of wind turbines in the wind farm
Let s be the spacing between the wind turbines

Ring formation


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The circumference of the ring formation is simply n times s.

Circumference = n x s

The diameter of the ring formation is simply n times s divided by PI.

Diameter = n x s / PI

Compact formation


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The area of the compact formation, for large n, is n times s squared. This is slightly too big an area for small n.

Area = n x s^2 (for large n)

The diameter of the compact formation, for large n, is 2 times s times the square root of n divided by PI. This is slightly too big a diameter for small n.

Diameter = 2 x s x SQRT(n/PI)

This is easily corrected for small n greater than 3 by adding a "compact area trim constant" (CATC) (which is a negative value so really it is a subtraction) to the s-multiplier factor.

The CATC is 4 divided by PI minus 2 times the square root of 4 divided by PI.

CATC = 4/PI - 2 x SQRT(4/PI) = - 0.9835

This CATC correction was selected to ensure that the compact formation diameter equation for n=4 evaluates to the same value as does the ring formation equation for n = 4, that being the largest n for which the ring and compact formations are indistinguishable.

The CATC works out to be minus 0.9835 which gives

Diameter = s x ( 2 x SQRT(n/PI) - 0.9835) (for n > 3)

Ratio of diameters


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It is of interest to compare the two formations of wind farm for the same n and s.

The diameter of the ring formation is larger by the ratio of diameter formulas in which the spacing s drops out.

Ring formation diameter : Compact formation diameter

n/PI : 2 x SQRT (n/PI) - 0.9835

This ratio can be evaluated for any n > 3 and here are some ratios with the compact value of the ratio normalised to 100% so that the ring value of the ratio will give the ring formation diameter as a percentage of the equivalent compact formation diameter.

Here are some examples,

n = 4, 100 : 100
n = 10, 123 : 100
n = 18, 151 : 100
n = 40, 207 : 100
n =100, 309 : 100
n =180, 405 : 100
n =300, 514 : 100
n =500, 656 : 100

As we can see that for big wind farms, with more turbines, the ratio of diameters increases.

Since the Dow equation for the power and energy of a wind farm is proportional to the diameter of the wind farm then it predicts that the power and energy of the ring formation wind farms will be increased compared to the compact formation wind farms by the same ratio.

In other words, the Dow equation predicts, for example, that a 100 turbine wind farm in the ring formation generates 3 times more power and energy than they would in the compact formation, assuming the spacing is the same in each case.

Practical application when designing a wind farm

My recommendation would be to prefer to deploy wind turbines in a wind farm in the ring formation in preference to the compact formation all other things being equal.

The compact formation can be improved up to the performance of a ring formation by increasing the turbine spacing so that the circumference is as big as the ring but then if a greater turbine spacing is permitted then the ring formation may be allowed to get proportionally bigger as well keeping its advantage, assuming more area for a larger wind farm is available.

The ring formation may be best if there is a large obstacle which can be encircled by the ring, such as a town or lake where it would not be possible or cost effective to build turbines in the middle of it and so a compact formation with larger spacing may not be possible there.

Where it is not possible to install a complete ring formation then a partial ring formation shaped as an arc of a circle would do well also.

Reservoir bed drain

The high pressure of water which is deeper than 100 metres has the potential to induce seismic activity or earthquakes in susceptible rock in which a new reservoir has been constructed.

Wikipedia: Wikipedia: Induced seismicity - Causes - Reservoirs.

The mass of water in a reservoir alters the pressure in the rock below and through fissures in the rocks, lubricates the fault, which can trigger earthquakes.
...
Unfortunately, understanding of reservoir induced seismic activity is very limited. However, it has been noted that seismicity appears to occur on dams with heights larger than 100 meters. The extra water pressure created by vast reservoirs is the most accepted explanation for the seismic activity.

Coire Glas/SSE/92 m

Hopefully, reservoir induced seismicity was an issue considered by the SSE when selecting Coire Glas for their hydro dam project.

I am speculating that this issue may be why the SSE have limited their dam to a height and their reservoir to a depth of 92 metres?

I would note however that the pressure in the head race tunnels which supply water from the reservoir to the turbines would be proportional to their depth below the surface of the reservoir and this could be as much as 500 metres deep, so there would seem to be some potential for water to penetrate the bed rock from the high pressure water tunnels and induce seismic activity even in the SSE case.

This is an issue which ought to have been addressed in the many previous pumped-storage hydro scheme projects, most of which seem to have a difference in head of more than 100 metres.

Given that "understanding ... is very limited" according to Wikipedia, though, I do wonder if the reservoir induced seismicity issue has not always been properly addressed in all previous dam and reservoir construction schemes where the great depth of water and susceptible geology ought to make it a relevant concern?

Coire Glas/Dow/317+m

I am proposing measures to counter the reservoir induced seismicity effect in the case that the geology of Coire Glas is susceptible to it and in the general case.

I propose the construction of a large reservoir surface drain to cover the whole reservoir bed and the reservoir sides too to try to stop the penetration of water under high pressure into fractures in the bedrock and so thereby stop this high pressure water from widening and extending bedrock fractures.

To illustrate my "reservoir bed drain" concept, I have drawn a diagram comparing the usual no drain on the left, with my proposed reservoir bed drain on the right.



Image also hosted here.

So my idea is that the top layer of the bed drain is as impermeable as practical, using perhaps a layer of reinforced asphalt concrete.

In engineering practice I believe that impermeable reservoir bed layers have used clay or clay with asphalt or even rubberised asphalt mixed with sand.

My basic idea is to construct an impermeable layer and to use whatever material is best for that.

Then working downwards, the permeable drain layers are increasingly bigger loose particles, with sand at the 2nd top then beneath that grit, then gravel, then small stones and finally below all those a layer of large stones.

The higher layers support the top impermeable layer which is under high pressure from the reservoir water and the lower permeable layers provide many small channels for any (hopefully tiny amounts of) water which forces its way through the supposedly impermeable top layer to drain down the slope of the reservoir bed to the base of the dam and then out under the dam through drain-pipes built into the base of the dam.

The bottom layer is another impermeable layer to try to make doubly sure that the relatively low pressure water that gets into the drain will find its way out through the dam drain pipes by following the course of the drain.

These kinds of layers of different sized loose particles have previously been used to make simple narrow drains and impermeable layers have been added to reservoir beds before now but whether professional dam engineers have ever covered the entire reservoir bed and sides with one large drain I don't know. If not, this could be named the "Dow drain" solution to reservoir induced seismicity!

Why not add a simple impermeable layer to the reservoir bed?

I think the additional complexity and expense of a bed drain (and drains for the sides too) is better than simply adding an impermeable layer.

Consider the fault condition of the two possible solutions.

If a simple impermeable layer fails, if it cracks or ruptures or disintegrates under the pressure changes, how would anyone know? It may look fine but be leaking high pressure water into the bedrock and inducing seismicity which OK the engineers would notice any earthquakes but so would everyone else, the earthquakes could cause damage or loss of life and it could lead to a loss of confidence in the project and in the engineers who built it. They could go to jail!

If the top impermeable layer of the bed drain fails then there would be some water pouring out of the drainpipes through the base of the dam when at most it should only be a tiny trickle of water. So the engineers would know there was a problem with the bed drain and they'd know to drain the reservoir and fix or replace the top supposedly "impermeable" layer, fix the bed drain so that it operated as it should.

So failure with the bed drain is noticed right away and it is not a catastrophic failure. Whereas failure with the simple impermeable layer may not be noticed until a catastrophic earthquake happens.

So this is why I think the bed drain is worth the extra complexity and expense. It is a more fault tolerant engineering solution.

reply to post by Mr Peter Dow


If you want to see how bad a pumped storage system can get, SO FAR, go look up the Taum Sauk Reservoir disaster from December 2005. That was only a billion gallons, imagine what the new ones that are being proposed will like at 25 to 30 billion gallons if they fail. Your comment on an impenetrable liner is a bit ridiculous, nothing is impenetrable, one 5.0+ earthquake within a 150 mile radius of a pumped storage facility has the ability to vibrate the foundation enough on a secured tailings pile to crack and thereby evacuate the upper reservoir.

The Taum Sauk was a good distance from any town, village or city and the settlement was $180 million in 2005 dollars. Some of the new proposed locations are within 200 yards of a town, village or city. Imagine the destruction with 25 to 30 times the amount of water, a local population of 4000 with an effected population of 40,000. The death toll could be very high and the property damage in the billions.

Cheers - Dave

Originally posted by Mr Peter Dow

You bring up good ideas and bad ideas. An example of the bad would be pumped storage where a company skims electricity at low cost during off-peak hours and generates electricity during on-peak hours.

Would you waste in times of plenty and starve in times of famine?



why not produce electricity on demand as always? you must understand that wind and solar are far from cheap as it is, if you need yet another investment like pumped storage that's typically more expensive per kW thanmost types of power plants yet cost energy, just to cure their shortcomings you are just compounding error - imho of course.

contrary to popular belief, cost matters and the notion that you can just flood large swaths of land without affecting nature is just as absurd as saving the planet by razing the Amazonian basin for crop derived fuel. besides, it's only a matter of time until a large dam breaks again (search for the 'banqiao dam' desaster) and i dare say that unlike nuclear, hydro isn't scary, it's absolutely deadly in the case of catastrophic failure. when that happens at the scale one can expect, this particular fad will be be shelved for good.