Flat-land Large-scale Electricity Storage (FLES)

A few weeks ago I attended a small, commercial, energy storage conference in Brussels organised by Energywise where I heard a most intriguing talk on building a large pumped storage hydro scheme in Holland. The talk was delivered by Dr Jan Huynen, the president of SOGECOM who struck me as being a very serious energy engineer. The project is nearing fruition, with a €1.8 billion price tag and 1.4 GW of supply for 6 hours yielding 8 GWh per daily cycle, this is no toy. Holland is of course totally flat!

Is this just another Green pipe dream? Or does it offer a solution to the apparently intractable problem of energy storage? There is of course nothing new about pumped storage hydro. But all existing schemes use natural relief and elevation to create the head required to store gravitational potential energy that creates pressure and power. What makes Flat-land Large-scale Electricity Storage (FLES) unique is that the whole system is located underground (Figure 1). This of course adds cost but also, as we shall see, it offers substantial benefits.

Figure 1 FLES employs a small surface reservoir and deep lower reservoir with all tunnels, pipes and generating kit below the surface [1].

Why Energy Storage?

Electricity demand in advanced societies follows a very specific and precise pattern that mirrors human and societal behaviour. Demand is always higher during the day than at night when most people are asleep. It is higher in winter when we spend more time indoors keeping warm. It is higher during the week when the wheels of commerce are more active. (Figure 2) The demand pattern may vary from country to country.

Figure 2 The very specific cyclical pattern of electricity demand reflects individual and societal adaptation to using the energy stores of fossil fuels and uranium in electricity production. Using energy stores has resulted in a very well ordered society that is not equipped to use the intermittent energy flows from renewable energy sources.

Society has evolved in this way because we had access to energy stores, namely fossil fuels and uranium. We can release energy from those stores at a rate that matches demand exactly.

It has now been decreed by the majority of OECD governments and organisations that we must abandon this system upon which our civilisation was built to use instead stochastic energy flows from renewable energy sources. This decree is based upon multiple layers of deception. But whether we like it or not, we now have significant and growing amounts of renewable energy flows on our electricity grids that threaten their integrity and our prosperity. The only way to convert third class energy flows into first class energy stores is to somehow store renewable electricity for use when we want to use it. As we have seen in recent posts, the scale of this challenge is formidable [2, 3, 4, 5, 6].

Without delving into the details there is only one storage show in town and that is pumped storage hydro. This technology alone provides the energy efficiency, storage capacity and power delivery to provide a meaningful and economically viable solution (Figure 3).

Figure 3 The chart compares the Power and Storage of batteries, compressed air / thermal and pumped storage. Note the Log – Log scale. Individual pumped storage schemes are 10 times bigger and are more energy efficient than the nearest compressed air rivals. Chart from [1] originally from RWE.

Historically, pumped hydro in Europe was built primarily to store surplus nuclear power at night and to release this surplus into the daytime peak demand. The business model was founded on price differentials between day and night time electricity prices. However, despite what appears to be clear social benefits, pumped storage in Europe remains an insignificant fraction of total generation [7]:

France 4.5 GW
Germany 6 GW
Austria 8 GW

Total pumped storage = 21.5GW compared with 423GW of installed generating capacity in those 4 countries (Austria 23 France 129 Germany 177 UK 94).

High capital cost and insufficient pay back is likely to be one obstacle to larger scale deployment of pumped storage. But environmental harm, public protest and a paucity of suitable sites have likely also played a role. Traditionally, pumped storage was the domain of mountainous countries and largely flat countries like Holland, Denmark and England were automatically excluded.

Going Underground

The Dinorwig pumped storage hydro scheme in N Wales was built into a mountain (Figures 4, 5), that once was a slate quarry, in order to minimise the environmental impact upon the Snowdonia National Park. Construction began in 1974 and took 10 years to complete. Dinorwig differs from FLES in that the upper and lower reservoirs are on the surface and the scheme is therefore constrained by surface relief.

Figure 4 The Dinorwig pumped storage scheme in Wales comprises two surface reservoirs offset by about 500 m relief.

Figure 5 The Dinworig inlet manifold provides testimony to large scale underground engineering works over 30 years ago.

Some vital statistics

Machine hall volume 211,140 m^3
Tunnels 16 kms
Reservoir volume 6.7 million m^3
Head 542-494 m
Power 1.8 GW
Energy stored 9.1GWh
Duration 5 hours
Cost £425 million

Flat-land Large-scale Electricity Storage

This is where Flat-land Large-scale Electricity Storage comes in. The concept is a very simple modification of technologies that have existed for decades. The upper reservoir may be located on flat land, almost anywhere. The lower reservoir is located below ground in a large excavated cavern. The machine hall that contains the turbines and pumps is located deep underground close to the lower reservoir (Figure 1). The concept offers three significant advantages over conventional pumped storage in that:

1) The head is not limited by natural relief but by the depth to which one may wish to mine that in turn may be controlled by geology. Hence energy storage capacity can be simply increased by digging deeper.
2) The surface expression on flat land would be a reservoir perhaps 400*400m surrounded by a grassy dyke (Figure 6). On flat agricultural land, forest, heath or wasteland the visual impact will be minimal. While the facility will have no recreational value, it will preserve the recreational value of mountainous areas.
3) Given a sound economic model, a scheme may be replicated many times over to provide scale

Figure 6 Artists impression of O-PAC on flat land near Maastricht, Holland. There is little to betray that fact that this is a 1.4 GW power station [1].

SOGECOM have identified and acquired a site near Maastricht in Holland to build the world’s first FLES facility christened O-PAC. In Holland, a land of soft sedimentary rocks, finding suitable strata for the lower reservoir presented a challenge solved by the identification of a thick (700m), hard, Carboniferous limestone bed at 1400 m depth.

The vital statistics are impressive.

Upper reservoir 400*400*16m
Water volume 2.5 million m^3
Head 1400m
Power 1.4 GW
Duration 6 hours
Energy stored 8.4 GWh
Cost €1.8 billion
Life of circa 100 years

The specifications of O-PAC are very similar to Dinorwig, the main difference being the smaller reservoir volume that is compensated by greater head. The main construction difference lies in the need to excavate a lower reservoir at depth that is 10 times larger than the machine hall excavation at Dinorwig. This obviously will add significant cost.

Business Model

The business model for O-PAC relies upon the diurnal price cycle where off-peak electricity is purchased at night and used to pump water that is released into the day time peak in demand. This price differential is quite significant, off peak below €30 / MWh and peak above €50 / MWh in Holland (Figure 7). However, as with all energy storage systems, O-PAC is not 100% efficient. With an estimated 80% round trip efficiency, 20% more electricity needs to be bought than can be sold.

O-PAC is designed for fast system response and is intended to respond to short time scale (15 minute)  fluctuations in the electricity market. Going forward, SOGECOM anticipate that higher penetration of renewables will create greater volatility, and with that, greater market opportunity. Hence the primary role of O-PAC will be to facilitate load balancing. Detailed modelling of the present and future market [8] implies 250 full cycles producing 2TWh of electricity / year. A back of envelope calculation based on €50 / MWh implies annual electricity sales of the order €100 million.

Figure 7 Dutch electricity demand, black upper curve, left hand scale, MW. Electricity prices, grey lower curve, right hand scale, € / MWh. Mid week off peak prices are often below €30 / MWh while mid week peak prices are typically above €50 / MWh [8] 

Concluding Thoughts

I have been puzzled by the status of UK and European energy storage. Politicians and renewables enthusiasts proclaim that intermittency will be solved by storage. And yet the scale of storage in Europe remains trivial compared with the expanding size of wind and solar power and in the UK companies are not exactly beating down the door to invest in new pumped storage projects.

Pumped storage hydro provides the most energy efficient, cheapest per MWh and most scalable storage option. How, for example, could hydrogen ever compete or be viable? With electricity – hydrogen – electricity round trip efficiency of the order 30%, at least 3 times as much off-peak electricity would have to be purchased than could be sold.

The massive Coire Glas pumped storage scheme in Scotland has been approved by government but still awaits an investment decision from Scottish and Southern Energy plc. Supposedly designed to store surplus wind power, I do not understand how they can make money storing water for several days awaiting a lull in the wind [2] but the substantially lower cost of this scheme (see below) may provide an explanation.

I’m uncertain if the paucity of new pumped storage projects is down to a lack of suitable sites or is it down to high capital costs? FLES – O-PAC may help resolve the former issue but it comes at a high price. Coire Glas comes with a price tag of €1.12 billion. With storage capacity of 30GWh (€37 million per GWh storage capacity) it is over three times larger than O-PAC (€214 million per GWh storage capacity). The cost of Coire Glas has been kept down by using a natural lake as the lower reservoir, but there is only so much pumping that can be done before the hydrology and eco-systems are wrecked.

In line with the thinking of Scottish Renewables, it seems that further substantial market incentives may be required to promote and expand renewable electricity storage [7].


[1] Flat-land Large-scale Electricity Storage; Global Energy Village 2015; Dr J. Huynen of SOGECOM.
[2] Energy Matters, Euan Mearns The Coire Glas pumped storage scheme – a massive but puny beast
[3] Energy Matters, Euan Mearns The Loch Ness Monster of Energy Storage
[4] Energy Matters, Roger Andrews El Hierro – another model for a sustainable energy future
[5] Energy Matters, Roger Andrews How Much Battery Storage Does a Solar PV System Need?
[6] Energy Matters, Roger Andrews A Potential Solution to the Problem of Storing Solar Energy – Don’t Store It
[7] Scottish Renewables Pumped Storage – Position Paper
[8] Valuation of Electricity Storage. Irina Zinkevich and Ruut Schalij, Energy Risk Advisory Group.

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44 Responses to Flat-land Large-scale Electricity Storage (FLES)

  1. Hans Erren says:

    I’have also seen recent plans for an underground flywheel, a heavy maglev train at 2000 km/h

  2. With the following assumptions:

    * Capital cost €1.8 billion
    * 100% equity financing
    * Input power 2 TWh/year
    * Output power 1.6 TWh/year (80% efficiency)
    * Input power purchased at €25/MWh
    * Output power sold at €55/MWh
    * No annual electricity price escalation

    The project has a payback period of 48 years and an IRR of 0.4% over its planned 100-year life.

    • Euan Mearns says:

      Roger, how does changing this to 2 TWh/y output affect your sum?

      • Roger Andrews says:

        Makes no significant difference, Euan

        I’m sure the O-PAC people have done their homework on this, but based on my crude approximation the project would need a price spread of at least 100 euros/MWh to make it a potentially attractive business proposition.

        With ultimate energy storage requirements in the TWh range we would also need to build hundreds of them.

    • Leo Smith says:

      I think buy/sell prices are very unrealistic there, esp if renewable power is in the offing.

      Those buy prices depend on overnight surpluses of fossil and nuclear: In reality most fossil stations shut down overnight and its only the nukes and a bit of coal that keeps going.

      Since those two technologies are slated to be axed, its the end of cheap night rates forever.

      • Steve Argent says:

        Beg to differ. High wind during a weekend night could see electricity prices going to zero (or negative), because wind farms get subsidy based on MWh produced [see Poyry reports]. Therefore they get the subsidy if someone uses their electricity, but don’t if they are constrained off due to lack of demand.

    • Willem Post says:


      With this scheme, a future could look like this:

      There is no upper limit with weather-dependent, variable renewable energy, if there is enough energy storage capacity.

      NOTE: This presupposes there would be no fossil fuel and nuclear energy in the future. Currently, they are used to:

      – Balance the variable energy and

      – Serve as energy reservoirs.

      A large number of distributed renewable systems (wind, solar, tidal, etc.), located in suitable places, would more or less continuously pump energy into distributed energy storage reservoirs (hydro, battery, etc.) and society would drain energy, as needed, from these reservoirs.

      For example: One hydro reservoir would be 1,000 ft or more below grade and wind energy would drive pumps to transport water from the lower reservoir to the upper reservoir located at grade level. The water from the upper reservoir would drive the turbine-generators located near the lower reservoir. Visible at grade level would be the upper reservoir and power lines. The lower reservoir would consist of a number of parallel, concrete-lined tunnels, about 50 ft in diameter, each about several miles long. They would be made with boring machines similar to those used to make tunnels through mountains, etc.

      NOTE: World energy storage capacity with batteries would be limited due to a lack of suitable materials. This would not be the case with water-filled, upper and lower reservoirs.

      Other renewable energy systems, mostly solar, would be integral with buildings/building complexes to make these buildings/building complexes near-zero energy or energy surplus.

      These buildings/building complexes would not have energy storage systems.

      They would be connected to the grid so they could draw whatever little energy they need from the reservoirs.

      Most of transportation would need to be electric. High-speed rail would almost entirely replace air transportation; any remaining air transport would be kept to a minimum by means of high taxes/passenger-mile.

  3. Phil Chapman says:

    First idea:
    Salt domes are relatively common geologic features, in Texas, Germany, Canada, the Middle East and elsewhere. They can be very large (up to kilometers in diameter), and the top of the salt can be anywhere from 100 to several thousand meters underground. It is easy to excavate a cavity in one of them: you just pump in fresh water, which dissolves the salt, and pump out the brine until the cavity is as large as you want. These cavities are used to store not only petroleum but natural gas, air for compassed air energy storage, and even helium. See http://geology.com/stories/13/salt-domes/ for more info.

    Excavating a large cavity in a deep salt dome for use in FLES would be much cheaper than digging such a cavity in solid rock, It would of course be necessary to seal the cavity so that the water did not continue dissolving the salt. Plastic sheet might work, or perhaps some kind of sprayed-on sealant.

    • Euan Mearns says:

      Phil, of your two ideas I think this one is best. Basically, a way needs to be found to reduce the construction cost / CAPEX. Dinorwig is built in slate, a low grade metamorphic rock that is quite hard to mine i.e. not soft. I’m not sure if digging a huge hole in soft sedimentary rock is cheaper than in for example granite. It will be easier to dig in soft rock but it will also require greater buttressing work.

      In a salt cavern, I imagine you would need a concrete liner, and there could be corrosion problems. The other thing with salt is that it moves all the time and that could cause structural integrity problems with the shafts etc.

      • Roger Andrews says:

        Can’t put my finger on anything specific, but I’d be leery of a design where the working fluid has the potential to dissolve the walls of the containment vessel.

        • Willem Post says:


          See my above comment.

          The world already has a lot of experience with digging large, concrete-lined tunnels.

          • Roger Andrews says:

            Yes, but so far as I know not in material that deforms plastically under load. And lithostatic pressures on the unsupported roof of the chamber will be on the order of thousands of psi.

          • Willem Post says:


            The tunnels would be similar to those under the Alps, which are many decades old.

            The chamber with T/Gs and pump rooms would have half cylindrical roofs.

            The Alps of Switzerland, France and Italy would be a natural, as some of the lakes could serve as upper reservoirs.

            It would be best to start while low-cost fossil energy at 5c/kWh is still available, instead of doing it with RE at 10 – 15 c/kWh.

  4. Phil Chapman says:

    2nd thought.

    We construct a very large spherical thin-walled tank, or perhaps a balloon, and sink it in the ocean, pumping in air to match the external pressure as it sinks. With near-perfect pressure matching, the stress in the material will be small.

    To match O-PAC, it would need to be a sphere 170 meters in diameter, and it would need 2,5 million metric tons of rock to sink it. At a depth of 1400 meters the air pressure would be about 140 atmospheres, or 2,000 psi, which is not too bad.

    To extract energy, water flows down a pipe into the balloon, displacing air through a separate pipe. The water drives a turbine at depth, and the airflow drives another at the surface. This is a combination of hydro and compressed air energy storage.

    To store energy, high-pressure air is pumped down its tube, displacing the water.

    This system could use fresh water from an upper reservoir. If salt water is not too corrosive, the ocean could be the upper reservoir.

    There is no doubt an optimal trade between depth and volume, so as to minimize cost. Perhaps it would work better with a collection of smaller sunk balloons.

  5. If any storage scheme becomes economically viable, I would think that nuclear, with its constant output and small footprint, using that storage, might be one of the most environmentally benign ways to back up wind and solar. The combination of wind, solar, and nuclear with that one missing piece, economically viable storage, might do the trick, at least to displace current levels of electricity generation. Replacing all energy use is another story. Sometimes I feel like we’re counting angels on the head of a pin.

    • Euan Mearns says:

      One of the attractions of FLES / O-PAC is that if our policy makers have a sudden rush of common sense and abandon renewables in favour of nuclear storage will still have a key role to play.

  6. cafuccio says:

    Hi Euan,

    I was wondering whether thre exists a system that attach with each offshore wind generator its own backup storage. Therefore we could imagine a lower but constant output…
    I then found this project:


    What do you think?

    • Euan Mearns says:

      This seems to be a variant of what Phil Chapman has suggested in one of his comments. I’m not sure what the MIT chaps are making. But I think making a large concrete tank on shore with a turbine on top and two shafts – one for water pumping in and out and the other for air / service access sounds like it might have potential. In design it would not be so very different to a concrete gravity base oil rig.

      One advantage of this type of system is that the water is displaced by pumping it out and sucking in air as opposed to pumping in air. The minute you begin to pump / compress air you loose energy due to adiabatic heating.

      I think its a good idea to mandate the generators of renewable electricity to provide and pay for the storage to convert the flow to dispatchable power.

  7. Euan Mearns says:

    Troll A, height 472 m. Cost $650 million. It would have about 1/3 the head of O-PAC and would have to use seawater as the top reservoir. But I’d have thought it would be relatively cheap to bolt on as many lower reservoir tanks as you wanted to in order to increase capacity.

  8. Leo Smith says:

    Euan: I think your figures on European pumped storage while correct (I haven’t checked) are misleading. The reality is that massive amounts unpumped of hydro power are in play. If that is limited not by power station capacity, but by rainfall and winter snow melt (and it is) it acts as a dispatchable half to undispatchable wind and solar. This game is played extensively in Scandinavia, Switzerland and France, and possibly elsewhere, to make renewables work a little better than they otherwise would,

    In short hydro power when you only have so much can act as hugely profitable peak generation capacity whenever wind or solar are not available.

    If it exists, the opportunity cost of adding wind or solar is very low and the dispatch problem does not arise. It is the one case where wind almost makes sense. hydro can be sold into peak demand markets and water conserved when renewable energy is peaking.

  9. A C Osborn says:

    I have to ask the question again, with the energy losses involved why bother?

    • Euan Mearns says:

      AC a CCGT is 40 to 60% efficient. And given that wind power does not use energy to be produced (apart from that used to make the turbines) a 20% energy loss to convert stochastic and useless wind power to despatchable energy is a trivial price to play.

      The argument against lies simply in the cost. And the cost escalates if you try to provide 100% backup storage for wind.

      The anti – renewables argument has been lost. And so I’m trying to move onto a more constructive footing. Wind is probably the worst kind of renewable energy. Cheap to produce but hopelessly erratic. But the tides are highly predictable. I want to look at a combination of FLES and Swansea. It will be hopelessly expansive. But might still be producing despatchable power in 100 years. Its worth thinking about.

      • manicbeancounter says:

        Wind power is not cheap to produce. There is both the huge upfront capital cost of the turbines, but the increased grid costs. This latter part is hidden from in the figures. I do not know how much of the costs of connection to the National Grid that a new wind farm has to pay for. Is it to the foot of the wind turbine; to the edge of the wind farm; the nearest part of the National Grid; or the nearest part of the National Grid that can handle the additional capacity?

        • Paul says:


          I would think the cost of connection to the Grid would be millions, or tens of millions

          However I wonder if this is usually not included within any costings, because any new commercial electricity power generating system would need access to the Grid (unless it already had one, such as a new nuclear plant replacing a decommissioned one, or a solar thermal plant replacing a coal station)?

          I believe this to be a real issue in the USA, where they have some excellent wind resource in the middle of the continent, but no transport (transformers, lines etc) infrastructure between that region and those with dense population and thus electricity demand. In these circumstances cost of Grid connection becomes relevant, since smaller, less efficient generation closer to demand areas can be more cost effective than large super efficient and low cost generation plants with no transport infrastructure

          To bring this back to the article posted. Perhaps this is why the Dutch are investigating novel storage close to demand areas, rather than build solar PV in the Sahara or wind farms on the Russian steppes?

        • Euan Mearns says:

          Onshore wind is the cheapest of the new renewables. I was thinking that FLES could be located on brownfield sites vacated by coal and gas fired power stations where the wires already exist. Setting costs aside, I’d have strong preference for a system where home grown surpluses of electricity were stored at home as opposed to thousands of kms of HVDC cables crossing hostile countries and oceans.

  10. It doesn't add up... says:

    I found this discussion:


    which brings a number of useful points to the table, based on input from engineers who know what they’re talking about.

    • It doesn't add up... says:

      Among the issues raised: we don’t have turbines that are built to handle a head of more than about 600m with reasonable output power; pumped hydro is not well suited to intermittent, unscheduled generators.

  11. Roger Andrews says:

    One of the defects of FLES is that you can’t sausage-machine it. Conventional generating plants have more or less standardized designs. You can build the same plant anywhere and be fairly certain that it’s going to work. FLES, however, is hostage to the geology (as is the “S” in CCS and to a lesser extent dams). What works in one place won’t necessarily work in another. Each project will be different. Each will require exhaustive site investigation work before an optimum design can be developed, and in some cases to determine whether FLES will work at all. Not necessarily the kiss of death, but it will certainly complicate planning.

    • manicbeancounter says:

      My initial thought was to maybe expand the capacity of disused mine workings.
      The salt mines of Cheshire are vast. In fact one mine is used for gas storage.
      Problem is that the water pumped out would be somewhat salty.
      An alternative is coal mines. But the pumped out water would be a bit discoloured and continual pumping of water could cause collapses of mine workings.
      In the Aberdeen area the granite might be a bit tough. In the south of England the chalk is a bit soft and permeable.
      Nearer my home, the former copper mines at Alderley Edge near Macclesfield are very spacious. Only the sandstone contains arsenic, and the mines are not deep enough.

      • Euan Mearns says:

        Kevin, The Dutch have looked into using old mines and it just doesn’t work. The lower reservoir is a pretty turbulent and energetic environment. And the water going through the turbines has to be clean.

        Salt mines would only work if you allowed the water to become saturated with salt – that would add some density and storage capacity. But creates problems with corrosion.

        I’m quite sure in the UK that suitable strata could be found. For example, the carboniferous limestone targeted by O-PAC could easily be present at depth in the SE UK.

        One thing I’d like to know is if it would be more economic to mine through hard stable rock like granite. Or to “tunnel” through soft sedimentary rocks.

  12. Paul says:

    How confident can we be that (to quote from the original article) “the higher penetration of renewable will lead to greater volatility in supply and therefore greater [financial] opportunities for [immediately dispatchable] storage”?

    I imagine that the more diversified the generation mix (if its raining, or the snow is melting hydo is charged & ready to go, if the sun is out PV is contributing, if it is windy etc etc, with more ‘base load’ generation from biomass / geothermal / wave / tidal etc. Europe is diverse and reasonably interconnected, so I imagine snow melt hydo servicing a lot of demand across the continent in the spring, even if its dark and still

    Is this a naive perception and that to truly become free of fossil fuels (and nuclear) we (in Europe) have to invest far more significantly in storage (be it pumped hydro, salt caverns, flywheels, batteries)?

  13. Yvan says:

    We had a similar design proposed here. It was a narrow but very deep shaft going into the ground. Been deep it would produce more kWh per m3 of water. Need less ground work to.

  14. disdaniel says:

    Build a dome/hemisphere with an air-shaft connection on top, drop it into the sea as deep as you want (anchor it to the seabed and maybe save a bunch on dome material cost). Pump air down (displacing water out into the sea) to “charge it up” at depth. Put a “cork” in it to store until needed. Remove cork and direct air through a turbine (at the surface) to discharge the “air/sea” battery. Should work at least as well as Phil Chapman’s second idea.

  15. Graeme No.3 says:

    Not applicable to Holland, but why not use the ocean as the lower reservoir?
    Put the upper reservoir on a cliff or plateau. Still expensive, but only one storage needed, and that would be accessible for repairs/maintenance.

  16. Stuart says:

    This design strike me as being far too capex intensive to ever be viable.

    It would be FAR more economic to have a very small delta h, of say 3 meters, and to have 30 times as much volume of water and locate the entire system on the surface.

    This could be achieved by simply building a perimeter dyke shaped like a rectangular figure of ‘8’ and transferring the water between the two reservoirs to create a head. Incidentally 1 of the two reservoirs could simply be the sea, further reducing the cost.

    Excavating a gigantic cavern hundreds of meters below the ground and locating large turbines in a location that is difficult to service is entirely pointless.

    Better still there are parts of the coast (88% of countries have a coast) where the ground is flat enough that the seawater rushes in twice a day and also out twice a day, and requires no wind turbines to drive it. Imagine that!!

    Self powered water.

    Now I’m not claiming the earth’s tidal movements are a perpetual motion machine but 4 billion years to date is pretty good compared to other contenders. Tides have washed over the earth’s coastlines uninterrupted for ~30% of the time the universe has existed (and this number is increasing every day).

    All that’s required is a wall (much cheaper than a bloody great subterranean cavern). Hopefully someone will one day invent bricklaying and make this vision a reality.

    • Euan Mearns says:

      If we use the proposed tidal lagoon in Swansea Bay as a yard stick:

      With an installed capacity of 320MW and annual generation of 495GWh


      A report by Poyry estimates capital costs at £913 million


      We see that this surface mounted system that will cause environmental harm is about one quarter the size of O-PAC in terms of output and storage for roughly the same price. Gravitational potential energy (head) is all important.

      Add to that O-PAC is a Dutch solution, and without checking, I’d bet the tides are not that large in Holland.

  17. philsharris says:

    Euan & Co
    This was part of a brief Review for the informal Claverton Energy Group in 2008 for publication in the OU-based journal ‘Renew’ (Prof Dave Elliott). I am no expert and culled knowledge from Claverton engineers and in this case (and also for the more difficult wave and tidal current energy) from Prof Dave Mackay. (Ref and pers com)

    Excerpt: “Tidal lagoons (with potential for pumped storage): Their environmental impact should be much less, and output more evenly-distributed than a Barrage. Potential to double as pumped storage compares favourably with a profitable hillside back-up solution for nuclear power (Dinorwig, Wales). Theoretically, pumped storage could turn 1.8GW of variable wind power into 1.9GW of steady power: a round-trip efficiency of 105% compared with Dinorwig 75% . Large sites (The Wash and Blackpool could each offer 10km by10km), with a combined average output of more than 800MW, should provide 1-2 percent of present UK electricity output at possibly lower cost than nuclear. Modest financial risks suggest a ‘no-regrets’ start.”
    Mackay 2007b http://www.inference.phy.cam.ac.uk/sustainable/book/tex/Lagoons.pdf

    Undergroud storage in Holland sounds feasible technology, but as always, may never get built on sufficient scale. I am still doubtful whether even the proposed new nuclear will ever get built in UK. .(With Chinese and French nuclear engineering and a millstone of a ‘forever-mortgage’ hung round our children’s necks?)

    • Graeme No.3 says:

      105% efficiency? I would say that was indeed theoretical (as opposed to practical).

      I presume they meant that the lagoon would generate with the tides, and use wind energy to top up the water level at low tide to extend the hours of power generation.
      I can think of better, and cheaper ways to get reliable generation.

    • Euan Mearns says:

      I’ve said this before, but modern capitalism is founded on cheap and growing supplies of energy from fossil fuel (FF). High rate of return on minimal capital. A project like O-PAC may have strategic importance but a trickle of profit takes a long time to repay the mortgage. But in 50 years time it would still be there, providing despatchable electricity at low cost.

      Don’t like the sound 10 by 10 km lagoons to produce 800 MW when a 0.4 by 0.4 km surface reservoir (O-PAC) can produce 1400 MW. In the same way I didn’t like David’s 100 * 100 km windfarms in the flow country of Sutherland.

      My current thinking is that O-PAC could only ever be scaled if built by government – they are the only institution with the funds and ability to underwrite the risks.

  18. David MacKay says:

    There was (roughly 10 or 15 years ago) a similar underground-pumped-storage plan designed for construction underneath Greater London. I’m sorry I don’t have any source to point to for this fact, but I heard it from reliable people. I think the plan was to use the Thames as the upper reservoir.

    • Graeme No.3 says:

      There was also a plan for a canal to bring sea water to the Dead Sea, generating hydro power as it flow into the depression. Seems more feasible than the Holland proposal, but the difficulty would be getting the electricity to Europe.

  19. manicbeancounter says:

    An alternative pumped storage scheme has been proposed for Belgium. This is to create an energy atoll offshore. Capacity is much smaller, and might be even more expensive.

    • Flanders has the same problem as the Dutch: it is rather flat. Therefor the proposal of the energy island before the Belgian coast to balance the load of the electricity supply of offshore windmills.

      It is basically a reservoir that would be emptied when there is an electricity surplus and filled when electricity is needed (it then drives a turbine).

      It was proposed several years ago and the plans changed location and size over the years. There was/still is a lot of protest against it and the proposal was recently rejected by the federal government.

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