Report

Implementation opportunities for

Blue Energyin The Netherlands

Haijer & De Reus

SummaryThis report summarizes the possible locations for the production of electricityfrom salinity gradients in the Netherlands. An introduction is provided thatexplains the basic principles and technologies of this ‘blue energy,’ and whythe Netherlands is an ideal place for its development.

For each location, the main advantages and disadvantages are given. Itis expected that the most likely location for further development will be theAfsluitdijk because it is the least challenging location, and because there areplans for renovation of the Afsluitdijk in the near future.

The highest potential is located at the Haringvliet and the Nieuwe Water-weg. When the technology matures, it is expected that a large scale salinitypower plant will be developed at one of these locations.

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ContentsSummary i

Contents ii

1 Introduction 11.1 Aim and Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Blue Energy 22.1 Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.2 Reverse electrodialysis . . . . . . . . . . . . . . . . . . . . . . . 22.3 Pressure retarded osmosis . . . . . . . . . . . . . . . . . . . . . 42.4 State of development . . . . . . . . . . . . . . . . . . . . . . . . 5

3 Blue Energy in the Netherlands 63.1 History of blue energy in the Netherlands . . . . . . . . . . . . 63.2 Local factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63.3 Stakeholders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.4 Current projects . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4 Implementation locations 104.1 Lauwersoog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.2 Afsluitdijk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.3 IJmuiden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.4 Rotterdam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5 Final Remarks 16

References 17

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1 IntroductionBlue Energy is used to describe the generation of electricity from water usingsalinity gradients. A salinity gradient is the difference in salt concentrationbetween water with a high and water with a low concentration of salt. Thechange in entropy during mixing of salt and freshwater has the potential toprovide significant amounts of energy.

Blue energy is especially relevant in the Netherlands, as there are a num-ber of locations where freshwater is released into salt water (e.g. the ‘Afs-luitdijk’ and the North Sea Canal). Being able to generate electricity at theselocations would provide the Netherlands with an interesting way of sustain-able power production.

Figure 1: Artist impression of a blue energy installation

1.1 Aim and Scope

In this report an outline of the most appropriate options and implementationsteps for blue energy in the Netherlands are presented. The first chapter isdedicated to provide an overview of the two most promising technologies.The second chapter describes the current situation in the Netherlands withrespect to blue energy. The third chapter summarizes possible locations ofimplementation for blue energy from the mixing of freshwater and sea water,and the main challenges for each location.

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2 Blue EnergyThis chapter provides insight in the driving force behind the technologiesfor salinity gradient electricity generation and provides a summary of thetwo most promising technologies for salinity gradient electricity. The mainfocus of the report is to describe the possibilities for these technologies inthe Netherlands. Therefore, this chapter cannot be considered as a completereview on the available literature.

2.1 Technology

The generation of electricity from salinity gradients is based on the entropyof mixing salt and freshwater. The physical principals behind this technologyare very old. The first mention of this technique was already in 1954. [1]

Ignoring the contribution of water, and assuming that the temperatureand pressure remain constant, the energy of mixing can be calculated usingequation 1. Here, x is the mole fraction and n is the total amount of salt (inmoles)

E = Gconc + Gdilute − Gbrackish (1)E = nRT (xsalt ln xsalt + xsweet ln xsweet − xbrackish ln xbrackish) (2)

The mixing energy for 1 m3 of seawater (0.5 mol/l NaCl) with 1 m3 offreshwater (0.01 mol/l NaCl) is about 1.5 MJ. For brine, this potential is over16.9 MJ per m3. [2]

The two most promising methods to harvest energy from salinity gra-dients are Reverse ElectroDialysis (RED) and Pressure Retarded Osmosis(PRO). Both technologies rely on the use of semi-permeable membranes togenerate an electric potential.

2.2 Reverse electrodialysis

Reverse electrodialysis utilizes two kinds of ion exchange membranes. Saltwater and freshwater are brought in contact facing an anion exchange mem-brane (AEM) on one side, and a cation exchange membrane (CEM) on theother side. Anions (Cl−) pass through the AEM while cations (Na+) passthrough the CEM. As a result, a potential difference arises. [3]

A minimal RED setup consists of 4 cells connected by 2 CEMs and 1AEM (or 1 CEM and 2 AEMs). Of the middle two cells, one is filled withsalt water and one is filled with freshwater. The two outer cells contain anelectrolyte solution with a redox couple (for example Fe2+,Fe3+) that is ox-idized/reduced to compensate for the net charge that is formed when theions pass through the membranes. The oxidation/reduction takes place at

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two electrodes. The potential difference between the electrodes is the elec-tricity gained.

The electrolyte is pumped around between the two outer cells to regener-ate the redox couple and to allow the transferred ions to travel back into thecell. See also figure 2. [4]

Figure 2: Schematic representation of a reverse electrodialysis stack of 4 cells. [4]

Electricity generation using reverse electrodialysis (RED) has already beenresearched in 1978 by the Southern Research Institute in the United States,but has not got great attention until about 1999. [5] Interest into the technol-ogy has risen quicly the last 10 years. In the Netherlands research towardsimplementation of RED is now being conducted by Wetsus1 and the Univer-sity of Wageningen. [6]

RED setups can easily be scaled up by stacking more cells on top of eachother, and have no moving parts except for the pumps. However, foulingof the membranes, their lifetime, the price of the membranes as well as theresistance over freshwater compartments are the main challenges to over-come before RED becomes commercially viable. The use of industrial wastestreams (brines, freshwater), might increase the viability on the short term.[6, 7, 8]

1Wetsus is a water research institute in Leeuwarden, the Netherlands

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2.3 Pressure retarded osmosis

Compared to RED, pressure retarded osmosis (PRO) is a more mechanicalapproach to obtain electricity from salinity gradients. PRO is based on os-mosis through a water-permeable - but not salt permeable - membrane. Theosmotic pressure - given by equation 3 - forces water into the salt solution.As a result, a pressure builds up until the pressure difference over the mem-brane is equal to the osmotic pressure. The obtained pressure in the salt watercompartments is used to drive a generator, which then generates electricity.[9, 2]

Π = iMRT (3)

As demonstrated in equation 3, the osmotic pressure only depends ontemperature (T), molarity (M), and the dissolution factor (i) - or Van ’t Hofffactor - which is 2 for NaCl. Thus, the osmotic pressure between seawaterand freshwater is approximately 20-25 bar. A pressure exchanger [10] is usedto keep the system under work pressure. (see Figure 3) [2]

Figure 3: Schematic representation of a pressure retarded osmosis setup consistingof 3 cells. [2]

A disadvantage of the PRO technology is that there are number of me-chanical steps involved. Namely the liquid turbine, the generator and thepressure exchanger. There is also a pressure difference over the membranesthat has to be supported. Calculations by Post et al show that for energy fromseawater and freshwater, RED is more efficient compared to PRO, but thatfor brines, PRO is more efficient compared to RED. [2]

Another disadvantage of the PRO system is that the water-permeablemembranes are more susceptible to bio-fouling compared to the ion perme-able membranes using the RED. [2]

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An advantage of the PRO system is that there is more experience withthis kind of membranes due to their common use in desalination plants.

Nonetheless, the preferred technology in the Netherlands is reverse elec-trodialysis. (see chapter 3)

2.4 State of development

On an abstract level, six stages of development for this innovation can bedistinguished. These are discovery, research (mW scale), small pilot (W-kWscale), large pilot plant (250 kW), the construction of a full sized plant (MW),and then broad application at multiple locations. Considering that a smallpilot is already operating in Harlingen (kW sized), and that the first plansfor a larger facility at the afsluitdijk are taking shape, the development iscurrently moving from the small to the large pilot stage.

If the plant at the Afsluitdijk is finished within 5 years, a full sized plantcould be in operation before 2020.

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3 Blue Energy in theNetherlands

The history and the factors that have contributed to the development of blueenergy in the Netherlands are discussed in this chapter. Implementation op-portunities are discussed in the next chapter.

3.1 History of blue energy in the Netherlands

Blue energy has had some attention in the oil crisis of the seventies, but inter-est has waned since that time. Currently, the Netherlands is the only countrywere the possibilities of blue energy using reverse electrodialysis are beingresearched. [11]

Blue energy has not been actively supported by the Dutch governmentin the early stages. After the discovery of new ion-permeable membranes byKEMA, KEMA tried to obtain grants from the government to proceed withresearch, but these applications have been refused on a number of reasons.Eventually KEMA obtained a new energy research start-up subsidy in 2003.[11]

Wetsus - a water research institute founded in 2004 - developed interest inthe blue energy principle soon after KEMA received the new energy researchstart-up subsidy and applied for financial support as well. Wetsus continuedwithout KEMA from there on, starting a number of Ph.D. projects on blueenergy.

In 2006 a spin-off of Wetsus was founded under the name REDstack.REDstack tries to commercialize to commercialize the use of reverse elec-trodialysis. REDstack has a SenterNovem subsidy for the development ofmembranes, and the company is involved at the operation of a demo at thesite of Frisia Salt in Harlingen2. REDstack has asked Royal Haskoning in De-cember of 2009 to apply for all necessary permits to build a blue energy plantat the Afsluitdijk. [12]

3.2 Local factors

The are a number of factors in the Netherlands that give an advantage in thedevelopment of blue energy. First of all there is a large amount of - inter-nationally recognized - expertise in water management in the Netherlands.Next to that, the University of Twente is one of the only universities in the

2Frisia Salt provides room for these projects in cooperation with Wetsus under the nameWetsalt

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world that has a dedicated department to perform research towards mem-branes; The Dutch government has started to participate actively in the de-velopment of blue energy, and the founding of Wetsus has helped to create apromising environment for the development of blue energy. [11]

Geographically the Netherlands obtains its freshwater via the rivers Rhineand Meuse and by rain. This water is transported to the sea via number ofways, but the main outputs are the Afsluitdijk, the Nieuwe Waterweg, theHaringvliet, and the North Sea Canal. [13, 6] Especially the abrupt separa-tion of freshwater and seawater at the afsluitdijk provides a great location forthe application of blue energy. (see also figure 6)

Not all locations where freshwater and seawater meat are suitable for theintroduction of blue energy. For optimal economic efficiency, a blue energyplant should be running at full capacity as much as possible. Figure 4 shows- for example - how the amount of discharged water differs significantly be-tween dry and wet periods.

Figure 4: Example of water released in Nieuwe Statenzijl in 2008. During dry peri-ods there is significantly less water released than in wet periods. [14]

In summary, both because of the interesting geographical location of theNetherlands and the availability of knowledge, government support and thefounding of Wetsus, the Netherlands is not only considered leading in thedevelopment of blue energy, but also one of the best places for its deploy-ment.

3.3 Stakeholders

There are a large number of stakeholders in the development of blue energy.Most of these are connect either via Wetsus or REDstack to the development.The government is involved on a number of levels, ranging from Senter-Novem subsidies to the involvement of the province of Friesland in Wetsus.Figure 5 shows the most important stakeholders and their connections.

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Figure 5: Stakeholders in the development of blue energy. Chart by Willemse et al.[11]

3.4 Current projects

As noted above, there are currently two projects to test RED technology out-side lab condition. The first is very small RED demonstration setup at FrisiaSalt and the first steps towards permits for the second at the Afsluitdijk havealready been made. Both are operated by REDstack.

Harlingen

REDstack currently operates a small scale blue energy project at the WetSaltsite in Harlingen. The setup has a capacity of 5m3/h of brine and 5m3/h ofcondensed water. This leads to an electricity production of 1-5 kW.

Next to this setup, there are two smaller setups that are used to test newmembranes and stack designs. These smaller setups are being tested withboth seawater/freshwater as well as brine/condensed water.

A third setup to test pretreatment procedures is also located at the WetSaltsite. This setup is used to test the water cleaning methods in order to reducefouling of the membranes.

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Afsluitdijk

REDstack has recently asked Royal Haskoning to file for all the necessarypermits to build a blue energy plant at the Afsluitdijk (at Breezandijk). Thecapacity of this plant is 200 m3/h of both freshwater and sea water, and theaim is to supply 50 kW of electrical power.

REDstack indicates that from these two locations the technology will befurther developed into large scale industrial and freshwater applications.Wetsus and REDstack have indicated that they eventually want to build amuch larger plant of 200MW at the Afsluitdijk.

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4 Implementation locationsMost of the freshwater that enters the Netherlands is released into the sea viathe Afsluitdijk, the North Sea Canal and Rotterdam (the Nieuwe Waterweg).Smaller amounts are released via a number of places such as Delfzijl, NieuweStatenzijl, Harlingen, Den Helder, and Katwijk. In figure 6 the size of themain streams is indicated. Table 1 summarizes the available data.

In this chapter the implementation opportunities at four locations are dis-cussed. These are: Rotterdam, IJmuiden, the Afsluitdijk and Lauwersoog.Locations at chemical plants, for example at AkzoNobel in Delfzijl, wherenot taken into account, the focus for this report is on freshwater applications.

Figure 6: The combined Rhine and Meuse provide by far the biggest amount fresh-water that is released into the sea. Flows are given in m3/s.

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Location Flow (Summer, m3/s) Flow (Winter, m3/s) SourceNieuwe Waterweg 2200 - [6]Afsluitdijk 326 650 [13]IJmuiden 89 91 [13]Lauwersoog 13 60 [15]Nieuw Statenzijl 3 16 [14]Delfzijl 2 12 [14]

Table 1: List of locations and their freshwater flows. Winter is taken as the wetperiod, from October until the end of April. The summer period is May until theend of September

4.1 Lauwersoog

Lauwersoog has the smallest water flow of the discussed locations, but isstill a very interesting location. Currently there is a dyke that separates thesalt Wadden sea from the Lauwers lake. Royal Haskoning has noted in 2002that a specific part of the Lauwers lake - the Marnewaard - can be adapted tobrackish water. The combination of these three resevoirs (freshwater, sea wa-ter and brackish water) is ideally suited for a blue energy plant. The brackishwater is then provided by the plant and not by the Wadden sea. [15]

Figure 7: Overview of the current situation in Lauwersoog

A disadvantage of this location is that the water from the Lauwers lakeis only released during low tide. This means that a continuous blue energy

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plant will need to either pump the brackish water into the sea, or will needextra storage room where the brackish water accumulates until it can be re-leased at low tide.

To implement blue energy at this location a number of steps should betaken. First it is important to do a decent study towards the possible ways ofimplementation. This should determine if a brackish buffer is necessary, andhow the flows of freshwater, sea water, and brackish water can be managedand how problems with the continuous flow of freshwater can be overcome.Next to these issues, there are no specific technical barriers to implement blueenergy in Lauwersoog. Thus, the next step would be to obtain funding (i.e.partner with a large energy producer), and to involve the local government.

4.2 Afsluitdijk

Both on the east and on the west side of the Afsluitdijk are sluices for therelease of water into the Wadden sea. These are respectively the LorentzSluices and the Stevins Sluices. Together, these sluices are responsible for therelease of all the water of the IJsel lake. In the summer this is about 326 m3/sand in the winter this can be up to 640 m3/s.

The abrupt separation of freshwater and sea water makes the Afsluitdijkan excellent location for the implementation of blue energy. A disadvantageis that the discharge of water is not continuous due to tides of the Waddensea.

However, there are plans to renovate the Afsluitdijk, and this would bethe ideal moment to create a brackish buffer where the brackish water can bestored before it is released into the sea at low tide.

REDstack has asked Royal Haskoning to obtain all the necessary permitsfor a plant at the afsluitdijk in December 2009. The size of this plant is cur-rently not publicly available. Clearly the first steps towards implementationhave already been made.

4.3 IJmuiden

IJmuiden has a pumping station to release extra water from the North SeaCanal into the North sea. Next to the pumping station are a number ofsluices that support the entry and exit of ships. The capacity of the station is260 m3/s, but under normal circumstances the average discharge is 90 m3/s.

An advantage in IJmuiden is that freshwater is already transported usingpumps. The flows in during the dry and the wet season are also similar. Thismakes the facilitation of a blue energy plant easier. The only remaining issueis that the pumping station is located inland (see figure 9), this means that a

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solution must be developed to prevent the mixing of brackish and sea waterin the inlet.

4.4 Rotterdam

By far the largest amount of freshwater is released via Rotterdam. This wateris mainly supplied by the Rhine and the Meuse and is on average 2200 m3/sduring the summer. This total an enormous amount of potential energy,which could be sufficient to supply over 6 million households with electricity.[6]

Post has studied the Rhine and the Meuse is more detail to look at the lo-cations where blue energy plants could be build. Water is discharged aroundRotterdam in two ways. The first is via the Nieuwe Waterweg, which dis-charges about 1300 m3/s, and the second is via the further south locatedHaringvliet, which discharges about 900 m3/s. [6]

Nieuwe Waterweg

The Nieuwe Waterweg is an open connection, and the water in this river isbrackish over a long distance because of the penetration of salt water. Thestudy does conclude that a blue energy plant could be build somewhat intothe harbor. Sea water is then supplied via the Hartelkanaal and freshwatercan be supplied by the Old Meuse. The brackish water is then dischargedinto the Nieuwe Waterweg where it flows back into the sea.

However, the economical importance of the Rotterdam harbor to the Nether-lands means that the implementation may not impact the commercial ship-ping that takes place in the port. As such, it seems unlikely that the Dutchgovernment will soon endorse a blue energy plant in the Rotterdam harborarea.

Haringvliet

The Haringvliet discharges less water than the Nieuwe Waterweg, but a bigadvantage over the Nieuwe Waterweg is that the Haringvliet has a strict sep-aration of freshwater and sea water. This makes the availability of freshwatereasier, but a disadvantage of a blue energy power plant at the Haringvliet isthat the amount of brackish water that enters the sea at this point will dilutethe sea water taken in, thus reducing efficiency.

The main barrier before implementation at the Haringvliet is the mixingof the discharged water with the intake. A solution towards this problemshould be developed before any other action is taken. A blue energy powerplant at the southern side of the Haringvliet, with a discharge tube in the saltwater of Grevelingen might be an option.

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Figure 8: Photograph of the pumping station at IJmuiden.

Figure 9: Overview of the current situation in IJmuiden. The lower canals are sluices,the upper canal leads to the pumping station.

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Figure 10: Overview of the current situation in Rotterdam.

Figure 11: Overview of the current situation in Haringvliet.

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5 Final RemarksSalinity gradient electricity is an interesting way to produce energy. Becausethe Netherlands is located at the sea front, and is well known for its expertisein water management, the development of salinity gradient energy has highpotential in the Netherlands. There are two main ways of generating blueenergy, from industrial streams and at places where freshwater is releasedinto sea water.

There are a number of locations in the Netherlands were blue energymight be implemented. It is expected that the initial development will be atindustrial sites that have brine and condensate waste streams because thesestreams have a larger concentration difference and are cleaner. Developmentfor freshwater/sea water applications will profit from the knowledge ob-tained during industrial deployment.

Currently, a 50 kW project at the Afsluitdijk is in its initial phase of design.Given that a plant at the Nieuwe Waterweg faces a number of political andtechnical challenges, it is expected that the first large scale plant will also bebuild at the Afsluitdijk. Especially since the developers Wetsus and REDstackare situated in the North.

When there is more familiarity with the technology, the next locations ofimplementation will most likely be the Haringvliet (due to its capacity), andLauwersoog (if building a 10MW plant is not prohibitively expensive).

When the technology becomes available in modules, and the price ofmembranes drop significantly, blue energy plants can also be build at smallerfreshwater outlets and it will then also become a profitable export product tocountries such as Egypt and Bangladesh (both of which have a large riverdelta.)

This report was written under the assumption that electricity from salin-ity gradients will eventually become profitable. However, nearly all of theavailable literature is provided by researchers and companies working for,or with, Wetsus. Scientific research towards blue energy by other sourceswould increase the robustness of the presented results.

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References[1] Pattle, R. E. Production of electric power by mixing fresh and salt water

in the hydroelectric pile. Nature 174, 660 (1954).

[2] Post, J. W. et al. Salinity-gradient power: evaluation of pressure-retardedosmosis and reverse elctrodioalysis. Journal of Membrane Science 288,218–230 (2007).

[3] Długołecki, P., Nijmeijer, K., Metz, S. & Wessling, M. Current status ofion exchange membranes for power generation from salinity gradients.Journal of Membrane Science 319, 214 – 222 (2008).

[4] Veerman, J., Post, J., Saakes, M., Metz, S. & Harmsen, G. Reducingpower losses caused by ionic shortcut currents in reverse electrodial-ysis stacks by a validated model. Journal of Membrane Science 310, 418 –430 (2008).

[5] Southern Research Institute. Energy by reverse electrodialysis. Finalreport to the US Department of Energy (1978).

[6] Post, J. Blue Energy: electricity production from salinity gradients by reverseelectrodialysis. Ph.D. thesis, Wageningen University (2009).

[7] Długołecki, P., Gambier, A., Nijmeijer, K. & Wessling, M. Practical po-tential of reverse electrodialysis as process for sustainable energy gener-ation. Environmental Science & Technology 43, 6888–6894 (2009).

[8] Veerman, J., Saakes, M., Metz, S. & Harmsen, G. Reverse electrodialysis:Performance of a stack with 50 cells on the mixing of sea and river water.Journal of Membrane Science 327, 136 – 144 (2009).

[9] Achilli, A., Cath, T. Y. & Childress, A. E. Power generation with pressureretarded osmosis: An experimental and theoretical investigation. Journalof Membrane Science 343, 42–52 (2009).

[10] Hauge, L. Pressure exchanger. US Patent 7306437 (2007).

[11] Willemse, R. Blue energy (salinity power) in the netherlands. Technicalreport by ECN (2007).

[12] REDstack. URL http://www.redstack.nl.

[13] Ministerie van Verkeer en Waterstaat. Waterhuishouding in het NatteHart. Eindnota 2000 (2000).

[14] Waterschap Hunze & AA’s. Water flows for nieuwe statenzijl and delfz-ijl. Dataset (2008).

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[15] Royal Haskoning. Basisdocument watervisie lauwersmeer. Govern-ment Report (2002).

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