Energy Accumulation System and Method

Field of the Invention The invention relates to energy accumulation system and method. In particular the invention relates to the storage of large quantities of potential energy that can be released on demand and converted into electrical energy.

Background to the Invention In Ireland and other island nations there are specific power generation problems. In most locations, consumption of electricity is highly non-uniform throughout the day. There are strong peaks in electricity demand and also periods when electricity consumption is significantly below the daily average. In the case of locations that are well linked into large-scale power grid, the peaks and troughs in the power consumption can be offset by sending power away from the region (exporting the power) during the time when the demand is low and importing when the power demand is high. This smoothens out the peaks and troughs. If there are locations separated by different time zones or different climate linked by the long distance grid, this transfer of power can substantially help in rectifying the problem. In contrast to this, in the case of an island, its geographical isolation often makes this approach impractical. Even if the island is connected to the grid linking it to other islands or continental grid, there may be substantial distances involved in transferring the electricity to consumers at other locations and other substantial limitations arising from an island location.

This makes the production of the electric power in such island locations more expensive. The island's economy has to maintain spare capacity for producing local power on demand when it is needed. Some power producing stations, e.g. coal power plants are not well suited for the rapid change in the amount of power they produce. These plants are optimised for operation at a certain constant power generation level. Gas power plants are more adapted to rapid boosting of the power generation when it is needed than coal plants but maintaining gas plants idle for most of the day just for the operation during short power generation peak times adds to the cost of the electricity production. Furthermore, the gas plants that can rapidly change the power output on demand are of the open cycle turbine type. These plants have rather low fuel efficiency compared to combined cycle plants.

Another source of power production is from renewable sources, e.g. wind farms or solar power plants. These sources are highly important in light of the growing concerns over effects of carbon dioxide on climate change and finite nature of fossil fuels as well as security of supply issues. However, these sources are intermittent and unpredictable by nature. Even in windy countries such as Ireland and United Kingdom, where fresh wind persists for most days of the year, the pattern of wind velocity is not correlated with the pattern of the daily usage of electricity. This limits the amount of power that can be introduced into the power grid from available renewable sources to some 10-20%. Reliable supply of electricity on demand is an essential requirement of the modern society.

One possible solution to provide energy quickly at peak periods is to store large quantities of energy that can be released on demand. The required power is compared with the national peak power requirement, of the order of 0.2 GW-10GW and the duration of time of the power release should be preferably at least 1 hour. More preferably the power should be sustained for the duration of time several hours or longer. Therefore, the desired energy storage capacity should be at least 0.2 GWh and more preferably greater than 50 GWh. Energy storage facilities are well known. Large quantities of energy can be accumulated using several different approaches, for example pumped water storage systems, pumps compressing gas into a high-pressure reservoir or accelerating heavy flywheel to high angular velocity.

In the case of the pumped water storage the energy is stored by pumping water up from a lower reservoir up to a higher reservoir and then allowing the water to flow down under the influence of the gravitation that releases the energy. The water falls down through electrical turbine and this produces the electric power. The pumped water storage facilities exist in many countries. In Ireland there is a pumped storage system at Turlough Hill, Co Wicklow. However, pumped storage in Ireland is not a major part of the energy supply scheme. Its peak power is only 250 MW and it cannot sustain the peak power for many hours due to the limited amount of the energy it can store. The construction of the energy reservoir is considered to be expensive due to the large costs of creating two reservoirs in mountainous terrain. The cost of construction of the water reservoirs represents a major component of the total costs of construction of pumped water storage facility.

Desirably, pumped water storage should satisfy all the following conditions:

1. The two reservoirs should be located relatively close to each other to reduce the loss of energy during the pumping stage and in particular during the energy release stage, e.g. less than 5 km or even more desirably less than 500 m from each other.

2. The reservoirs should be of substantial size so that they could retain substantial amount of energy.

3. The lower reservoir should be located away from the towns so that if there is sudden accidental release of energy from the upper reservoir, it flows away from population centres as a precaution against accidents.

4. The upper reservoir should be located preferably on top of a solid rocky foundation so that the dam built to retain water in the upper reservoir is structurally solid and placed on solid foundation. This is necessary to avoid accidental collapse of the dam and accidental uncontrollable release of large amount of energy with the flowing water.

5. There should be a substantial height difference between the lower and the upper lakes. This is necessary to increase the amount of energy that can be retained by the pumped water storage facility. The height difference preferably should be greater than 10 m and more desirably it should be much greater than this.

Conventional pumped water storage systems is well known, for example US Patent Number US7,003,955, Davis, teaches a pumped storage power system utilising low lying storage lakes with the small height difference between the upper lake and the lower lake, down to several metres. In particular the patent teaches utilising low lying lakes on a sandy terrain.

The small height variation between the two reservoirs leads to the situation when the water level variation in the reservoirs significantly changes the pressure in the conduit and consequently the rotational speed of the hydro-turbine. This problem is addressed by US Patent Number US6,420,794, Cao. US6,420,794 teaches that a additional reservoir called back up reservoir coupled to the delivering reservoir by means of adjusting valve. According to this US patent this allows for maintaining the level of water in the upper reservoir constant throughout the operation of the pumped storage and the speed of hydro-turbine constant.

A water pumped storage system, where sea water is used as the pumped medium, was developed in Okinawa Prefecture, Japan. The published results of the project [Hitachi Review, Vol. 47 (1998) No5, page 199] indicate that the key problem identified with using sea water is the prevention of corrosion of the essential elements of the power generator and prevention of the growth of marine flora within the generator. It appears from the published description that the key issue that is to be addressed is to seal off the rotor. The pump turbine contains many narrow spaces and the wicket gate is expected to sustain large pressure differential. This according to the authors of the Hitachi Review makes it difficult to apply the proper corrosion prevention measures. In the Okinawa project the power house is located in the tunnel, drilled into the mountain and located below the sea level. The turbine is located below the sea level. The pipe connecting the turbine to the sea, called tailrace is of the length comparable to that of the pipe connecting the upper dam with the turbine called penstock. The tailrace is tilted down away from the sea towards the turbine. The penstock and the tailrace are drilled into the rock formation of the hill sloping towards the sea and installed with no external access to them. It is likely for the problems of enhanced corrosion and growth of the marine organisms and the large costs of construction of the upper reservoir that the technical solution tested in Okinawa Prefecture has not become more common place and was not replicated at other locations. In addition the upper dam in the Okinawa pumped storage is made artificially; it is not made on the basis of the natural existing landscape. The dam is of regular octagonal shape and all the walls of the dam are artificially laid.

The fact remains that sea water pumped storage has not become a commonplace technology for reasons outlined above and the main water pumped storage almost with no exception remains the conventional pumped storage utilising fresh water sources between two water reservoirs. One of the main problems with the conventional approach to water pumped storage utilising two fresh water lakes, in the case of Ireland and other island regions of broadly similar size, such as the United Kingdom, is that due to the relatively small size of the island it is difficult to locate the reservoirs that would satisfy all the above conditions. In Ireland there are several ranges of mountains. These are often small mountains that may be often more appropriately called hills. These have been formed as a result of the ice formation that altered the landscape during the ice advancement and retreat. Therefore, unlike conventional mountains, the mountains in Ireland are rather smooth. Due to the small size of the mountainous areas in Ireland and due to the relatively smooth surface of the mountains, it is difficult to locate areas that would satisfy the above conditions as expected for a conventional pumped water storage system. Furthermore, the situation is complicated by the fact that most areas that would be suitable to locate the lower reservoir are picturesque and therefore contain population and visitors. These areas are often serve as tourist attractions and therefore there are additional expected safety issues such as prevention of the accidental collapse of the reservoir with the sudden uncontrollable release of large amounts of energy with the flood of water washing down from the upper reservoir on the populated areas.

Objects of the Invention

It is the object of the present invention to provide a system for the storage of large quantities of energy that can be released on demand, preferably within minutes of the request for energy being received.

It is also the object of the present invention to provide the power levels that could be substantial by comparison with the entire power peak power requirements for a particular region.

It is a further object of the present invention to provide energy accumulating system that can sustain the power levels for the durations of one hour or more, that is the time comparable or longer than the typical durations of peaks in the power consumption. It is another object of the invention to reduce the demand on the power generation stations such as coal or gas power plants during the peak electricity demand times.

It is another object of the invention to reduce or moderate the increase in the installed capacity of the coal and gas power generating stations and as result reduce the cost of the electricity generation in the jurisdiction.

It is another object of the invention is to reduce the dependence of island regions on the imported fossil fuels.

It is another object of the invention to increase the number of electricity users that can be supplied power from the existing gas and coal power stations and still meet the peak power demand.

It is also the object of the invention to facilitate introduction of the greater fraction of the energy from renewable sources such as wind into the electrical power grid.

It is also the object of the invention to provide the energy accumulating system that can be easily constructed using natural terrain of an island region.

It is also an object of the present invention to provide the energy accumulating system that is easy to construct at relatively low cost.

It is also an object of the present invention to provide the energy accumulating system that is clean to operate.

It is also an object of the present invention to provide an energy accumulating system that allows for convenient visual inspection of all key components of the energy storage system.

It is also an object of the present invention to provide an energy accumulating system that can provide cranking power to restart unrelated facilities of the users that loose power due to storms or blackouts. It is another object of the present invention is to provide the energy storage medium having higher gravimetric density than the one utilising fresh water and as such higher energy storage density.

Summary of the Invention

According to the present invention there is provided, as set out in the appended claims, an energy accumulation system comprising at least one reservoir, for storing sea water, elevated above sea level and located in the vicinity of sea shore; at least one turbine located in the vicinity of the sea level and substantially below the level of at least one of said reservoirs, said turbine being connected to at least one power generator; at least one conduit connecting said at least one reservoir to said turbine, wherein the downward flow of sea water from the reservoir through the at least one conduit serves to engage with and rotate said turbine and generator for the purpose of generating electrical power.

Ideally, the resistance to the flow of the sea water from the point of exit from the turbine to the sea should be less than the resistance to the flow from the water reservoir to the turbine.

Ideally, the invention provides at least one main pump connected to an electrical grid system and capable of pumping the sea water from the sea level to the level that is substantially above the sea level; at least one conduit coupling the main pump with the reservoir and at least one conduit coupling the pump with the sea.

In one embodiment, there is provided a secondary pump located substantially at the level of the reservoir and capable of pumping the water from the reservoir into the conduit joining the reservoir with the turbine. The power rating of the secondary pump is substantially lower than the power rating of the main pump.

Suitably, there is at least one valve installed on the conduit. Optionally, there is at least one valve installed on the conduit joining the reservoir with the main pump. Preferably, there is at least one filter installed on the line joining the reservoir with the turbine preventing solid elements travelling with the water flow from passing through the turbine.

In another embodiment, the turbine is a reversible turbine that can rotate the power generator during the draining of the reservoir and adapted to operate as a pump during the pumping of water from the sea into the reservoir.

In a further embodiment the system comprises means for supplying and retaining hot water in a storage compartment in the vicinity of turbine for at least some of the period of time when the turbine is not operational. The hot water can be used for the purpose of suppressing the growth of marine organisms in the turbine.

Ideally the energy accumulation system comprises means for supplying and retaining hot water in the compartment in the vicinity of the main pump for at least some of the period of time when the main pump is not operational. The hot water is used for the purpose of suppressing the growth of marine organisms in the turbine.

Suitably, the reservoir is located on top of a cliff. The cliff can comprise hard granite- like rocks and/or basalt-like rocks or another type of rock of low primary and secondary water permeability.

The reservoir can be located at a terrain surrounded by natural elevations substantially at two sides and two manmade walls located substantially at two remaining sides. Alternatively, the reservoir is located at a terrain surrounded by natural elevations substantially at three sides and a manmade wall located substantially at the remaining side. It will be appreciated that the reservoir can be constructed at a location of a natural existing lake by extending the volume of the water that can be stored in the lake by means of artificially extending some of the boundaries of the lake to a greater height. It will be further appreciated that the reservoir can be constructed at a location of a natural existing lake by extending the volume of the water that can be stored in the lake by means of extending depth of the lake. Ideally, the sea water reservoir is created in a valley with a neck-like escape and a dam is placed at the narrow escape route from the valley. The dam can be curved into the valley. The sea water reservoir can be created in a saddle-like landscape and two dams are placed at the two narrow escape sides of saddle.

Suitably, the sea water reservoir is created in a landscape characterised by three or more elevations and three or more escape routes and dams are placed at the narrow escape sides in between the elevations. The water reservoir can be located in the geographic location characterised by strong persistent winds throughout most of the year. The dams can be curved into the direction of the water reservoir to be created.

Preferably, the bottom of the reservoir is sealed to prevent leakage of the sea water into the ground.

Suitably, the intake of the conduit is located substantially at the bottom of the reservoir. The intake of the conduit can be separated from the rest of the reservoir by a filtering system that prevents entrance of the solid debris into the conduit.

In a further embodiment the system comprises means to pump the water from the sea level to the reservoir, wherein the power for the pump is powered by renewable sources of energy. Ideally the substantial fraction of the power required for the pump is taken from wind energy.

Suitably the system comprises means for filling the conduit with liquid that kills the growth of marine creatures in the conduit. The liquid can be hot water.

In another embodiment the conduit can be composed of a steel lining enclosed in a concrete reinforcement cage.

In another embodiment the conduit can be composed of a polymer lining enclosed in a reinforcement cage. In another embodiment the reinforcement cage is a steel pipe with the wall thickness in the range of 15 to 50 mm with water tights welds to sustain pressure in the range of 10 Bar to 100 Bar.

In a further embodiment there is provided an additional conduit that serves as an exhaust from the turbine, hereinafter the exhaust conduit, so that the water passes through the conduit connecting the reservoir with the turbine, hereinafter the reservoir conduit, then the turbine itself and then the exhaust conduit and such that the resistance to the water flow in the exhaust conduit is negligibly small by comparison with the resistance to the flow in the reservoir conduit.

Ideally, there is provided additional conduit connected to the pump, hereinafter called pump exhaust conduit that allows draining the water from the corrosion sensitive parts of the pump back into the sea during the pump operation.

Preferably, the floor of the water reservoir is sealed with water resistant means preventing the leakage of sea water into the ground. Suitably, the water resistant means is a water impermeable polymer material laid on at least some areas of the floor. The water resistant means can be a concrete layer on at least some areas of the floor. Suitably the water resistant means comprises grouting the floor of the valley to be flooded fully or partially.

In one embodiment the water resistant means comprises grouting the floor of the valley along the lines of the increased secondary permeability to water which are identified as result of the prior geological investigation of the site.

In another embodiment the turbine is adapted with an overflow vessel that is drained during the operation of the turbine and prevents the overflow of water into the sensitive parts of the turbine or hydroelectric generator. The pump can be equipped with the overflow vessel that is drained during the operation of the turbine and prevents the overflow of water into the sensitive parts of the pump. In a further embodiment the invention provides a method for the fabrication of energy- intense products such as cement, silicon, aluminium, magnesium, construction bricks or the like that require persistent energy supply and are manufactured using the wind energy reprocessed by the energy accumulating system.

In one embodiment the system comprises means to pump the water from the sea level to the reservoir, and said power for the pump is powered fully or partially by renewable sources of energy.

In one embodiment wherein the system comprises means to pump the water from the sea level to the reservoir, and said power for the pump is powered by at least one wind farm.

In one embodiment the system comprises means to pump the water from the sea level to the reservoir, and said power for the pump is powered by at least one dedicated wind farm.

In one embodiment the conduit comprises a steel conduit lined by a polymer lining.

In one embodiment the conduit comprises an open canal linking the turbines and pumps with the sea. The canal can be equipped with a mesh to prevent arrival of sea fish from the sea to the pumps and turbines. Suitably the canal is up to 2 km long.

In one embodiment a power house is located in the open and/or above ground. The power house can be located at the end of the canal linking it with the sea that is distal from the sea.

In one embodiment the variation of the water level height in the reservoir with respect to the power house during the normal course of the operation is less than 20%.

In one embodiment the floor of the water reservoir is sealed with water resistant means preventing the leakage of sea water into the ground. The water resistant means is a polymer material laid on at least some areas of the floor of the valley. In another embodiment there is provided a sea water reservoir for use in an energy accumulating system constructed on the floor of a glacial valley comprising areas of low water permeability rock.

In a further embodiment the invention provides a method for construction of a dam in an energy accumulating system as claimed in any preceding claim wherein the dam is mainly of rock filled type and the material for the dam comes partially or fully from the material excavated from digging the canal serving as conduit for connecting the power house with the sea. Suitably, most of the material removed from the canal construction is removed from the area in the vicinity of the location of the power house at the part of the canal distal from the sea.

Brief Description of the Drawings

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 shows the schematic representation according to one aspect of the present invention;

Figure 2 shows another embodiment of the energy accumulating system according to the invention;

Figure 3 shows where the inlet from the reservoir floor is coupled to the conduit according to another aspect of the present invention;

Figure 4 illustrates an energy accumulation system using a secondary pump;

Figure 5 illustrates an embodiment of the energy accumulating system with conduits partially embedded into the structure of a cliff;

Figure 6 illustrates an embodiment of the energy accumulating system that utilises several conduits;

Figures 7 to 1 1 show alternative embodiments to construct a reservoir for use in the energy accumulation system of the present invention; Figure 12 illustrates the energy accumulation system in combination with a renewable energy source; and

Figure 13 illustrates a perspective cross sectional view of the turbine according to the present invention. Detailed Description of the Drawings

Fig. 1 shows the schematic representation of the present invention, indicated generally by the reference numeral 1. It shows one embodiment of the energy accumulating system according to the invention. There is provided a water reservoir 2 located in the vicinity of the sea or ocean coastal line 3, preferably at the distance d of 10 km or less away from the costal line. The reservoir 2 is located on top of a solid surface 4 that is not readily prone to the effects of the coastal erosion. For example this could be rocky surface of granite-like stones or similar surface. In the ideal case the solid surface could be a rocky cliff with relatively flat top in the vicinity the sea or ocean coastal line 3. Preferably the reservoir is located at the elevation h of some 50 metres above the sea level or greater. The reservoir could be located at the height as large as 600 metres or even higher but it could also be the head as low as 70 m. The reservoir is connected by means of at least one conduit 80 to a turbine 5. This could be a Francis turbine or another turbine suitable for operation at a high pressure difference. The turbine 5 is mechanically coupled to a hydroelectric generator 6 either directly or through a series of gears. There is also provided a separate pump 7. The pump could be based on a Francis turbine or another suitable turbine depending on the elevation h. There is at least one conduit 8 coupling the pump 7 to the ocean water and at least one more conduit 9 coupling the pump to the water reservoir 3. Both, the pump 7 and the hydroelectric generator 6 are connected to the electric grid 10. There are also valves 11 and 12 that can disconnect the conduits 80 and 9 from the water reservoir 2 on demand. The dimensions of the reservoir 2, the conduits 80 and 9, the height of the turbine and the pump inlet with regard to the sea level are shown schematically and not to scale. It will be appreciated that the sea level also changes with tide.

The energy accumulating system can also include various control and automation systems. These will be known in the field of pumped power storage facilities and are not shown in the figure 1. Preferably, the surface area of the reservoir is at least some 10 ⁴ m ² , and possibly can be as large as 10 ⁷ m ² or even greater. The depth of the reservoir is preferably greater than 1 m, more preferably it could be 10 m to 50 m at the deepest point, and could also be greater than that, e.g. over 100 m. The principle of the operation of the present invention is as follows. During time intervals of the low energy consumption, the pump 7 pumps the water from the ocean up along the conduit 9 into the water reservoir. For this the valve 12 is kept open and the 11 is either kept closed or open. During the intervals of increased energy consumption the valve 1 1 is open. In this case the water pressure of the water from the water reservoir 2 rotates the turbine and the rotor of the hydroelectric generator and this generates electric power. Both the pump 7 and the hydroelectric generator 6 are connected to the power grid 10 so that they can take the power from the grid or put in the power into the grid.

The power used to energise the pump during the water pumping could be used from the wind powered electricity generators fully or partially. This will increase the portion of the wind energy that could be introduced into the electric grid without losing the reliability of the supply. If the option of energising the water pumps fully from the wind power generators is employed as mentioned above, the energy accumulation system can also be powered by its own dedicated set of wind farms.

The conduit can be a pipe with the diameter of 0.4 to 5 m. The conduits of diameter even greater than 5 m could be used for energy accumulation systems rated for very high power, e.g. in excess of 1 GW. Preferably, the pipe should be tested to withstand the pressure well in excess of the value of pgh, where p is the gravimetric density of water (sea water), g is the acceleration due gravity and h is the height of the water reservoir with respect to the sea level. Depending of the height of the water reservoir, the likely value of the pressure could be around 4-100 bars. The conduit could be engineered in such a way that it could sustain greater pressure at the lower part of it that is proximal to the seal level and could sustain lower pressure at the other end of the conduit that is proximal to the water reservoir 2. The conduit should also be able to withstand higher pressure to account for the effect of pressure surges known also as water hummer. The conduit can be assembled in the way that it has lining resistant to corrosion from the sea water, e.g. lining of polymer material or high grade steel that is corrosion-resistant. This lining can be encased in a concrete reinforced by steel bars and rods. Polymer lining could be enclosed in steel reinforcement conduit. The conduit could be made of steel with the wall thickness of 15 to 50 mm. The wall thickness of somewhat outside this rage could also be used. The steel sheets of the conduit could be welded together to withstand the pressure of in excess of 10 Bar. The steel conduit could be covered by a protective layer of a polymer or epoxy. The conduit can also be of cross-sectional area other than circular. The cross-sectional area of the conduit connected to the pump 7 could differ from the cross-sectional area of the conduit connected to the turbine 5.

An embodiment of the invention utilising more than one water reservoir can be used. The reservoirs can be located at substantially the same height with respect to the sea level or at different heights. This can allow increasing the amount of energy that could be stored in the energy accumulating system. The water reservoirs can be interconnected with each other or they could also be individually connected with the turbine by means of separate conduits. It will be appreciated that the conduits can also be connected with several turbines, several pumps or several reversible pump/turbines.

In order to stop the leakage of the seawater from the water reservoir into the water table, it is beneficial to seal the floor of the reservoir with water tight means such as a polymer film or grouting. The grouting could be applied by drilling the holes in the ground and injecting the grout under pressure to seal the cracks in the rock below the surface. The locations where the grouting is applied are preferably the locations of higher water permeability of the rock. These locations could be identified by means of the geological investigation of the site. This will limit escape of the sea water into the water table of the water reservoir 2 and therefore prevent the soil salination in the vicinity of the energy accumulating system. The floor can be sealed by means of watertight construction materials such as concrete or concrete treated with water repellent. During the power generation phase of the operation of the system the water reservoir could be emptied fully or only partially. This depends on the demand and pattern of the cycle of electricity usage.

Fig. 2 shows another embodiment of the energy accumulating system whereby there is no separate pump. The turbine is employed to pump the water up to the reservoir 2. For this the turbine 5 is operated in reverse, i.e. it is rotated by means of the hydroelectric generator operated in reverse. Therefore, the turbine consumes the energy from the electric grid when pumping sea water during off peak power demand periods. The end of the conduit distal from the sea is shown split in two on the schematics. This is only given as an example. It could also be the same conduit all the way from the reservoir to the turbine or alternatively it could have more than two inlet pipes at the point of entry into the reservoir 2. This point of entry could be constructed as inlet tower.

Fig. 3 shows the inlet 81 from the reservoir floor connected to the conduit covered by a filter 20 that stops large solid elements from entering into the conduit. The filter 20 can be a mesh or another suitable barrier that is not transparent to the solid elements such as pieces of mud, etc.

Fig. 4 shows an alternative embodiment of the energy accumulating system that does not rely on valves. The conduits 80 and 9 enter into the water reservoir in such a way that the water cannot escape from the reservoir under the influence of gravity. In order to direct the water towards the turbine, there is a pump 30 that can pump the water from the water reservoir 2. The power ratings of the pumps 7 and 30 can differ from each other.

Fig. 5 shows an embodiment of the energy accumulating system with conduits partially embedded into the structure of a cliff. The conduits can indeed be laid underground at least for part of their length. Alternatively they could be laid over ground and then fully or partially covered by rock and soil.

Fig. 6 shows an embodiment of the energy accumulating system that utilises several conduits 9a, 9b, etc, for filling the water reservoir and several conduits 80a, 80b, etc, for draining the water reservoir. These could be connected to several pumps, indicated as pump 7a, pump 7b, etc. and also to several turbines, indicated a turbine 1 , turbine 2, etc. The conduits could contain valves 1 1a, l ib, 12a and 12b and operate as described in relation to the embodiments presented in Figs. 1-5. Alternatively the energy accumulating system could consist of several reservoirs connected to different pumps and different turbines. Several pumps could be connected to one reservoir or several reservoirs could be connected to one pump. Likewise, several turbines could be connected to one reservoir or several reservoirs could be connected to one turbine. The dimensions of the reservoir 2, dimensions of the conduits, valves and elevations of the pumps and turbines are shown in Fig. 6 schematically, without relevance to real dimensions. The pumps, turbines, generators and motors are positioned in one or multiple power house building. These will be well known to those skilled in the art and not shown in Fig. 6. The conduits are shown schematically with multiple bends. It is desirable to minimise the number of bends as each such bend introduces energy losses in the conduit. Ultimately the layout of the conduits, bends along the conduits are determined in relation to the specific sites and their topology. It may be desirable to have rather smooth bends with greater curvature radius to minimise the losses in the conduits.

Fig. 7 illustrates how the water reservoir can be constructed in such a way that it beneficially utilises the landscape of the coastal areas. It is highly desirable to locate the water reservoir so that it utilises valley shape profile. The valley can be sealed to form a water reservoir using a manmade dam 40. It will be appreciated that the dimensions of the conduits and the reservoir are not shown to scale.

The saddle type landscape can also be used. This requires sealing the saddle-shape by means of two dams 40a and 40b as shown in Fig. 8. The choice of the location for the water reservoir is crucial to minimise the cost of construction of the energy accumulating system. The effort should be to reduce the height of the dam and also its length. It should be considered the fact that the dam should be located on a solid surface that is not prone to movement of ground. Preferably, the dam can be located on a neck- type escape from a valley as shown in Fig. 9. The dam position may also be chosen taking into account water permeability characteristics of the rock in the valley including the primary and secondary water permeability. If one of the areas in the valley is found to have high water permeability it may be possible to position the dam in such a way as to keep such area outside the flooded area of the reservoir 2, i.e. on the dry side of the dam.

Fig 9 shows the profile of lines of equal height. The height difference between the lines is 10 metres. The numbers at the lines 300, 310, 320, 330 indicate the height of the locations with respect to the sea level. The proposed dam 40 is located preferably at the neck-like exit from the valley and for additional strength it could be curved towards the valley. In this way the structure is capable of withstanding greater value of the pressure and also the risk of the dam sliding down the hill is reduced as the dam is placed like a plug in a narrow escape location. The position of the conduit 80 is shown as schematic indication only and it could also exit the valley though other parts of the valley periphery.

Fig. 10 shows another desirable location for the water reservoir with respect to the landscape. The water reservoir is created at the saddle-like landscape by placing two dams 40a and 40b, preferably at the two narrow escape points from the saddle-like location. The lines indicate lines of equal height with respect to the sea level and the numbers by the lines give an example of the height in metres with respect to the sea level. The dams can be curved towards the water reservoir to be created as shown in Fig. 10. It may be the case that the decision on whether one, two or three dams are required for a specific valley, is defined by the engineering considerations for the dam height. For example, it could be that the for the dam height of up to X m, one dam is required; if the height exceeds X, then the second dam needs to be constructed at another location of the valley and if the height exceeds Y, then the third dam needs to be constructed at yet another location and so on.

Fig 11 shows another desirable location for the water reservoir with respect to the landscape. The water reservoir is created in between three or more elevations. The dams 40a, 40b, 40c are placed preferably at the narrow escape locations in between the elevations. Fig. 11 shows three dams created. Other numbers of dams may be needed depending on the landscape. The dams could be curved towards the water reservoir to be created. As in Figs 9 and 10, the lines indicate the height of the locations with respect to the sea level measured in metres as example only. The position of the conduit 80 is shown as schematics only. The size of the conduit is not shown in proportion to the size of the valley.

Fig. 12 schematically shows the energy accumulating system placed in conjunction with the wind farm 50. It is advantageous to locate the energy accumulating system of the invention in the areas of the fresh persistent wind for the purpose of including a substantial proportion of the wind energy into the energy mix processed by the energy accumulating system. The wind farm 50 is a single large wind farm or a multitude of wind farms connected to the energy accumulation system. The term for the connection point 10, as known to those skilled in the power systems, is substation. The substation can be located at one location, or could comprise multiple substations remote from each other. The substation includes step up and step down sections to adjust the voltages from the hydro generators, motor, wind farms and transmission grid. This will be well known to technicians skilled in the art of power transmission and will not be discussed in the present invention.

Fig. 13 shows the turbine in operation according to the present invention, indicated generally by the reference numeral 60. It shows the Francis turbine 60 with a conduit 61 connected to it. The turbine 60 is coupled to a hydroelectric generator (not shown) by means of a shaft 62. There is gap 66 provided between the runner 68 and a spiral case 69. The spiral case is static and the runner rotates in it. This gap also experiences large pressure applied to it and therefore there is water stream along the shaft 62. In order to prevent the escape of water along the shaft into the compartment of the hydroelectric generator, there is a jet blocker 63 installed on the shaft 62. The jet of the water escaping along the shaft is stopped by the jet blocker and then redirected downwards towards a drainage plate 64. The jet blocker 63 and the drainage plate 64 are enclosed into the overflow vessel 67. The overflow vessel has drainage conduits 65 leading from it to the outside. If required the drainage can be further assisted by the pumping the water out of the overflow vessel. Several jet blockers could be installed in one overflow vessel and several overflow vessels could be installed in one turbine or one pump. It will be appreciated that pumps that pump the water to the water reservoir could also be equipped with a similar overflow vessel. Other embodiments of the overflow vessels can be devised according to the invention. Such overflow vessels assist in suppression of corrosion in the sensitive areas of the turbine 60. The areas that are in constant contact with the sea water could be made of high grade stainless steel or treated with protective polymer coatings.

In another embodiment conduit 8 is in the form of an open canal. The length of the canal can be up to 10 km. The cross section of the open canal can be in the range of 50 m ² to 800 m ² but in some cases it could be outside this range. The canal is equipped with a mesh to stop the sea organisms and the fish from entering the pump turbines. The area of the screen should be such that the flow velocity of water at the power plant operating at full power for energy storage is below the limit velocity set for the fish to swim against the flow. This is usually in the range of 1 m/s or below. The power house should be located at the end of the canal distal from the sea. This allows for shorter penstock and thus for lower losses in the penstock.

The turbines of the pumps should be located below the sea level to allow for the inlet pressure and thus prevent cavitation at the turbines. The depth of the submergence of the turbines depends on the height h of the water level in the reservoir. As it will be appreciated by those skilled in the art, the required submergence is in the range of 10-40 m for the head height h in the range of 40-400 m.

According to the invention it is preferable to position power house accommodating the turbines, pumps, generators and motors, in the open area as opposed to the tunnel. This will reduce the costs of construction of the energy accumulation system. According to the invention, it is further advantageous to minimise the movement of the material in and out of the construction site. It is advantageous to construct the dam of the rock- filled type with water impermeable surface facing the reservoir. The volume of the rock required for construction of the dam for the 50-100 GWh energy accumulating system is in the range of 1 to 20 million m ³ of rock. According to the invention it may be advantageous to source the rock in the vicinity of the site for the dam construction and furthermore, it may be advantageous to place most of the rock produced from excavating the canal to erect the dam. This minimises the movement of the rock within the construction site and brings down the construction costs.

According to the invention it will be possible to reduce the variation of the water level in the reservoir with respect to the power house during the normal operation. In the conventional pumped storage plant the head height varies due to the change in levels of both, the lower reservoir and the upper reservoir. In the present invention the lower reservoir is the sea and therefore its level is substantially fixed (apart from the tidal variation that is negligibly small). This reduces the variation of the water level and increases the round trip power efficiency of the plant. This also simplifies operation of the plant and allows for employing the more simple type and robust generator, the fixed speed synchronous generator, for greater amount of the energy stored.

The invention provides for the suppression of the growth of marine organisms in the conduits, the pump, the turbine, the overflow vessels and other sensitive locations of the system that need to be kept clean. According to the invention this can be done in three different ways.

First, some elements of the energy accumulating system are lined with the materials and polymer coatings to which the sea organisms bind with reduced affinity, i.e. the materials that tend to remain clean in the sea water conditions, for example using Teflon™ coatings.

Secondly, the energy accumulating system has provisions for access of hot and retention of hot water in some compartments that come in contact with the sea water. For this, the hot water is allowed into some areas of the energy accumulating system and retained there long enough the kill the marine organisms that settled in such areas. For example, once a week, the hot water is allowed into the compartment around the runner 68 and the spiral case 69 and retained there for the duration of e.g. 1 hour. After that the hot water is flushed from the compartment either into the sea or to the water reservoir 2. The temperature of the water is high enough to destroy the marine organisms, for example 50-100 C. The frequency of the procedure and the duration of the retention of hot water can be determined by the speed at which the marine organisms re-settle in the system. Different compartments could be treated at different times, for example, runner and spiral case could be treated on Mondays, and the overflow vessel could be treated on Tuesdays and different sections of the conduit could be treated on other days of the week. This schedule is only given here by way of example. In order to retain hot water in different compartments of the energy accumulating system, there is additional system of valves isolating these compartments. For example, in order to retain hot water in the spiral case 69, one could install the valve at the conduit 61, which is not shown in Fig. 13. To allow for the access for hot water the energy accumulating system can be provided with an external source of hot water or external heaters heating the water in the external compartments with the subsequent transfer of it into the desired compartment of the energy accumulating system. Alternatively, the different compartments of the energy accumulating system could have the heaters embedded into it. For example, one could have heaters installed into the out walls of the spiral case 69. To allow access of the hot water to different compartment of the energy accumulating system, there is provided as system of additional pipes and valves linking these compartments with the source of the hot water.

Thirdly, different compartments of the energy accumulating system can be subjected to a liquid that kills the marine organisms by chemical or biological action. There is countless number of chemicals that kill marine organisms, for example: acids, such as e.g. diluted HCl, H ₂ SO ₄ etc, bases such as KOH, NaOH etc, concentrated solution of the sea salt, various salts with the antibacterial action e.g. CuSO ₄ , various herbicides and pesticides. Again, in order to allow the access of liquid that destroys marine organisms by chemical or biological action, there is provision of the additional pipes and valves such as described above in relation to the method utilising the hot water.

It will be further appreciated that the system of the present invention can be employed in combination with industrial production that requires large amounts of energy and persistent uninterrupted energy supply that utilises the energy. For example, the energy accumulating system described above can be used to supply the energy required in the production of cement of aluminium, of molybdenum, of titanium, of silicon. In combination with the dedicated wind farms supplying energy to the energy accumulation system, this produces a brand new class of products: products manufactured without carbon dioxide emission. At present the interest in manufacturing of products without damaging carbon dioxide emissions increases rapidly due to the increased awareness of the seriousness of the climate change caused by the burning fossil fuels.

It will be appreciated that the invention provides a method of construction of the dam for the energy accumulation system wherein the dam is mainly constructed as rock filled dam and the material removed from construction of the canal is transferred mainly to erect the dam. In one embodiment of the invention the energy accumulation system comprises energy storage capacity to overcome the wind intermittency and convert wind into a predictable source of energy available on demand.

It will be appreciated that the invention provides a method for manufacturing of goods without incurring carbon oxide emissions to the atmosphere and associated damage that utilises the energy accumulating system as in any preceding claim with the energy for the power generating system being mainly supplied from dedicated wind farms.

It will be appreciated in the context of the present invention that the term 'sea' shall mean any sea surrounding the island of Ireland, or other islands, including the Atlantic Ocean and other oceans. The term 'sea- water' is considered to cover both sea and/or ocean water.

The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.