The present invention relates to a device for storing energy and retrieving energy in a controlled way for feeding a power grid, comprising the features as indicated in the preamble of claim 1. The invention also relates to a method as identified in claim 17.

It is known in the art to store energy in disk springs . For example, Chinese utility model CN 2899074 relates to an energy storing device applying a disk spring for closing a power circuit within milliseconds. Hence, said known method is not suitable for feeding a power grid.

The invention aims at providing an improved device and method of the kind mentioned in the preamble.

The invention further aims at providing a device and method that allows storing and retrieving energy, in particular electric energy, simply and highly efficient.

The invention also aims at providing a device and method for storing energy by using materials that can be easily reused.

So as to obtain at least one of the above mentioned aims, the invention provides a device as mentioned in claim 1. This device has the advantage that energy is stored efficiently and can be retrieved very efficiently as well. An additional advantage is that the device can be made of easily reusable materials, substantially of metals.

It has also shown that the device and method according to the present invention operates at low costs without use of rare earth metals, in contrast to when using batteries. Such synergistic effect is a surprising and advantageous effect.

The invention therefore relates to a device for storing energy in deformable elements, comprising: - a drive apparatus for inducing a deformation of said deformable elements by applying energy and - a generator for retrieving energy by reverting said deformed elements to at least part of said induced deformation or to a non-deformed state, said device being characterized in that at least part of the deformable elements are comprised of disk springs with an outer diameter of at least 0.04 m. Disk springs with the said range of diameters, i.e. at least 0.04 m require a compression energy, and hence provide a relaxation energy, that allows one to yield an energy recovery for feeding a power grid.

According to a preferred embodiment, the disk springs are placed: [a] in series; [b] parallel; or [c] in a combination thereof. An advantage of a stack with parallelly placed disk springs is that the compression force of each disk spring in the stack is added, such that a relatively high total compression force is obtained. If, on the other hand, a large displacement path is required with a relatively small total compression force, disk springs may be positioned in series. A combination is possible as well, by applying a combination of a series of parallel disk springs, for example a large number of sub-stacks of 5 parallel disk springs, wherein the sub-stacks are placed in series in the total stack. As a matter of fact, any number of disk springs may be parallelly placed in a sub-stack for providing a desired result as regards retrieved relaxation energy.

A still higher retrieval of energy may be obtained when applying disk springs having a larger outer diameter, for example of at least 0.1 m, preferably at least 0.2 m or at least 0.4 m, more preferably at least 0.6 m, still more preferably at least 0.9 m.

So as to have a device as compact as possible, while still yielding a high energy output, the disk springs preferably have an outer diameter of maximally 3 m, more preferably maximally 2 m, still more preferably maximally 1.5 m.

The disk springs may have a thickness that is common in the art for disk springs of the size as indicated above. Preferably, the thickness is at least 2 mm, but this will depend on the actual outer diameter of the disk spring that is applied. A disk spring with a smallest diameter according to the present invention may have a thickness of about 2 mm, whereas disk springs with a diameter of more than 0.9 m may have a thickness of at least 1 cm or even more, for example up to 2 cm or even up to 3 cm, or if applicable up to 4 cm or even 5 cm.

A compact device is preferably obtained by applying disk springs that each have a mutually aligned central opening, a tensioning and relaxation element for inducing a deformation or reverting said deformation of said deformable elements, extending through said aligned central openings. The stack of disk springs can be simply incorporated in a cylindrical or tube-like container or the like whereas the said tensioning and relaxation element, for example a cable, extends longitudinally through the disk springs' central openings. No elements extend outside of the disk springs yielding a compact device.

Feeding a power grid with the device according to the invention is made simple when said generator is an electric generator embodied for generating alternating current upon reverting said deformed elements to at least part of said induced deformation or to a non-deformed state. An electric generator will by definition induce an alternating current. A simple embodiment is obtained when the tensioning and relaxation element, preferably a cable or a like flexible element, is wound on a drum when tensioning the stack of disk springs and unwound from the drum upon relaxation thereof. The rotating drum may drive the generator so as to generate power.

A simple embodiment providing ease of operation is obtained with a device wherein the disk springs are stacked and wherein central openings in the disk springs are mutually aligned, wherein a first end of said stack of disk springs abuts a fixed abutment surface and a second end of said stack of disk springs comprises a retraction surface, a tensile element being coupled to said retraction surface with a first end and extending substantially to ^¬ wards said abutment surface and wherein a second, opposite end of said tensile element is operatively coupled to at least one of: the drive apparatus for inducing a deformation of said deformable elements by applying energy and the generator for retrieving energy by reverting said deformed elements to at least part of said induced deformation or to a non-deformed state.

As indicated above in general terms, it is preferred that said tensile element (referring to the element both in a tensioning and in a relaxation operation) extends substantially from the retraction surface towards said abutment surface through said disk springs' central

obtained .

Hereinafter,

generally indicat

Preferably,

away from the ret

least one of the

gearbox. When a s

ratus may wind up

press the stack o

sile element may

erator and feed t

"power grid" may

a domestic power grid for providing energy to a single house, or a company power grid for providing energy to a company, like an office building, a factory or a hospital. Larger applications are envisaged as well, where a national power grid, or national electricity grid, is fed.

Preferably, each disk spring has a compression strength of at least 2 kN, more preferably at least 5 kN or even at least 10 kN. Similarly, each stack of disk springs preferably has a compression strength of at least 50 kN, preferably at least 1 00 kN, more preferably at least 250 kN, still more preferably at least 500 kN, most preferably at least 800 kN . Basically, any number of stacks may be combined depending on the amount of energy available for compressing the stacks. Especially when solar energy or wind energy is generated in solar parks or wind parks, huge abundance of electricity may be available for storing in a device according to the present invention. Therefore, sufficient energy may thus be retrieved at a later time for feeding a domestic, company or national electricity grid.

A preferred embodiment is obtained when the tensile member is wound on a drum, said drum being connected to at least one of the drive apparatus and the generator by means of a gearbox.

A further enhanced embodiment is obtained with a device according to the invention wherein tensile elements of different stacks are operatively coupled to at least one of the drive appa- ratus and the generator. As a consequence, a higher total compression force is required for compressing the stacks with the result that a higher energy yield may be obtained when relaxing the stacks. Since stacks of smaller length can be applied, the device may be more compact. In this embodiment, it is preferred that each tensile member is wound on a drum, said drum being connected to at least one of the drive apparatus and the generator by means of a gearbox .

In this embodiment, it is even more preferred that at least two tensile members are wound on a same drum.

So as to obtain total control on the energy retrieved and the frequency of the alternating current generated by the generator, the gearbox is preferably embodied for providing a variable gear ratio .

As an alternative embodiment, at least two drums may be oper- atively coupled to a same axis, each drum being embodied for winding a tensile element of a stack.

According to a further aspect, the present invention relates to a method for storing and generating electric power with a device according to the invention, comprising the steps of:

in a device comprising:

- a drive apparatus, being operatively coupled to the disk springs, for inducing a deformation of said deformable elements by applying energy and

- a generator, being operatively coupled to the disk springs, for retrieving energy by reverting said deformed elements to at least part of said induced deformation or to a non-deformed state, and wherein at least part of the deformable elements are comprised of disk springs with an outer diameter of at least 0.04 m;

- inducing a deformation of disk springs from a non-deformed or a partly deformed state to a relatively more deformed state by applying energy to the drive apparatus, and

- reverting the disk springs to a non-deformed state or a relatively less deformed state while retrieving energy from the generator. This method provides the advantages as indicated above with respect to the device according to the invention.

The preferred embodiments of the device as indicated and dis- cussed above, may be incorporated as such in the method, yielding the same advantageous results.

In particular, the method may preferably comprise the step of winding the tensile member on a drum, said drum being connected to at least one of the drive apparatus and the generator by means of a gearbox so as to mutually rotate said drive apparatus or said generator concurrently with said drum.

As already indicated above, it is preferred that the method yields alternating current by rotating said generator. The elec- trie current obtained may be fed directly into the power grid.

So as to easily adapt the electric current generated by the generator to a local power grid' s frequency, the generator is preferably coupled to said drum by means of a variable gearbox and wherein a control mechanism controls the gear ratio of the gearbox for yielding an electric output of 50 Hz or 60 Hz alternating current .

Hereafter, the invention will be further described by means of a drawing. The drawing shows in:

Fig. 1 a schematic flow diagram of an application of the device according to the invention,

Fig. 2 a first stack of disk springs,

Fig. 3 a second stack of disk springs,

Fig. 4 a third stack of disk springs, and

Fig. 5 a perspective view of a disk spring.

The same and similar parts and features have been denoted by the same reference numerals in the figures. However, for ease of understanding the figures, not all parts that are required for a practical embodiment have been shown in the figures.

Fig. 1 shows an implementation of the device 1 according to the present invention. The device 1 comprises four stacks 2 of disk springs 3, 4. The stack 2 of disk springs 3, 4 may be positioned horizontally, vertically or any slant position in between. Disk springs 3, 4 may be identical, but differences in individual disk springs within a single stack 2 or in different stacks 2 may be present, for example in any of material composition and thickness . Fig. 5 shows a perspective view of such disk spring 3; 4. In the embodiment as shown in Fig. 1, the disk springs 3, 4 are stacked in series, where an outside 5 of a first disk spring 3 is directed towards an outside 6 of a second adjacent disk spring 4. Fig. 2 and 3 show this positioning in more detail.

Fig. 2 shows two disk springs 3, 4 placed in series.

Fig. 3 shows two sets of two disk springs 3, 4 placed in series and as such yielding a stack 7 of disk springs 3, 4. Hence, four disk springs 3, 4 are placed in a stack 7 in series.

Contrary to such positioning in series, a parallel positioning is possible as well, as shown in Fig. 4. Fig. 4 shows a combination of disk springs 3, 4 in a single stack 8. Four sets 9, 10, 11, 12 of disk springs 3, 4 are shown, each set 9, 10, 11, 12 comprising four disk springs 3; 4 that are placed in parallel. These four sets 9, 10, 11, 12 are mutually placed in series. Compared with the embodiment as shown in Fig. 3, the total force for compressing the stack 8 according to Fig. 4 is four times higher than the force required compressing the stack 7 according to Fig. 3 in a same relative amount, since the stack 8 according to Fig. 4 has four series of four parallelly placed disk springs 3, 4.

In other words, Fig. 4 shows four sets 9, 10, 11, 12 each comprising four disk springs 3, 4. In each set the disk springs 3 are positioned parallelly, i.e. an outside 5 of a first disk spring 3 is directed towards, and abuts an inside 13 (as shown in Fig. 5) of an adjacent disk spring 3. Analogously, in each set the disk springs 4 are positioned parallelly, i.e. an outside 6 of a first disk spring 4 is directed towards, and abuts an inside 14 (as shown in Fig. 5) of an adjacent disk spring 4.

Referring to Fig. 1, the disk springs 3, 4 are each provided with a central opening 15 (see Fig. 5) . The disk springs 3, 4 are stacked such that the openings 15 in the disk springs 3, 4 are mutually aligned. A first end 16 of said stacks 2 of disk springs 3, 4 abuts a fixed abutment surface 17 whereas a second end 18 of said stacks 2 of disk springs 3, 4 comprises a retraction surface 19. A tensile element 20, preferably a flexible element like a rope or cable 20, is coupled to said retraction surface 19 with a first end 21 and extends from said retraction surface 19 towards said abutment surface 17.

A second, opposite end 22 of said tensile element 20 is oper- atively coupled to at least one of a drive apparatus 23 for inducing a deformation of said spring disks 3, 4 by applying energy and a generator 24 for retrieving energy by reverting said deformed spring elements 3, 4 to at least part of said induced deformation or to a non-deformed state.

Preferably, the first end of the tensile element 20 is fixed ^¬ ly connected to a retraction element 25 that abuts the second end 18 of the stack 2 of disk springs 3, 4. The said retraction ele ^¬ ment 25 abuts the retraction surface 19.

At its second end 22 the tensile element 20 is connected to a drum 26 that can be rotated so as to wind up said tensile element 20. As a consequence, when winding up the tensile element 20 on the drum 26, the stack 2 is compressed into the direction of and against the fixed abutment surface 17.

The drum 26 is operatively coupled to an axis 27. Upon rotation of the axis 27 in a first rotation direction, the drum is rotated as well, with the consequence that the tensile element 20 is wound up on the drum 26 and the elements 3, 4 of the stack 2 are deformed into an at least partially compressed state. Upon rotation in an opposite second direction the tensile element 20 is unwound from the drum 26 and the elements 3, 4 of the stack 2 are deformed to at least part of the induced deformation or to a non- deformed state.

An electric motor 23 is operatively connected to the axis 27 for rotating same in a desired direction, which will be the first rotation direction for compressing the elements 3, 4. Such may be performed when a surplus of energy is available so as to store this amount of energy in the device 1 according to the present invention. A lock may be provided for keeping the elements 3, 4 in a compressed state.

When energy is required, the elements 3, 4 may be unlocked after which the elements 3, 4 tend to return to their uncompressed state, inducing a rotational movement of the axis due to unwinding tensile element 20 from the drum 26. A generator 24 is provided, operatively coupled to the axis 27, for generating electric energy upon rotation of the axis 27.

A drive gear 28 and/or any other kind of reducing element 29 may be provided for controlling rotational speed of the generator 24. For example, it may be advantageous to yield an alternating current with a frequency of 50 or 60 Hz, depending on the power grid .

Fig. 5 shows a perspective view of a disk spring 4; 5. The disk spring's inside and outside are clearly visible.

The invention is not limited to the embodiments as mentioned above and as shown in the drawings. The invention is limited by the claims only.

The invention also relates to all technical features, ele ^¬ ments and parts as such that can be applied without any of the other technical features, parts and elements while still yielding advantageous results. The invention also relates to all combinations of features described here independently of each other.