EP0024071A1

EP0024071A1 - Energy system

Info

Publication number: EP0024071A1
Application number: EP80900319A
Authority: EP
Inventors: Peter Olof Broberg; Karl Alex Krister Karling
Original assignee: KARLING KARL ALEX KRISTER
Priority date: 1979-02-13
Filing date: 1980-08-25
Publication date: 1981-02-25
Also published as: SE7901237L; WO1980001705A1

Abstract

Un systeme producteur d'energie ayant des moyens adaptes pour prelever de l'energie dans un milieu en ecoulement et comprenant au moins un corps (10) qui est plus leger que le milieu et possede un rapport portance/trainee eleve. Le corps (10) est auto-stabilisant dans le sens d'ecoulement du milieu et peut etre pilotes en direction de sorte que l'on peut lui faire faire un mouvement periodique ascendant et descendant d'une amplitude nettement superieure a la plus grande dimension du corps. Chaque membre comprenant un ou plusieurs corps (10) est relie a une corde (11) de transmission du mouvement ascendant et descendant a un ensemble (12) entraine par celle-ci.An energy producing system having means suitable for taking energy from a flowing medium and comprising at least one body (10) which is lighter than the medium and has a high lift / drag ratio. The body (10) is self-stabilizing in the direction of flow of the medium and can be piloted in the direction so that it can be made to make a periodic upward and downward movement of an amplitude clearly greater than the largest dimension. from the body. Each member comprising one or more bodies (10) is connected to a rope (11) for transmitting the upward and downward movement to an assembly (12) driven by it.

Description

ENERGY SYSTEM

This invention relates to an energy system comprising at least one energy input member and an assembly driven by said member.

The energy system to be described in the following makes use of the wind' as driving power, but other media are also useful, such as flowing water, provided that the conditions indicated hereinbelow are satisfied.

A disadvantage which is inherent in conventional wind- driven power stations is that forpractical reasons, to avoid the necessity of erecting high towers, one is under the obligation of locating the wind energy input member of the construction near the ground where the average wind^' velocity is subject to great local variations (turbulence and velocity gradients in the ground interface) . Whether the principle of vertically journalled or horizontally journalled rotors is chosen, the wind turbine plant will therefore become relatively large and bulky and difficult to service and maintain without the aid of heavy lifting appliances and scaffolds. An obvious solution therefore is to raise the wind energy input member by means of an aerostat to such an altitude that it enters undisturbed air where the average wind velocity is higher and free from turbulence and other local irregularities. The applicable practical lower alti- tude limits are from about 150 to about 200 overplains and oceans, from about 300 to about 400 m over wooded country¬ sides, and from about 500 to about 600 m over heavily broken South-Swedish and Central-Swedish districts and over cities with multi-storey blocks. An aircraft based wind energy system as described above-and-having a complete wind turbine assembly, such as a wind rotor, however, suffers from several drawbacks.

In addition to its own weight and that of the anchorage rope, the craft must carry rotor, gearcase and generator. The torque and the gyratory forces of the rotor must be compensated for, which further increases the weight.

A practical problem associated with airborne wind rotor systems is that the generator and the rotor are heavy units and must therefore be placed near the centre of gravity to avoid weighty ballast.

Apart from high average wind velocity and less tur¬ bulence there may be mentioned on the credit side of air¬ borne wind^' rotor systems less but more widespread noise, and on the debit side that crafts filled with helium or hydrogen gas and satisfying the above requirements will become, in comparison with ground-based systems, large, expensive, more complicated and necessitate more main¬ tenance and also require extremely heavy and bulky ground installations. The use of airships for recovering wind energy therefore results in advantages but also in obvious disadvantages.

One object of the present invention therefore is to try and exploit the advantages while simultaneously avoiding the disadvantages. This is here realized by directly utilizing the wind forces acting on the aerostatic craft. Said craft is then formed as an airfoil or wing of large extension in the direction of span width and provided with aerodynamic stabilization (like an airplane) so that it always adjusts itself in the wind direction similar to a weather-vane.

Said wing or airplane-like aerostatic craft is caused to adjust itself with the use of aerodynamic control sur¬ faces (by ropes or other control systems) so as to take an angle of attack to the air stream,, which gives an optimum buoyant force and an optimum lift-drag ratio. The buoyant force is transformed into energy in that the craft is caused to release a periodical up and down movement. This movement is transferred via a rope to a ground-based driven assembly which may comprise a transmission, a device for equalizing the energy and a pump, generator or the like.

During the up movement the craft is accelerated by the aerostatic forces to^" a velocity which may be many

OMPI times greater than the wind velocity, a favourable air¬ foil shape (high side relation) providing very high effi¬ ciency (energy increments substantially from aerodynamic but also aerostatic forces) . During the down movement (which to advantage can be effected more rapidly than the up movement) it is true that energy is needed for counter¬ acting the aerostatic forces, but the wing can then be so adjusted as to compensate for part of the aerostatic forces by a negative buoyant force. The assembly thus functions as a very low-speed 2-stroke engine, which may make it necessary to use an energy equalizing device (fly-wheel, hydraulic accumulator etc.) and which may make the building of systems including a plurality of crafts favourable. The movement of the craft is controlled by means of an automatic pitch control system the primary task of which is to ensure that the craft has an optimum position with regard to the wind. Thus, the craft may suitably be provided with an elevator system^"like that of an airplane. To compensate for turbulence and non-uniform wind direction the control, system may optionally be supplemented with a yaw and roll control system which parries arising distur-. bancies. However, the craft is designed so as to be self- stabilizing in the roll and yaw sense like an airplane, which may make a yaw and roll control superfluous.

By positioning the driven assembly on the ground and having the wind energy input member effect an up and down movement said member will be considerably less bulky than when the driven assembly is supported above the ground. Moreover, a high efficiency can be attained since it is possible by modern technology to give the craft a rela¬ tively high lift-drag ratio (of the order of 10 to 20) simultaneously as high craft velocities relative to the wind velocity can be attained with the aid of the aero- static buoyant force. In addition, noiseless operation is obtained because of low-frequent undulations. Besides, the control system which controls the adjustment of the craft (trimming) relative to the wind is relatively simi _

OMPI WIPO and light-weight.

For storage of the energy there may be imagined a fly-wheel/free-wheel or some kind of pump (hydraulic or pneumatic) utilized for converting kinetic energy into potential energy. It is also advantageous, with this solution of the problem, to utilize a craft of high lift-drag ratio and small zero resistance (resistance at an angle of attack of.0) , whereby the height of the craft will be small with resulting small surface area exposed to the wind, thereby permitting the craft, when taken down because of heavy weather, to be parked in a recess in the ground or behind a low wind-guard.

The invention will be described in greater detail hereinbelow with reference to the accompanying drawings which highly schematically illustrate the idea of the invention. In the drawings: Fig. 1 in side view and partly in section shows a wind energy system according to the invention. Figs. 2 and 3 show a plan view and front view, respectively, of an aerostat utilized in the system shown in Fig. 1. Figs. 4, 5 and 6 illustrate ^'the theory underlying the invention. Fig-. 7 shows the efficiencies of different wind energy systems. Fig. 8 in side view and partly in section shows a modified embodiment of the invention. Figs. 9 and 10 in side view and front view, respectively, show an other embodiment of the invention. Fig. 11 in side view and partly in section shows still another embodiment of the system according to the inven¬ tion. Figs. 12 and 13 in side view and partly in section and plan view, respectively, show a further embodiment of the system according to the invention. Figs. 14a, 14b, 14c-19a, 19b, 19c show various embodiments of wind energy input members, and Figs. 20, 21 and 22 show examples how the power in a rope is caused to drive a gear-wheel coupled to a driven assembly. Fig. 1 illustrates the principle of the invention. An airship 10 filled with helium or hydrogen gas and having the form of an aerostat is connected via a rope 11 to a driven assembly 12 comprising a rope drum 13, a

OMPI variable gear/reel regulator 14 and a generator 15. As will appear from Figs. 2 and 3, the aerostat 10 has a span width considerably in excess of its longitudinal exten¬ sion. With the aid of a control means 20 to be described more in detail in the following, the aerostat 10 can be caused to effect an up and down movement under the action of the wind. Said movement is supplied via the rope 11 to the rope drum 13 to drive the generator 15. Before a detailed description of the- system is entered upon, the theory underlying the invention will be elucidated with reference to Figs. 4-6.

According to Fig. 4, the aerostat 10 effects an up and down movement with a stroke length designated SL. The transport distances are designated A and B, while the turning points of the aerostat 10 are designated C and D. The substantial take-up of energy takes place on the transport distances A, B. At the turning points C, D the take-up of energy falls towards zero and the turning time should therefore be as short as possible relative to the time of transport. Restricting factors are acceleration durability of the aerostat lifting surface, the capacity of the control system and the dynamic loads on the rope. For take-up of energy on the distance B, i.e. in the downward direction, the aerostatic load on the rope must be high (overdimensioned supporting capacity of the craft) . The control system ensures that the craft always has the optimum angle of adjustmentw,ith regard to the wind.

According to the theory advanced by Albert Betz in 1927 a maximum of 59.3% or 16/27 of the energy contents in the air stream passing within the sweep area (calcu¬ lated at a right angle to the wind direction) of a wing or rotor can be exploited. In this case the aerodynamic efficiency of the system is considered to be 100%.

This implies that theoretically a wind velocity of 6 m/s will give 75 W/m² and a wind velocity of 12 m/s will

2 give 600 W/m . According to Betz the maximum energy con¬ tents per unit of surface area can be written as follows: 2 3

^{* **• =} I ^Vo ^[ I ^{• '} *T- ' - °'^{593 s}" - °*^{593 *} 9o ^{• V}o

where 0.593 is the Betz coefficient

A = the sweep area of the wing, rotor ( 1-Lwind) v = average wind velocity within area A p = air density

q = P Vo² = dynamic pressure (mean value within A) . o -_j—

To obtain the maximum possible effect of the plant the wing sweeping over area A shall have the lowest possible zero resistance (air resistance at an angle of adjustment giving the lowest resistance) , a high lift/ drag ratio at the best angle of adjustment with a minimum of resistance losses shall permit being set atan optimum angle of -adjustment (attack) in relation to the wind and have a velocity in the direction L of the buoyant force (at right angles to the wind direction) which is high relative to the velocity of the wind (preferably at least three times greater than V ) . For illustration of the angles and velocities occurring in conjunction with the aerostat, reference is made to Fig. 6 which shows the aerostat in pull action. The following calculations can be made on the basis of said figure:

Vres,, = ~ ^~7² + W - 2VW • cos φ

W vert = W ^* cos(φ -90°) (pull <

Pull action = Vres > W

Push action = Vres < W

In the special case when γ = 90° - φ, W will be =V

In the above formulae and in Fig. 6 V ^*= wind velocity W = circuit velocity

OMPI /to IPO ^v _res = resulting velocity (air flow velocity)

W vert = vertical component of circuit velocity

(climbing speed)

V rope = unwinding speed of the rope

<_^" = elevator angle

Y = angle of air flow α = angle of attack φ = angle of circuit ^" φ-c = 90 implies push action φ = 90 implies vertical climb φ ^~> = 90 implies pull action ψ = angle between aerodynamic buoyant force and retardation force in rope γ+φ+θ = angle of rope at aerostat

With the suggested rotor-less system the lifting surface can be given such a shape that relatively high lift-drag ratios are obtained. The harmful resistance (zero resistance) is limited to a frictional resistance on the lifting surface, a resistance induced by the control system and the resistance of the anchoring rope. In total, these increments are low compared with those of other air-borne and ground-based installations. A prerequisite is that the air stream round the construction is not decelerated by other objects. In this respect, the system according to the invention has excep¬ tionally good prerequisites.

It is fully possible to obtain in a simple manner an optimum positioning of the craft during the entirework cycle with theuse of an aerodynamic control system, similar to that of an airplane, or a cable system. In bothcases it is considered that the control has but a small influence on the harmful resistance.

High normal velocities are readily attained with this system because the stroke length SL is large and the acceleration and retardation times are small in relation to the time of a work cycle. Collectively, this implies that a very high efficiency (of the order of 85 to 90%) is theoretically obtained during the upward phase of the movement. To this comes an effect increment because of aerostatic forces which, however, are partly eliminated by the effect loss during the downward phase of the movement. Inhibiting factors are restrictions in the freedom of designing the wing profile and structurally warranted restrictions of the side relation. Finally, the mean efficiency for the entire working cycle will sink because of losses at the turning points.

Assuming that a craft having a ratio of aerostatic force to craft + rope weight of -Λ.2.5, a wind velocity of 5 m/s, equal times for up and down movements, and no aerodynamic compensation of the aerostatic force-during the downward travel, there is obtained during the upward travel a mean efficiency, of 90 to 100% (including assist¬ ance of aerostatic forces) and in total for the entire period 40 to 50% of Betz* theoretical value. This implies that during the upward and downward travels the. craft will move at a velocity of between 4 to 5 times the wind velocity. (With a 50 craft this implies that one will obtain a mean effect of about 0.3 mW at a wind velocity of 5 m/s at altitude and a stroke length of 300 m) . By increase of the stroke length, improvement of the speed at the turning points and in¬ crease of the speed of the downward movement it is possible to increase said values.

By estimation, the mean efficiency of the system will lie somewhere between the efficiency of impeller turbines and Darrieus turbines, as will appear from Fig. 7

The aerostat 10 shown in Fig. 1 is caused to effect the movement illustrated in Fig. 4 under the action of a wind the direction of which is indicated by the arrow 26 in Fig. 4. The rope 11 is unwound from and wound onto the drum 13 at this movement of the aerostat, and the rope drum 13 drives the generator 15 over a variable gear or reel regulator 14. Before reaching the rope drum 13 the

OMPI rope 11 passes a έάpe guide 18 which is mounted in a rotatable device 19 on the upper side of a housing 16 which contains the driven assembly 12. Also mounted on the upper side of the housing 16 is a frame 17 on -vfehich the aerostat 10.can be anchored after being hauled down, for instance on inspection and servicing or in hard weather. At some distance from the aerostat 10 the rope 11 is connected to a pitch/roll control device from which three, ropes 11a, lib and lie extend" to the aerostat 10. The angle attack of the aerostat 10 is regulated by means of the control device 20 and the ropes lla-llc so that the aerostat performs the movements shown in Fig. 4. The stroke length SL is adjusted at the correct value, which preferably is at least 100 m and often much more, for instance 300 m. As will appear from Fig. 1, the aerostat 10 may have a yaw servo 21 and yaw control 22. As will appear from Figs. 2 and 3, the. extension of. the aerostat transversely of the wind direction (span width) is con¬ siderably larger than its extension in the wind direction, whereby the desired high lift/drag ratio is obtained. The control or regulating devices, of the aerostat 10 are no part of the present invention and this is the reason why they are only hinted at in the drawings, such as a robot pilot 23, a control servo 24 or an aerodynamic control surface (pitch/roll control) .

For a practical utilization of the energy with the embodiment of the energy system shown in Fig. 1 a device is required which "counter-holds" the movement, such as an electrical or mechanical counterweight or spring system. A logical way of simplifying the system and eli¬ minating the need for such a counter-hold is, as shown in Fig. 8, to connect two aerostats 10 to one end each of the same rope and to cause said aerostats to operate in push pull -fashion. In Fig. 8 two frames 61 are spaced apart and each carry one rope guide 18 and a return pulley 27. The housing 16 containing the driven assembly 12 is positioned between said frames 61. The rope 11 thus runs from one aerostat 10 via one rope guide 18, return pulley 27, the driven assembly 12, the other return pulley 27 and the other rope guide 18 to the other aerostat 10. The aerostats 10 operate in push pull fashion, i.e. when one aerostat is in its uppermost position the other aerostat is in its lowermost position. To protect the aerostats in heavy weather they are taken down and placed on a carriage 28 which is then driven into a hangar 29 with-the aid of a ramp 30. This system operates very satisfactorily and there is no risk of interference between the aerostats 10 since the rope 11 is very long. ^'

Figs. 9 and 10 show another embodiment of the energy system according to the invention, in which a plurality of aerostats 10 are connected to the same rope 11, the ends of which are united so that the rope 11 forms a closed loop. The rope 11 is passed about two rope pulleys 31 which drive the generator 15 via a transmission (not shown) . All aerostats 10, as already indicated, have aerodynamic control surfaces (rudders) which are connected to a central control system which adjusts each aerostat 10 so that .an optimum effect is obtained. The aerostats 10 are aerodynamically stabilized in the pitch/roll and yaw senses. In order that the energy shall be exploited also during their downward movements the aerostats, same as in the embodiments earlier described, are aerostaticall overbalanced to such an high extent that as large a nega¬ tive (downwardly directed) buoyant force as possible can be taken out during the downward movements. The rope pulleys 31 are mounted in a frame 32 which is journalled on a swivel table 36 whereby the frame 32 can be feathered with the aid of a servo device indicated at 35. Beneath the path of movement of the aerostats 10 hauling-in and anchorage means 34 may be provided, to which the aerostats can be. fastened for instance in heavy weather. The achor- age means 34 can, if desired, be arranged to be driven on a track (not shown) for transporting the aerostats to a hangar or other place of protection.

As will appear from Fig. 10, the aerostats in this

OMPI embodiment are arranged in pairs and connected to a shaft 62 which fitsinto a corresponding fastening of the endless anchorage rope 11. In this embodiment use is made of a plurality of aerostats the dimensions of which are 5 preferably reduced in relation to the aerostats used in the earlier described embodiments. The embodiment accord¬ ing to Figs. 9 and 10 is particularly well suited for large installations.

Fig. 11 shows a further embodiment of the invention

10 in which two aerostats 10 operate in push pull fashion like in the embodiment according to Fig. 8, but are united with a rope 11 with a number of turns on the rope drum. Said rope 11 can be wound via rope guide 18 and return pulley 27 onto and unwound from the rope drum 52.

15 Said rope drum 52 is journalled in a housing 50 which is rotatable with the aid of a swivel table 51. The movement of the rope drum 52 is transmitted to a generator 15 via a shaft 53 and transmission means 54. Same as in the embodiment according to Fig. 8 one aerostat 10 moves

20. downwards when the other moves upwards, the rope 11 being wound onto or unwound from the drum 52 with resulting rotation of said drum 52 and the drive shaft 53 coupled thereto.

Figs. 12 and 13 show another way of exploiting the

25 movement of the upwardly and downwardly moving aerostats 10. In this embodiment there are provided three aerostats 10. By means of a rope 11 which is controlled in the manner earlier described by a rope guide 18 and return pulley 27, each of the aerostats 10 -.is coupled via a

30 winch 60 to a crank 59 of a crank shaft which is generally designated 56 and which is vertically journalled in bearings 57, 58 in a frame 55. As will appear from Fig. 13 the cranks 59 make an angle of at 120 with each other and the aero¬ stats 10 accordingly operate with a mutual phase shift of 5 120 . In this embodiment the crank shaft 56 will be rela¬ tively large and heavy, but the advantage is gained that the mass of the crank shaft serves as an energy equalizer and permits rotation in one direction at a relatively

constant rpm. Same as in the preceding embodiment the rotation of the crank shaft is transmitted via a shaft 53 and transmission means 54 to a generator 15.

The aerostats utilized in the various embodiments can as will readily be realized by those skilled in the art of aerodynamics, be formed in different ways and Figs. 14a, 14b, 14c-19a, 19b, 19c illustrate different embodiments which are^'all well suited for use in connec¬ tion with the present invention. These embodiments will not be discussed in greater detail, and it shall only be mentioned that they are aerostatically overbalanced, i.e. the aerostatic buoyant force is larger than the proper weight of the craft plus the weight of the rope when said rope is fully unwound. Being yaw and roll stable, the aerostats adjust themselves in the current rope direction. As earlier stated, the energy production takes place in that the craft is periodically caused by the control system to change its angle of adjustment.. As a result, a corresponding periodical variation of the aerodynamic buoyant force is attained. The buoyant force is utilized for raising and lowering the craft the rope of which is always kept taut by the assembly on the ground or by being coupled in push pull fashion with another similar craft. The aerodynamic force which is always in effect and which during the downward phase of the movement of the aerostat can be compensated for by a negative aero¬ dynamic buoyant force, contributes to the bias of the rope. This results in a higher average effect. The control devices of the aerostats and the means for regulating said devices are not shown and described in greater detail since, as already indicated, they are no part of the invention and, besides, are self-explanatory to those skilled in the art of aerodynamics.

As will appear from the embodiments illustrated, take-off of power can take place in different ways. Figs. 20, 21 and 22 show by way of example how one can proceed with the use of two rope pulleys 37, 38 which are driven by two aerostats operating in push pull fashion in the

- E OMPI manner illustrated in Fig. 8. Each of the rope pulleys 37, 38 is fixed to a shaft 39 and 40, respectively, and the rope 11 is so arranged with the aid of return pulleys 47 and 48 that it passes about the greater portion of the circumference of the pulleys 37, 38. Each of the rope pulleys 37 and 38 is coupled to a gear wheel 43 and 44, respectively, via a clutch 41 and 42, respectively, and the gear wheels 43, 44 mesh with a common, gear wheel 45 on a drive shaft 46 which is coupled to a generator via a transmission (not shown) . It will be seen from Figs. 21 and 22 that by operation of the clutches 41 and 42 rela¬ tive to the movements of the aerostats and the direction of movement of the rope 11, respectively, the gear wheel 45 can be caused to rotate in the same direction. When the rope 11 moves in the direction indicated by the arrow 49 the clutch 41 is engaged while the clutch 42 is disengaged, the gear wheel.45 rotating clockwise. When the rope 11 moves in the reverse direction the clutch 41 is disengaged while the clutch-42 is engaged, and the gear wheel 45 still rotates clockwise.

Claims

1. Energy system comprising at least one energy input member in a flowing medium, and an assembly (12) driven by said member, c h a r a c t e r i z e d in that the energy input member comprises at least one body (10) which adjusts itself in the direction of the flow of medium, is lighter than the medium and the ex¬ tension of which in said direction is considerably smalle than its extension at right angles to said direction in the same plane, said body (10) when influenced by said medium being caused by a change of the angle of attack ^* to perform a periodical up and down movement of an amplitude substantially in excess of the largest dimensio of said body, and that the energy input member is connect to said driven assembly (12) by means of a rope (11) .

2. The system of claim 1, c h a r a c t e r i z e in that two energy input members, each comprising at leas one body (10), are united each with one end of the same rope (11) and adapted to operate in push pull fashion.

3. The system of claim 1 or 2, c h a r a c t e r - i z e d in that the rope (11) is connected to a rotary rope drum (13) which is coupled to a machine (15) to be driven, such as a generator.

4. The system of claim 1, c h a r a c t e r i z e in that the rope (11) forms a closed loop and that a plurality of energy input members are fixed to the rope at substantially the same mutual intervals, and that the rope (11) is adapted to drive at least one rope pulley (31) coupled to a machine (15) to be driven, such as a generator.

5. The system of claim 1, c h a r a c t e r i z e d in that at least two energy input members are provided, each of which is coupled via a rope (11) to a crank (59) of a crank shaft (56) connected to a machine (15) to be driven, such as a generator.

OMP 15

6. The system of any preceding claim, c h a r - a c t e r i z e d in that the body (10). is a winged aerostat.

7. The system of any preceding claim, c h a r ¬ a c t e r i z e d in that the driven assembly (12) is located in a frame or building in connection with which there are provided means (28, 30) for accommodation and anchoring the energy input member or members in protected position.