GB2484891A

GB2484891A - Intermediate mechanical energy store

Info

Publication number: GB2484891A
Application number: GB1014120.8A
Authority: GB
Inventors: Demetrios Demetriou
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-08-24
Filing date: 2010-08-24
Publication date: 2012-05-02
Also published as: GB2477222B; GB201014120D0; WO2012025720A1; GB201102990D0; GB2477222A

Abstract

A mechanical energy store 1 uses springs 10 or weights or flywheels to store energy from a variable source such as wind, waves or river water flow. The stored energy is delivered e.g. to a generator at an adjustable constant rate, independent of the input. There may be input and output step-down and step-up gearboxes.

Description

Intermediate Mechanical Energy Store [1MES]

BACKGROUND

The invention is the actualization of the following concept: Utilization of a mechanical storage device that will absorb energy from a source at various rates and it will transfer the stored energy to an output according to its ratings. In this context, the "invention" comprises the parts between the input from a source (e.g. a wind turbine collecting energy from wind) and the output (e.g. an electrical generator). "System" comprises all the parts needed to transfer energy from the source to a load. In a particular application, the system will include a windmifl, the invention, an electrical generator and connection to the load. A "load" in this case may be composed of dump load resistors, the supply grid, storage battery and! or ultra-capacitor arrays, a consumer's electrical installation or any combination of these.

Motivotlon for the invention Wind speeds fluctuate and therefore the power density of the wind is not constant. As a resuft the energy coming from a given windmill does not flow in a constant rate. That is why we usually quote average speeds. Even an average speed may vary from day to day, month to month, seasonally and even yearly. Yearly averages tend to be comparable for a given location.

However, momentary or short-term wind speed predictions are essentially impossible. Even at places that there is usually very little wind it is possible on a stormy day to get wind gusts of more than 25m!s. Wind turbines need to be protected from such extreme situations.

If the windmill is mounted directly to a generator these fluctuations pass on to the latter.

Electrical generators work optimally at certain speeds (for which they are designed for). The performance of generators (even the so-called variable speed generators) is less than optimum at speeds which deviate from the rated value. This causes extra losses by either: Because of the frictional forces involved in the mechanica' construction of turbines there is a minimum (cut-in) wind speed at which they start operating. All in all, there is a whole range or spectrum of wind speeds at which a windmill can operate.

There were two triggers for the invention of IMES: 1. Reduced output of existing turbines due to a narrow band of wind speeds used.

Most existing systems have "cut-infl speeds of more than 4m/s. At the cut-in speed the efficiency is very small and it increases gradually until the rated speed which is usually to 12m/s. For higher wind speeds, the speed of rotation of the turbine is maintained at the level corresponding to the rated wind speed and if the wind reaches a very high speed (cut-off speed) the turbine brakes are applied to reduce the generator's rotational allowable speed or to deviate (furling System) the wind turbine from the casting winds for safety reasons. All this, means that there is a narrow band of speeds -close to the rated speed -at which the system operates.

2. Reduced output due to reduced efficiency of generators in existing systems In smaller systems, which produce DC, the generator operates at varying speeds depending on the wind speed. Even the "variable speed" generators do not exhibit their highest efficiency at all speeds. At the rated speed the efficiency is optimum but at lower or higher speeds it is reduced.

Therefore, it should be advantageous to come up with a system that can work efficiently in a wider range of wind speeds that would enable the generator to work at its optimum efficiency.

If the aforementioned invention is employed, energy from the windmill wifl be stored until there is enough in store to enable the generator to operate according to its ratings. This means that the generator, when operated, will be working at its rated values. There will be no need fDr slowing down the turbine, except for safety reasons if they arise, and the efficiency of the generator will be optimized.

ft was soon enough realized that the same idea can be applied in other cases besides wind power. Any other energy source of time-variable power density can be used; for example sea or lake waves either hitting the shore or n the deep, water flow in a river or stream, rain water flowing down a roof etc. If it is feasible to collect the energy at a variable rate and store it to an IMES, the latter can be driven in such a way as to deliver the energy according to demand.

Description

According to the principle of conservation of energy, the energy of the output is equal to the input energy reduced by losses in a given system. Considering energy flow per unit time, Le.

power, we can state that the output power is equal to the input power less power losses in the system.

ln rotational energy the power is proportional to the product of the Torque with rotational speed (RPM). The power and Torque transferred from the turbine to the step-down gear system determine the RPM at the input. Neglecting losses, the product of the Torque with RPM at the output will be the same as in the input. Given a gear ratio of n, the output RPM changes by n; therefore, the output Torque changes by the inverse of n to keep the product constant. lf n<1, RPM decreases and Torque increases; if n>1, RPM increases and Torque decreases. In practice, the Torque will have a lower value than the one predicted here due to the losses.

The storage part of the invention will be made up either of falling weights, or extending! contracting springs or another mechanical storage system or combination of two or more of these. The exact form and constituent parts will depend upon the amount of energy to be stored, the size and the materials of the system.

The invention will also include an output gearbox with a gear ratio designed to match its output RPM to the rated rotational speed of the generator.

The system will be equipped with sensors and controls to safeguard operation within safe limits.

The description of the prototype that follows refers to an IMES suitable for a windmill and driving an electrical generator and the storage part is made of steel springs. These springs are extended to store energy and deliver their energy to an electric generator when recoiling to their original shape. This is the prototype being tested and it will be the first application.

For any parts mentioned refer to Figure 1.

Energy is transferred from the turbine's shaft to a step-down gearbox. This minimizes the initial torque needed to rotate the turbine and this makes it easier to capture energy from lower speed winds.

Although low speed winds have much lower energy density they blow for longer times than high speed winds. In this way, their energy content is not trivial. Extracting energy from these winds, therefore, can make a difference. On the other hand, extending the usable wind speed spectrum upwards can mean that quite significant amounts of energy beyond what usual systems capture will be harnessed.

Energy is stored in the springs as explained below, with reference to Figure 1. The stored energy is released when the springs reach their upper limit. By setting this upper limit of extension of the spring we secure that the elastic range of the spring properties is not exceeded. At the same time the output of the generator is steady and regulated. Energy is being r&eased from the springs (or any other storing devices used) while they contract back to their original shape. The times needed for the springs to extend and contract depend both on the wind speed and the demand of the generator.

The principles of operation of the system are described herein further below.

The system consists of: 1. The cabinet 2. The pole where the blades are mounted (not shown for clarity) 3. The flexible drive transferring the rotational energy from the blade's shaft.

4. The step-down gearbox and its 5. Sprocket mounted at its output shaft.

6. The idler arm to keep the chain tensioned and in place within the sprockets.

7. The idler arm's sprocket at extended spring(s) position.

8. The endless chain loop.

9. The steel U sections which the gearboxes and generator are mounted 10. The extension springs.

11. The batteries compartments. (also 15) 12. The pivot point for the pole.

13. The steel p'ate base 14. The hooks for the springs lower.

16. The upper plate with hooks for springs mountings.

17. The roller sprocket to drive the chain with the springs.

18. The driver sprocket of the chain and springs mounted on the shaft of the step-up gear box.

19. The step-up gearbox to drive the generator.

S

20. The box containing the rect1er from AC to DC to charge the batteries and inverter to AC 50Hz for grid tie-up (single or three-phase).

21. Brake plates, (Electronic circuit controller for the operation of the brake pads is not shown. The lower and upper limit switches also not shown).

22. The Generator 23. The idler arm's sprocket at origin spring(s) position Operation As we can see from Figurel the system decouples the input from the output. The energy transfer from the impeller (turbine) by the flexible drive to the output shaft of the step-down gearbox's shaft sprocket drives a chain loop which only extends the springs.

-Sprocket 5 receives the motion through a step-down gear box. Even at low input speeds, the low torque produced can be used to rotate this system.

-Sprocket 18 rotates an alternator through a step-up gear box.

-A chain loop 8 (i.e. a chain loop with large circumference) is threaded' through sprocket 5, sprocket 8 and idler arm's sprocket 7, 18 and a freewheel' sprocket 17.

-When the brakes are applied to the generator, sprocket 17 is lifted; Potential Energy is then stored in the springs.

-Sprocket 5 and sprocket 18 are uni-directional and can only rotate in the same direction.

-If sprocketl8 is still and sprocket 5 is rotating, sprocket 17 is pulled upwards and energy is stored. If sprocket 5 is still sprocket 17 falls and energy is transferred to sprocketl8 which rotates the alternator.

-Most of the time, both sprocket 5 and sprocket 18 are rotating but at different rates while sprocket 17 is moving up or down when there is excess energy received or delivered.

For a given system the aim would be to match the rotating speed of sprocket 18 to the requirements of the alternator (or other electricity generator) and design the system so that 1MES will effectively be smoothing the inhomogeneous input.

This can be compared to the working of a smoothing capacitor used after a rectifier stage in a DC power supply.

The overall effect is that energy can be delivered at a stable rate, corresponding to the demand or capability of the generator.

The Electronic brakes controller was designed to meet specific tasks; although it could be achieved in full mechanically, due the high cost of additional hardware, it was decided to use simple and inexpensive electronics. It is simplified in an effective way and electronics will also a very small consumption of power. The brakes controller operates when applying and releasing the brakes for less than 200ms; during activation the consumption is less than 4 watts.

Claims

CLAIMS1. A method incorporaUng deve and its peripherals that can be used to store mechanical energy in a way that can be delivered at a uniform rate. lt can receive energy from a source at varying rates and it can deliver the stored at an adjustable constant rate.
2. The inventbn includes a gearbox which will transfer the input energy from the source to a mechanical energy storage system with minimum losses while adjusting the torque to a proper value, allowing the system to harness energy from winds spanning a wide spectrum of wind speeds, starting from speeds lower than 3m/s.
3. The invention includes a second gearbox which wiU transfer the stored energy from the store to the output with minimum losses while adjusting the torque to a proper value for the device or part receiving the output, allowing the system to operate the device on the output (e.g. an electrical generator) at its optimal ratings.
4. The actual storage part may be comprised of weights being lifted or springs being extended or contracted or a rotational device such as a fly-wheel or any other component that can store mechanical energy or any combination of these.
5. Components implementing the process as in claim I may include such peripheral parts as gearboxes such that the speed of rotation or oscillation at the input is matched to the storage part and the output of the said storage part is matched to the part receiving the output. Typical input and output parts are a wind turbine and an electrical generator respecUvely.
6. Other peripherals to implement the process as in claim I pertaining to the input may be a. a wind turbine wh guiding tail and tower to convert wind energy to rotational kinetic energy, or a b. paddle or other device to convert energy from waves hitting the shore into rotational kinetic energy, or c. a float or other device to convert water wave motion into rotational kinetic energy, or d. a waterwheel or other device to convert energy of flowing water into rotational kinetic energy
7. Other peripherals to implement the process as in claim I pertaining to the output may be a. an electric generator to convert the stored energy into electricity, or b. a mechanical pump to draw water from a well, a lake or the sea or send water to a reservoir or both, or
8. The output of the said generator in claim 6a may be connected to: a. an inverter for feeding the electricity supply grid, or b. a charger to charge electrical batteries and/ or ultra-capacitor banks for storing electrical energy, together with an inverter for connecting to a local consumer's network, or c. load resistors, or d. a switching device for some or all of 8a, b, and c e. batteries (lead-acid, lithium or other cells) and ultra-capacitors to store electrical energy.
9. Other peripherals to implement the process as in claim I may be various sensors such as limit switches, frequency meters, wind speed meters, proximity sensors, acceleration sensors etc which will be used for monitoring and controlling the process.
10. Other peripherals to implement the process as in claim I may be a servo-operated disc or other brake system (mechanical) which may be used to slow down or stop completely the wind turbine in case a. of excessive wind that may damage the system, or b. when the stored energy is too high compared to the possible output power.
11. Other peripherals to implement the process as in claim I may be a servo-operated disc or other brake system (mechanical) which may be used to slow down or stop completely the electrical generator in case a. of excesshie output power exceeding its specilications, or b. while waiting for the store to accumulate enough energy so as to enable the generator to operate at its rated values c. ratchet wheels to allow rotation in only one direction d. unidirectional bearings
12. A microprocessor or other control device to process signals from the various sensors and a. drive such peripheral devices as servo mechanism for braking or releasing the turbine and! or the generator, or b. drive other corresponding peripherals pertaining to input from other than wind energy.c. switching on or off devices and parts as in claim 8.
13. Furthermore, a housing cabinet for those parts that need protection will be needed.
14. A generator which will run at its optimal rating according to any example and claims ito 14 herein before described and illustrated in the accompanying figure 1.