Flywheel energy storage
Flywheel storage is a method in the mechanical energy storage, in which a flywheel ( in this context, also called " rotor " ) is accelerated to a very high speed, and thus the energy is stored as rotational energy. The energy is recovered by the rotor inductively coupled to an electric generator, thereby braked and its rotational speed is reduced.
Used, they are usually to balance peak loads, smoothing power spikes, recuperation of electric vehicles and also as UPS systems in hospitals and industrial plants.
Principle of operation
A typical system consists of a flywheel (rotor) that is connected to an electric motor-generator combination.
To charge the storage, the flywheel is set in motion, for instance by means of an electric motor. A high rotational speed corresponds to a high rotational energy. By means of a generator connected to this energy may be converted back to electrical energy when required. In this case, the flywheel is its kinetic energy to the motor. Induced by the engine rotation represents the voltage recovery of the energy
Nature of the stored energy
Where stands for the rotating body or in the integral for its volume and the speed of that body.
Practical technology
Most flywheel storage systems use electricity to accelerate the rotor and brake. But there are also systems in development that directly use mechanical energy.
The rotors of advanced systems are manufactured from carbon fiber composites and rotate at 20,000 to 50,000 revolutions per minute. To keep the friction losses, evacuated housing and magnetic bearings are used. Such systems can be fully charged in just a few seconds to minutes, as opposed to the hours needed to recharge some battery types, even though there are batteries that can also be charged in a few minutes.
Some emergency power higher performance also include a flywheel that is kept by an electric motor into rotation. In case of power failure, a preheated diesel engine via an electromechanical clutch from the state is rapidly rotated. The flywheel reliably delivers the energy for starting the diesel engine and to bridge the time until the engine can deliver full power.
In Formula 1 FIA rules rotating mass storage to be charged during braking and when accelerating again consumed ( KERS ), but has so far ( 2012) no team used a flywheel KERS on a race weekend; previously only battery - KER- systems were used. A ( electro-) mechanical solution can be found, however, in the Porsche 911 GT3 R Hybrid and the Audi R18 e -tron quattro.
Pros and Cons
The benefits include the ultra-short access times, the possible deep discharge, a good efficiency as short-term storage (95%), low operating costs and good environmental compatibility.
A major disadvantage is the high self-discharge (about 50 % per hour ), which can be caused by air friction and losses of the camp. Magnetic bearing and the shoring of the flywheel in a vacuum tank can minimize these losses dramatically ( to 0.1 % to 10% for flywheels of wound CFRP and 80,000 revolutions per minute). Another disadvantage is the high weight of the flywheel older type of steel. For the storage of 10 kWh flywheel mass about 1.6 tons were needed.
Modern flywheels are due to the lighter materials and a much higher rotational speed with far less mass. Approximately 160 kg flywheel mass is only needed for 10 kWh.
Disadvantage can also, just for use in moving objects ( vehicles, etc.), affect the fact that already cause small changes in the rotational axis enormous gyroscopic forces. These must be collected on the one hand, on the other hand they change the vehicle behavior such as when cornering. But should be noted stabilizing behavior of such a memory and the ( possibly positive ).
Also, security measures against a failure of the rotor necessary, which may itself have a negative impact on the weight ratio.
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To increase the efficiency of the memory, new materials (mainly new composite materials, and new ceramics ) to be developed, the bearing losses are reduced by a factor of 5 to about 20.