Nature gave man a variety of sources of energy: the sun, wind, rivers and others. The disadvantage of these free energy generators is the lack of stability. Therefore, during periods of excess energy, it is stored in storage devices and spent during periods of temporary decline. Energy storage devices characterize the following parameters:
- amount of stored energy;
- the rate of its accumulation and return;
- specific gravity;
- energy storage periods;
- reliability;
- manufacturing and maintenance costs and others.
There are many methods for organizing drives. One of the most convenient is the classification by the type of energy used in the drive, and by the method of its accumulation and return. Energy storage devices are divided into the following main types:
- mechanical;
- thermal;
- electric;
- chemical.
Potential energy storage
The essence of these devices is simple. When lifting the load, potential energy accumulates; when lowering, it does useful work. Design features depend on the type of cargo. It can be a solid, liquid, or loose substance. As a rule, the designs of devices of this type are extremely simple, hence the high reliability and long service life. The storage time of stored energy depends on the durability of the materials and can reach millennia. Unfortunately, such devices have a low specific energy consumption.
Mechanical storage of kinetic energy
In these devices, energy is stored in the movement of a body. Usually this is an oscillatory or translational motion.
Kinetic energy in vibrational systems is concentrated in the reciprocating motion of the body. Energy is supplied and consumed in portions, in time with the movement of the body. The mechanism is quite complicated and moody in setting. Widely used in mechanical watches. The amount of stored energy is usually small and suitable only for the operation of the device itself.
Gyro Energy Storage
The stock of kinetic energy is concentrated in a rotating flywheel. The specific energy of the flywheel significantly exceeds the energy of a similar static load. There is the possibility in a short period of time to receive or return significant power. The energy storage time is short and for most designs it is limited to a few hours. Modern technologies make it possible to bring the energy storage time to several months. Flywheels are very sensitive to shock. The energy of the device is directly dependent on the speed of its rotation. Therefore, during the accumulation and release of energy, a change in the speed of rotation of the flywheel occurs. And for the load, as a rule, a constant, low speed of rotation is required.
More promising devices are super-handwheels. They are made of steel tape, synthetic fiber or wire. The design may be dense or have empty space. In the presence of free space, the turns of the tape move to the periphery of rotation, the moment of inertia of the flywheel changes, part of the energy is stored in the spring subjected to deformation. In such devices, the rotation speed is more stable than in solid structures, and their energy consumption is much higher. In addition, they are safer.
Modern super-flywheels are made from Kevlar fiber. They rotate in a vacuum chamber with a magnetic suspension. Able to save energy for several months.
Mechanical drives using elastic forces
This type of device is capable of storing enormous specific energy. Of mechanical drives, it has the highest energy consumption for devices with dimensions of several centimeters. Large flywheels with a very high rotation speed have a much greater energy intensity, but they are very vulnerable to external factors and have a shorter energy storage time.
Mechanical drives using spring energy
Able to provide the largest mechanical power of all classes of energy storage. It is limited only by the tensile strength of the spring. The energy in a compressed spring can be stored for several decades. However, due to constant deformation, fatigue accumulates in the metal, and the capacity of the spring decreases. At the same time, high-quality steel springs, subject to operating conditions, can work for hundreds of years without a noticeable loss of capacity.
The functions of the spring can be performed by any elastic elements. Rubber tows, for example, are tens of times superior to steel products in energy storage per unit mass. But the service life of rubber due to chemical aging is only a few years.
Mechanical drives using compressed gas energy
In this type of device, energy storage occurs due to gas compression. In the presence of excess energy, the gas is pumped under pressure into a cylinder using a compressor. As necessary, compressed gas is used to rotate the turbine or generator. At low power, it is advisable to use a piston motor instead of a turbine. Gas in a tank under a pressure of hundreds of atmospheres has a high specific energy density for several years, and in the presence of high-quality fittings - for decades.
Thermal energy storage
Most of the territory of our country is located in the northern regions, so a significant part of the energy is forcibly spent for heating. In this regard, it is necessary to regularly solve the problem of maintaining heat in the drive and extracting it from there if necessary.
In most cases, it is not possible to achieve a high density of stored thermal energy and any significant periods of its conservation. Existing effective devices due to a number of their features and high prices are not suitable for widespread use.
Heat storage
This is one of the oldest ways. It is based on the principle of accumulation of thermal energy during heating of a substance and heat transfer during its cooling. The design of such drives is extremely simple. It can be a piece of any solid substance or a closed container with a liquid coolant. Thermal energy storage devices have a very long service life, an almost unlimited number of energy storage and release cycles. But the storage time does not exceed several days.
Electric energy storage
Electric energy is the most convenient form in the modern world. That is why electric drives are widely used and most developed. Unfortunately, the specific capacity of cheap devices is small, and devices with a large specific capacity are too expensive and short-lived. Electric energy storage devices are capacitors, ionistors, and batteries.
Capacitors
This is the most popular form of energy storage. Capacitors are capable of operating at temperatures from -50 to +150 degrees. The number of energy storage-release cycles is tens of billions per second. By connecting several capacitors in parallel, you can easily get the capacity of the required size. In addition, there are variable capacitors. The capacitance of such capacitors can be changed mechanically or electrically or by temperature. Most often, variable capacitors can be found in oscillatory circuits.
Capacitors are divided into two classes - polar and non-polar. The service life of polar (electrolytic) is less than non-polar, they are more dependent on external conditions, but at the same time they have a larger specific capacity.
As energy storage capacitors are not very successful devices. They have a small capacity and an insignificant specific gravity of stored energy, and its storage time is calculated in seconds, minutes, rarely hours. Capacitors are used mainly in electronics and power electrical engineering.
The calculation of the capacitor, as a rule, does not cause difficulties. All the necessary information on different types of capacitors is presented in technical manuals.
Ionistors
These devices occupy an intermediate place between polar capacitors and batteries. They are sometimes called "supercapacitors." Accordingly, they have a huge number of charge-discharge stages, the capacity is greater than that of capacitors, but slightly less than that of small batteries. Energy storage time - up to several weeks. Ionistors are very temperature sensitive.
Power batteries
Electrochemical batteries are used if you need to store a lot of energy. Lead-acid devices are best suited for this purpose. They were invented about 150 years ago. And since then nothing fundamentally new has been introduced into the battery device. Many specialized models have appeared, the quality of components has increased significantly, and the reliability of the battery has increased. It is noteworthy that the device of the battery, created by different manufacturers, for different purposes differs only in minor details.
Electrochemical batteries are divided into traction and starting. Traction are used in electric vehicles, uninterruptible power supplies, power tools. Such batteries are characterized by a long uniform discharge and its large depth. Starting batteries can produce high currents in a short period of time, but deep discharge is not acceptable for them.
Electrochemical batteries have a limited number of charge-discharge cycles, on average from 250 to 2000. Even in the absence of operation, after a few years they fail. Electrochemical batteries are temperature sensitive, require a long charge time and strict observance of the operating rules.
The device must be recharged periodically. The battery installed on the vehicle is charged by the generator. In winter, this is not enough, a cold battery does not take charge well, and the energy consumption for starting the engine increases. Therefore, it is necessary to additionally charge the battery in a warm room with a special charger. One of the significant disadvantages of lead-acid devices is their high weight.
Batteries for low power devices
If mobile devices with low weight are required, then the following types of batteries are chosen: nickel-cadmium, lithium-ion, metal-hybrid, polymer-ion. They have a higher specific capacity, but the price is much higher. They are used in mobile phones, laptops, cameras, camcorders and other small-sized devices. Different types of batteries differ in their parameters: the number of charging cycles, shelf life, capacity, size, etc.
High-capacity lithium-ion batteries are used in electric vehicles and hybrid cars. They are light weight, large specific capacity and high reliability. At the same time, lithium-ion batteries are very flammable. Ignition can occur from a short circuit, mechanical deformation or destruction of the case, violation of the charge or discharge of the battery. It is rather difficult to extinguish a fire due to the high activity of lithium.
Batteries are the basis of many devices. For example, the energy storage device for a telephone is a compact external battery packaged in a rugged, waterproof housing. It allows you to charge or power your cell phone. Powerful mobile energy storage devices can charge any digital devices, even laptops. In such devices, as a rule, lithium-ion high-capacity batteries are installed. Energy Storage for Home also not dispense with batteries. But these are much more complex devices. In addition to the battery, they include a charger, a control system, an inverter. Devices can work both from a stationary network, and from other sources. Output power averages 5 kW.
Chemical energy storage
Distinguish between "fuel" and "non-fuel" types of drives. They require special technologies and often bulky high-tech equipment. The processes used make it possible to obtain energy in different forms. Thermochemical reactions can occur both at low and high temperatures. Components for high temperature reactions are introduced only when it is necessary to obtain energy. Before that, they are stored separately, in different places. Components for low-temperature reactions are usually in the same container.
Fuel accumulation of energy
This method includes two completely independent steps: energy storage (“charging”) and its use (“discharge”). Traditional fuel, as a rule, has a large specific energy capacity, the possibility of long-term storage, ease of use. But life does not stand still. The introduction of new technologies places increased demands on fuel. The problem is solved by improving existing and creating new, high-energy fuels.
The widespread introduction of new samples is hindered by insufficient technological processes, a large fire and explosion hazard in work, the need for highly qualified personnel, and the high cost of technology.
Fuelless chemical energy storage
In this type of storage, energy is stored by converting some chemicals to others. For example, hydrated lime goes into quicklime when heated. During "discharge", the stored energy is released in the form of heat and gas. This is exactly what happens when slaking lime with water. In order for the reaction to begin, it is usually sufficient to combine the components. In essence, this is a type of thermochemical reaction; it only proceeds at a temperature of hundreds and thousands of degrees. Therefore, the equipment used is much more complicated and expensive.