Source of Energy: Energy Density
Energy is stored, either within a specific geographic area, or on a larger scale (like the sun). The stored energy can be used on demand until it is exhausted (“renewable” energy only makes sense if it can be regenerated on the human timescale). We divide energy into primary energy and secondary energy. Primary energy refers to the fossil energy that has existed "naturally" for a long time, for which we only need to pay the extraction fee. Secondary energy refers to man-made energy, for which we not only need to pay for mining, but also for storage.
The energy that can be exploited is not only stored in nature in different forms, but also stored in different densities.
The utility of electric energy can be seen intuitively through the following simple examples. For 1kW·h electric energy, the following things can be done:
1) A car with a fuel consumption of 8L per 100km travels 1km.
2) The electrical energy required for the refrigerator to operate for one day.
3) Provide overnight lighting for a home.
4) Produce 200g steel or 100g plastic.
In France, the average annual electricity consumption per person is 40MW·h, that is, 4.5kW·h per person per hour.
Transformation of energy storage.
Depending on the application, stored energy can be released in the form of power [in watts (W)] or energy [in joules (J) or watt-hours (w h)], which is the accumulation over time. The energy storage device can release the stored energy immediately with a certain power, which is very useful in practical applications.
Different application strategies for energy storage lead to different energy storage solutions.
The energy is stored in the energy storage device, and after energy conversion and transformation, it is supplied to the user in the form most suitable for the application. Electric energy is one of the storage forms of energy, and it is undoubtedly the most flexible and convenient application form currently known.
The problems involved in energy storage are both technical and economic, and the corresponding solutions are closely related to their specific application goals. Energy storage technology for the purpose of electricity storage is not a stopgap measure, especially in the application of the grid. Currently, there are at least two distinct energy storage application needs to illustrate this point.
1) Mobile applications, such as mobile phones and various handheld devices. The purpose of energy storage is to ensure the normal operation of the device, or to act as a power "buffer", providing a high enough power output when the device needs pulsed power.
2) Stationary applications, such as energy storage in power grids, require higher energy and power.
Pulse use case for energy storage
A pulsed power system needs to release the stored energy in a short period of time. Energy is generally stored in the form of electromagnetics (electric or magnetic fields), which can be supplied in a very short period of time (milliseconds) under the action of fast switching. Therefore, for a specific capacity of energy storage W, the output power P=W/t will be very large.
For example, for series capacitor energy storage systems (Marx Generators), the main factors affecting energy release are:
1) Electrical characteristics (R, L, C) of the tank circuit.
2) Impedance characteristics (R, L, C) of the charging circuit.
3) The initial state of the energy storage system.
4) Characteristics of the switching system (R, L, t).
The voltage of the energy storage system for pulsed applications can reach several million volts, the peak discharge current can reach several million amperes, and the pulses may be single pulses or pulse trains of several kilohertz.
Capacitive energy storage systems generally include capacitor banks and closed switches (V), while inductive energy storage systems include energy storage inductors, closed switches (l) and open switches (V).
figure ：Series capacitor energy storage system
Switchgear can be of the following types:
1) Gas switch: high-voltage spark gap, ignition tube, thyratron, etc.
2) Semiconductor switches: Thyristor, GTO, IGBT, MOSFET, SRD (Super Fast Recovery Diode), etc.
3) Solid state switch: fuse.
For capacitive energy storage systems, the Max generator can obtain very high voltage values by first charging the capacitors in parallel and then discharging them in series as shown in the figure.
Pulsed energy has been used in many industrial and scientific fields, such as radar, particle accelerators, strong magnetic fields, lasers, electric guns (electron beam weapons), etc.
figure ：Max generator capacitor energy storage system circuit
Grid application case of energy storage
Since electrical energy is difficult to store efficiently and in large quantities, maintaining a balance between power generation and consumption at all times is important for
It is very important to the power system, and the electricity consumption is constantly fluctuating with different times of the day or seasons, so the problem of energy storage will be more prominent in the grid. energy storage by storing electricity and using it
In other periods after that, this coupling relationship between power generation and electricity consumption is effectively broken.
Therefore, it is necessary to store energy in some form (such as mechanical energy, thermal energy, chemical energy, etc.), and
When needed, the stored energy is converted into electrical energy through conversion devices (such as batteries, generators, etc.) and released. Most of the energy conversion devices are based on power electronic devices, and their conversion efficiency (80%-90%) is related to the cost and economy of the energy storage system.
Energy storage can be applied to all aspects of electrical energy, including power generation, transmission, distribution and consumption.
When energy storage is applied to power systems, it must not only meet the technical performance requirements, but also have certain economic benefits.
beneficial. In an increasingly open electricity market, the price of energy is likely to be different at different times of the year or even the day (following the market principle of balancing supply and demand), and the difference in electricity price between peak and valley of electricity consumption determines how much energy storage can be stored. important factor in making profits. As an important means to enhance the flexibility of the power system, energy storage also
Subject to the following factors:
1) The cost of an energy storage system is closely related to the type of energy storage technology used and its actual configuration capacity.
2) Even the same type of energy storage technology has different benefits in different electricity markets or different operators
is different.
3) Several important factors that affect operators' assessment of the benefits of energy storage systems, including the type of power source in the grid and its
ratio, the degree of grid congestion, etc.
Energy storage can play a number of different roles in the power system, including:
1) Power peak regulation.
2) Load tracking (smooth transient electrical shock).
3) Improve power quality, including current, voltage and frequency.
4) Support grid operation when the grid operation state deteriorates.
5) Power grid balance adjustment under the high penetration rate of renewable energy generation.
6) Improve the utilization rate of power assets.
In microgrids or independent power systems, some intermittent power sources (such as wind power, solar power
In these cases, the application scheme of energy storage needs to be carefully studied according to its technical performance and economic performance. In general, energy storage overcomes the shortcomings of intermittent power sources in the following ways:
1) Maximize the use of renewable energy such as photovoltaics to generate electricity.
2) Utilize power generation locally to improve the efficiency of the system.
3) Improve the flexibility and efficiency of the energy management system.
4) Ensure the safety of users' electricity consumption when the power grid is cut off.
Under the different application goals mentioned above, several key technical performance and economic indicators of energy storage (investment cost,
Energy and power density, cycle life, environmental impact, etc.) govern the choice of energy storage technology.
As industries in today's world are increasingly connected to the grid, momentary power outages or prolonged power interruptions
It will cause huge economic losses (according to statistics, the annual loss of power outages in the United States is as high as tens of billions of dollars). This loss can be compared to the cost of energy storage deployed to avoid outages to assess the benefits of energy storage.
The operation and management of electric energy needs to be carried out at the level of the entire grid, by systems based on information and communication technology (ICT).
The unified implementation of the system management center, even the widely developed distributed power generation can be incorporated into the management system. In addition to traditional control management, the entire power generation, energy storage and electricity consumption can be efficiently organized through virtual power station technology.