From the perspective of the entire power system, the application scenarios of energy storage can be divided into three scenarios: the power generation side, the transmission and distribution side, and the power consumption side.
These three scenarios can be divided into energy demand and power demand from the perspective of the grid. Energy-based demand generally requires a longer discharge time (such as energy time shift) but does not require a high response time.
In contrast, power demand generally requires fast response capability, but generally, the discharge time is not long (such as system frequency modulation).
In practical applications, it is necessary to analyze the energy storage technology according to the needs of various scenarios to find the most suitable energy storage technology.
Role In Power Generation
From the perspective of the power generation side, the demand terminal of energy storage is the power plant.
Due to the different influences of different power sources on the power grid, and the dynamic mismatch between power generation and power consumption caused by the unpredictable load side, there are many types of demand scenarios for energy storage on the power generation side, including energy time shift, capacity units, load tracking, Six types of scenarios including system frequency regulation, reserve capacity, and grid-connected renewable energy.
Energy Time Shift
Energy time-shifting is to achieve peak shaving and valley filling of electricity load through energy storage, that is, the power plant charges the battery during the valley period of the electricity load, and releases the stored electricity during the peak period of the electricity load.
In addition, it is also an energy time-shift to store the curtailed wind and photovoltaic power of renewable energy and then move it to other time periods for grid connection.
Energy time-shifting is a typical energy-based application. It does not have strict requirements on the time of charging and discharging, and the power requirements for charging and discharging are relatively wide.
However, due to the user’s electricity load and the power generation characteristics of renewable energy, the application of capacity time-shifting frequency is relatively high, more than 300 times per year.
Due to the difference in electricity load in different time periods, coal-fired power units need to undertake peak shaving capacity, so a certain amount of power generation capacity needs to be set aside as the capacity for corresponding peak loads, which makes thermal power units unable to reach full power and affects the economics of unit operation. sex.
The use of energy storage can charge when the electrical load is low, and discharge when the electricity peak is used to reduce the load peak.
The substitution effect of the energy storage system is used to release the capacity of coal-fired power units, thereby improving the utilization rate of thermal power units and increasing their economy.
The capacity unit is a typical energy-based application. It does not have strict requirements on the time of charging and discharging, and the power requirements for charging and discharging are relatively wide.
However, due to the user’s electricity load and the power generation characteristics of renewable energy, the application frequency of capacity time shift is Relatively high, around 200 per year.
Load tracking is an auxiliary service that dynamically adjusts to achieve real-time balance for slowly changing and continuously changing loads.
The slow-changing continuous variable load can be subdivided into basic load and climbing load according to the actual situation of the generator operation.
Load tracking is mainly used for the climbing load, that is, by adjusting the output size, the climbing rate of the traditional energy unit can be reduced as much as possible. , so that it transitions as smoothly as possible to the dispatch instruction level.
Compared with capacity units, load tracking has higher requirements on discharge response time, and the corresponding time is required to be at the minute level.
Frequency changes will affect the safe and efficient operation and life of power generation and electrical equipment, so frequency regulation is very important.
In the traditional energy structure, the energy imbalance of the grid in a short time is adjusted by traditional units (mainly thermal power and hydropower in my country) by responding to the AGC signal.
With the integration of new energy sources, the volatility and randomness of wind and solar power grids exacerbate the energy imbalance in a short period of time.
Traditional energy sources (especially thermal power) have a lag in responding to grid dispatch commands due to their slow frequency regulation.
Malfunctions such as reverse regulation will occur, so the added demand cannot be satisfied.
In comparison, energy storage (especially electrochemical energy storage) has a fast frequency modulation speed, and the battery can flexibly switch between charging and discharging states, making it a very good frequency modulation resource.
Compared with load tracking, the load component change cycle of system frequency modulation is in the order of minutes and seconds, which requires a higher response speed (generally a second-level response).
The adjustment method of the load component is generally AGC. However, system frequency modulation is a typical power application, which requires fast charging and discharging in a short period of time.
When electrochemical energy storage is used, a large charging and discharging rate is required, so it will reduce the life of some types of batteries, thereby affecting their battery life. economical.
Reserve capacity refers to the active power reserve reserved for ensuring power quality and safe and stable operation of the system in case of emergencies in addition to meeting the expected load demand.
Generally, the reserve capacity needs to be 15~20% of the normal power supply capacity of the system, and the minimum value should be equal to the unit capacity with the largest single unit installed capacity in the system.
Since the reserve capacity is aimed at emergencies, the annual operating frequency is generally low. If the battery is used as the reserve capacity service alone, the economy cannot be guaranteed.
Therefore, it is necessary to compare it with the cost of the existing reserve capacity to determine the actual cost of the reserve capacity. substitution effect.
Grid-Connected Renewable Energy
Due to the randomness and intermittent characteristics of wind power and photovoltaic power generation, their power quality is worse than that of traditional energy.
Since the fluctuation of renewable energy power generation (frequency fluctuation, output fluctuation, etc.) Power-type applications also have energy-type applications, which can generally be divided into three types of applications: renewable energy time shift, renewable energy generation capacity solidification, and renewable energy output smoothing.
For example, in response to the problem of photovoltaic power generation abandoning light, it is necessary to store the remaining electricity generated during the day for discharge at night, which belongs to the energy time shift of renewable energy.
For wind power, due to the unpredictability of wind power, the output of wind power fluctuates greatly and needs to be smoothed, so power-based applications are mainly used.