June_Energy Storage｜Energy Storage System Grid Saver

Green energy is the savior of climate change, but it's also the nemesis of the grid.

Although green energy will play an important role in the future demand for electricity, and its contribution to global warming needs no further elaboration, the rapid development of related industries has been accompanied by the emergence of unstable power grids caused by green energy in recent years, both in Taiwan and in other countries around the world. The reasons for this can be broadly categorized into two issues. One is the mismatch between the instability of solar and wind power and the differences in electricity consumption patterns. The second reason is that most of the power grids are built around thermal and nuclear power plants, which can generate stable power, and are therefore less able to cope with the large voltage and cyclical variations of green energy, and are less stable when there is insufficient reserve capacity.

As the name suggests, "energy storage" is the concept of converting excess electrical energy into other forms in an "energy storage system". According to the form of conversion of the energy storage system, it can be roughly divided into physical energy storage and chemical energy storage. Physical energy storage is the process of storing electrical energy without chemical reaction, only using physical phenomena (such as potential energy, kinetic energy, etc.) or simply maintaining the form of electrical energy itself by using the material science storage, the energy density is lower than that of the chemical energy storage, but because of the physical energy storage system is usually larger in size, it possesses the advantages of large-scale energy storage, and in addition to physical energy storage, the physical energy storage system is more mature due to its earlier development and technology, compared with chemical energy storage, the operation of the physical energy storage system is much more complicated than that of chemical energy storage system, and the physical energy storage system can be used in the storage of electrical energy in a more efficient manner. In addition, physical energy storage has lower operating costs and higher safety than chemical energy storage due to its earlier development and mature technology.

Chemical energy storage is the use of chemical reactions to convert electrical energy into chemical energy for storage, compared with physical energy storage, chemical energy storage system in terms of volume, start-up speed, energy density have better performance, our daily life when we see a variety of batteries is the application of chemical energy storage.

Classification and Role of Energy Storage Systems in the Grid

In the power grid, the energy storage system is mainly used to stabilize the grid, reduce peaks and fill in valleys, and provide backup power to enhance the overall resilience of the power grid.

1. Grid stabilization: Under normal load, the frequency of power supply in the grid is 60 Hz. When there is insufficient reserve power, the frequency will drop, which in turn will affect the performance of the power-using facilities and even cause damage to the power-using equipment. When the energy storage system senses a drop in frequency in the grid, it responds quickly in milliseconds to replenish the frequency on the grid and stabilize the grid frequency. In addition to the fast frequency response, the energy storage system also helps to stabilize the voltage. If the voltage drops due to insufficient grid reserve, in order to meet the same power level, electrical equipment (appliances) will draw more current from the grid, which may cause the appliances to heat up and catch fire. When the energy storage system detects a voltage shortage on the grid, it can react immediately to compensate for the virtual power, thus stabilizing the voltage.
2. Peak Shaving and Valley Filling: An energy storage system stores excess electricity during low demand periods and releases it during peak demand periods to smooth the demand curve and reduce the pressure on the power grid. The energy storage system is built near the green power generator, charging excess power into the energy storage device during the peak generation period, and then supplying it through the power grid to the nodes that need it during the off-peak period, or sending it back to the large-scale power plant for regulation to ensure stable power output.
3. Backup power: Separate energy storage systems can be used as a backup power source to provide power in emergencies to ensure the normal operation of critical facilities, and through the configuration of inter-regional energy storage systems can be divided into small and medium-sized regional micro-grids to avoid the overall grid due to regional power outages caused by insufficient backup resulting in power jumps; thus reducing the occurrence of large-scale power outages.

According to the installation location and application, it can be divided into pre-meter storage system and after-meter storage system. Pre-meter energy storage is the energy storage system installed between the meter and the power plant, the pre-meter energy storage system is usually a large facility, larger capacity, able to provide a large amount of power storage and release, the main purpose is to compensate for the gap between the green energy generation from the peak, and the residual power storage to regulate the power grid. The energy storage in front of the meter can be further subdivided according to its functionality into the frequency regulation and standby service type: sReg (static frequency regulation and standby), which quickly adjusts the frequency upwards when the frequency of the grid decreases; dReg (dynamic frequency regulation and standby), which can quickly charge and discharge electricity in both directions to stabilize the voltage and frequency of the grid; and the composite type of E-dReg (Enhanced dynamic frequency regulation and standby), which includes frequency regulation and stabilization, which not only adjusts the frequency upwards and downwards, but also supports high-power charging and discharging. In addition to the ability to adjust the frequency up and down, the system can also support high-power charging and discharging. Currently, Taiwan's pre-metered energy storage is traded in the form of barter contracts and corporate power transmission. However, due to the overheated investment in pre-metered plants in the past few years, there will be an oversupply of these systems in mid-2023, which will lead to a temporary moratorium on accepting applications for this type of E-dReg and E-dReg storage systems in 2023.

Behind-the-meter storage refers to the energy storage equipment installed between the meter and the user. Such systems are usually small or medium-sized, suitable for domestic, commercial and industrial users, and are mostly installed in factory areas, on the roofs of company buildings and on the rooftops of general households, with a relatively small overall energy storage capacity. The overall energy storage capacity is relatively small. Since the space for installing behind-the-meter energy storage systems is relatively small, the demand for energy density is higher and the unit cost is also higher. The main function of behind-the-meter storage is to improve the power management and reliability of power consumption, such as emergency backup power, power saving for off-peak power control in factories, and improving the stability of power consumption of power-sensitive equipment. Due to the high installation cost of behind-the-meter storage, the payback time is still more than 10 years, so in the past few years, except for the specific power quality and uninterruptible demand of enterprises, the market is not willing to invest in behind-the-meter storage. 2024/4/15 the day of the blackout, Taiwan Power Company Limited (Tepco) with the demand for competitive bidding method, emergency with the installation of behind-the-meter storage system companies to buy electricity, the highest price of up to 12 NTD for one kilowatt hour, so that the various sectors gradually see the behind-the-meter storage market. However, in order to encourage the development of the behind-the-meter market, it is still necessary to rely on the government's policy support to further reduce the cost recovery time in order to promote the advancement of the industry as a whole.