After years of construction and renovation, the power supply capacity of China’s distribution network has been significantly improved, and it can basically meet the needs of China’s social and economic development. The technical performance of the equipment is backward, and accidents occur frequently, which seriously affects the development of people’s lives and economic construction. With the development of electricity and the establishment of the electricity market, the weak links of the distribution network are becoming more and more prominent.
1. Problems existing in China’s distribution network
1) The power point of the power distribution network lags behind the urban construction and development, the expansion of the city scale and the establishment of the business district limit the capacity of the power point and the output of electric energy, especially the construction of the transmission channel of the power distribution line is backward.
2) The urban construction speed is rapid and the load growth rate is high, but the power supporting construction is not timely, the radius of the transmission line is small, the line is long, and the electric energy cannot be transmitted, the bottleneck effect is relatively prominent, and the phenomenon of “stuck neck” occurs.
3) The outlet channel is not compatible with the urban planning. In some places, underground cables are used. When construction and investment are not allowed, overhead wires are used. When conditions are limited, insulated wires are used, which makes network wiring complicated.
4) The wires of the early construction lines are thin and disrepaired for a long time, there are many high-energy-consuming equipment, high line loss rate, small cross-sectional area of wires and large reactive power deficit, resulting in a lot of waste of energy and environmental pollution.
5) The unreliable factors of power supply increase, the investment in the distribution network is insufficient, the equipment is aging and the technical performance is poor, and the power supply accident is frequent.
6) Power outages for users in prosperous urban areas and important places will affect social security and the economic market. The transformation of the urban power grid involves a wide range of requirements, and the power outage is difficult.
Figure 1 shows the changing trend of electricity consumption by different industries and residents in China in 10 years.
As can be seen from Figure 1, the demand for electricity growth in the whole society is obvious, but the growth rate of electricity consumption in different industries is different. continuously decreasing. For the above reasons, it is necessary to upgrade and transform the distribution network.
2. The principle of energy storage devices to delay grid upgrade
The key to the impact of energy storage devices on the planning, operation and control of traditional power grids is that energy storage technology separates power generation from electricity consumption in time and space. Figure 2 reveals the essence of energy storage.
A-Traditional load electricity, it is the instant space transfer of energy.
B–The energy storage of the energy storage device installed at the power generation end, which is the energy storage on site and released at a later time.
C–energy storage installed at the non-generating end, which represents the off-site storage and off-site release of energy.
It can be clearly seen from Figure 2 that the electric energy has changed from the original “production-transmission-distribution-use” to “production-transmission-distribution-storage-use”. The production and use of electrical energy no longer occur simultaneously.
The power system in the 21st century takes green, high-efficiency, flexibility and reliability as its construction goals. Under such conditions, how to provide users with high-quality electric energy while reducing the cost of power grid operation, maintenance, upgrade and addition, so as to provide users with good prices Cheap electric energy has become the main goal and research direction of electric power workers. Energy storage equipment can solve this problem very well. It can reduce the capacity demand of the transmission and distribution network without changing the original operating line, reduce system congestion, and provide users with higher quality and stable power. And the funds originally used for power grid construction can also be invested in other businesses, bringing double benefits to the power company. When the load of a line exceeds its capacity, the power company needs to upgrade or expand the power distribution network. The traditional method is to upgrade or expand transformers and cables. However, with the development of energy storage technology and its cost reduction in recent years, it has become a reality for the energy storage system to delay the construction of the power grid. Moreover, using the energy storage system to delay the construction of the power grid can realize the wireless circuit modification of the power grid, which is more convenient and faster than the traditional power grid construction. Traditional grid planning or grid upgrades and expansions are costly, especially in congested urban areas. If the load growth will exceed the load capacity of the distribution line, the power grid company must carry out large-scale line reconstruction, which will seriously affect the daily life of the residents and bring inconvenience to the development of the city, while the installation of the energy storage system does not require The large-scale transformation is more in line with the three requirements of green, flexible and reliable power system. Moreover, energy storage devices with a certain capacity can delay large investment in distribution network, which is beneficial to grid companies to reduce total costs, improve equipment utilization, allow funds to flow to other important engineering projects, and reduce large investment risks for capacity expansion, because With factors such as uncertainty in load forecasting, these additional (part of) capacities may never be used.
3. Analysis and calculation of energy storage device delaying power grid upgrade
When the load of a certain line of the power grid exceeds its capacity, the power grid needs to be upgraded or added. The traditional measures include upgrading or adding substation transformers, transmission and distribution lines, etc. Traditional grid planning or grid upgrades and expansions are costly, especially in congested urban areas. Under the premise that the energy storage technology continues to mature and the cost of the installation continues to decrease, when the load growth will exceed the load capacity of the distribution line, the power company can consider using the smaller capacity energy storage device installed at the overload node to delay the The larger capital investment brought by the upgrade of the transmission and distribution network delays the upgrade of the distribution network:
1) Overload situations are rare and only occur within a few hours of a day;
2) The supplied load grows slowly;
3) The traditional upgrade method does not work, such as wireless road corridors, and the wiring cannot be laid considering environmental and aesthetic factors.
The upgrade of the distribution network is expensive, and the small-capacity energy storage system can delay the relatively large investment, and the “leverage” effect is obvious. Once the energy storage system forms a scale effect, the energy storage system can improve the equipment utilization rate of power generation, transmission and distribution links, and reduce the corresponding power supply and grid construction costs. This will completely change the construction mode of the existing power system and promote its transformation from an extensional expansion type to a connotative and efficiency-enhancing type.
The following will analyze and calculate the number of years that the energy storage system delays the construction of the power grid.
The power grid construction needs to consider the growth of the load. Assuming that the annual growth rate of the load is r, the continuous growth of the load causes the upper-level network to expand the power supply capacity or increase the power supply equipment, including: adding distribution transformers, rebuilding or expanding lines. The energy storage system is configured in the distribution station to store energy when the load is low, and discharge to cut the peak when the load is peak, which can meet the supply of the load. Assuming that the peak shaving rate of the energy storage system is 1, the year in which the energy storage system can delay the upgrading and transformation of the power grid can be determined by the following formula:
In the formula, ΔN – the number of years that the grid construction is delayed by the configuration of the energy storage system.
According to the statistics of Shanghai, the annual growth rate of load in Shanghai in 2010 was 9.07%. According to Shanghai’s “Twelfth Five-Year Plan” report, the annual growth rate of electricity consumption in Shanghai in 2015 was 6.37%, and the annual growth rate of electricity was 6.37%. It is 6.34%; while the annual growth rate of electricity consumption in Shanghai in 2020 is 2.32%, and the annual growth rate of electricity is 3.04%. It can be seen that the annual growth rate of load in Shanghai is decreasing year by year. Here, different load growth rates and the peak shaving rate of the energy storage system are used for analysis and calculation. The calculation results are shown in Table 1.
From the data in the table, it can be seen that with the increasing investment of energy storage system in Shanghai and the trend of gradually slowing power growth, the effect of energy storage system in delaying the construction of power grid will become more and more obvious.
According to the above analysis and calculation, it can be seen that when the load grows rapidly and the configuration capacity of the energy storage system is low, the energy storage system can delay the construction of the power grid for a limited period of time, but compared with the speed of power grid construction, there is still time to The advantages. When the load growth tends to be saturated and the configuration capacity of the energy storage system increases, the role of the energy storage system in delaying the construction of the power grid will become more and more significant. It can be seen from this that with the development and maturity of the technology, the cost of the energy storage system decreases year by year, and the energy storage system will become an effective measure to delay the construction of the power grid and balance the peak load of the system.