The user-side battery energy storage device has been widely used in Japan, the United States and Europe, and its applications are mostly LL+UPS mode and LL+EPS mode. Taking sodium-sulfur batteries as an example, from 1992 to 2007, there were a total of 196 projects of sodium-sulfur battery energy storage applications in the world, with an installed capacity of 270Mw. The installed capacity of +EPS mode and LL+UPS mode reaches 100Mw. With the breakthrough of China’s battery energy storage technology, battery energy storage pilot projects have been successfully carried out one after another. At present, the reliability rate of power supply of China’s urban distribution network is still in the second stage, and the power supply capacity of the power grid is tight during peak load periods. At the same time, it can also be used as a UPS to maintain the continuity of power supply, reduce the scrap of production products caused by sudden power failure, and at the same time, the energy storage device can continue to supply power for a period of time during the power failure, reducing production losses caused by power shortages. In general, the user-side battery energy storage device has the following economic benefits:

1) By storing electrical energy from the power grid when the electricity consumption is low, it can be used to supply power when the electricity consumption peaks, so that the capacity utilization rate of the transformer can be improved, and the installation capacity of the transformer and the power consumption loss can be reduced;
2) Reduce the investment in power equipment and the expenditure on basic electricity charges;
3) Reduce the electricity purchase cost under the peak-valley electricity price difference;
4) Improve the reliability of the user’s power supply and reduce the economic loss of the user due to power shortage.

1. Reduce the construction capacity of users’ distribution substations

For large and medium-sized users, whether they use single-shift production or three-shift production, there is a certain peak-to-valley difference in the load curve, but the peak-to-valley difference of single-shift enterprises is relatively large, while the three-shift system The basic load of the enterprise is large and lasts for about 24 hours, and the peak-to-valley difference is smaller. When they plan and build their special power distribution stations, they all need to determine the capacity of the special power distribution system according to their own maximum load demand (considering seasonal load peaks), especially when the reliability of power supply is high. , it is also necessary to consider increasing the redundancy of the power distribution system to improve the reliability of power supply of the power distribution station. However, if BESS is installed on the low-voltage side of its power distribution system, it can purchase electrical energy from the power grid and store it when the power consumption is low, and release the power for self-supply when the power consumption peaks, which can reduce the power that needs to be absorbed from the power grid during peak load. , thereby reducing the capacity of the power distribution system to be constructed and saving the investment of the corresponding capacity. Therefore, the corresponding income generated by BESS is equivalent to the present value E of each year, which can be expressed as:

In the formula, P-the critical power required to flatten the load curve Pc=Pmax-Pa;
B—The unit cost of the user’s power distribution system (10,000 yuan/MW);
Ye – the fixed asset depreciation rate of the user’s power distribution equipment;
Pmax – the long-term maximum charge and discharge power of the battery pack (MW), that is, the rated power;
Pis – maximum daily load (MW);
7–The energy storage efficiency of the energy storage device, including the loss of the grid-connected equipment and the charge and discharge loss of the battery;
P.-The daily average power of the load, Equation (1) shows that when the energy storage capacity achieves complete peak shaving and valley filling, its role in reducing the construction capacity of the substation decreases as its capacity continues to increase.

2. Reduce the basic electricity charges of users under the capacity electricity price system

The electricity sales price refers to the price at which electricity supply companies supply and sell electricity to electricity users. It is scientifically and rationally formulated according to the characteristics of electricity production and the characteristics of electricity consumption categories of electricity consumers, and considering the industrial policies of the country in different periods, and in accordance with the principle of fair burden. There are two current electricity sales pricing methods in China, namely the single-system electricity price and the two-part electricity price. The two-part electricity price is relative to the single-system electricity price, which is the electricity price of large-scale industries, which includes the basic electricity price, the electricity price and the power factor adjustment electricity price. The two-part electricity price is a price model designed according to the characteristics of the cost of the power industry. It properly expresses all the costs borne by the power company. Therefore, it is a reasonable method to calculate and collect electricity charges for users.

The two-part electricity price is divided into two parts. One part is called the basic electricity price, and when calculating the basic electricity price, the unit is kVA of the user’s equipment capacity or the user’s maximum demand kilowatt; The unit of electricity. The sum of the two electricity prices calculated separately is the total electricity fee payable by the user. Of course, users who implement the two-part electricity price billing method also implement the method of adjusting the electricity price by interest rate. The basic electricity fee in the two-part electricity price is fixed, and the basic electricity fee paid by the user every month is only related to its capacity or demand, and has nothing to do with its actual electricity consumption. Therefore, the smaller the actual electricity consumption, the higher the average electricity price of the household; conversely, the greater the electricity consumption, the lower the average electricity price of the household.

In the current situation of insufficient power supply, if users shift the load from the peak period to the trough period, the electricity price per kWh can be significantly reduced. According to the lack of power supply in the power grid during the flood season mainly during the peak period of electricity consumption, in order to ensure the safe and stable operation of the power grid, reduce the power outages in disorder, and achieve “no power cuts due to power restrictions, no production reductions due to peak shifts”, the analysis of large industrial electricity customers The load law and characteristics of the grid, encouraging users to use low-valley electricity can help users reduce electricity bills, increase the load rate of the power grid accordingly, play the role of peak-filling and valley-filling, and enable both suppliers and consumers to obtain certain economic benefits from cost reduction benefit.

Since the basic electricity fee in the two-part electricity price is fixed, when calculating the basic electricity fee, the kilowatts of the maximum demand value of electricity or the kilovolt-ampere of the installed capacity of the electrical equipment shall prevail, and the actual electricity consumption shall prevail. It doesn’t matter. Thereby promoting the rational use of electrical equipment by users, while improving the power factor of electricity consumption and improving the utilization rate of equipment. For example, a factory has a 315kVA three-phase transformer, the original load is 210kw, the average power factor is 0.7, and now the production development load has increased to 280kw, whether it is necessary to increase the capacity of the transformer.

It is known by calculation: 0 When the load is 210kw, S=P/cosp=(210/0.7)kVA=300kVA, at this time the transformer can meet the power supply needs; ②When the load increases to 280kw, S=P/cosp=( 280/0.7) kVA=400kVA, the original transformer can no longer meet the normal power supply needs. If the method of increasing the transformer capacity is adopted, the basic electricity fee will be increased while the equipment investment is increased. If measures are taken to increase the average power factor from 0.7 to 0.9, then S=(280/0.9)kVA= 311kVA, and the transformer can meet the needs at this time, no need to increase the capacity. Thereby greatly reducing the cost of electricity.

After applying for a special distribution transformer, large and medium-sized users need to pay the basic electricity fee every month according to the maximum demand applied for, regardless of whether they use electricity or not. The installation of the energy storage system can cut off the bees and fill the valley, reduce the electricity load of users during peak hours, and at the same time can realize four-quadrant operation, smoothly adjust the reactive power of the load, thereby reducing the distribution and transformation capacity required by the distribution station. Correspondingly, the monthly capacity electricity fee that users need to pay is reduced. The corresponding annual return E2 can be expressed as (2):

In the formula, e, — the basic electricity fee that the user needs to pay according to the maximum demand [10,000 yuan/(Mw.year)].

Read more: Investment Cost Analysis of Energy Storage Installations and Valuation Models for Battery Energy Storage Installations in Distribution Networks