- Investment cost analysis of energy storage device
The electrical schematic diagram of the energy storage device is mainly composed of grid connected equipment (including AC side switch and transformer), rectifier / inverter equipment and battery pack. Of course, there is a secondary control system, so we need to analyze the investment cost of each part. The investment cost of the energy storage device mainly includes the investment cost and operation and maintenance cost of the energy storage device.
1.1. Investment cost
The investment cost of energy storage device mainly includes: station site construction cost, electric energy conversion equipment cost (including AC side transformer and circuit breaker, rectifier / inverter system), energy storage system cost (mainly battery pack and battery pack management system). The cost is converted to the annual present value, which can be expressed as the construction cost of GI station site (10000 yuan);
k. – unit cost of electric energy conversion equipment (10000 yuan / MW);
KW — unit cost of energy storage system [10000 yuan / (MW. H)];
λ P — station site cost and depreciation rate of fixed assets of grid connected equipment;
λ W – depreciation rate of fixed assets of battery pack;
Because the life cycle of battery pack is different from that of station site cost and grid connected equipment cost, the service life of battery pack is generally half of that of grid connected equipment, which is 15 years. Therefore, the depreciation rate of fixed assets is different. Based on the service life of the whole energy storage station of 30 years, the battery pack needs to be completely replaced in the 15th year, with additional secondary investment.
1.2. Annual operation and maintenance cost
The annual operation and maintenance cost of energy storage device is mainly determined by its scale, CM – annual operation and maintenance cost per unit capacity.
- Value evaluation model of battery energy storage device in distribution network
Based on the previous cost and benefit analysis, it can be seen that under the current fixed on grid price mechanism, the benefits that really belong to the power grid company are only to reduce the benefits of power grid expansion capacity, reduce the benefits of total network loss and reduce the reserve capacity required for new energy power generation; A large part of the arbitrage of low storage and high generation of energy storage devices and reducing the reliability cost of power grid belong to power plants and users. At present, when the unit cost of battery is high, it is difficult to realize profit only considering the income of a certain subject, and it is impossible to reasonably evaluate the real value of battery energy storage device. Considering the value of all aspects of the energy storage device, the total value evaluation model of the energy storage device can be established as follows:
Taking the load data of one tenth of the load scale in Shanghai for analysis, under the current electricity price system and power grid, this paper studies the annual total value of various battery energy storage technologies, and obtains the change curve of the annual total value of energy storage devices under various battery energy storage technologies with the energy storage capacity and the annual return on investment curve.
2.1 Economic value analysis of sodium sulfur battery energy storage device
Variation curve of annual return of sodium sulfur battery energy storage device with energy storage capacity under different rated charge and discharge time (T), and variation curve of annual return on investment of sodium sulfur battery energy storage device with energy storage capacity under different rated charge and discharge time (T). From this, we can see that the energy storage device can achieve profitability, but its one-time fixed asset investment cost is very large, so its annual return on investment is low; In particular, the unit cost of the battery is very high, which makes the investment cost rise rapidly and the annual return on investment decrease rapidly with the increase of the rated charge and discharge time.
2.2. Comparison of economic value of various battery energy storage technologies
At present, several battery energy storage technologies with mature technology and high voice are mainly sodium sulfur battery, lithium battery, nickel hydrogen battery and liquid flow battery. They are applied to the power system and have the same function. The main difference lies in their energy storage efficiency and unit cost of battery. According to the technical parameters and unit cost of various battery energy storage technologies, T-8 is obtained through model analysis, From their economic value curve, we can see that at present, sodium sulfur battery has the best economy, followed by lithium battery, and liquid flow battery has the worst economy. Click here to open to learn more about batteries.
2.3 Economic analysis of energy storage capacity in Shanghai in the 12th Five Year Plan
Based on the analysis that the newly built energy storage capacity of Shanghai in the 12th Five Year Plan is 30MW, since the valley load duration of the power grid is 8h, t-8h is taken. At present, among these batteries, sodium sulfur battery has the lowest cost, so it has good economy. However, compared with its high one-time investment cost of 782 million, without considering its tax rate and annual depreciation loss rate, its annual return on investment is relatively low, only 5.5%, only slightly higher than the bank interest rate. After taking into account the tax payable, the energy storage device is in a state of loss. Moreover, only E1, E2 and E are benefited by power grid companies, while E3 and es are benefited by power plants and users respectively. Therefore, under the current conditions, the application and promotion of battery energy storage technology still needs national policy support.
Through the analysis of various values of battery energy storage devices in distribution network, we can draw a conclusion:
1) According to the current research on the application of battery energy storage, the role of battery energy storage device in other aspects, such as restraining low-frequency oscillation, improving transient voltage stability and frequency modulation, is obvious, but the benefits generated by this part of the role are difficult to be measured by economic indicators. This project only evaluates its static economic benefits, so the value obtained will be lower than the actual economic benefits.
2) In the current situation of small application scale and high cost of high-capacity battery, the investment return rate of battery energy storage project invested by power grid companies is very low, but battery energy storage is beneficial to the safe and reliable operation of power grid, and a large part of the benefits generated by battery energy storage belong to the economic benefits of the whole society. Therefore, the initial development of battery energy storage technology needs the support of national policies, When the application scale increases and the cost decreases, its market-oriented development can be realized.
3) Among several kinds of batteries with mature technology and more applications at present, the technical performance and unit cost of sodium sulfur battery have advantages over other batteries, and the sodium sulfur battery has large energy density, which is suitable for application in the distribution network of large cities with tight land use. Therefore, at present, sodium sulfur battery is the most economically feasible.