Analysis of Core Operational Performance Indicators for Energy Storage Power Stations
The issuance of Document No. 136 indicates the withdrawal of the “strong allocation” model, signaling a transition for energy storage projects from a primarily policy-driven approach to a fully market-driven development model. As these projects enter the electricity market, energy storage power stations will engage in various market activities and provide services to generate revenue, whether in the electricity spot market, ancillary services market, or the low storage-high discharge operational model for commercial and industrial energy storage. The industry will face the natural market principle of “survival of the fittest.”
In the early stages of market development, the quality of energy storage equipment has varied significantly. Some manufacturers prioritize marketing over research and development, leading to energy storage projects that focus more on construction than on operational efficiency. This has resulted in low overall utilization rates and highlighted various issues, with the actual operational performance of projects not receiving adequate attention or analysis.
In the future, the operational capability of energy storage projects will be the most crucial factor in assessing the performance level of power stations. The profitability of different projects will vary, and even within the same region and type, energy storage power stations may experience significant differences in revenue due to varying operational performance. The key to evaluating the operational performance indicators of energy storage power stations lies in the following four aspects:
- Grid-Connected Performance of Energy Storage Stations: For energy storage stations that are subject to grid dispatch control, including both power side and grid side storage, the grid connection performance must meet the operational safety and stability requirements of the power system. In practice, after connecting to the grid, energy storage stations need to engage third-party inspection agencies to conduct grid connection tests. These tests evaluate the station’s power control, primary frequency modulation, inertia response, fault ride-through, operational adaptability, power quality, and automated dispatch to meet relevant technical standards. If energy storage stations do not meet the grid connection performance indicators, it can adversely affect their normal commercial operations and subject them to evaluations under “two regulations.” For instance, regarding primary frequency modulation, energy storage stations should possess this functionality with a deadband set at ±(0.03~0.05) Hz, a modulation deviation rate of 0.5~3%, and a modulation response time not exceeding 4 seconds.
- Charge and Discharge Efficiency: Charge and discharge efficiency is a critical indicator for evaluating the performance of energy storage stations. It is defined as the ratio of the discharged energy at the grid connection point to the charged energy over the evaluation period, reflecting the efficiency of energy conversion. This efficiency is closely related to equipment selection, engineering design, operational methods, and auxiliary power consumption. Improving the charge and discharge efficiency of energy storage stations can reduce energy losses, enhance their support and adjustment capabilities for the grid, and thus generate greater revenue. For example, newly commissioned shared energy storage projects have a single charge and discharge efficiency of around 82% to 89%, with an annual efficiency ranging from 76% to 86%. Additionally, as the lifespan of energy storage batteries increases, efficiencies are expected to decline by 1% to 2%. Variations in charge and discharge efficiency among different projects can be addressed by selecting energy-efficient transformers, low-loss energy storage converters, enhancing battery temperature control design, and optimizing the operational strategies for thermal management equipment.
- Availability Rate: The availability rate indicates the operational reliability of energy storage equipment. It is the ratio of the sum of charge and discharge times plus standby time to the total evaluation period. Due to varying quality levels among manufacturers’ energy storage devices, the availability rates can differ significantly across projects. For example, some lithium battery energy storage stations can achieve near “maintenance-free” operation with high stability, while others frequently encounter various equipment failures, such as abnormal communication of storage units, frequent voltage alarms during charge and discharge, overheating of IGBT modules, and leaks in liquid cooling pipelines. These issues necessitate frequent outages for repairs, increasing operational and maintenance costs while reducing the availability of the energy storage station.
- Available Charge and Discharge Capacity: The available charge and discharge capacity of energy storage stations is not only related to charge and discharge efficiency but also closely linked to the State of Health (SOH) of the storage batteries. As batteries age during use, their charge and discharge performance will experience permanent degradation, leading to a gradual decline in available capacity. The SOH is correlated with the charge and discharge rates of the energy storage system, the depth of discharge, and is also affected by the type of storage batteries, operational temperature, and the topology of the storage units. For instance, while battery manufacturers claim their products can achieve 8,000, 10,000, or even 15,000 cycles, the actual cycle numbers can vary widely under the same evaluation standards (e.g., 25°C, 80% SOH). Some manufacturers fail to meet their claimed lifespan, with certain projects experiencing significant battery retirements within three years, significantly underperforming compared to the anticipated full life cycle capacity.
Conclusion: Understanding these core operational performance indicators is essential for the successful deployment and management of energy storage power stations, especially as the market shifts towards a more competitive landscape.
