250kW/522kWh Hotel Energy Storage Project Overview

Chapter 1 General Description 

1.1 Overview 

This project is a 250kW/522kWh energy storage project for a hotel. The project includes the energy storage system and related power distribution facilities, cable laying, and ancillary systems. Economic benefits are primarily achieved through peak shaving and valley filling. 

1.1.1 Project Background 

As new energy sources, represented by wind and solar power, gradually replace traditional fossil fuels like thermal power, the "random, intermittent, and fluctuating" output characteristics and "low inertia, weak support, and weak disturbance resistance" of new energy power generation will pose severe challenges to the power system. 

Energy storage is the best "buffer" and "shock absorber" for achieving incomplete real-time energy and power balance and comprehensively and efficiently addressing the prominent ‍problems of the new power system. It is an important technology and basic equipment supporting the new power system. 

The main benefits are: first, leveraging the "peak-shaving" role of large-scale energy storage to ensure a secure energy and power supply; second, leveraging the "peak-regulating" role of energy storage to enhance the absorption capacity of new energy sources and support the high-proportion, large-scale access of new energy to the grid; and third, leveraging the rapid response capabilities of energy storage for active and reactive power to enhance the frequency and voltage regulation capabilities of the power system, effectively supporting the safe and stable operation of the power grid.

1.1.2 Necessity of Project Construction 

(1) It helps alleviate peak grid pressure. This energy storage system charges during off-peak and flat periods and discharges during peak periods, which helps reduce the electricity load during peak electricity price periods, thereby reducing pressure on the power grid, delaying grid renovation time, alleviating power supply pressure, and promoting the healthy and long-term development of the power industry. 

(2) It helps reduce enterprise electricity costs. In the time-of-use electricity market, electricity users can arrange their electricity consumption plans according to their actual situation. The energy storage facility can charge when the electricity price is low and discharge when the electricity price is high, transferring the electricity demand during periods of high electricity price to periods of low electricity price, thereby helping users reduce overall electricity costs without changing user behavior. (3) It helps improve the reliability of electricity supply for enterprises. Energy storage systems can generate economic benefits by taking advantage of peak and off-peak electricity price differences during normal times. At the same time, energy storage systems can also serve as backup power sources for electricity users, supplying power to users when the power grid is insufficient or when there is a grid failure, thereby improving the reliability of power supply.

1.1.3 Basis for Compilation 

(1) GB/T 14549-1993 "Power Quality - Harmonics in Public Power Grids" 

(2) GB/T 34120-2023 "Technical Specification for Energy Storage Converters in Electrochemical Energy Storage Systems" 

(3) GB/T 34131-2023 "Technical Specification for Lithium-ion Battery Management System for Electrochemical Energy Storage Power Stations" 

(4) GB/T 34133-2023 "Technical Specification for Testing Energy Storage Converters" 

(5) GB/T 36276-2023 "Lithium-ion Batteries for Power Storage" 

(6) GB/T 36547-2024 "Technical Regulations for Grid Connection of Electrochemical Energy Storage Systems" 

(7) GB/T 36549-2018 "Operating Indicators and Evaluation of Electrochemical Energy Storage Power Stations" 

(8) GB/T 36558-2023 General Technical Conditions for Electrochemical Energy Storage Systems in Power Systems 

(9) GB/T 40090-2021 Operation and Maintenance Regulations for Energy Storage Power Stations 

(10) GB/T 40595-2021 Technical Specifications and Test Guidelines for Primary Frequency Regulation of Grid-Connected Power Sources 

(11) GB/T 42288-2022 Safety Regulations for Electrochemical Energy Storage Power Stations 

(12) GB 50116-2013 Design Code for Automatic Fire Alarm Systems 

(13) GB 50229-2019 Fire Protection Design Code for Thermal Power Plants and Substations 

(14) GB 50370-2005 Design Code for Gas Fire Extinguishing Systems

1.2 Energy Storage System Scheme

The total capacity of the energy storage project is 250kW/522kWh. The recommended system connection scheme for this project is: a 250kW/522kWh energy storage power station connected to the 380V side bus of a 10kV user station via one circuit. 

The main equipment of the energy storage system includes: 2 sets of energy storage cabinets and 1 set of grid-connected cabinets.

(2) Energy Storage Battery Selection

Currently, electrochemical energy storage technologies mainly include lead-acid batteries, lead-carbon batteries, redox flow batteries, sodium-sulfur batteries, and lithium iron phosphate batteries. 

This project plans to use lithium iron phosphate batteries. Based on a survey of mainstream manufacturers' products, the recommended capacity for a single cell is not less than 314Ah.

(3) Power Conversation System (PCS) Selection

This system uses a rated output power of 125kW, a three-level topology supporting bidirectional energy flow, and a wide range of battery voltages.

(4)Energy Management System (EMS)

EMS integrates advanced computer hardware and software technology, automatic control technology, and network communication technology to realize real-time monitoring, control, alarm, and energy management functions for all station equipment, and can maximize the satisfaction of the requirements for safe, stable, and efficient operation of the power system.

1.3 Electrical Engineering

1.3.1 Primary Electrical Equipment

(1) Main Electrical Wiring

This project is equipped with 2 sets of energy storage cabinets and 1 set of grid-connected cabinets. This project connects a 125kW/261kWh energy storage system to the 380V side of the 10kV user station, adding a total of 1 outgoing cabinet.

(2) Electrical Equipment Layout

The energy storage power station mainly consists of 2 energy storage cabinets and 1 grid-connected cabinet, occupying an area of approximately 21 square meters. A fireproof wall will be newly built around the energy storage power station.

1.3.2 Secondary Electrical Equipment

(1) Monitoring System

The energy storage power station is designed for unmanned operation, employing a centralized monitoring scheme based on a computer monitoring system. The task of the computer monitoring system is to automatically monitor and regulate the BMS, PCS, EMS, and other electrical equipment according to the requirements of the power system and the power station's operating mode. 

The computer monitoring scope includes: batteries, energy storage converters, station power supplies, and DC systems. 

The energy storage power station is equipped with a data server to collect information from the bidirectional converters and batteries, and connects to the computer monitoring system via Wi-Fi, 4G network, or communication cables.

(2) Relay Protection 

The electrical equipment within the energy storage power station employs microprocessor-based protection to meet information transmission requirements. Relay protection is configured according to the "Technical Specification for Relay Protection and Automatic Safety Devices" GB14285.

1.3.3 Communication System 

The energy storage power station's communication system mainly comprises three parts: system communication, internal communication, and communication with the public network. The task of the energy storage power station's system communication is to manage production operations and scheduling within the power station, and to provide information transmission channels for relay protection, remote control, metering, and computer monitoring systems.

1.4 Civil Engineering 

The proposed energy storage power station has a total capacity of 250kW/522kWh. The total land area is approximately 21 square meters. 

The geological conditions of the energy storage power station site are stable and meet the requirements for safe site selection. There are no issues related to environmental protection, military impacts, mineral overlay, cultural relic protection, or engineering geology within the site, making the construction conditions favorable. 

The energy storage system will be installed within the park using a poured concrete foundation, requiring a leveled site. The foundation is 0.25m above the outdoor ground level and is constructed with C30 concrete. Firewalls should use independent foundations.

1.5 Construction Organization Design

The construction period consists of two parts: the preparation period and the main construction period. The preparation period mainly includes the construction of temporary production and living facilities, engineering design, and equipment procurement. The main construction period includes site leveling, foundation and equipment installation. Planned construction period: approximately 2 months.

1.6 Fire Protection Design

(1) Fire Protection Design Principles

The fire protection work policy of "prevention first, combined with firefighting" will be implemented. The fire protection design of the project will be considered in conjunction with the overall layout, and various fire protection measures will be adopted for different structures and facilities. Since the energy storage power station is far from the city center, fire protection will focus on self-defense and self-rescue. (2) Overall Fire Protection Design Scheme The overall fire protection design of this project adopts comprehensive fire protection technical measures, addressing fire prevention, monitoring, alarm, control, fire extinguishing, and escape from all aspects to minimize the possibility of fire and ensure that any fires that do occur can be extinguished quickly, minimizing fire losses and ensuring the safe evacuation of personnel during a fire. Fire water systems and fire-fighting equipment are installed within the energy storage power station. 

The energy storage power station is equipped with one set of fire hydrant equipment. Based on the site survey, the original 10kV user station's west-side fire hydrant is approximately 10 meters away from the energy storage power station. Therefore, the fire water intake for this energy storage power station will be sourced from the west-side fire hydrant of the 10kV user station.

Chapter 2 Power System Analysis

2.1 Regional Energy Structure and Current Status of the Power System

The region's power grid is still dominated by coal-fired power plants, posing significant economic and technical challenges to the low-carbon transformation of these plants. However, the region's renewable energy capacity is rapidly increasing, and actively developing local energy storage power stations can provide a better grid operating environment for clean and renewable energy sources such as photovoltaics and wind power.

2.1 Necessity of Energy Storage Power Station Construction

2.2 Energy Storage Devices Can Replace Traditional Grid Upgrade Measures

Power grid companies aim to provide safe, reliable, and high-quality power services while minimizing the costs of grid operation, maintenance, and upgrades, thus offering users affordable and high-quality electricity. Energy storage technology is one means to achieve this goal. It improves power quality, increases power supply reliability, and reduces costs by reducing the demand for transmission and distribution network capacity, alleviating system congestion, and delaying grid upgrades and expansions. 

When the load on a line exceeds its capacity, the distribution network needs to be upgraded or expanded. Traditional measures include upgrading or expanding substation transformers and transmission and distribution lines. With the development of energy storage technology and the decrease in the unit cost of energy storage devices, energy storage devices are increasingly being used in power grids to improve power supply reliability and power quality. Furthermore, a significant advantage of energy storage devices is being recognized: they can replace traditional grid upgrade measures, delaying investment in lines and transformers and achieving "wireless solutions." The same applies to end users; increasing energy storage reduces the likelihood of needing to expand distribution capacity.

2.2.3 Improving Enterprise Power Reliability

Energy storage power stations can ensure the stable operation of the power system by releasing stored energy when power supply is insufficient. For enterprises, the stability and reliability of the power system are crucial; power outages or voltage fluctuations can severely impact production. Installing energy storage power stations can effectively improve power reliability and ensure smooth production.

2.2.4 Optimizing Resource Allocation

Energy storage power stations can store energy during periods of low electricity demand and release it during peak periods to meet demand. This can alleviate the imbalance between power supply and demand to some extent and reduce enterprise electricity costs. Simultaneously, energy storage power stations can maximize resource utilization and improve overall resource efficiency.

2.3 Power System Analysis of the Station Area

2.3.1 Overview of the Power System of the Station Area

This project involves commercial and office power consumption, resulting in a high power load. The power distribution is as follows: There is one 10kV user substation. The 10kV user substation has two 10kV incoming lines and three 10kV/380V transformers (capacity: 315/630/1600kVA), with a total capacity of 2545kVA.

2.3.2 Power Load Analysis of the Station Area

Based on user electricity bills, the monthly power load from February 2024 to December 2024 is as follows:

By further querying the user's monthly electricity consumption curve from February 2024 to December 2024, it can be concluded that the user's overall electricity demand was relatively unstable over the past 11 months. Among them, the electricity consumption of the second incoming line (April and October) was relatively low. When considering the total number of charging and discharging days of the energy storage system throughout the year, the first incoming line energy storage system is calculated as 11 months, i.e., 335 days; the second incoming line energy storage system is calculated as 10 months, i.e., 305 days, with an average of 320 charging and discharging days per year.

2.4 Analysis of Electricity Prices in the Industrial Park

2.4.1 Time-of-Use Division of Electricity Prices in the Industrial Park

The current time-of-use division is shown in the figure.

Peak And Valley Time Division

2.4.2 Time-of-Use Electricity Pricing Analysis for Plant Area This project applies a two-part time-of-use electricity pricing system (general industrial and commercial electricity, voltage level 10kV) to electricity users. The 2024 10kV general industrial and commercial two-part time-of-use electricity pricing is shown in the table below:

Time-of-use Electricity Price Chart

The electricity price is calculated based on the 2024 electricity bill provided by the user; the actual price will be based on the monthly bill from the power company. 

The operation of the electrochemical energy storage system needs to consider the impact of basic electricity fees and power regulation fees. Therefore, when configuring the energy storage capacity, it can be charged and discharged twice, provided that the basic electricity fee capacity in the park allows. 

Referring to the 2024 10kV general industrial and commercial two-part time-of-use electricity price data (for general industrial and commercial electricity users), the average time-of-use electricity price in 2024 was: Pulse 0.1976 USD/kWh, Peak 0.1515 USD/kWh, Normal 0.0943 USD/kWh, Valley 0.0490 USD/kWh. 

3.5 Charge/Discharge Frequency and Characteristic Analysis

The function of the energy storage system in this project is peak shaving and valley filling (peak-valley arbitrage), that is, charging during valley and normal periods and discharging during pulse and peak periods. Based on the time-of-use pricing, each day has one valley period, three normal periods, and two peak or slack periods. One to two charge-discharge cycles can be performed daily. Energy management should monitor load power demand in real time, and the discharge power of the energy storage should not exceed the real-time total power value of the electricity load. 

The planned installed capacity of this energy storage project is 250kW/522kWh. Considering comprehensive factors such as rectifier and inverter losses, line and transformer losses, battery internal resistance losses, and self-consumption losses (temperature control), the overall system efficiency is tentatively considered to be 86%.

(1) During the valley period, charge at a 0.5C rate until the SOC reaches 100%;

(2) During the normal period, charge at a 0.5C rate until the SOC reaches 100%;

(3) During the peak period, discharge at a 0.5C rate until the SOC reaches 10%;

(4) During the  pulse period, discharge at a 0.5C rate until the SOC reaches 10%; Two charge-discharge cycles are completed daily, with a minimum of 320 charge-discharge days per year.

3.6 System Access Scheme Based on the above analysis, considering user load conditions, minimizing energy loss during voltage boosting and the principle of proximity to the power grid, the 250kW/522kWh energy storage power station will be connected to the 380V side bus of the 10kV user station in the park via a single circuit.

Chapter 3 Overall Design and Power Generation Calculation of Energy Storage System

3.1 Overall Design Scheme

This project adopts a centralized system configuration scheme, with all energy storage system units centrally located in the same selected area. This energy storage power station includes 2 energy storage cabinets and 1 grid-connected cabinet. It includes monitoring devices, lithium iron phosphate batteries, PCS, BMS, EMS, cooling devices, a booster system, and a fire extinguishing system.

The operating DOD of this energy storage power station is considered to be 90%. Taking into account rectification and inverter losses, line losses, battery internal resistance losses, and self-consumption losses (including temperature control), the charge/discharge efficiency is tentatively considered to be 93%. The energy storage power station has an operating life of 15 years (two charge-discharge cycles, twice a day). The energy storage system is connected to the 380V side bus of the 10kV user station in the park at a 380V voltage level.

Each energy storage system's battery system contains several standard battery clusters. Each battery cluster consists of battery modules, a BMS, a high-voltage box, and a battery rack. A standard battery cluster BMS system is divided into two levels, including a data acquisition module and a secondary main control module.

The PCS requires the product to be safe and reliable, with harmonic current controlled within the national standard range. The converter must possess grid-connected operation, protection, communication, power factor adjustment, active power regulation, and other functions.

3.2 Electrochemical Energy Storage and Its Applications

Electrochemical energy storage has technological advantages such as good equipment mobility, fast response speed, high energy density, and high cycle efficiency. It is currently a key area of research and innovation and a major growth point for the energy storage industry in various countries. Electrochemical energy storage technologies mainly include lead-acid (lead-carbon) batteries, lithium-ion batteries, flow batteries, and sodium-sulfur batteries. Among them, lead-carbon batteries and lithium-ion batteries have developed rapidly, leading the commercialization of electrochemical energy storage.

3.3 Energy Storage System Architecture and Design Principles

3.3.1 Energy Storage System Architecture

An energy storage system consists of battery cells, BMS, PCS, energy management system (EMS), and corresponding protection and control units.

3.3.2 Energy Storage System Design Principles

1. Reliability

System reliability encompasses four aspects: maturity, fault tolerance, recoverability, and safety. Maturity refers to the system's ability to avoid failure due to inherent faults. The hardware and software configuration of this project should meet the requirements of low failure rate, low fault tolerance, and high availability. Fault tolerance refers to the system's ability to maintain the specified performance level in the event of a fault or violation of specified interfaces. The hardware and software configuration of this project should meet the requirements of high dead-proof and high fault-proof. Recoverability refers to the system's ability to rebuild the specified performance level and recover directly affected data in the event of a failure. Safety refers to the electrochemical energy storage power station possessing safety protection functions such as module-level safety disconnection and cluster-level current sharing control, and should have intra-cell short-circuit detection. The hardware and software configuration of this project should meet the requirements of high reusability and high recoverability.

2. Advanced Technology

The advanced technology of the system is reflected in the selection of widely used products and solutions in the industry. The technology selection is forward-looking, ensuring that it remains mainstream and receives sufficient technical support for the next few years.

3. Practicality: The selected hardware and software solutions should fully integrate with the business characteristics and the current architecture of the battery energy storage power station. While ensuring system reliability and availability, they should maximize practicality and ease of use, achieving features such as a user-friendly interface, intuitive operation, practical functionality, rapid system response, convenient deployment, and stable operation. This will facilitate user operation and improve operational efficiency.

4. Standardization: System configuration must adhere to the principle of standardization. Hardware and software selection should generally adopt standard products that follow industry norms and are supported by mainstream domestic and international organizations or enterprises.

5. Investment Savings: In addition to meeting the above important principles, the selection of hardware and software configurations should also consider the need for investment savings, prioritizing hardware and software products with high function-to-price ratios and high performance-to-price ratios. The selection of products and features should be based on the principles of "optimal cost per kilowatt-hour and safety first" in the design of the overall power station solution. 3.4 Comparison of Energy Storage System Technology Routes

3.5 Selection of Main Equipment for Energy Storage Systems

3.5.1 Product System Introduction

This product is an outdoor liquid-cooled integrated cabinet for commercial and industrial energy storage, providing users with peak shaving and valley filling, capacity reduction and demand reduction, power capacity expansion, and demand response services. It can be widely used in charging stations, commercial buildings, manufacturing, and other industrial and commercial scenarios.

1) The rated output power of a single system is 125kW, and the system can store 261kWh of energy;

2) Multiple units can be connected in parallel, with a maximum power of 1.25MW and a maximum energy of 2.61MWh;

3) This product adopts liquid-cooled temperature control technology, resulting in smaller and more uniform temperature differences between clusters;

4) To meet the needs of more customers, it can be used with photovoltaic inverters to achieve photovoltaic access (AC side);

Energy storage system application scenarios

3.5.2 System Composition

1) The energy storage system of this product mainly includes a Pack, an AC/DC control system (integrated BMS and AC/DC power distribution), a PCS, a fire protection system, and a liquid cooling system.

2) The fire protection system of this product is equipped with composite detectors (built-in smoke sensors, gas sensors, and temperature sensors), water immersion sensors, aerosol detectors (or perfluorohexanone), explosion-proof valves, and other fire protection facilities, making the product safer.

3) This product is equipped with an EMS energy management system to achieve efficient and reliable energy management, and enables remote monitoring via Ethernet and 4G network access.

4) This product is equipped with multiple disconnection devices, including circuit breakers, three-stage fuses, and contactors, to achieve reliable power outage and ensure personal and equipment safety.

System Principle Topology Diagram

3.5.3 Core Modules

3.5.3.1 Battery Pack

1. This battery pack uses 314Ah iron phosphate battery cells, offering excellent safety, high energy density, and low cost.

2. This battery pack boasts an IP67 high protection rating, employs pollution-free modular assembly, ensures high structural reliability, and minimizes maintenance costs.

3. This battery pack utilizes liquid cooling plates for superior temperature performance.

4. This battery pack is equipped with explosion-proof valves and an MSD (Medium-Density Detector), enhancing product safety.

3.5.4 Power Conversation System (PCS)

PCS is a bidirectional current-controlled converter connecting the energy storage battery system and the power grid. Its main function is to realize energy exchange between the battery and the grid, control and manage the charging and discharging of the battery, and achieve bidirectional conversion between DC and AC. It can convert AC to DC to charge the battery, and vice versa. 

This system uses a rated output power of 125kW, a three-level topology supporting bidirectional energy flow and a wide range of battery voltages.

4.5.7.3 Liquid Cooling Unit

The liquid cooling unit is used to regulate the Pack temperature, ensuring it always operates within a suitable temperature range to maintain optimal system performance. It has the following functions:

1. Precise measurement and monitoring of coolant temperature.

2. Effective heat dissipation when Pack temperature is high, preventing thermal runaway accidents.

3. Preheating when battery temperature is low, raising battery temperature and ensuring charging and discharging performance and safety at low temperatures.

4. Cooling is achieved through coolant circulation (50% ethylene glycol aqueous solution, freezing point -35℃), resulting in a more uniform temperature difference between battery clusters.

4.5.7.4 AC/DC Control System

The AC/DC control system box integrates the BMS main control, DC, and AC power distribution.

4.5.7.5 BMS

1. Collects all information from the battery system, receiving cell information from the Pack slave controller and transmitting the battery system information to the EMS;

2. Calculates battery SOC and SOH based on the collected information and executes overall control of the battery system;

3. Ensures stable and safe battery function by monitoring battery status in real time;

4. Extends battery life by monitoring battery consistency.

4.5.7.6 EMS

1. The EMS is an important component of the energy storage system. It communicates with devices such as the PCS, BMS, meters, fire protection systems, and liquid cooling systems to control the entire energy storage system. It can achieve peak shaving and valley filling, demand control, smoothing new energy fluctuations, dynamic capacity expansion, and optimized energy storage revenue. It also has advanced functions such as time-based demand protection, time-based reverse power protection, dynamic multi-level protection, and weighted allocation of energy storage power.

2. The EMS collects data and signals from local devices and ensures the safe, reliable, efficient, and economical operation of the energy storage system through internal control strategies

4.5.7.7 Fire Protection System

This system is equipped with a highly efficient and reliable fire protection system that can automatically activate and immediately extinguish fires in the event of a fire.

System-level Fire Protection:

1. The system installs a composite detector (with built-in combustible gas detector, heat detector, and carbon monoxide detector) and perfluorohexanone extinguishing agent on the top of the battery compartment. When one of the three detectors in the composite detector detects an anomaly, the system will stop operating and report the anomaly. When two anomalies are detected, the extinguishing agent will be released to extinguish the fire, and a feedback signal from the extinguishing agent will be sent to the EMS. The EMS can then relay the information to the site monitoring system or the user.

2. A water immersion sensor is installed at the bottom of the battery compartment. When the water immersion sensor detects an anomaly, the system will stop operating and report the anomaly.

3. A limit switch is installed on the top of the battery compartment to control the switch of the fire-fighting lights and to check whether the detection door is closed tightly to prevent water vapor from entering.

Fire Protection Diagram

3.6 Energy Storage System Power Analysis

The installed capacity of the energy storage power station in this project is 250kW/522kWh. Assuming two charge-discharge cycles per day and an estimated 320 operating days per year, the system operates as follows: The peak-valley time schedule for the power grid is as follows:

The following charging and discharging periods are planned for this project.

Based on the pulse-peak-valley electricity price for industrial and commercial use, and using lithium battery parameters, the calculation formula for the charging and discharging capacity of the energy storage power station is determined as follows:

Charging capacity (grid-connected capacity) = Energy storage battery capacity / Unidirectional charge/discharge efficiency x Battery degradation coefficient x Number of charge/discharge cycles per year

Discharge capacity = Energy storage battery capacity x DOD x Unidirectional charge/discharge efficiency x Battery degradation coefficient x Number of charge/discharge cycles per year

The energy storage power station operates at a DOD of 90%, and the one-way charging and discharging efficiency is approximately 93%. Calculated over 15 years, the energy storage power station operates for a total of 200 days in valley charge-peak discharge and normal charge-peak discharge modes; 60 days in valley charge-pulse discharge and normal charge-peak discharge modes; and 60 days in valley charge-peak discharge and normal charge-peak discharge modes. The project operates for a total of 320 days per year.

The electricity price for charging the energy storage power station from the grid is the valley and normal electricity price; the electricity price for discharging is the peak and pulse electricity price. Therefore, the economic benefits can be calculated simply by calculating the total annual charging and discharging capacity of the energy storage power station.

The electricity price is calculated based on the user's 2024 electricity bill; the actual price will be based on the power company's monthly bill.

The projected charging and discharging capacity of the energy storage power station over 15 years is shown in the table below.

Energy Storage Power Station Charge and Discharge Volume Prediction Table

Conclusion: The energy storage power station of this project operated for a total of 200 days in valley charging-peak discharging and flat charging-peak discharging modes; 60 days in valley charging-pulse discharging and normal charging-peak discharging modes; and 60 days in valley charging-peak discharging and flat charging-pulse discharging modes. The project operates for a total of 320 days per year. Considering the energy storage power station's operating DOD of 90%, unidirectional charging and discharging efficiency of approximately 93%, and a 15-year degradation coefficient of 5% for the first year and after technical upgrades, and 2% for the remaining years, the estimated first-year charging volume from the grid is 323.3 MWh, and the first-year discharging volume is 279.62 MWh; the total charging volume over 15 years is 4532.72 MWh, and the total discharging volume over 15 years is 3920.33 MWh; the average annual charging volume over 15 years is 302.18 MWh, and the average annual discharging volume over 15 years is 261.36 MWh.

Chapter 5 Electrical Design

4.1 Design Principles

(1) Based on the position and role of the battery energy storage power station in the regional power grid system, and following the principle of reasonable layering and zoning according to the grid voltage level and power supply area, the energy storage system should be connected to the appropriate voltage network.

(2) Energy storage power stations should preferably be connected to the user-side distribution bus in a multi-point decentralized manner.

(3) When designing the connection system, a combination of near and far-reaching solutions should be considered, minimizing redundant construction and investment waste.

4.2 Connection Voltage Levels

The recommended grid connection voltage levels for electrochemical energy storage systems in GB/T 36547-2018 "Technical Regulations for Connection of Electrochemical Energy Storage Systems to the Power Grid" are as follows:

Energy Storage System Grid Connection Voltage Level

According to GB/T 36547-2018, 400V can be selected as the access voltage level for this energy storage project. 

The enterprises in this project are 10kV users, and each has at least two transformers in its distribution room. Based on the user's electricity consumption, the voltage level for the 250kW/522kWh energy storage system in this project complies with the relevant State Grid specifications.

4.3 Access Scheme

This project plans to adopt the "user-side 380V access" scheme, with one access point for the energy storage system. It will connect to the newly added 380V distribution cabinet at the 10kV user substation in the industrial park. The specific wiring for the energy storage is as follows:

Energy Storage System Wiring Diagram

4.4 Primary Electrical System

4.4.1 Main Electrical Wiring

This project consists of 2 energy storage cabinets and 1 grid-connected cabinet, with a total energy storage capacity of 250kW/522kWh.

It is planned to connect to the 380V side busbar of the 10kV user substation in the industrial park via one circuit. Based on the project's power supply and distribution situation, the energy storage system will be connected via a low-voltage distribution cabinet added to the 380V distribution room of the 10kV user substation in the industrial park. Each energy storage system has a capacity of 125kW/261kWh.

The energy storage will be connected to the grid via low-voltage cables laid to the energy storage junction box in the user-side distribution room. The grid-connected cabinet will be equipped with meters.

By collecting load power or current values, the collected information will be sent to the energy storage EMS to control the energy storage charging and discharging power. (Energy storage charging power + load power) ≤ maximum allowable load of the transformer; energy storage discharging power ≤ load power.

4.4.2 Power Collection Line Scheme

(1) The energy storage system is connected to the grid via low-voltage cables laid to the energy storage junction box in the user's distribution room.

(2) The cable laying method is selected according to the actual site conditions. For routes with multiple cables concentrated in one location, cable trenches or cable trays within the station (≥4 cables) are used. Other routes use conduit or direct burial, employing single-hole Φ150 galvanized steel pipes or single-hole Φ150 MPP pipes with a burial depth ≥600mm.

(3) Flame retardant measures for cables shall comply with the requirements of relevant regulations such as the "Design Standard for Power Engineering Cables" (GB50217-2018).

(4) The power cables are selected as halogen-free, low-smoke, flame-retardant, cross-linked polyethylene insulated, polyethylene sheathed, copper conductor cables, and low-voltage power cables.

(5) The control cables are selected as halogen-free, low-smoke, flame-retardant, fire-resistant, copper core, cross-linked polyethylene insulated, polyolefin inner sheath, copper tape shielding, steel tape armor, and polyethylene or polyolefin outer sheath. (6) Computer cables shall be halogen-free, low-smoke, flame-retardant, fire-resistant, copper core, cross-linked polyethylene insulation, twisted pairs, copper wire braided sub-shielding, polyolefin sheath, copper wire braided overall shielding, steel tape armor, and polyolefin outer sheath.

4.4.3 Lightning Protection and Overvoltage Protection

To ensure the safe operation of the power system and the safety of the energy storage system and its ancillary facilities, battery energy storage power stations must have good lightning protection, lightning protection, and grounding protection devices.

(1) Grounding Device

a. Scope of Protective Grounding

According to the "Code for Grounding Design of AC Electrical Installations" GB/T50064-2014, all parts requiring grounding shall be reliably grounded.

b. In the energy storage area, a single grounding network shall be used for protective grounding, working grounding, and overvoltage protection grounding. According to the clause explanation in the "Technical Specification for Secondary Wiring Design of Thermal Power Plants and Substations" DL/T5136-2012, the logic grounding resistance value of electronic devices shall not exceed 1Ω. Therefore, the total grounding resistance value of the entire station shall be controlled to be less than 1Ω. The soil resistivity in the project construction area is relatively low. Conventional copper-plated steel rods can be used as grounding materials for the plant site. The grounding wire lifespan is considered to be 15 years based on the power station's operating time.

c. All equipment should be grounded according to regulations. Each grounding part of electrical equipment should be connected to the grounding main line via a separate grounding branch line. It is strictly prohibited to connect several grounding parts in series within one grounding wire. Both ends of the channel steel of each foundation of high- and low-voltage power distribution equipment should be reliably connected to the indoor grounding main line.

(2) Overvoltage Protection

a. Direct Lightning Protection

Independent lightning rods should be installed within the site area, with their down conductors connected to the entire station's grounding network. The grounding device should make full use of natural grounding bodies, primarily by laying horizontal grounding networks. Reducing grounding resistance mainly relies on large-area horizontal grounding bodies, which have the functions of equalizing voltage, reducing contact potential and step potential, and dissipating current. b. Lightning surge protection for power distribution equipment. According to the "Code for Grounding Design of AC Electrical Installations" GB/T50065-2011 and the "Code for Overvoltage Protection and Insulation Coordination Design of AC Electrical Installations" GB/T50064-2014, the surge arresters in the existing 10kV power distribution equipment in the plant area are used to protect against lightning surges and other overvoltages.

4.5 Electrical Secondary Equipment

The energy storage power station is equipped with one computer monitoring system to realize real-time monitoring and energy management functions. The computer monitoring system meets all design functions required for the safe operation monitoring and control of the energy storage power station, such as protection, control, communication, and measurement functions. It can realize comprehensive automated management of the energy storage power station, processing and transmitting various real-time data and information to the central control center. Energy management functions include energy balance and automatic scheduling, mode control, etc.

The power supply for the energy storage station control layer and related secondary equipment utilizes the self-powered energy storage system. A UPS power supply is also configured to provide power to critical loads; the UPS capacity is tentatively considered to be 2 × 5kVA.

4.5.1 Computer Monitoring System

(1) Management Mode

This project is a newly built conventional energy storage power station. Designed according to relevant regulations and specifications, the control system adopts a computer monitoring system scheme, designed as an unmanned station. The energy storage power station will construct a fully automated system, possessing all remote control functions such as telemetry, remote signaling, remote adjustment, and remote control, as well as clock synchronization functions. It should have the ability to exchange information with remote dispatch centers and monitoring centers, and implement control strategies such as peak shaving, system frequency regulation, peak regulation, and reactive power support according to its functional positioning.

(2) Design Principles

The equipment configuration and functional requirements of the computer monitoring system of this energy storage power station are designed according to the unmanned operation mode. The main design principles are as follows:

a. The computer monitoring system of the energy storage power station is uniformly networked.

b. Information within the energy storage power station is shared and unique. The monitoring host of the energy storage power station computer monitoring system shares information resources with the remote data transmission equipment, protection and fault information management system, and microcomputer anti-misoperation system, avoiding duplicate data collection and saving investment. c. The monitoring of all equipment within the energy storage power station is completed by the energy storage power station computer monitoring system; no other conventional control panels or simulation panels are required.

d. The hardware and software configuration of the energy storage power station computer monitoring system should support network communication technology and communication protocol requirements.

e. The network security of the energy storage power station computer monitoring system should be strictly implemented in accordance with the "Regulations on Security Protection of Secondary Power Systems".

(3) Main Functions The computer monitoring system integrates advanced computer hardware and software technology, automatic control technology, and network communication technology to realize real-time monitoring, control, alarm, and energy management functions for all equipment in the station, maximizing the satisfaction of the requirements for safe, stable, and efficient operation of the power system. The system is mainly used for monitoring data from various measurement, control, protection, and other equipment within the energy storage power station, and can be extended with advanced application functions.

(4) System Structure The system structure is a network topology. The energy storage power station acts as a network terminal for the remote control center, while also being relatively independent, forming a self-contained system within the station. A layered, distributed, and open network system is used to connect the various devices. The electrochemical energy storage system utilizes a Battery Management System (BMS) to monitor the voltage, current, temperature, SOC, and SOH of the batteries within the storage cabinet in real time. This data is transmitted via Ethernet to the EMS server. The monitoring system collects information from the PCS and BMS, uploading it to the Central Control Management Unit (CCM) within the EMS cabinet, and receiving control information from the CCM to distribute to each device. The EMS cabinet is connected to the central control center via Ethernet.

The network within the energy storage station handles various access requests between the server and client workstations, as well as the transmission of data from the bay layer, ensuring rapid adjustment and response of the entire energy storage system.

4.5.2 Relay Protection and Automatic Safety Devices

1. The PCS is equipped with anti-islanding protection, AC overcurrent protection, AC overvoltage protection, AC undervoltage protection, AC overfrequency protection, AC underfrequency protection, phase sequence error protection, overload protection, DC overcurrent protection, DC overvoltage protection, DC undervoltage protection, DC reverse polarity protection, internal short circuit protection, overtemperature protection, insulation protection, abnormal switch status protection, derating protection, and power module (IGBT) protection. When a short circuit occurs on the low-voltage side of the transformer, the PCS can quickly provide protection, preventing further damage. For DC systems, the BMS system has a comprehensive and rigorous monitoring and protection scheme.

2. Overcurrent protection should be installed on the 380V lines in this project. If the overcurrent protection time limit is no greater than 0.5-0.7 seconds and there are no protection coordination requirements, instantaneous overcurrent protection is not required. Lines originating from important substations should be equipped with instantaneous overcurrent protection. When instantaneous overcurrent protection cannot meet selective operation requirements, a slightly time-delayed instantaneous overcurrent protection should be installed.

4.5.3 Electricity Metering

Electricity Billing

Recommended Access Scheme for Primary System: Install a gate electricity meter at the access point for billing compensation.

Configure a single meter at the billing gate point. The accuracy requirement for the electricity meter is not less than 0.2S class. The configuration of the electricity metering device should comply with the "Technical Management Regulations for Electricity Metering Devices" (DL/T448-2000).

Use three-phase smart electricity meters, which should at least have bidirectional active power metering function, event recording function, and the ability to collect information such as current, voltage, and power consumption. They should be able to realize data storage and uploading, and be equipped with a standard communication interface, with the ability to communicate locally and remotely through the electricity information acquisition terminal.

4.5.4 Other

(1) Automatic Fire Alarm System

The energy storage system container in this project is equipped with a fire alarm system.

In case of fire, the signal is transmitted to the fire detector on the energy storage cabinet through the automatic or manual alarm button. After receiving the fire signal, the fire detector issues an alarm signal. Fire protection systems for other electrical equipment are designed in accordance with the "Fire Protection Design Standard for Thermal Power Plants and Substations" GB50229-2019, the "Typical Fire Protection Code for Power Equipment" DL5027-2015, and the "Design Code for Power Engineering Cables" GB50217-2018.

(2) Video Security Monitoring System The image monitoring system provides remote monitoring of the site and conducts regular inspections of the main equipment and safety of the energy storage power station. This system can record monitored scenes for accident analysis. The video security monitoring system is primarily installed in the energy storage area. At this stage, it is designed to monitor the energy storage power station without blind spots; further optimization will be implemented in the next stage.

This image monitoring system consists of a control station, cameras, video cables, control cables, and infrared beam detectors. The control station is located in the main control room and consists of a microcomputer controller, keyboard, mouse, monitoring station host, and hard disk recorder. The microcomputer controller has a computer communication interface to connect with the superior dispatch department's computer to control the camera, pan-tilt-zoom (PTZ) camera, and switch images. (3) Operation Platform This energy storage power station is connected to the user's operation monitoring platform.

4.6 Communication The energy storage power station's communication system mainly consists of three parts: system communication, internal communication, and communication with the public network. The task of the energy storage power station's system communication is to provide a communication channel for the owner's competent department to conduct production scheduling and modern management within the energy storage power station, and to provide information transmission channels for relay protection, remote control, metering, and computer monitoring systems. Internal communication provides services for the energy storage power station's production operation and dispatch command.

Chapter 5 Project Budget

5.1 Preparation Instructions

5.1 Project Overview The planned total installed capacity of the energy storage project is 250kW/522kWh, with a planned construction period of approximately 2 months.

Static Total Investment: USD 106,605;

Dynamic Total Investment: USD 110,676.

5.2 Total Investment The total investment is divided into static total investment and dynamic total investment, where:

Static total investment includes equipment and tool purchase costs, construction and installation costs, construction costs, design and supervision fees, and basic contingency funds.

Dynamic total investment includes equipment and tool purchase costs, construction and installation costs, construction costs, design and supervision fees, basic contingency funds, construction period interest, and working capital.

5.3 Budget Table

Chapter 6 Revenue and Cost Calculation

6.1 Revenue and Cost Calculation

The scale of this energy storage power station is 250kW/522kWh, with a project cycle of 15 years (technical upgrades will be made in the 9th year based on the actual technical parameters of the energy storage batteries). The investment cost is approximately USD 109,902.

Specific calculations are as follows:

Calculation conditions: 320 operating days per year, two discharges and two charges per day. Except for January, July, and August, each day will consist of one round of Valley Charge-Peak Discharge + one round of Normal Charge-Peak Discharge; July-August will consist of one round of Valley Charge-Pulse Discharge + one round of Normal Charge-Peak Discharge; January will consist of one round of Valley Charge-Peak Discharge + one round of Normal Charge-Pulse Discharge.

Energy storage operating life: 15 years.

The overall charge/discharge efficiency of the energy storage is assumed to be 85% (93% charging, 93% discharging), and the depth of discharge (DOD) is assumed to be 90%. The total installed capacity of the energy storage is 522 kWh, with a single charge capacity of 485.46 kWh and a single discharge capacity of 436.91 kWh in the first year.

Cell capacity degradation is assumed to be 5% in the first year, and 2% annually thereafter.

If the cell capacity degradation falls below 80% by the end of the 8th year, the cells will be replaced. From the 9th year onwards, the energy storage charge/discharge capacity degradation calculation will restart until the end of the 15th year, when the project's operational cycle concludes.

5. Electricity prices are based on the average electricity prices from January 2024 to December 2024, namely:

Pulse period electricity price: 0.1976 USD/kWh

Peak period electricity price: 0.1515 USD/kWh

Normal period electricity price: 0.0943 USD/kWh

Valley period electricity price: 0.0490 USD/kWh The calculated total revenue for the energy storage project in the first year is approximately 109,902 USD.

Annual Revenue Forecast Table

6.2 Economic Benefits

Total Investment: USD 109,902

Annual Utilization Days: 320 days

Operating Life: 15 years (Technical upgrades will be carried out in the 9th year based on the actual technical parameters of the energy storage battery. The cost of this upgrade is calculated at USD 0.056 Wh in this financial model)

Annual Operation and Maintenance Costs: Approximately USD 1,385

Comprehensive financial indicators