NB/T 11809-2025 in English

Standard Development Background and Technological Evolution

NB/T 11809-2025, "Design Guidelines for Integrated Photovoltaic and Molten Salt Energy Storage Power Generation Projects," is a key industry standard issued by the National Energy Administration on June 30, 2025, and will officially come into effect on December 30, 2025. The standard was compiled by the China Hydropower and Water Resources Planning and Design Institute and co-authored by several organizations, including PowerChina Central South Survey and Design Institute Co., Ltd.

As my country deepens its efforts to achieve its dual carbon goals, installed photovoltaic power generation capacity continues to grow. However, the intermittent and unstable nature of photovoltaic power generation poses challenges to the safe operation of the power grid. Molten salt energy storage technology, with its ultra-long regulation time (up to 10 hours), high cycle life (over 25 years), and low cost, has become a key technical solution for peak and frequency regulation when a high proportion of renewable energy is integrated into the grid.

Key Points of Core Technology Innovation

This standard systematically specifies the design requirements for integrated photovoltaic and molten salt energy storage power generation projects for the first time. The main technological breakthroughs are reflected in:

System Configuration Optimization Design

Chapter 6 of the standard details the technical requirements for the configuration of an integrated power generation system. Key technical parameters include the PV system capacity, molten salt thermal storage hours, and rated power of the steam turbine generator set, which must be determined through technical and economic comparisons. System configuration should comprehensively consider factors such as the project's functional positioning, solar energy resources, and the current status of the power system.

Key Technical Equipment Specifications

Molten Salt Electric Heating System

Article 6.3.2 of the standard stipulates that molten salt electric heaters can be selected from three types: resistive, electromagnetic, and electrode. When selecting a molten salt electric heater, special consideration should be given to the impact of PV power generation output characteristics on equipment life and efficiency. Electric heaters can be composed of multiple devices connected in series or parallel. The total power and power per unit should be determined through technical and economic comparisons.

Molten Salt Heat Storage System

The standard recommends the use of a high-low temperature dual-tank heat storage method (Section 6.3.4). The total mass of the molten salt medium should be determined based on factors such as the medium's thermal properties, operating temperature range, and operating mode. Storage tank design must meet the following requirements:

• Total volume = dead volume + effective volume + volume affected by seismic sloshing + safety margin (≥3%)
• Design positive pressure ≤ 2kPa, design negative pressure ≥ 0.25kPa
• Design temperature for high-temperature storage tanks ≥ the maximum operating temperature at the outlet of the molten salt electric heater + 10°C

Pump and valve system configuration

The standard stipulates that the number of cold salt pumps and hot salt pumps must be at least two (one in service and one backup). When selecting a pump, the head must be accurately calculated, taking into account factors such as static pressure differential, pipeline resistance, and equipment resistance to ensure stable system operation.

Power Forecast and Operation Control

Chapter 7 of the standard requires that integrated power generation projects must possess functions such as active power control, reactive power control, voltage control, frequency support, fault ride-through, and photovoltaic-storage coordinated control. The automatic power generation control system should accommodate various operating modes, including smoothing power output, tracking planned output, peak shaving and valley shifting, and participating in system frequency regulation.

Project Layout and Safety Requirements

General Layout Principles

Chapter 8 of the standard stipulates that the molten salt energy storage power generation area should be located near the outgoing line of the access system within the project area. Flood control standards: PV sites must comply with GB 50797, molten salt energy storage sites with GB/T 51307, and other independent areas with a flood control standard of no less than a 50-year flood.

Special Fire Safety Provisions

Chapter 12 of the standard sets out special requirements for molten salt fires: Water and foam should not be used as extinguishing agents for molten salt fires (Article 12.3.7). Areas where molten salt electric heaters are located should be equipped with fire sand boxes, fire buckets, and fire shovels. Oil-immersed transformers with a capacity ≥90 MV·A should be equipped with automatic fire alarm and automatic fire extinguishing systems.

Structural Design Standards

The design service life of photovoltaic support structures is 25 years, and for buildings (structures) 50 years. Molten salt storage tank foundations require insulation and ventilation to prevent changes in the mechanical properties of the foundation soil due to overheating. Tank foundations should undergo deformation verification, temperature effect calculations, and stress calculations.

Electrical and Control System Integration

Chapter 9 of the standard recommends the use of centralized control and single-point grid connection. When designing the main electrical connections, if a booster station is constructed for both molten salt energy storage and photovoltaic power generation, a three-winding transformer should be used as the main step-up transformer. The monitoring system should include the photovoltaic power generation monitoring system, the molten salt energy storage and its auxiliary control systems, and the booster station monitoring system. Each subsystem should be relatively independent, yet form a unified, station-wide monitoring platform.

Molten Salt Electric Heating Power Supply System

The power supply for the molten salt electric heater should be drawn from different collector buses of the photovoltaic power generation system in proportional capacity. The power distribution equipment should be located in a distribution room close to other electrical equipment within the molten salt heat storage area. The power supply system must consider the impact of the different control and heating principles of the molten salt electric heater on the power factor of the electrical system.

Environmental Protection and Implementation Recommendations

Environmental Protection Requirements

Chapter 13 of the standard emphasizes that environmental protection and soil and water conservation facilities should be designed, constructed, and commissioned simultaneously with the main project. Sewage and wastewater should be collected, transported and treated separately, and the quality of water discharged to the outside should comply with the requirements of GB 8978. The impact of electromagnetic radiation from the project on the surrounding environment should comply with the provisions of GB 8702.

Project Implementation Recommendations

1. Preliminary Demonstration Phase: Focus on solar energy resource analysis, site selection, and technical and economic comparison to determine the optimal system configuration plan
2. Design Phase: Strictly follow the standard requirements to design each system, paying special attention to the safety protection and fire protection design of the molten salt system
3. Construction Phase: Strengthen quality control to ensure the manufacturing and installation quality of key equipment such as molten salt storage tanks and pipelines
4. Operation Phase: Establish a comprehensive operation and maintenance system, regularly check the status of molten salt system equipment, and ensure safe and stable operation

The implementation of NB/T 11809-2025 will provide standardized technical support for the construction of integrated photovoltaic and molten salt energy storage power generation projects in my country, promote the deep integration of new energy and energy storage technologies, and assist in the construction of new power systems and the realization of dual carbon goals.