Energy Storage Using Abandoned Coal Mines and Salt Caverns: International Experience and Potential for Vietnam

1. Introduction

As the energy transition accelerates toward renewable sources such as solar and wind, grid stability has become a critical challenge. Energy storage systems (ESS) are key to balancing supply and demand, minimizing curtailment, and enhancing grid reliability. One promising approach under global research and deployment is utilizing abandoned coal mines or salt caverns for energy storage in the form of compressed air or pumped water, leveraging existing underground spaces. Vietnam, with its network of decommissioned coal mines and abundant hydropower potential, can learn from international models to develop sustainable energy storage solutions.

2. Overview of International Projects

2.1 Salt Cavern Energy Storage

Salt caverns are ideal “underground energy reservoirs” due to their mechanical stability and high pressure tolerance. Notable projects include:

• Germany – Huntorf & McIntosh
  Compressed Air Energy Storage (CAES) facilities in Huntorf (1978) and McIntosh (1991, USA) have demonstrated industrial-scale energy storage. Excess electricity compresses air into the cavern, which is later expanded through turbines to generate electricity when needed.

• China – Qinghai & Yulin Projects
  China is developing large-scale CAES projects using decommissioned salt caverns. The Qinghai CAES project, expected to reach 300 MW, integrates with wind power to stabilize variable renewable energy output in western provinces.

2.2 Coal Mine Energy Storage

Abandoned coal mines can be repurposed for compressed air or pumped water storage:

• Germany – Projekt Energiespeicher Lausitz
  Several decommissioned coal mines in Germany are being assessed for CAES and pumped water storage. Utilizing existing underground infrastructure reduces costs compared to excavating new caverns.

• China – Shanxi & Inner Mongolia
  China is piloting CAES systems in abandoned coal mines, paired with wind and solar power. These projects achieve hundreds of MWh of storage capacity, enhancing grid flexibility.

2.3 Pumped Hydro Storage (PHS)

PHS remains a mature and highly efficient energy storage technology:

• Vietnam’s Potential
  Vietnam has numerous large hydropower reservoirs suitable for PHS development. Excess electricity can pump water to an upper reservoir, which can then be released to generate electricity during high demand periods, supporting renewable energy integration, particularly in Central and Central Highlands regions.

3. Potential Applications in Vietnam

3.1 Utilizing Abandoned Coal Mines

• Vietnam has a significant number of decommissioned coal mines in Quang Ninh, Thai Nguyen, Quang Binh, etc.

• These mines could be converted into CAES or pressure energy storage facilities, saving the cost of new excavation.

• Challenges include ensuring mechanical stability, preventing air leakage, and managing pressure and temperature conditions.

3.2 Developing Pumped Hydro Storage

• Vietnam’s topography and existing hydropower infrastructure are favorable for PHS.

• Advantages: mature technology, high conversion efficiency (~70–85%).

• Limitations: high initial investment, environmental and social impact assessments required.

3.3 Integrating with Renewable Energy

• PHS or CAES projects can be integrated with solar and wind power to stabilize electricity supply, reduce curtailment, and improve grid reliability.

• Example: using surplus electricity from Central Vietnam’s solar plants to compress air or pump water to upper reservoirs.

4. Conclusions and Recommendations

• Energy storage using abandoned coal mines and salt caverns is a viable solution, successfully implemented in countries such as Germany, the USA, and China.

• Vietnam can leverage its existing decommissioned coal mines for CAES and expand pumped hydro storage at existing reservoirs.

• Recommendations:

  1. Conduct detailed technical surveys of abandoned coal mines to evaluate their suitability for energy storage.

  2. Develop pilot PHS projects integrated with renewable energy to assess efficiency and cost-effectiveness.

  3. Pursue international collaboration for CAES technology adoption and risk management, ensuring safety and environmental protection.

• Implementing these solutions will help Vietnam develop a clean, reliable, and sustainable energy system in the long term.