Innovative Energy Storage System from China

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As Renewable Energy Grows, So Does the Need for Storage
In the face of the dynamic development of renewable energy sources, energy storage technologies are becoming increasingly important. One of the most promising innovations has been presented by researchers from the Northeast Electric Power University in China. Their project introduces a novel Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) system, where traditional air compression technology is enhanced by the force of gravity.

Compressed Air and Constant Pressure – A New Standard in Energy Storage

Classic CAES (Compressed Air Energy Storage) systems store energy by compressing air to high pressure. However, in traditional solutions, air pressure changes during the charging and discharging cycles, which affects the system’s efficiency and operational complexity. The Chinese researchers designed an isobaric system, meaning the pressure in the air tank remains nearly constant during operation.

How is that possible?
The key lies in the use of a flexible air bladder placed at the bottom of an abandoned vertical mine shaft, topped by a heavy steel block. As compressed air is pumped into the bladder, its volume increases and the weight is lifted. However, due to the constant mass and contact surface area, the pressure remains virtually unchanged. During discharge, the block descends, pushing the air out of the bladder at the same pressure.

Energy, Exergy, and Economics

The research team ran detailed simulations using MATLAB, analyzing the system’s energy, exergy, and economic aspects. The key performance metrics are impressive:

  • Energy efficiency: 87.1%
  • Exergy efficiency: 70.07%
  • Energy density in air: 2.68 kWh/m³
  • Energy density per unit of occupied space: 2.29 kWh/m³

The system utilizes surplus energy from solar PV, wind power, or the grid to drive the compressor. Compression occurs in five stages, with five intercoolers used to recover the heat generated during compression.

Gravity and Heat Recovery – A Breakthrough Combo

The most significant innovation compared to classic CAES systems is the isobaric operation and the use of gravitational potential as the driving force for air expulsion during discharge. The steel block, with a density of 7870 kg/m³, acts as a pressure stabilizer and a natural “piston” — operating entirely passively and without any power input.

Exergy analysis revealed the biggest losses occur during the turbine stage (35.21%) and compression stage (30.98%). Intercoolers and reheaters recover some of this energy, though their exergy efficiency stands at 63.54% and 50.60%, respectively.

Is It Economically Viable?

The cost of electricity produced by the system is estimated at $0.0804/kWh, making it competitive with many other storage technologies. Assuming a 25-year lifespan and 350 days of operation per year, the system yields:

  • Net Present Value (NPV): $1.6 million
  • Internal Rate of Return (IRR): 17.93%
  • Discounted Payback Period (DPP): 8.36 years

The economic model used the following input prices: charging energy cost ($0.04/kWh), discharging energy price ($0.18/kWh), weight cost ($0.10/kg), and heating water ($0.018/kWh).

Repurposing Mining Infrastructure – A Sustainable Approach

Using abandoned mine shafts as air reservoirs reflects a sustainable approach to energy. Rather than building expensive pressure tanks, the system repurposes existing industrial infrastructure.

Although still in the simulation stage, this concept has the potential for real-world application, especially in regions with disused mines and growing renewable energy surpluses. Thanks to its simplicity and high efficiency, this AA-CAES system could become a viable competitor to battery storage and pumped hydro storage.

Source: ess-news.com

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