As the global push for carbon neutrality accelerates, managing the massive energy demands and waste heat of industrial sectors has become a critical challenge. Industrial energy systems currently account for nearly 40% of global electricity demand growth. To address this, scientists are increasingly turning to a promising long-duration energy storage technology: the Carnot battery.
A newly published study in the journal ENGINEERING Energy by a research team from Zhejiang University and affiliated institutes offers a major breakthrough in making Carnot batteries more practical and efficient for real-world industrial applications. The researchers have developed a novel "quasi-dynamic" mathematical model to optimize Thermally Integrated Carnot Batteries (TI-CB) under the unpredictable, fluctuating conditions typical of factory environments.
The Challenge of Fluctuating Waste Heat Unlike conventional lithium-ion batteries, Carnot batteries store excess electricity in the form of thermal energy (heat) by creating a temperature difference between hot and cold reservoirs. When the grid needs power, this stored heat is converted back into electricity. TI-CB systems, which utilize an Organic Rankine Cycle (ORC), are particularly well-suited for capturing and upgrading low-to-medium grade industrial waste heat (typically between 60°C and 90°C).
However, real-world industrial environments are rarely perfectly stable. Waste heat temperatures and flows fluctuate constantly. "Most previous studies relied on steady-state models that fail to capture the dynamic nature of industrial waste heat conditions," the research team explains. "Our goal was to understand how these systems perform when operating under off-design, fluctuating conditions over long periods."
A New Modeling Framework To solve this, the researchers developed a quasi-dynamic mathematical model paired with a dynamic evaluation framework that accounts for the time delays between charging and discharging phases. By running thousands of simulations using multivariable sampling, they could systematically observe how different design parameters influence overall efficiency.
Key Findings for Future Engineering The study yielded several crucial insights for the future commercial deployment of Carnot batteries:

• The Discharging Phase is Highly Sensitive: The researchers found that fluctuations in the mass flow rate during the energy discharging phase (the ORC cycle) have a far more significant impact on the system's overall round-trip efficiency than fluctuations during the charging phase (the heat pump). This highlights that engineers must prioritize control strategies on the discharging side to maintain stability.
• The Cost of High Temperature Differences: While higher heat source temperatures generally improve performance, increasing the temperature difference of the heat source leads to irreversible heat losses, causing the round-trip efficiency to drop steeply from 62.6% to 45.8%.
• Selecting the Right "Blood" for the Battery: The system's working fluid is critical. The study compared several fluids and found that while R1336mzz(Z) offered the highest peak thermodynamic performance, it was highly volatile under changing conditions. Conversely, the fluid R1233zd(E) provided the best stability across the entire operating range, making it the most reliable choice for practical engineering applications.

This comprehensive modeling approach bridges the gap between theoretical thermodynamics and practical engineering. By providing a clear roadmap for how to handle off-design fluctuations, this research brings Carnot batteries one step closer to widespread deployment, offering a powerful tool to decarbonize industrial parks and stabilize grids powered by intermittent renewable energy.
DOI: 10.1007/s11708-026-1055-3