China’s State Power Investment Corp (SPIC) has commissioned what it calls the world’s first ultra‑high‑temperature heat‑pump energy storage system, a megawatt‑scale “Carnot battery” that marks a major step in bringing thermo‑mechanical storage into real‑world grid applications. Branded “Chuno”, the system was formally launched in Beijing on December 25 following a pilot campaign and independent performance testing.
Developed by SPIC’s Central Research Institute, Chuno couples a heat‑pump cycle with a heat‑engine cycle to store off‑peak or surplus renewable electricity as high‑temperature heat and low‑temperature cold, then convert that thermal gradient back into power on demand. The company positions the project as a bridge between research prototypes and bankable infrastructure for long‑duration storage, an area of growing urgency as China’s wind and solar build‑out accelerates.
How a 560°C Carnot battery works
Unlike lithium‑ion systems that store energy electrochemically, SPIC’s Carnot battery uses air as the working fluid in a closed thermodynamic loop. In the charging phase, electricity drives a high‑temperature heat pump that compresses the air, pushing its temperature above 560°C; this heat is transferred into a molten‑salt thermal storage medium in a heavily insulated “hot tank.”
After surrendering heat, the still‑pressurised air is expanded and cooled to as low as –60°C, with the cold captured in a corresponding “cold tank.” When the grid needs power, the stored temperature difference between hot and cold reservoirs drives turbomachinery in a heat‑engine cycle, generating electricity while also offering the option to supply useful heat and cooling for nearby industrial or district‑energy users.
SPIC says the integrated system uses high‑temperature compressors, high‑ and low‑temperature turbines, ultra‑high‑temperature heat exchangers, molten‑salt storage and advanced controls, with heavy‑equipment support from Harbin Electric on key rotating machinery.
Performance: 1 MW/4 MWh, >65% efficiency
According to SPIC, the commissioned pilot is rated at 1 MW/4 MWh, placing it squarely in the multi‑hour, long‑duration segment of the storage spectrum. The system has completed seven full charge–discharge cycles under third‑party testing by the Xi’an Thermal Power Research Institute, meeting or exceeding its design targets and operating stably across the test window.
Crucially, SPIC claims a round‑trip electricity‑to‑electricity efficiency exceeding 65%, with no degradation in cycle efficiency across operating conditions, and an effective energy density of 80–120 kWh per cubic metre of storage volume. While this falls short of the 75–85% efficiencies typical of lithium‑ion battery systems, SPIC argues that the absence of electrochemical capacity fade and the use of abundant, non‑critical materials make Chuno more akin to long‑life infrastructure than a consumable asset.
Because the system relies on tanks, turbomachinery and thermal media rather than specific underground geology, SPIC also emphasises that it avoids the siting constraints that limit pumped‑hydro or some compressed‑air energy storage (CAES) projects.
Target markets: from renewable firming to industrial parks
SPIC says the Carnot battery is aimed first at grid‑side long‑duration storage, helping to firm variable wind and solar output and provide flexibility services in conjunction with thermal or nuclear plants. The ability to run for several hours at rated power positions it as a candidate for evening peak‑shaving, intra‑day shifting and ancillary services in regions facing growing curtailment of renewables and stressed transmission corridors.
At the same time, the company highlights industrial parks and high‑energy‑use campuses as promising deployment sites, arguing that the system’s capacity to co‑deliver heat, cooling and electricity could significantly improve project economics where all three services have local demand. In such settings, waste cold could support refrigeration or data‑centre cooling, while high‑grade heat could feed process steam networks or district heating stacking revenue streams on top of grid services.
A new contender in the long‑duration storage race
Globally, Carnot batteries have been explored for years by research groups in Europe, the US and the UK, typically achieving 50–55% efficiency at more moderate temperature ranges of 200–500°C. Analysts note that SPIC’s system stands out for pushing the hot reservoir above 560°C and the cold to –60°C, delivering one of the largest temperature gaps and highest reported efficiencies in the field to date.
China’s power system with rapidly growing wind and solar fleets, rising curtailment and an expanding need for mid‑ to long‑duration flexibility is seen as an ideal proving ground for such technology. Observers suggest that if SPIC can scale from the current 1 MW/4 MWh pilot to multi‑hundred‑megawatt installations over the next few years, Carnot batteries could emerge as a serious competitor to CAES and a complement to lithium‑ion in the country’s energy‑transition toolkit.
For now, the Chuno project offers a concrete proof‑of‑concept: an ultra‑high‑temperature Carnot battery that has cleared third‑party testing and moved out of the lab and into the grid‑connected world—putting thermo‑mechanical storage firmly back on the energy‑innovation map.