Stâlpu, Romania
A battery-storage hall fire required a difficult, prolonged intervention. IGSU did not establish the cause in this release.
Incident reportDSU / IGSU
Technology
How ROCAS immersion cooling works, how it compares with cold-plate liquid cooling, and why thermal control belongs in the investment decision.
The difference starts at the cell.
Three ways to remove heat from a battery module. AI-generated concept renderings; illustrative architecture, not product photographs.
| Design decision | Cold-plate liquid cooling | ROCAS dielectric immersion |
|---|---|---|
| Heat transfer | Cell to interface to plate to coolant. | Cell surface to dielectric fluid. |
| Temperature uniformity | Depends on plate contact and flow distribution. | Broad fluid contact supports more uniform temperatures. |
| Hot spots | Heat must travel to the cooled contact area. | Direct heat pickup helps manage local hot spots. |
| Electrical insulation | Coolant stays inside a sealed plate circuit. | Electrically insulating fluid surrounds the cells. |
| Fire protection | Plate heat removal plus BMS and system protection. | Direct heat absorption can help limit propagation. |
| Service requirements | Coolant, pumps, seals, circuit integrity and plate contact. | Fluid condition, compatible seals, circulation and gas management. |
How immersion cooling works
Battery packs heat up as current flows through them, so every pack needs cooling. In a ROCAS immersion system the LFP cells sit in a dielectric fluid that does not conduct electricity. The fluid takes heat directly from the cell surface, helps limit thermal propagation between cells and keeps cell temperatures stable, which supports a longer cycle life.
The design uses two fluids. Besides the dielectric fluid, a water-glycol circuit handles extreme ambient temperatures. Two loop variants are available: the dielectric fluid circulates directly to the chiller and is cooled there, or it stays inside the pack and is cooled by the water-glycol circuit.
- Pumps, the heart
- Keep the coolant moving through every pack.
- Pipes, the arteries
- Carry the fluid to and from the battery packs.
- Dielectric fluid, the blood
- Surrounds the LFP cells and absorbs heat at the cell surface. The fluid is produced by Shell.
- Chiller, the lungs
- Removes the heat and returns the circuit to its target temperature.
Make every cycle count.
Look beyond the purchase price and compare the capital allocated to each cycle over the operating life. Illustrative 0.5C scenario.
Initial CAPEX
EUR per MWh
+17.6%
Cycle-life assumption
Equivalent full cycles
+71.4%
Capital per cycle
EUR per initial MWh per cycle
−31.4%
Illustrative assumptions, not guaranteed product performance. CAPEX per cycle: 170,000 / 7,000 = 24.29 and 200,000 / 12,000 = 16.67. Comparable qualification and equal scope assumed. Excludes energy, losses, OPEX, augmentation and discounting, so this is not a full LCOS. Actual life depends on duty cycle, calendar ageing and end-of-life criteria. The cycle-life values are scenario assumptions: the ROCAS datasheets rate the liquid-cooled models at 8,000 cycles (0.5P, 25 ±2°C, 70% SOH) and the immersion models at 10,000 cycles, with test conditions stated in the project offer.
Fire risk is an investment risk.
A fire can damage assets, stop dispatch and disrupt the site. Evaluate protection before you buy.
Czajków, Poland
A container battery fire prompted continued cooling, thermal monitoring and the evacuation of nearby people.
Incident reportPSP Poznań
Victorian Big Battery, Australia
Fire spread to a neighbouring Megapack during commissioning. Investigators identified a probable coolant leak and electrical faults.
Incident reportPhoto: FRV / ABC; findings: Energy Safe Victoria
Real incidents illustrate BESS fire exposure; they are not a controlled comparison of cooling methods. The cooling configurations at Stâlpu and Czajków are not established here. Immersion does not guarantee zero fire risk. Images and credits from the ROCAS safety presentation.
Cell-level thermal control
Direct fluid contact helps remove heat and manage hot spots.
Layered protection
Combine immersion with BMS, detection, gas management and fire suppression.
System-level validation
Select tested configurations, documented operating limits and a defined maintenance plan.
Download the comparison
A three-page summary of the comparison, the lifecycle scenario and the safety case.
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