What Is a Thermal Battery for Data Centers? (And How TES Actually Works)

Engineers increasingly call a thermal energy storage (TES) tank a thermal battery. The name is a useful analogy, a TES tank stores cooling the way a battery stores electricity, but the physics is different and the economics depend on how your data center buys power. This article explains what a thermal battery is and how the storage actually works.

A thermal battery for a data center is a thermal energy storage (TES) tank, usually a large stratified chilled-water tank, that stores cooling by charging at off-peak or low-load times and discharging during peaks. It works by exploiting the heat capacity of water: a temperature difference across a large volume holds usable cooling, which the plant draws later to cut chiller runtime when power is expensive or scarce.

A battery decouples when energy is made from when it is used. A TES tank does the same for cooling: it makes chilled water when it is cheap or abundant and spends it when cooling is expensive or the chillers are constrained. The stored medium is water at a temperature difference, not a chemical cell, but the load-shifting value is real.

• Decouples cooling generation from cooling use.
• Charges when power is cheap or abundant.
• Discharges during peaks or constraints.
• Medium is water delta-T, not chemistry.

During charging, chillers (or free cooling) push chilled water into the tank, usually stratified so cold sits at the bottom and warm returns to the top. During discharging, the plant draws the cold layer and returns warmer water, shrinking the usable delta-T. A diffuser at the inlet keeps the layers from mixing. The Italy Sardinia chilled process water tank (2025, 30,549 m3) is a large coated water tank built for process duty; it is analogous evidence of our ability to build large stratified storage, not a data-center delivery.

• Charge: chillers or free cooling fill the tank.
• Stratify: cold bottom, warm top.
• Discharge: draw cold, return warm.
• Diffuser limits mixing and preserves delta-T.

Usable cooling is the volume times the usable delta-T times water density and specific heat. A wider allowable supply-temperature swing stores more per cubic meter. The Singapore buffer tank (2020, 3,462 m3) shows how a modest volume still provides meaningful buffer duty when matched to the load step.

• Capacity = volume x usable delta-T x density x Cp.
• Wider allowable swing stores more.
• Tank height aids stratification.
• Volume matched to load step, not guess.

A thermal battery smooths the cooling load so fewer chillers run at peak, shifts demand to off-peak tariffs, and provides reserve during a chiller trip. It is most valuable where electricity rates swing by time of day or where grid carbon intensity varies. The table contrasts it with a plain buffer tank.

• Shifts load to off-peak tariffs.
• Cuts chiller count at peak.
• Bridges a chiller trip.
• Best where rates or carbon vary by time.

We have not delivered a data-center thermal battery in this project library. The large water and buffer tanks we cite (Italy Sardinia 30,549 m3, Singapore 3,462 m3) are analogous infrastructure, delivered for industrial and process clients, showing our capability to build large coated stratified storage. They are not presented as data-center projects.

• No data-center TES in library.
• Citations are analogous, not claims.
• Large coated tank capability is real.
• Specify your duty for a real design.

No. The name is an analogy; a thermal battery stores cooling in water at a temperature difference, while an electrical battery stores chemical energy. The load-shifting principle is similar.

Usable cooling is volume times usable delta-T times water density and specific heat. A wider allowable supply swing increases storage per cubic meter.

In cold climates the loop may use glycol or the tank may be insulated and indoor; the medium and freeze protection follow your climate and loop design.

Below a certain load, the capital and footprint rarely pay back. The case strengthens with larger loads and time-of-use or carbon-varying tariffs.

Indirect. By cutting chiller runtime at peak and enabling free cooling, a TES can lower energy, but the direct PUE win depends on climate and control strategy.

Not in our project library. We cite large coated water and buffer tanks delivered for other clients as analogous capability, not as data-center deliveries.

A thermal battery is a TES tank that stores cooling in water at a temperature difference and discharges it when needed, exactly the load-shifting logic of an electrical battery applied to cooling. Capacity is volume times usable delta-T, and the value grows with time-of-use tariffs and peak constraints. The physics is straightforward; the payoff is a siting, tariff, and control question rather than a technology risk.