HomeCruise Ship Thermal Batteries: Can Stored Waste Heat Replace Boiler Fuel in Port?

Cruise Ship Thermal Batteries: Can Stored Waste Heat Replace Boiler Fuel in Port?

September 16, 2026

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Cruise Engineering Report | 2026

Cruise Ships Throw Heat Away at Sea, Then Burn Fuel to Make It Again in Port

There is something hard to ignore once you look at a cruise ship's heat balance. While the engines are working at sea, there can be more usable heat than the ship needs. A few hours later, the same vessel is alongside with propulsion shut down, thousands of people still showering, eating and using hotel services, and an oil-fired boiler may be burning fuel to replace the heat that was rejected earlier. New cruise-ship research puts a serious number on the opportunity. Store part of that excess heat while sailing, hold it in a silica-gel and water system, then bring it back during the port stay. On the vessel modeled by researchers, the optimized system removed roughly 90% of annual oil-fired boiler heat demand.

5.20 → 0.51 GWh/year of modeled oil-fired boiler heat after optimized thermal storage.
4.69 GWh Annual boiler heat displaced by stored engine waste heat.
1,530 t Approximate annual CO₂ reduction in the optimized simulation.
421 t Silica-gel adsorbent in the selected optimized design.
930 m³ Approximate total thermal-storage system volume.
€270k/yr Modeled annual marine gas oil cost reduction.
The important number is not 4.69 GWh by itself. The optimized system reduced annual boiler thermal demand from 5.20 GWh to 0.51 GWh, a reduction of about 90%. It did this without producing additional energy. It simply moved useful engine heat from the part of the itinerary where it was abundant to the part where it was scarce.

The Ship Behind the Study

This was not a small expedition vessel or a theoretical hotel load. The researchers built the storage system into an annual energy-performance model of a large Mediterranean cruise ship with substantial passenger and machinery loads.

Reference Ship Study Value Engineering Relevance
Length 331.5 m Large contemporary cruise-ship scale.
Passengers Up to 6,330 Large continuous domestic-hot-water and hotel demand.
Crew About 1,700 More than 8,000 people aboard at full occupancy.
Diesel generation 2 × 14.4 MW + 2 × 19.2 MW 67.2 MW installed generating capacity creates substantial recoverable heat when engines are loaded.
Oil-fired boiler 7 MW Supplies heat when waste-heat recovery cannot meet thermal demand.
Boiler steam production 12.5 t/h at 8 bar, 170°C Shows that port heat is a meaningful machinery load, not a minor domestic-water issue.
Operating pattern Mediterranean itinerary Repeated sailing and port cycles create frequent opportunities to charge and discharge storage.
Main thermal users DHW, HVAC heat, pools, laundry, galley, service tanks, engine-room services The thermal network serves far more than passenger showers.

A Thermal Battery, But Not an Electrical Battery

“Thermal battery” is useful shorthand, but there are no lithium cells here. The studied system is a closed-cycle sorption thermal energy store using silica gel as the adsorbent and water as the working fluid.

At Sea Engines produce excess recoverable heat
Charge Hot jacket water heats the silica gel
Desorb Water leaves the silica gel as vapour
Store Water and regenerated adsorbent remain separated
In Port Water vapour is returned to the adsorbent
Discharge Adsorption releases useful heat
Replace Boiler firing falls sharply
Working Pair

Silica Gel + Water

Both are familiar materials. Silica gel is commercially available, while water is non-toxic and acts as the adsorbate and refrigerant in the closed cycle.

Charge Temperature

95°C Optimized Case

The selected design used a 95°C desorption temperature, placing the system in a range compatible with high-temperature engine jacket-water recovery.

Storage Advantage

Heat Without Keeping a Tank Hot

Once the adsorbent and water are separated, the stored energy is retained as adsorption potential. That can reduce the standing-loss problem associated with simply holding hot water for later use.

The Optimization Result Is More Interesting Than the Maximum Result

Researchers simulated 9,408 combinations of storage size, desorption temperature, control-bank count and demand coverage. Savings climbed quickly as adsorbent mass increased, but the curve eventually flattened. Once the system reached roughly 450 to 500 tonnes of adsorbent, adding substantially more material produced little additional annual boiler savings.

258 to 3,101 m³ Storage volumes examined across the simulation set.
117 to 1,404 t Adsorbent-mass range tested.
65°C to 95°C Desorption-temperature range evaluated.
~450–500 t Region where additional storage began delivering sharply diminishing returns.
421 t Adsorbent mass ultimately selected by the multi-objective optimization.
930 m³ Selected system volume after balancing savings against onboard size and weight.

More Storage Eventually Becomes Dead Weight

Adsorbent Mass Approximate Annual Boiler Savings Utilization Trend Owner-Level Read
100–120 t Capacity constrained Mean utilization roughly 83–85% Small unit works hard, but leaves recoverable heat on the table.
230–250 t About 3.5 GWh/year Mean utilization around 72% Large jump in savings while installed capacity is still well used.
~350 t About 4.6 GWh/year Mean utilization around 60% Much of the attainable benefit has already been captured.
450–500 t Roughly 5.1 GWh/year in parametric cases Mean utilization falls to roughly 48% The curve begins to flatten. Space and weight start increasing much faster than savings.
~1,400 t Only slightly above the 450–500 t region Maximum utilization falls to roughly 35% A much larger installation delivers very little additional useful heat.

The Optimized Case in One Table

Annual Result Without TES Optimized TES Change
Recovered useful heat 87.7 GWh 92.4 GWh +4.69 GWh
Dissipated heat 36.8 GWh 31.7 GWh −5.10 GWh
Oil-fired boiler heat 5.20 GWh 0.51 GWh −4.69 GWh
Boiler fuel 0.55 kt/year 0.05 kt/year About −0.49 kt/year
Fuel cost €300k/year €29.4k/year About −€270k/year
CO₂ 1.70 kt/year 0.17 kt/year −1.53 kt/year
NOx Reference boiler emissions Sharply reduced −45.7 t/year
SOx Reference boiler emissions Sharply reduced −26.5 t/year
PM2.5 Reference boiler emissions Sharply reduced −1.38 t/year
930 m³ is the part nobody should skip over. The fuel and emissions numbers are attractive, but this is not a box that disappears into a machinery-space corner. The optimized layout still carries about 421 tonnes of silica gel and occupies roughly 930 m³. On a cruise ship, volume has commercial value. Every serious business case has to compete against cabins, stores, machinery access, tanks, ducting, piping and other retrofit projects.

Hot Water Tank or Sorption Storage?

Sorption is not the only way to move heat from sea passage to port. A separate 2023 cruise study found that a 600 m³ hot-water storage tank could cover 97% of port heating demand on its modeled vessel. That does not make the two studies directly comparable, but it does make one point clear: shipowners should compare thermal-storage technologies, not assume the most sophisticated option automatically wins.

Option Strength Trade-Off Best Fit
Hot-Water Storage Simple hardware, familiar pumps, tanks and heat exchangers. Tank must remain hot; insulation and sensible-heat temperature range limit usable stored energy. Short-duration cycling where sufficient tank volume already exists.
Silica-Gel / Water Sorption Stores heat as adsorption potential and can hold it with very low standing thermal loss after separation. Vacuum equipment, adsorber design, heat and mass transfer, large equipment volume and additional controls. Repeated sea-to-port heat shifting where waste heat and thermal demand are separated in time.
Heat Pump + Shore Power Turns electricity into useful heat with a coefficient of performance greater than direct resistance heating. Requires electrical capacity at berth and adds large electrical loads precisely when shore connection demand may already be high. Ships with reliable low-carbon shore electricity and suitable low-temperature heat sources.
Electric Boiler Simple conversion from electricity to steam or hot water. Large electrical demand and no multiplier effect from recovered waste heat. Peak or backup duty where shore/grid capacity is plentiful.
One useful reality check: the initial sorption design in the 2026 study stored about 20.1 MWh in roughly 1,034 m³ of complete system volume. That works out to only about 19.4 kWh of useful capacity per cubic metre at ship-system level. Material-level storage-density figures for silica gel can look much higher because they do not include the evaporator, condenser, adsorber structure, heat exchangers, piping, vacuum space and integration hardware.

Shore Power Does Not Automatically Shut the Boiler Down

FuelEU 2030

The Requirement Is Electrical

From 2030, applicable passenger ships at covered EU ports must use shore power or qualifying zero-emission technology for their electrical power demand at berth. Heating demand does not disappear just because the generators stop.

Port Emissions

Boilers Can Remain

The U.S. EPA makes the same distinction in its shore-power guidance: shore power can cut auxiliary-engine emissions, but it does not itself address boilers or other shipboard combustion sources that still need to operate alongside.

That creates an interesting pairing: shore electricity handles the ship's electrical hotel load while stored waste heat handles part of the thermal hotel load. Instead of replacing one decarbonization technology with another, the ship could use both to reduce combustion at berth.

The Retrofit Case Gets Stronger When These Conditions Line Up

Ship Condition Effect on Thermal Storage Case Reason
Frequent port calls Strong positive More charge/discharge cycles create more opportunities to replace boiler fuel.
Substantial 85–95°C recoverable heat underway Strong positive The storage system needs enough useful-temperature heat to regenerate the adsorbent.
High boiler use in port Strong positive Creates a clear fuel-saving target.
Expensive distillate fuel in port Positive Each displaced MWh of boiler heat becomes more valuable.
Available lower-deck volume and weight margin Critical A several-hundred-tonne, several-hundred-cubic-metre installation can be difficult on an existing ship.
Waste heat already fully utilized underway Weakens case Storage only helps when there is heat available to shift.
Very low port thermal demand Weakens case There is little boiler fuel to displace.
Large electric heat-pump installation planned Requires comparison The best answer may depend on electricity price, grid carbon intensity, shore connection capacity and available waste-heat temperature.

The High-Value Equipment Is Around the Storage Material

1
Adsorber Modules Silica-gel beds integrated with finned or enhanced heat exchangers to improve heat and vapour transfer.
2
Waste-Heat Heat Exchangers High-temperature jacket-water interfaces, isolation equipment and hydraulic integration.
3
Evaporators & Condensers The water side of the closed adsorption cycle requires dedicated phase-change equipment.
4
Vacuum & Valve Systems Vacuum integrity, switching valves and vapour management become critical to reliable cycling.
5
Pumps & Thermal Loops High- and low-temperature circuits must connect machinery waste heat to storage and storage back to ship thermal users.
6
Energy Management Controls Bank sequencing, state-of-charge logic and itinerary-aware controls determine when modules should charge or discharge.
7
Digital-Twin Engineering The research shows that route, demand and engine loading can matter as much as nominal storage capacity.
8
Retrofit Integration Weight, stability, machinery-space access, structural foundations, piping routes and class approval may decide whether the project is practical.
9
Commissioning & Lifecycle Service Vacuum performance, sorbent condition, heat-exchanger fouling, valves and controls will all need long-term monitoring.
Research basis: Barone et al., “Waste-heat-to-demand matching in cruise ships through sorption thermal energy storage: Modelling, validation and optimisation,” Applied Thermal Engineering, Vol. 304, 2026, Article 132638. Additional context: Brækken et al., Energy Conversion and Management 288 (2023) 117121 on cruise hotel energy and hot-water thermal storage; IMO GreenVoyage2050 shore-power guidance; Regulation (EU) 2023/1805, FuelEU Maritime Article 6; U.S. EPA Shore Power Technology Assessment. The 2026 sorption study was available online in August 2026 and appears in the September 2026 journal volume.

Cruise Thermal Battery Sizer

A quick planning model for the sea-to-port heat shift. It estimates storage capacity, approximate system volume, annual boiler heat displacement, fuel savings and CO₂ reduction.

Port Boiler Load 0 MW
Practical Storage Target 0 MWh
Approx. System Volume 0 m³
Heat Coverage Per Call 0%
Annual Boiler Heat Avoided 0 GWh
MGO Avoided 0 t/yr
Fuel Cost Avoided €0
CO₂ Avoided 0 t/yr
Port heat covered by stored waste heat 0%
Planning assumptions: 92% charge-to-use efficiency, based approximately on the 2026 study's 5.0 GWh charged / 4.6 GWh delivered relationship; 85% oil-fired boiler efficiency; MGO lower heating value 11.9 MWh/t; 3.12 t CO₂ per tonne of MGO; system-volume proxy of 19.4 kWh/m³ derived from the study's initial 20.1 MWh / 1,034 m³ configuration. The per-person boiler load is an adjustable planning proxy, not a class or design standard. Actual sizing requires hourly thermal-demand, waste-heat, itinerary, temperature, stability, machinery-space and class analysis.
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