AI services have moved from niche tools to everyday utilities. Search, recommendations, language models, and computer vision all run on clusters of powerful GPUs that work around the clock. That jump in activity shows up on the power bill. In 2025, global electricity use by AI data centers is widely estimated in the hundreds of terawatt hours. That is on the scale of what a small country uses in a year, and demand is still climbing.
The strain is visible in several places. Utilities face long queues to connect new sites. Substations and transmission lines need upgrades. Cooling systems must handle far higher rack densities than a few years ago. A typical modern AI rack can draw well over 100 kW. Multiply that by hundreds or thousands of racks and you see why lead times, interconnect agreements, and backup strategies now drive build schedules as much as real estate or server supply.
Operators have three goals that often pull in different directions. Keep uptime high. Keep costs and emissions manageable. Keep growth on track. That is a hard set of targets to meet with traditional backup alone. This is why long duration storage is getting attention, and why flow batteries are now part of many strategy discussions.
Why lithium-ion backup is running into limits
lithium-ion batteries power phones and cars (EVs) very well, and they have served data centers for short ride-through events. In an AI facility, the use case looks different. Workloads are heavy. Charging and discharging can be frequent. Grid interruptions may last longer than a few minutes.
Here are the common pressure points that operators report:
- Duration: Lithium ion is great for minutes, not always for hours. When weather, grid constraints, or curtailment events run longer, a bigger energy buffer is needed.
- Cycle life under stress: High depth of discharge and frequent cycling shorten lifespan. Replacement programs add to operating cost and maintenance windows.
- Thermal risk at scale: Large banks concentrate energy in a small footprint. That raises the bar for fire detection, suppression, and insurance requirements.
- Materials and sustainability: Lithium and certain metals carry supply chain and environmental challenges. Scaling those materials for every campus is not easy.
- Total cost across years: The upfront price can look acceptable, but the long view includes augmentation, replacements, safety systems, and downtime.
lithium ion will remain useful for fast response and short duration tasks. For multi-hour support and deep integration with onsite renewables, many teams want an alternative that scales energy capacity without pushing thermal risk or replacement rates. That is where flow batteries enter the picture.
Understanding Flow Battery Technology
A flow battery stores energy in liquid electrolytes held in external tanks. During charge and discharge, the liquids move through a cell stack separated by a membrane. The stack sets how much power you can deliver at once. The tank size sets how much total energy you can store.
Think of it like a small power plant fed by two tanks. If you want more power, you add more stacks. If you want more energy, you enlarge the tanks. Because the energy sits outside the stack, the system can grow without cramming more reactive material into a tight box. Many systems use vanadium based electrolytes, while others use iron-based formulations.
This architecture is attractive for sites that need steady output for hours, can allocate some floor space or yard space for tanks, and prefer low fire risk.
Advantages that fit AI data centers
- Scales cleanly: To extend runtime, you increase tank volume. The cell stack and controls stay the same design. That makes long duration storage more straightforward than building bigger lithium ion rooms.
- Lower fire risk: The electrolytes are typically non-flammable, and operating voltages are low. Facility and insurance teams appreciate reduced hazard profiles.
- Long life: Many systems are rated for ten thousand to twenty thousand cycles with minimal degradation. Over a ten-year horizon that can simplify budgets and maintenance.
- Multi-hour support: Flow batteries are built for hours, not just minutes. That is a better match for grid constraints, weather events, and renewable smoothing.
- Friendly to renewables: Charging from onsite solar or wind and discharging during the evening peak is a natural use case. The system can also handle peak shaving, load shifting, and some grid services.
- Material re-use: Vanadium and iron electrolytes can be recycled or re used. That helps with sustainability targets and end of life planning.
Flow Battery Limitations You Should Know
No technology is perfect. Here are the common tradeoffs you will see in the spec sheets and proposals:
- Upfront cost: The installed cost per kWh is still higher than many short duration lithium ion projects. Prices should improve with scale and standardized designs.
- Space and weight: Tanks, pumps, and piping add footprint. Edge sites or urban campuses may not have the room. New builds can plan for it more easily than retrofits.
- Efficiency: Round trip efficiency often falls in the 70 to 85 per cent range. Lithium ion can reach 90 per cent or more. Your energy model should reflect that.
- Power density: Instantaneous power per square meter is lower than dense lithium ion racks. If you need very high bursts in a tight footprint, you may still pair with lithium ion.
- Market maturity: Fewer large vendors, fewer integrators with deep reference lists, and a learning curve for facility teams and local authorities.
- Supply chains: Electrolyte production and long lead items need clear planning. Contracts should set service levels and warranties that match data center expectations.
How operators can evaluate fit?
A practical evaluation usually covers five areas:
- Use case clarity: Decide whether you need three to six hours of backup, renewable shifting, peak shaving, or all of the above. Duration and duty cycle drive the design.
- Site planning: Confirm space for tanks and service access. Check structural loads, secondary containment, and fire life safety plans. Early conversations with the authority having jurisdiction save time later.
- Controls and integration: Align the battery management system with your power management, generators, and renewables. The goal is simple logic. Charge when power is cheap or available onsite. Discharge when the grid is tight or prices rise.
- Service model: Clarify who maintains pumps, membranes, and stacks. Get performance guarantees and spare parts commitments in writing.
- Financials: Model total cost of ownership over ten to fifteen years. Include energy losses, avoided diesel runtime, demand charge savings, and revenue from grid services if available.
Cost and ROI snapshot
Here is a simplified way to frame the economics. Assume a campus needs 50 MW of additional flexible capacity with a four-hour duration. That is 200 MWh of storage. A long duration system might carry a higher upfront cost than a short duration lithium ion room, but it can:
- Avoid several hours per month of peak demand charges
- Reduce the number of diesel test runs and fuel deliveries
- Enable larger onsite solar with fewer curtailment losses
- Qualify for utility incentives in markets that pay for capacity or flexibility
When you spread those benefits over a decade and factor in lower augmentation needs, the numbers become competitive. However, the exact answer depends on your power prices, local incentives, and the value your business places on resilience and emissions.
Where flow batteries add the most value
Flow batteries are strongest in these scenarios:
- New builds with space: Greenfield sites that can place tanks near electrical rooms or yards.
- Campuses with onsite renewables: Solar or wind combined with storage to cover the evening ramp or poor weather days.
- Regions with tight grids: Places with interconnect delays or frequent curtailment events.
- Facilities with high resilience targets: Sites that want a buffer beyond a few minutes but prefer to minimize diesel use.
They are less ideal where land is limited, where only very short ride through is required, or where very high power in a tiny footprint is the only goal.
Outlook for the next five years
We expect three trends:
- Standardized designs: Skids, tanks, and controls that ship as repeatable blocks will reduce engineering time and cost.
- Better integration with grid programs: Utilities want flexible load and storage. As tariffs and incentives mature, revenue stacking becomes simpler.
- Broader supplier base: More manufacturers and integrators will enter the market. That brings competition, more service coverage, and a healthier ecosystem.
Lithium ion will not disappear. It will sit beside flow batteries for fast response and short duration roles. The mix will depend on site goals and local grid conditions.
Conclusion
Flow batteries are not a cure all for every data center challenge. They are, however, a serious option for long duration backup, renewable integration, and risk reduction. They bring lower fire risk, long service life, and scalable energy capacity. The tradeoffs are real. You need more space, you accept a bit less efficiency, and you plan for a newer supply chain.
If your roadmap includes larger AI clusters, more onsite renewables, or tighter utility connections, it is worth running the numbers. Start with a pilot that reflects your actual duty cycle. Use that data to build a business case and a design standard you can repeat across sites.
Power will shape the next phase of AI growth as much as chips and models. Teams that plan storage with the same care they apply to compute will move faster and spend smarter. Flow batteries give you one more lever to pull as you balance uptime, cost, and sustainability in the years ahead.
