In the 2010s, diesel generators were the standard backup for grids, homes and commercial buildings. Back then batteries had limited adoption in this application due to high manufacturing costs and perceived limitations in charging and discharging, which is a critical requirement for utility-scale uses.

But in the last 15 years, batteries have gained the trust and adoption of utility companies and developers, and are now seen as a proven technology to support energy backup. Early battery chemistries like lithium iron phosphate (LFP) set the foundation for alternative energy support. Now, chemistries are evolving to meet the demands of a modern infrastructure — powered by multiple types of energy producers.

Let’s look at a single energy consumer: data centers. Data centers are expected to pull 130 GW of power by 2030. Developers know this, which is why the U.S. data center sector had contracted 50 GWs of clean energy, 29 GW from solar and 13 GW from wind, at the end of the third quarter in 2024. By the end of this year, contracted solar capacity is projected to double that of wind, after solar secured nearly half of all corporate renewable deals by the end of 2024. This is excellent, because we need to harness power from all available sources if we expect to meet growing demand. However, solar and wind supply is largely daytime-dependent and weather-sensitive, meaning it can’t provide a constant stream of power to data centers on its own. On cloudy days or during nighttime hours, many data centers still rely on the grid. And the grid remains tightly tethered to fossil fuels.

Variable renewable energy (VRE) sources, like solar and wind, operate roughly 40% of the time. To maintain 100% uptime, data centers that use VRE sources must either produce enough energy during high sun and wind times to store excess for use during the gap periods, or pull from peaker plants. Here’s the problem with relying on peaker plants or LFP storage alone:

• Structural inadequacy: Using peaker plants to balance VRE can’t support the weight of multi-hour or multi-day stability. LFP batteries can balance a routine evening, but they can’t power a data center during a prolonged three-day storm or a widespread dunkelflaute event, because they only hold, on average, four hours of power.

• Environmental contradiction: Peaker plants are often the least efficient and most polluting sources of energy, operating sporadically yet generating disproportionate greenhouse gas emissions and local air pollution.

This is where long-duration energy storage (LDES), which stores 10 or more hours of power, or ultra-LDES, which stores 100 or more hours of power, becomes essential. While short-duration LFP can handle daily fluctuations, ultra-LDES is required to work alongside existing sources to ensure a stable power supply.

The value of utra-LDES extends well beyond simply filling short gaps. It introduces system-wide flexibility that fundamentally changes how energy flow and infrastructure is managed. Multi-day capacity directly addresses the vulnerability of relying on an hourly battery for an ongoing crisis. It provides a safety net against major outages and unforeseen events, ensuring the grid can withstand a wide range of challenges. 

Ultra-LDES creates value by:

• Shifting days of load: This capacity directly solves the multi-day reliability crisis. It ensures grid stability over consecutive days by bridging the vast gap between hourly battery duration and smoothing seasonal mismatches, mitigating the risk of energy deficits during sustained weather-driven scarcity.

• Mitigating grid congestion: Ultra-LDES acts as a local pressure valve. By placing multi-day storage assets strategically, the grid can absorb excess power precisely where it is generated, reducing strain on overloaded transmission lines. This local storage allows the grid to operate more efficiently, preventing the need for costly, time-consuming curtailment of energy that would otherwise be wasted.

• Unlocking transmission value: Ultra-LDES maximizes the value of existing infrastructure. By shifting power flows from high-congestion times to low-congestion times, these assets enable new opportunities for efficient energy delivery. This approach provides transmission services without requiring billions in new steel and wires, ensuring every existing dollar of infrastructure investment is fully utilized.

The core benefit is that ultra-LDES fundamentally expands the grid’s operational ceiling, providing the high-duration, clean power required to achieve true system-level resilience.

The future of energy will be measured in days, not hours. Multi-day, ultra-LDES provides resilience, firming and system-wide benefits. The energy industry is moving beyond “good enough” solutions, embracing innovation to build a grid defined by security and reliability. The true legacy of this transition will be a power system that operates reliably and year-round for every community. 

This transition goes beyond just new hardware, it demands a new philosophy. The benchmark of success is a coordinated system. This means integrating short-duration solutions like LFP for daily stability while using multi-day, locally stored capacity to ride out a major storm or a crisis ensuring that power remains on when it is needed most.

By making the necessary investment in ultra-LDES today, the energy sector is establishing the energy independence that the modern economy and national security demand. The true legacy of this transition will be in the certainty that coordinated storage delivers. It will be a power system defined by resilience and reliable operation for all.