“How much energy do I really have?” — The question costing storage owners millions
Every megawatt-hour matters. Grid demand spikes, prices surge, and systems are pushed to their limits. Energy storage system operators need to know how much energy they can count on and how quickly they can deploy it. The catch? In most grid-scale battery energy storage systems (BESS), that number is fuzzier than it seems.
Imagine operating a 100 MWh battery energy storage system. In practice, most operators hold back 10-15% of that capacity to avoid overestimating available capacity and risking a shortfall on any market commitments. That safety buffer—built around measurement uncertainty—means you’re only dispatching 85 MWh.
In today’s volatile energy markets, that 10-15% margin isn’t just a technical issue. It’s a missed opportunity. Every unclaimed megawatt-hour represents lost revenue, stranded grid support capacity, and a system falling short of its full potential. Worse, usable energy loss doesn’t stop at estimation errors. Over time, hidden imbalances between individual cells begin to chip away at overall system performance, further reducing capacity and complicating operations.
Understanding State-of-Charge (SoC) CalibrationKnowing how much energy is available to dispatch at any given moment is core to profitability. This is where SoC calibration comes into play: a software-enabled process that allows the battery management system (BMS) to track the state of charge of the battery with a high degree of precision.
This level of accuracy is especially important in systems using LFP batteries. Known for their long cycle life and safety, LFP batteries are widely used in grid-scale projects—but they come with a challenge: their relatively flat voltage curve between 25% and 90% SoC makes it difficult for the BMS to accurately determine SoC by the voltage curve alone during regular operations.
This is particularly problematic in markets where batteries operate within a narrow SoC band—often between 30% and 70%—to deliver ancillary services. If a battery stays in this range for too long, the SoC error grows. While this may not be a problem most of the time, it means that when a large grid disruption happens, the battery asset owner may overestimate the true SoC of the battery, and lose the ability to dispatch during a valuable price spike.
Over time, even small measurement errors can compound. Without proper calibration, SoC estimations will drift, eroding confidence in available capacity and reducing both performance and revenue. Proper SoC calibration corrects for charge-counting errors and re-aligns the system’s internal tracking to reflect reality so operators can dispatch with confidence, optimise system performance, and avoid leaving value on the table.
Calibration solves one side of the equation: knowing how much energy is available. But ensuring that all of that energy can actually be accessed requires another key function—cell balancing.
Cell Balancing: Preventing Stranded EnergyCell balancing ensures that all cells within a battery string maintain similar SoC levels. For utilities and asset owners, this alignment is critical to avoid missing opportunities during time-sensitive grid service windows. The total energy available for charging and discharging is constrained by the most extreme cells: the lowest SoC during discharge, and the highest SoC during charge.
If just one cell deviates from the average, system-wide performance suffers. Energy becomes stranded, unavailable when it’s needed most. Effective cell balancing maximises usable capacity, prolongs asset health, and ensures that every cell contributes to system performance to its fullest potential.
SoC calibration and cell balancing don’t operate in isolation—they work together to optimise the usable energy in a BESS facility. While SoC calibration corrects errors in the measurement of charge levels, cell balancing ensures uniform charging and discharging across all cells. When both are managed effectively, they eliminate stranded energy, increase usable capacity, and enable operators to extract greater value from their assets.
The impact is tangible: more energy available for grid services, more accuracy in market participation, and more confidence in operational planning.
The Value of Automation in SoC Calibration and Cell BalancingManually managing calibration and balancing across millions of cells isn’t scalable. Achieving these outcomes consistently without disrupting system availability requires automation. Sophisticated software can now handle these functions with precision, ensuring they are performed regularly and strategically.
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