Why ELCC is becoming the grid’s next big storage metric 

Most discussions of battery capacity leave out a key metric: whether the storage system can contribute electricity at a specific time.  

“The goal with having capacity or reliability markets is to make sure there are adequate amounts of supply whenever there is energy demand,” explained Arvin Ganesan, the CEO of utility-scale thermal storage startup Fourth Power. He told ESS News that nameplate capacity doesn’t truly measure that.   

That’s where effective load carrying capability (ELCC) comes in.   

“ELCC looks at a resource’s ability to contribute energy when the grid needs it the most,” Ganesan said. “It’s a more precise way of measuring how much reliability a resource can contribute.” 

Measuring with ELCC compared to capacity is growing more and more critical, particularly in regions like CAISO, PJM and MISO with consistent end-of-day peaks and high penetration of renewables and short-duration storage. 

Those short-duration systems can shave two-to-four hours off of the peak, Ganesan explained, adding that it’s “like cutting off the top of a mountain.”  

“The peak isn’t as high, but it leaves you with a longer plateau instead of a spike,” he said. In his eyes, the biggest causal relationship isn’t between renewable penetration and the need for storage, but instead between short-duration and long-duration storage systems.  

“Two-to-four hour batteries are creating a world where we actually need longer-duration systems in order to deliver the same ELCC,” Ganesan added.  

As more short-duration systems come online, they’ll also become derated, meaning that they can’t be relied upon to provide enough power to contribute during the whole peak period.  

That makes balancing current and future grid needs a complex equation.  

“A six-hour battery might have perfect ELCC today, but five years from now there might be too many of them,” Ganesan noted, adding that this would flatten the peak even more and derate the battery.  

“That puts people in a horrible position. They either have to build or buy something that provides perfect ELCC right now, or they can spend a lot of money to overbuild their capacity to make sure they have enough ELCC in 20 years, even though they don’t need it yet.”  

That could be thermal storage’s place to shine.  

“Our system allows the battery to grow with the grid,” Ganesan said. Fourth Power’s system converts electricity into heat that’s stored in carbon blocks before being turned back into electricity as needed.   

Instead of buying too little or too much capacity, Ganesan explained that Fourth Power “gives them an option that allows them to future-proof the battery’s capacity value,” which also helps utilities not threaten ratepayer dollars from over- or under-building. 

“Everytime you build a battery, someone is paying for it, and that someone is a ratepayer who’s likely struggling with bills,” Ganesan said. “The role of utilities needs to be to create the most efficient power mix possible that keeps energy affordable for ratepayers.” 

“You can’t just build more to solve your problems,” Ganesan added. “The check still gets cashed by someone, and the way out of that is to optimize and diversify your energy mix to include short-duration, long-duration and flexible energy storage technologies.”