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The Midcontinent Independent System Operator (MISO) is looking at adapting its existing tariff structure to accommodate several medium-term energy storage projects.MISO delivers an open access electricity transmission service and monitors high-voltage transmission throughout the Midwest and southern United States, as well as in Manitoba, Canada.

According to MISO officials, while its markets incorporate short-term storage reserves, there is growing interest in medium-term energy storage solutions.

The independent system operator’s storage repertoire also includes longer-term reserves such as pumped hydro.

However, the operator's tariff is only structured in a way that supports battery storage projects with the potential to supply energy for several hours.

According to Utility Dive, MISO officials said that they are seeing “increased interest in energy storage projects within the 15-state system, but so far have no place for them in the grid operator's tariff.”

Jennifer Richardson, MISO external affairs policy officer was reported saying: “We’ve had kind of fits and starts with this issue.

"But as far as having a clear policy, well, that’s never happened."

MISO principal advisor of market development and analysis, Yonghong Chen, added: “Medium-term storage is gaining a lot of interest. Storage is a broad range of emerging technology… it can be complicated."

Market interest in battery energy storage

According to RTO Insider, which originally published the story, the system operator said that it had been approached by “several market participants who are considering battery storage options for the future.”

In July 2015, Indianapolis Power & Light Company (IPL) invested in a 20MW advanced battery – with service expected to begin in June this year. It marks MISO’s first grid-scale energy storage array.

IPL, which is owned by AES, provider of advanced battery technology to the electric sector, is reported to have 116MW of energy storage projects in operation and 268MW in construction or late-stage development worldwide.

Kelly Huntington, IPL president and CEO, said: "Energy storage is a smart way to cost-effectively address a number of grid challenges including variability of energy supply and demand, while also improving the reliability of the grid.”