Study unveils secrets of long-duration storage

About 30% of energy storage procurement decision makers interviewed for the ESS study Beyond Four Hours said long-duration storage was “very important” for their business already. Image: ESS.

About 30% of storage procurement decision makers interviewed for the ESS study Beyond Four Hours said long-duration storage was “very important” for their business already. Image: ESS.

By Jason Deign

More than half of upcoming energy storage projects could require assets with a discharge duration of around four hours or more, according to new research.

About 30% of energy storage procurement decision makers interviewed for the ESS study Beyond Four Hours said long-duration storage was “very important” for their business already.

Another 30% said they were currently considering long-duration storage projects, 20% said it would be important in future and 10% considered it as part of a broader portfolio. Only 10% said it was not applicable to their business.

The research, carried out among energy storage procurers and project developers in association with Energy Storage Report, revealed a wide range of definitions for what constitutes a ‘long-duration’ asset.

But six out of 10 respondents claimed a requirement of more than four hours, which is generally considered beyond the cost-effective range of lithium-ion batteries commonly used for shorter-duration electricity storage. 

Potential long-duration storage contenders

This points to an upcoming battle for supremacy among potential long-duration storage (LDS) technology contenders, as currently there is no established leader in this field.

Study respondents cited a number of very different technologies, including thermal, cryogenic, liquid air and compressed air energy storage, as being of interest for long-duration applications.

However, said the study, for electrical storage “flow battery systems are undoubtedly the technology most would consider using for LDS deployments at the moment.”

For long-duration discharge times, flow batteries can offer a better levelised cost of energy than lithium-ion chemistries because of the number of megawatt hours and frequent cycling required, notes the research.

“A flow battery does not fade [in capacity or efficiency] with frequent cycling and over time, so it offers a highly competitive price per MWh in four-hour-plus applications,” it says. 

Advantages of the technology

Other advantages of the technology include low operations and maintenance costs and fast response times, allowing a single battery to be used for energy and power applications.

Also, flow battery variants that do not use exotic or toxic materials, such as the all-iron chemistry commercialised by ESS, have the potential for very significant long-term cost reduction and are environmentally benign, says the report.

Ultimately, cost reduction could be a crucial factor in deciding long-duration storage winners since, as with short-duration applications, economics are the most important deciding factor for project owners and developers.

With long-duration storage, capital cost emerged as the most important single procurement criterion. “This is understandable since availability of capital can be a limiting factor for energy storage projects,” the report notes.

Alongside capital cost, energy storage procurers valued the financial strength of the vendor. Other criteria that were found to have significant impacts on decision making included:

  • The safety of the technology.
  • The levelised cost of storage in specific applications.
  • An asset’s ability to be used flexibly and to provide short-duration storage.
  • Its energy density or footprint.
  • Its loss of capacity or power over the project’s life. 

Keen to evaluate long-duration storage

Overall, survey respondents seemed keen to evaluate long-duration storage on a range of measures.

“A critical question when evaluating any storage technology is not just ‘how much does it cost?’ but also ‘what value can it deliver?’” said one.

The research comes amid growing interest in new storage applications that extend beyond the classic short-term ancillary services use cases that have proved most profitable for grid-scale battery systems until now.

As the study points out, island communities, mining operations and community-scale micro-grids are increasingly looking to self-consume renewable energy on an almost continuous basis.

In most cases this can only be achieved with long-duration storage or a complex combination of intermittent renewables with non-intermittent sources such as mini-hydro or biogas. 

Requirement likely to grow

Furthermore, the requirement for long-duration storage is likely to grow in established energy markets as the penetration of intermittent renewable generation grows.

Bloomberg New Energy Finance’s Global Energy Storage Forecast, 2016-24, for example, predicts that by 2024 renewable energy will have reached 29% grid penetration in Germany to 39% in California.

Writing in the Foreword to the report, Michael Niggli, current ESS board member and former president and chief operating officer of San Diego Gas & Electric, says: “We’re still just scratching the surface.

“Our battery arrays today can help us for seconds, minutes, maybe a couple of hours. But what will happen as our renewable penetration grows and our fossil-fuel plants close down?

“The current duration levels of storage will no longer do. That is why I think we need to start looking at the next frontier for electricity storage: that which can take us to at least four hours and beyond.”

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