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Energy Storage, Dynamic Line Ratings Yield More Efficient Grid

Energy storage and dynamic line ratings are among the evolving technologies poised to have a positive effect of the Texas electrical grid, panelists at TransmissionHub’s TransForum Texas in San Antonio said on Jan. 30.

Panel members said many of those technologies, particularly storage technologies, are in their infancy and not yet being broadly accepted.

“We’re kind of where personal computing was in the ‘80s and cell phones were in the early ‘90s,” Robert King, president and founder of the Texas Energy Storage Alliance, said. “I think storage is at that same awkward age. Utility operators don’t know how much they need storage because they haven’t had an opportunity to use it.”

While thermal storage and flywheels were mentioned briefly during the discussion, most of the talk centered on the most popular form of energy storage, which at present is battery storage. The largest battery storage facility in the United States is the 36-MW battery operated by Duke Energy (NYSE:DUK) at its 153-MW Notrees wind project in West Texas, which panel member Becky Diffen, an attorney with the law firm Vinson & Elkins, had a part in developing.

Diffen noted that batteries can help manage the variability of wind generation but, while other storage technologies can be employed to shift the time energy is used, battery storage is rarely used for that purpose. The greatest value battery storage provides is that of ancillary services, including frequency regulation, voltage support, and non-spinning reserves, she said.

King acknowledged that other technologies were better suited than batteries for providing certain benefits. Thermal energy storage, which relies on sodium to store heat during the day and uses that heat for energy generation after the sun goes down, was better suited than battery storage for shifting time of energy use.

Each evolving form of technology has its own set of challenges, panel members agreed. Chief among them is quantifying the benefits of each type of technology. Coupled with the high price of many storage technologies, the difficulty of quantifying benefits makes storage a difficult sell, though King said it can be done.

“For storage to make economic sense, you have to find ways to stack the benefits together and to monetize multiple benefits from a given battery project to make the economics of it work,” he said.

One method of obtaining a synergy of benefits is to pair a battery with a generation asset. Such a pairing would improve the value of the generation asset and simultaneously leverage the value of the storage device, he said.

“A generator that takes 30 minutes or an hour to come up to full power could team up with a battery that could come on instantaneously, and sell much more ancillary services while the power plant [ramps] up,” King said.

Other challenges include the technical and legal challenges of incorporating storage onto the grid, then dealing with the operational changes that storage system creates.

“If you just have a wind farm, it’s either generating or it’s not, and power is either going onto the grid or it’s not,” Diffen said. With a battery in place, power from the wind farm could be flowing to the battery, the grid, or both, while the battery could either be supplying power to the grid or taking power from it.

The variety of power flows presents challenges for measuring and metering as well as the challenge of aligning the revenues from the various flows, she said.

Another challenge is actually getting storage devices deployed and connected to the grid. One panel member said there are numerous companies that manufacture storage, but very few that are developing storage projects.

“There’s lots of battery companies just hoping that someone will come along and buy their storage and figure out how to integrate it into a project,” King said. “Everybody is talking about it, but there are actually very few companies out there who are competent and capable of doing the front-end development work.”

King said the state of storage development today reminded him of wind power in the 1990s, “where there was a handful of people trying to put land [deals] together with [power purchase agreements].” As with wind in its early days, he sees the state of storage development today as a “real area of opportunity.”

In King’s opinion, the greatest potential for energy storage development rests with private sector developers rather than with utilities.

“Utilities are not the most innovating companies out there,” he said. “They generally like to [adopt a technology] after it’s been proved up, for a lot of reasons which are very good. They’re risk-averse.”

However difficult to measure at present, King believes the benefits will justify both the effort and the development costs. As an example, he pointed to the ability to use large-scale storage batteries as a sort of “[uninterruptible power supply] on steroids” for industrial applications.

“If [a battery] could carry a factory in Texas for 10 minutes, it would allow [that] factory to participate in responsive reserve, which pays about $120,000 per megawatt-year, as opposed to emergency response service, a different demand response program … that only pays about $50,000” per megawatt-year, King said. Such an arrangement would more than double the payment a customer could get, shortening the potential payback time for the battery. 

Getting More Out of Transmission

While energy storage can help smooth the flow of power along the transmission system, another evolving innovation discussed was dynamic line ratings, which can increase the capacity of those transmission lines.

Although static rating is the common utility practice, rating transmission lines dynamically to account for the effects of changing environmental conditions is not new. Idaho Power investigated dynamic line rating as early as 1984, according to Jake Gentle, an electrical engineer with Idaho National Laboratories. However, the state of the support infrastructure kept the approach on the back burner until advances associated with the development of wind farms facilitated a renewed interest in the practice.

“The big change was [that the cost of] wireless communication came down,” Gentle said. “The cost came down for weather station monitoring mostly due to the wind farm development and the need for [associated] data.”

Access to wind and temperature data is crucial to the development of a dynamic rating for a given transmission line, he said.

“What we’re doing is taking that static rating and increasing its accuracy by monitoring a lot of those variables like wind speed, wind direction, ambient air temperature and solar radiance to then feed those calculations that determine the static line ratings in near-real time,” he said. “We’re typically seeing between 10 percent and 30 percent [increase in line rating] conservatively.”

That additional capacity brings with it numerous benefits, he said.

“Due to the concurrent cooling effect, you may be able to undersize the connection from your wind farm to your next tie-in.” he said. “You may be able to save a little bit of cost on the project by modifying that conductor size or the circuits it has to be fed through.”

Side benefits of dynamic line ratings could include fewer transmission lines and therefore less environmental impact, according to the panel’s moderator, Carey King, assistant director of the energy institute at the University of Texas at Austin.

Finally, panel members acknowledged the challenges of funding such projects.

Significant revenue streams are critical to getting large storage projects built, “which is one of the reasons you don’t see developers doing it,” Diffen said.

In addition to assurances of long-term revenue, lenders are concerned about the emerging nature of storage applications and are hesitant to lend for unproven technology, she added.

Government funding has occasionally played a role. For example, the Notrees project was supported by a $20m grant from the U.S. Department of Energy, which paid for 50 percent of the project, according to Diffen.

Other sources of government funding could proven beneficial, she said, noting that other forms of renewable energy qualify for federal tax credits. However, most storage projects do not currently qualify for federal tax credits. If that were to change, Diffen said, “that could really help get things off the ground in the same way that tax credits have helped get wind and solar off the ground.”

Idaho Power is a subsidiary of IDACORP (NYSE:IDA).

The next TransForum, TransForum West, will take place in San Diego May 6 & 7. Click here for more details.

This article was originally published on TransmissionHub and was republished with permission.

Lead image: Wind turbines and transmission via Shutterstock

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