Energy storage goes generation-agnostic: In the Caribbean and California, storage + natural gas ups efficiency and resilience

Electric system resilience is a bit like climate change. Our warming planet didn’t cause this year’s catastrophic hurricanes in the Caribbean — Irma and Maria — but it may have intensified them and the damage they left behind on island after island in the region.

Similarly, said Brian Perusse of AES Energy Storage, no one measure or technology alone could have kept electric grids in the region running during the storms. For example, 20 megawatts (MW) of storage the company installed earlier this year in the Dominican Republic helped but were not the only reason the island’s grid was able to ride out some outages and wild frequency fluctuations caused by the storms.

“In a complex system, it’s a combination of things that happened,” said Perusse, who is the company’s Vice President of Global Marketing Strategy. “It’s hard to point to a specific asset (and say) if not for that plant, we would have had a blackout.”

Rather, he said, the storage — two 10-MW installations, each located next to natural gas-fired plants — provided fast, accurate response to frequency fluctuations. As a result, the two plants were able to keep running at a time when about 40 percent of the island’s generation capacity had been taken offline due to the storm.

Because of the storage, ““there was a bigger punch,” Perusse said. “These plants were working three times as hard as normal to help keep the Dominican grid operating.”

Almost a month after Maria, with major portions of Puerto Rico and the U.S. Virgin Islands still without power, electric power sector  discussions about how best to help have often centered on the potential of solar plus storage to provide both emergency electricity and longer-term grid resilience. But AES’s experience in the Dominican Republic suggests an even wider range of options, such as using storage to improve the efficiency and resilience of existing, traditional generation.

In a blog on the AES website, Praveen Kathpal, the company’s Vice President for Market Development, argues that “the best and most cost-effective way to achieve resilience for entire communities is through development of unbreakable grids, ones that are impervious to disruptions in the first place and ‘self-healing.’”

Resilience, he says, should encompass a mix of technologies and strategies, from microgrids, and underground power lines, to storage support for larger plants.

“Energy storage provides a buffer between supply and demand that enables electric systems to rebalance during and after a disturbance,” Kathpal writes.

Nick Esch, Senior Research Associate for the Smart Electric Power Alliance (SEPA), sees the co-location of storage with traditional generation, such as peaker or other natural gas plants, as an emerging trend that could have a big impact on the power sector.

SEPA’s 2017 Energy Storage Market Snapshot notes that Imperial Irrigation District, a public power utility in Southern California, is using a 30-MW battery to provide frequency response and blackstart capabilities for one of its major gas plants.

AES has a number of utility-scale projects, including a power purchase agreement with Southern California Edison for the repowering of SCE’s 1,284-MW gas-fired plant, which will include 100 MW of storage.

Energy storage, he said, “can act like car suspension; it allows the power plant to keep generating at a steady, even rate, which can be a lot more efficient financially. And when the battery is not doing that, it can be used for something else — maybe providing backup generation. It’s not required that batteries serve just one purpose.”

That versatility, he said, could drive further growth in the U.S. energy storage market, while accelerating the integration of storage on the grid.

Storage goes where the value is

The Dominican Republic is located just 237 miles northwest of Puerto Rico. But that distance and other differences between the two islands were critical in the extent of damage Irma and Maria inflicted on their respective electric systems — and their ability to recover after the storms.

For example, while Maria hit Puerto Rico full on as a very strong Category 4 hurricane — virtually destroying the island’s electric system —  it had slowed to a Category 3 by the time it sideswiped a portion of the Dominican Republic. Both islands experienced heavy rain, winds and power outages during Irma. In the Dominican Republic, that storm left 700,000 people without power, said Manuel San Pablo, Regulatory Director of AES Dominica, an AES subsidiary and independent power producer on the island.

In a recent case study, AES documented how its two 10-MW storage units — each located at an AES Dominica natural gas plant — played a part in keeping the lights on for many customers during Irma. With 40 percent of normal generation capacity offline and many distribution lines down, the resulting frequency fluctuations could have triggered blackouts.

Instead, the storage units provided split-second response to those fluctuations — across a much wider range of frequency values — keeping the system in balance, and the available power plants in operation. The speed of response was essential, since natural gas plants generally have slower ramping times — 5-10 minutes.

The Dominican Republic is one of a growing number of examples of the versatility storage can bring to the grid across different types of generation — traditional or renewable, centralized or distributed. Roy Torbert, a principal with the Rocky Mountain Institute and Carbon War Room’s Islands Energy Program, sees it as an essential part of almost any scenario being discussed for rebuilding energy systems in the Caribbean or for grid modernization on other islands.

The use of storage in the Dominican Republic is, he said, “not at all outside the norm of what a lot of islands are going to be considering.”

While both the Dominican Republic and Puerto Rico have natural gas plants, he said, “the rest of the Caribbean is smaller; the vast majority of countries are running on diesel. However, energy storage works well with natural gas or diesel. With an island grid that is fragile, energy storage provides a whole suite of value. It will let you operate more efficiently. It makes the grid more reliable.”

With prices going down and the technology becoming better understood, Torbert sees a virtuous cycle for storage on all grids.

Perusse agrees: “Energy storage starts in areas where value can be created or increased right away, including advantages from frequency response or variable generation management. Quickly thereafter, storage benefits migrate into longer term – to the two-to-six-hour range – helping with overall efficiency.”

“It’s fascinating where you’ll see it,” he said. “I think of it like a transformer. It will be embedded across the network; it will be everywhere.”