Iron-Air Energy Storage Finishes What Natural Gas Started

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The Intertubes lit up last week after Phase 1 of the massive Sherco solar power plant in Minnesota officially went online, partially replacing the capacity of the nearby Sherco coal power plant. Somewhat lost in all the excitement is a an iron-air energy storage system to be co-located with the solar array. Though it weighs in at only 10 megawatts, the pilot-scale system will unlock the full 24/7 potential of solar power, leapfrogging over coal to threaten natural gas as well.

Energy Storage Finishes The Job

Before we get to the Sherco coal-to-solar project, let’s take a quick look at the role of natural gas in the demise of coal power. The renewables-friendly administration of former President Obama is credited with killing off coal jobs, but natural gas beat them to the punch. A fresh torrent of domestically produced natural gas entered the market as the Bush presidency drew to an end, and gas began pushing coal out of the power generation sector by the time Obama took office in 2009.

In 2020 the US Energy Administration took stock of the situation and determined that natural gas replaced the vast majority of the 121 coal power plants that closed during an 8-year period beginning in 2011 and ending in 2019, well into the first Trump administration.

Judging from his 2019 State of the Union speech, Trump had already given up on the idea of saving all your coal jobs as a losing proposition, and the numbers back him up. The EIA counts 103 coal-to-gas conversions or replacements from 2011 to 2019. Of that figure, 86 involved boiler-only conversions and and 17 increased their capacity by upgrading to combined cycle technology.

“The decision for plants to switch from coal to natural gas was driven by stricter emission standards, low natural gas prices, and more efficient new natural gas turbine technology,” the EIA concluded.

For wind and solar, the missing piece of the puzzle was energy storage. Arrays of lithium-ion batteries enable grid managers to sock away spare kilowatts during off-peak demand hours and deploy them as needed. With a typical duration of 4-6 hours (or more, in some cases), Li-ion technology provides enough energy storage to handle daily demand cycles and the occasional brief emergency. That can reduce if not eliminate the construction of new gas “peaker” plants to meet local spikes in demand.

More Energy Storage, Less Natural Gas

In spite of their relatively short duration, lithium-ion energy storage systems are already putting the squeeze on natural gas.

At the beginning of this year, EIA projected that planned gas capacity additions for 2024 would top out at just 2.5 gigawatts, the lowest such figure in 25 years.

Those 2.5 gigawatts are a drop in the bucket compared to the total added capacity figure for all utility scale energy projects, which EIA projected at 62.8 gigawatts. “This addition would be 55% more added capacity than the 40.4 GW added in 2023 (the most since 2003) and points to a continued rise in industry activity,” EIA noted.

It remains to be seen if the EIA forecast pans out by the end of this year. If it does, solar will take the lion’s share of the credit for added capacity at 36.4 GW or 58%, with battery-type energy storage following at 14.3 GW or 23%.

“We expect a record addition of utility-scale solar in 2024 if the scheduled 36.4 GW are added to the grid. This growth would almost double last year’s 18.4 GW increase, which was itself a record for annual utility-scale solar installation in the United States,” EIA enthused.

Wind additions have slowed over the past two years but EIA projects the industry will also chip 8.2 GW into the capacity addition pool.

The Long Duration Difference

All else being equal, energy storage supports the case for introducing more wind and solar into the grid, more quickly. The problem is that all else is not equal. As of last year the US grid was still 60% dependent on fossil energy, while demand is going through a growth spurt fueled by data centers among other factors. Renewable energy needs to scale up, and that will require new energy storage systems that store more energy for longer periods of time.

The rule of thumb for the US Department of Energy is 10 hours of storage at minimum, towards a goal of 100 hours or more. As explained by the agency’s Pacific Northwest National Laboratory, long duration energy storage systems are ” large energy storage installations that can store renewable energy until needed and can provide a much-needed solution for a reliable and decarbonized grid.”

Currently, pumped storage hydropower is the only widely used technology to meet the 10-hour mark, a position it has held since first introduced about 100 years ago.

Long Duration Energy Storage For A Gigantic Solar Power Plant

The Energy Department has been supporting the efforts of private sector innovators to help diversify and expand the long duration field. Among that group is the Massachusetts startup Form Energy, which has been organizing a commercial-scale manufacturing facility for its iron-air technology at the site of a former steel plant in West Virginia, on the Ohio River.

Iron-air batteries generate electricity when iron is exposed to oxygen and begins to rust. When the battery recharges, the rust re-forms into metal and the discharge process can begin again.

Xcel expect the iron-air batteries to store enough energy to last for 100 hours, or more than four days.”The multi-day energy storage systems will strengthen the grid against normal day-to-day, week-to-week, and season-to-season weather variability, as well as to extreme weather events such as severe winter storms and polar vortex events,” Xcel explains.

That’s a perfect fit for mega-scale renewable energy projects like the new Sherco solar power plant.

Phase 1 went into operation last month and was officially marked with a ribbon-cutting ceremony on November 19. Its capacity tops 220 megawatts, replacing the capacity of one unit at the Sherco coal plant. If all goes according to plan, two more construction phases will bring the capacity of the solar array to 710 megawatts by 2026, making it the biggest solar power plant in the US to date. In the meantime, the coal plant is retiring in phases and will be out of the picture by 2030.

Adding to the scale of the Sherco project is Xcel’s proposed Minnesota Energy Connection, a new 4,000 megawatt  transmission line that will leverage the Sherco facility to bring more renewable energy to the Upper Midwest grid.

Form Energy’s iron-air battery will certainly have plenty of work to do once it begins operating sometime before the end of 2026. If the 10-megawatt trial meets expectations, Form will have plenty more where that came from. The company expects to produce 500 megawatts’ worth of its iron-air batteries per year at its West Virginia facility.

Xcel is also trialing the iron-air solution at another retiring coal power plant, the Comanche Generating Station in Colorado, so stay tuned for more on that.

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Image (cropped): Biggest solar power plant in the US to showcase new coal-killing long duration iron-air energy storage technology (courtesy of Xcel Energy).