2021 was a big year for energy-related news, what with the ongoing hunt for new forms of energy storage and cleaner if not carbon-free electricity and events and research that spotlighted the weak links in our power grid. As the pandemic continued to grind on, it was actually comforting to know that smart people in the energy sector were working hard to keep the lights on, advance the technology, and improve people’s lives. IEEE Spectrum did its best to cover those developments, and these were the stories that our readers liked best.

Gravity Energy Storage Will Show Its Potential in 2021

Why was this Spectrum’s most popular energy story of the year? Well, let’s think. As power grids everywhere increasingly rely on intermittent renewable energy, batteries and other forms of energy storage that can even out the bumps in supply and demand are taking on a crucial role. No battery is perfect, however, so engineers keep pushing for new and improved ways to store those electrons. The gravity batteries described in this story lift giant weights in the air or up mine shafts to store excess electricity, releasing the weights later on to recover the stored energy. One of the companies featured in the story, Gravitricity, completed its 250-kilowatt gravity-battery demonstrator in Edinburgh last April and is now working on a full-scale deployment at a mine in the Czech Republic.

Lithium-Ion Battery Recycling Finally Takes Off in North America and Europe

Battery makers around the world are cranking out lithium-ion batteries of various flavors as fast as they can. While lithium isn’t exactly in short supply, extracting it from the ground exacts a huge environmental cost. Thus the recent boom in battery recycling—and readers’ interest in this story on how the industry is expanding beyond China and South Korea and into the United States, Canada, and Western Europe. Last May, one of the story’s featured startups, Canada’s Li-Cycle, announced it would begin recycling the manufacturing scrap from Ultium Cell’s US $2.3 billion EV battery plant—that’s GM’s and LG Chem’s new mega-gigafactory in Lordstown, Ohio.

Here’s How We Could Brighten Clouds to Cool the Earth

Geoengineering—altering the planet to mitigate the worst effects of climate change—is an idea that has taken on new currency of late. As global temperatures rise, greenhouse gases accumulate, and all signs point to Really Bad Things happening in the coming decades, Spectrum readers are clearly looking for a way out of our current climate predicament. This article, by researchers at the Palo Alto Research Center (PARC) and the University of Washington, is one possible answer. The basic idea is to add particles of sea salt to the atmosphere to brighten clouds and cool the planet. We’ll still have to do the hard work of cutting carbon emissions, but geoengineering could be a way to buy us some time.

Solar-to-Hydrogen Tech Sees “Remarkable” Efficiency Jump

Another big development in the energy sector is the return of the hydrogen economy. This time around, though, the emphasis is on “green hydrogen”—that is, hydrogen produced using clean energy such as solar or wind power. Most of the world’s hydrogen comes from deeply polluting methods. And most green hydrogen production still relies on electrolyzers, which themselves consume lots of electricity. This story looks at promising research out of Japan’s Shinshu University on light-absorbing materials to split water into hydrogen and oxygen directly—cutting the electrolyzer out of the equation. As the story notes, it will take quite a bit more R&D until this method is “ready for prime-time hydrogen production.”

China Says It’s Closing in on Thorium Nuclear Reactor

Also getting a second look: nuclear power! While some recent efforts call for radical new reactor designs, this report highlights an old approach with a modern spin. Molten salt nuclear reactors fueled by thorium were first investigated at Oak Ridge National Laboratory in the 1950s. A new molten salt reactor reportedly being built by China follows the Oak Ridge design but also incorporates the same kind of high-temperature salt pumps used in concentrated solar-power plants.

What the Texas-Freeze Fiasco Tells Us About the Future of the Grid

In this clear-eyed consideration of last winter’s deadly deep freeze in Texas, Robert Hebner, director of the Center for Electromechanics at the University of Texas at Austin, describes the converging factors and troubled history that contributed to the catastrophic blackout. “It seems pretty clear that what happened in Texas was likely preventable with readily accessible and longstanding engineering practices,” Hebner concludes. “But a collective, and likely implicit, judgment was made that the risk to be mitigated was so small that mitigation would not be worth the cost. And nature ‘messed’ with that judgment.”

One Atmospheric Nuclear Explosion Could Take Out the Power Grid

Another popular story in the “things that are bad for the power grid” category was this piece by national security writer Natasha Bajema. She looked at a recent study out of the U.S. Geological Survey and the University of Colorado on the likely effects of detonating a several-kiloton nuclear weapon in the atmosphere and generating a high-altitude electromagnetic pulse (EMP). (To be fair, Foreign Policy, in a similar 2020 examination, rated the EMP problem as very much outsized and “the last thing you need to worry about in a nuclear explosion.”) The conductivity of the Earth, the Geological Survey scientists discovered, plays an important role in the outcome, with low-conductivity regions most at risk of suffering a “grid-crippling power surge,” as the electric field travels out through high-voltage power lines. Here’s hoping that doesn’t happen in 2022, or any other year.

Off-Grid Solar’s Killer App

Spectrum contributing editor Peter Fairley traveled to Kenya to report on a boom in agriculture driven by off-grid solar power and efficient solar-powered irrigation pumps. The pumps tap into vast stores of groundwater that lie not too far underground and cover much of sub-Saharan Africa. Solar-irrigation technology, combined with microlending payment plans, lets small farmers boost crop yields, lengthen growing seasons, and neutralize the effects of drought. It’s a win-win-win for a part of the world that could really use a victory right now.

How Much Energy Does It Take to Grow a Tomato?

Lastly but never leastly, Spectrum columnist and deep thinker Vaclav Smil contemplated the energy footprint of the tomato. Field tomatoes, unsurprisingly, are the least energy-intensive to produce, while raising hydroponic tomatoes grown in greenhouses can consume 60 times as much energy. Food for thought as we close out 2021.

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