The weakness of energy systems powered by the sun and the wind is their intermittency. Where will the energy come from when the sun isn’t shining and the wind isn’t blowing? Professor Jacobson addresses this in two ways, vastly increasing the nation’s peak hydroelectricity capacity and deploying energy storage at a vast scale. “To repower the world, we need to expand a lot of things to a large scale,” Professor Jacobson told me. “But there is no reason we can’t scale up.” Actually, there are reasons. The main energy storage technologies he proposes — hydrogen and heat stored in rocks buried underground — have never been put in place at anywhere near the scale required to power a nation, or even a large city. His system requires storing seven weeks’ worth of energy consumption. Today, the 10 biggest storage systems in the United States combined store some 43 minutes. Hydrogen production would have to be scaled up by a factor of 100,000 or more to meet the requirements in Professor Jacobson’s analysis, according to his critics.
Could the entire American economy run on renewable energy alone?
This may seem like an irrelevant question, given that both the White House and Congress are controlled by a party that rejects the scientific consensus about human-driven climate change. But the proposition that it could, long a dream of an environmental movement as wary of nuclear energy as it is of fossil fuels, has been gaining ground among policy makers committed to reducing the nation’s carbon footprint. Democrats in both the United States Senate and in the California Assembly have proposed legislation this year calling for a full transition to renewable energy sources.
They are relying on what looks like a watertight scholarly analysis to support their call: the work of a prominent energy systems engineer from Stanford University, Mark Z. Jacobson. With three co-authors, he published a widely heralded article two years ago asserting that it would be eminently feasible to power the American economy by midcentury almost entirely with energy from the wind, the sun and water. What’s more, it would be cheaper than running it on fossil fuels.
And yet the proposition is hardly as solid as Professor Jacobson asserts.
In a long-awaited article published this week in The Proceedings of the National Academy of Sciences – the same journal in which Professor Jacobson’s manifesto appeared – a group of 21 prominent scholars, including physicists and engineers, climate scientists and sociologists, took a fine comb to the Jacobson paper and dismantled its conclusions bit by bit.
“I had largely ignored the papers arguing that doing all with renewables was possible at negative costs because they struck me as obviously incorrect,” said David Victor of the University of California, San Diego, a co-author of the new critique of Professor Jacobson’s work. “But when policy makers started using this paper for scientific support, I thought, ‘this paper is dangerous.’”
The conclusion of the critique is damning: Professor Jacobson relied on “invalid modeling tools,” committed “modeling errors” and made “implausible and inadequately supported assumptions,” the scholars wrote. “Our paper is pretty devastating,” said Varun Sivaram from the Council on Foreign Relations, a co-author of the new critique.
The experts are not opposed to aggressive investments in renewable energy. But they argue, as does most of the scientific community represented on the Intergovernmental Panel on Climate Change, that other energy sources – atomic power, say, or natural gas coupled with technologies to remove carbon from the atmosphere – are likely to prove indispensable in the global effort to combat climate change. Ignoring them risks derailing the effort to combat climate change.
But with the stakes so high, the gloves are clearly off.
Professor Jacobson is punching back hard. In an article published in the same issue of the Proceedings and in a related blog post, he argues that his critics’ analysis “is riddled with errors and has no impact” on his conclusions.
In a conversation over the weekend, he accused his critics of being shills for the fossil fuel and nuclear industries, without the standing to review his work. “Their paper is really a dangerous paper,” he told me.
But on close examination, Professor Jacobson’s premise does seem a leap of faith.
Renewable sources provide only about a tenth of the United States’ energy consumption. Increasing the penetration of intermittent energy sources from the sun and the wind is already proving a challenge for the electricity grid in many parts of the world.
Professor Jacobson not only claims renewables’ share can be ramped up on the cheap to 100 percent within a few decades, but also that it can be done without bioenergy, which today contributes about half of the country’s renewable-energy production.
And yet under the microscope of the critics – led by Christopher Clack, chief executive of the grid modeling firm Vibrant Clean Energy and formerly with the National Oceanic and Atmospheric Administration and the University of Colorado, Boulder – his proposed system does not hold together.
The weakness of energy systems powered by the sun and the wind is their intermittency. Where will the energy come from when the sun isn’t shining and the wind isn’t blowing? Professor Jacobson addresses this in two ways, vastly increasing the nation’s peak hydroelectricity capacity and deploying energy storage at a vast scale.
“To repower the world, we need to expand a lot of things to a large scale,” Professor Jacobson told me. “But there is no reason we can’t scale up.”
Actually, there are reasons. The main energy storage technologies he proposes – hydrogen and heat stored in rocks buried underground – have never been put in place at anywhere near the scale required to power a nation, or even a large city.
His system requires storing seven weeks’ worth of energy consumption. Today, the 10 biggest storage systems in the United States combined store some 43 minutes. Hydrogen production would have to be scaled up by a factor of 100,000 or more to meet the requirements in Professor Jacobson’s analysis, according to his critics.
Professor Jacobson notes that Denmark has deployed a heating system similar to the one he proposes. But Denmark adapted an existing underground pipe infrastructure to transport the heat, whereas a system would have to be built from scratch in American cities.
A common thread to the Jacobson approach is how little regard it shows for the political, social and technical plausibility of what would undoubtedly be wrenching transformations across the economy.
He argues for the viability of hydrogen-fueled aviation by noting the existence of a hydrogen-powered four-seat jet. Jumping from that to assert that hydrogen can economically fuel the nation’s fleet within a few decades seems akin to arguing that because the United States sent a few astronauts to the moon we will all be able to move there soon.
He proposes building and deploying energy systems at a scale that has never been achieved and at a speed that nobody has ever tried. He assumes an implausibly low cost of capital. He asserts that most American industry will easily adjust its schedule to the availability of energy – unplugging when the wind and sun are down regardless of the needs of workers, suppliers, customers and other stakeholders.
And even after all this, the system fails unless it can obtain vast amounts of additional power from hydroelectricity as a backup at moments when other sources are weak: no less than 1,300 gigawatts. That is about 25 percent more power than is produced by all sources combined in the United States today, the equivalent of 600 Hoover Dams.
Building dams is hardly uncontroversial. So Professor Jacobson proposes adding this capacity with “zero increase in dam size, no annual increase in the use of water, no new land,” simply by adding a lot more turbines to existing dams. It is not obvious that so many of them can be added, however, or at what cost. Especially considering they would be unproductive 90 percent of the time and for use only as a backstop. What’s more, adding turbines does not increase the available energy at any given time unless there is more water pushing through them.
Ken Caldeira of the Carnegie Institution for Science, one of the lead authors of the critique, put it this way: The discharge rate needed from the nation’s dams to achieve the 1,300 gigawatts would be equivalent to about 100 times the flow of the Mississippi River. Even if this kind of push were available, it is not hard to imagine that people living downstream might object to the release of such vast amounts of water.
“The whole system falls apart because this is the very last thing that is used,” Professor Clack noted. “If you remove any of this, the model fails.”
It is critically important to bring this debate into the open. For too long, climate advocacy and policy has been inflected by a hope that the energy transformation before us can be achieved cheaply and virtuously – in harmony with nature. But the transformation is likely to be costly. And though sun, wind and water are likely to account for a much larger share of the nation’s energy supply, less palatable technologies are also likely to play a part.
Policy makers rushing to unplug existing nuclear reactors and embrace renewables note: Shuttering viable technological paths could send us down a cul-de-sac. And we might not be possible to correct course fast enough.
Correction: June 20, 2017
An earlier version of this column included an outdated affiliation for one scientist, Christopher Clack. He is now chief executive of the grid modeling firm Vibrant Clean Energy; he is no longer with the National Oceanic and Atmospheric Administration and the University of Colorado, Boulder.
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