The falling cost of renewable energy and energy storage, combined with the flexibility of Direct Air Capture (DAC) as a “negative emissions” option for sucking carbon dioxide out of the atmosphere, could point to a major opportunity to drive down carbon pollution and get climate change under control, according to a new paper in the open-access journal Earth’s Future.
Both sets of technologies “have challenges to overcome. Shifting away from fossil fuels and towards renewable electricity requires accommodating the variable nature of, for example, wind and solar power. Negative emissions techniques, meanwhile, face challenges of cost, scale, and acceptability before being ramped up,” write report authors Jan Wohland, Dr. Dirk Witthaut, and Dr. Carl-Friedrich Schleussner, in a guest post for Carbon Brief. “But what if the dual challenges facing renewables and negative emissions could be tackled together?
Based on their paper, it turns out that “there is considerable potential for combining a renewables-reliant electricity system with DAC.”
The three authors open their narrative with the dramatic rise of renewable generation over the last two decades: onshore wind is now the cheapest form of electricity in many locations, the plummeting cost of photovoltaic solar has taken energy modelers by surprise, and options like energy storage and integrated grids are helping to address the intermittency of renewable power sources.
All of those factors can help bring down the cost of negative emissions options that were previously considered too expensive to warrant serious consideration.
While DAC is still seen as a niche technology, the authors point to a key characteristic that could bring it closer to prime time if it’s combined with renewables.
“Put simply, you can switch on DAC whenever renewable generation is high and leave it off at other times,” making it “more cost-effective by using excess wind or solar power during periods of high supply, low demand, and low prices,” they write. “On top of that, DAC could be deployed in a decentralized fashion, which can help alleviate local grid congestion.”
To assess the potential, Wohland, Witthaut and Schleussner modeled a “net-neutral” European grid where any carbon dioxide emissions were offset by Direct Air Capture. They hit the target “with a renewable penetration of just above 100% and at least 30 gigawatts (GW) of DAC,” they write. The threshold of just above 100% was essential, they add, since that’s the point where excess power would either be wasted, or allocated to DAC at reasonable cost.
“We also find that storage technologies and DAC are not competing, but complementary,” they state. “Increases in storage size allow for reductions of remaining carbon emissions and enable more efficient use of DAC.”
In their modeling, the authors tested a range of scenarios for DAC, from 30 to 300 gigawatts. At all levels, they found that electricity grids still produced net emissions if they limited their reliance on renewables, but reached the net-neutral goal with higher renewable penetration.
“There are still many uncertainties to consider, perhaps most importantly, whether or not the approach we have laid out is economically practicable,” the authors acknowledge. Even with affordable electricity, DAC capital costs would have to fall—or carbon prices would have to increase—at least tenfold. But “it is possible both conditions could be met as the technology is scaled up and global efforts to mitigate climate change become more tangible.”
While DAC is “clearly not a silver bullet for carbon dioxide removal,” they conclude, “it does come with system-friendly features. And given the need for negative emissions, the concerns about land-based options, and the rapid technological and cost evolution of renewables, our first results indicate that it might be worth a closer look.”