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Broad range of technologies could firm up wind and solar generation in net zero carbon dioxide emission electricity systems

Alicia Wongel and Ken Caldeira · Findings · 2023

Key finding. Letting many firming technologies compete in a stylized net-zero electricity system and then sequentially removing the most valuable one at each step shows that reliable wind-and-solar systems do not depend on the feasibility of any particular firming technology.

A stacked bar chart of system cost in euros per megawatt-hour of met demand, from 0 to 300, with about thirty bars along the horizontal axis. Each bar is labelled with the firm technology whose removal increases total cost the most at that step, starting with hydro and BECCS and running through storage technologies and demand management to a final bar for a system with only solar and wind. Cost rises gently across most of the sequence and then climbs steeply in the last few bars.
Each bar removes the technology that was most valuable in the previous one. Cost rises only gradually as one option after another is taken away — the optimizer keeps finding substitutes — and jumps sharply only at the far right, where nothing is left but wind and solar. Figure 2 from Wongel and Caldeira (2023), Findings. Reproduced under CC BY-SA 4.0. Extracted from the published PDF and resized for web display.

What question did this research address?

Wind and solar need something to cover the hours they cannot. The candidates are numerous — dispatchable generators, storage of several kinds, atmospheric carbon dioxide removal, demand management — and because there are so many, studies usually assess one or a small handful at a time.

That leaves an unanswered question of a different shape: not which firming technology is best, but whether the whole approach depends on any single one of them being available.

What did we find?

Firming technologies are defined broadly as anything that makes electricity available when wind and solar generation falls short of demand — dispatchable generation, storage, carbon dioxide removal, and demand management all qualify.

Rather than compare candidates head to head, the method builds a least-cost system, removes whichever firming technology proved most valuable, re-optimizes, and repeats.

Systems remain reliable through that sequence. When the best option is taken away, the optimizer substitutes others, and the result is a system that still meets demand.

The conclusion is therefore about the class rather than the members: the availability of *some* firming capability matters, but the identity of the winner does not.

Why does it matter?

It shifts what a bet on wind and solar depends on. If reliability required one specific technology — long-duration storage, say, or direct air capture — then that technology failing would sink the whole approach. It does not.

That is a useful counterweight to the common argument that a wind-and-solar system is hostage to an unproven storage breakthrough. Many roads lead to a firm system, and the optimizer will take whichever is open.

It also reframes research strategy. Because no single firming technology is indispensable, spreading effort across several is more robust than concentrating it on the current favourite — the same portfolio logic that the cost-uncertainty work reaches from a different direction.

Citation

Alicia Wongel and Ken Caldeira (2023). Broad range of technologies could firm up wind and solar generation in net zero carbon dioxide emission electricity systems. Findings.

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