If there is any vision of reaching very high levels of renewable energy that has captured the public imagination, it is the work of Stanford Professor Mark Z. Jacobson. Jacobson and his team’s 2015 work on the technical and economic feasibility of moving the United States to 100% renewable energy was a watershed moment for clean energy advocates, as one of the first times that a vision was presented for moving the nation’s entire energy supply – electricity, transit, heat and industry – to 100% renewable energy.
And while this work has been widely promoted and cited, the assumption that we can reach this level of renewable energy deployment in a cost-effective manner may simply be too good to be true.
In the latest edition of the Proceedings of the National Academy of Sciences (PNAS), 21 leading scientists have issued a rebuttal to Jacobson’s work, finding that a policy proscription that overpromises on the benefits of relying on a narrower portfolio of technology options could be counterproductive, seriously impeding the move to a cost-effective decarbonized energy system”.
Evaluation of a proposal for reliable low-cost grid power with 100% wind, water and solar is not the work of a fossil fuel or nuclear front-group, either. The paper’s 21 authors include U.C. Berkeley’s Daniel Kammen, who has done some very significant work on renewable energy, as well as climate scientist Ken Caldeira, under lead author Christopher T.M. Clack of the National Oceanic and Atmospheric Administration (NOAA).
These authors cite a number of problems with Jacobson’s work, stating that the analysis involves “errors, inappropriate methods, and implausible assumptions”. Specifically, the paper notes that while Jacobson may have demonstrated theoretical feasibility, that “it is important to understand the distinction between physical possibility and the feasibility in the real world.”
A primary issue is Jacobson’s limitation of scope, in attempting to model a system with only wind, water and solar (including some geothermal, tidal and wave energy), Jacobson excluded a large number of technologies, including grid-scale battery storage, which the authors argue make “climate mitigation more difficult and expensive than it needs to be”.
It is important to note here that other studies, including those by the U.S. Department of Energy’s National Renewable Energy Laboratories (NREL) and Climate Policy Initiative include electric vehicle charging and/or grid-scale battery storage as a central feature of scenarios to reach high levels of renewable energy.
This failure to look at previous studies is another concern of Evaluation. “Their study does not provide credible evidence for rejecting the conclusions of previous analyses that point to the benefits of considering a broad portfolio of energy system options,” stated the paper.
But the paper also looks at specific technical concerns, and argue that Jacboson has failed to model both hydroelectric capacity expansions, transmission expansions, and assume the “free time-shifting of loads at large scale in response to variable energy provision”. In general, the authors found that Jacobson’s paper failed to model transmission, reserve margins and frequency response, but still claimed reliability.
However, there are also curious statements in Evaluation regarding the roles of other technologies. The article in PNAS notes that Jacobson excludes nuclear, biomass and other technologies, however the limited ability of nuclear power plants to ramp makes existing nuclear technologies fundamentally incompatible with high wind and solar scenarios.
In general, both Jacobson’s study and the PNAS article critiquing it are receiving a large amount of press. In the ensuing debate over whether or not it is possible and desirable to reach 100% renewable energy, other studies, such as the recent report by Climate Policy Initiative which modeled penetrations up to 70% wind and solar with other renewables, large amounts of battery storage and considerable natural gas backup, are overlooked.
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Why should ( existing ) nuclear be required to ramp so as to support intermittent VRE ? One could conversely criticise VRE for not being dispatchable .
Surely the challenge is minimising emissions at the lowest overall cost while maintaining system reliability ?
VRE is not dispatchable; instead it is cheap (and getting cheaper all the time), quick to deploy, and does not carry the risks or produce the waste that nuclear does. Therefore, there has been no real contest in the market as to which solution we will deploy. Thus, other parts of the power system will have to ramp to accommodate what Michael Liebreich calls “base-cost” renewables.