The Sustainable Development Solutions Network (SDSN) launched the SDSN USA network in December 2018 to mobilize academic institutions throughout the country to work towards the U.N. sustainable development goals.
Yesterday, SDSN USA launched the Zero Carbon Action Plan (ZCAP), building upon the success of the Deep Decarbonization Pathways Project. Evolved Energy Research partnered in this effort by creating a set of economy-wide transition strategies that would allow the U.S. to reach carbon neutrality by 2050 and that are robust against a wide range of uncertainties. Using these modeling results, nearly 100 researchers within the SDSN network dove deeper into sector-specific analysis and ultimately created a set of policy recommendations for federal, state, and local government.
The report can be downloaded on the ZCAP website.
The modeling work underpinning ZCAP has been submitted for academic publication and will posted on the EER website when available. The ZCAP work was also the subject of a recent Energy Transition Show podcast. In this podcast, reference was made to a figure illustrating balancing in a high renewables system, shown below, along with an explanation.
The left panel of the figure shows non-thermal net load, meaning gross load minus variable energy resource (VER) output (predominantly wind and solar). The negative values indicate there is more renewable output than electrical load. High VER systems designed to provide sufficient energy in high-demand parts of the year will over-generate at other periods, both within a day and over the year. The remaining hours in which renewable output is insufficient to meet demand are due to especially high load (e.g., August late afternoons with high cooling demand), low renewable output, or a combination (e.g., December evenings with high electric heating demand and comparatively low renewable output).
The middle panel shows how different non-thermal balancing resources are employed to address the oversupply of renewable energy. Some level of curtailment of wind and solar is economic, but too much is not. Batteries can economically time-shift renewable generation from surplus to deficit periods over a day; however, batteries are not cost-effective for balancing on longer time scales. Flexible end-use loads (e.g., EVs and water heaters) are similarly valuable for short-term balancing. Instead, industrial-scale flexible loads can address energy surpluses lasting periods of days to months. These loads produce useful products from generation that would otherwise be curtailed and support integration of very high levels of renewables. Electrolysis of water simultaneously balances the system and produces valuable fuels (hydrogen, and synthetic hydrocarbons made with hydrogen) for applications that are difficult to electrify. Flex-fuel boilers use electricity during periods of overgeneration. Other large industrial loads such as desalination could also potentially operate flexibly.
The right panel of the above figure shows “residual load,” which is what remains of net load after deploying all the non-thermal balancing loads in the middle panel. The contrast between the left and middle panels and the right panel illustrates how the provision of capacity (MW) in a decarbonized electricity system is fundamentally separate from the provision of energy (MWh). The system is designed around supplying as much low-cost VER as possible, with non-thermal balancing loads to utilize surplus electricity. Dispatchable capacity is needed to address the residual reliability needs of the system. The capacity resource that pairs best with a high renewable systems is gas-fired capacity without carbon capture, due to its low capital cost. Gas capacity ramps up and down to support the whole system in the limited hours where there is a need for generation beyond wind, solar, hydro, and nuclear. This gas capacity can burn hydrogen or other clean fuels to further reduce electricity emissions.
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