Like many utilities, Duke Energy is working with NREL to explore paths to a low-carbon grid, as well as opportunities to reduce carbon emissions in consultation with policymakers and regulators. In 2021, North Carolina passed legislation codifying a 70% emissions reduction target for 2030 and a net-zero carbon dioxide emissions target for 2050, with Duke Energy also setting its own target of net-zero CO2 emissions.2 emissions system by 2050.
Achieving these goals and providing reliable and affordable power in the Carolinas is a central focus of Duke Energy’s long-term planning. To support this transition, the National Renewable Energy Laboratory (NREL) is involved in a multi-year project with Duke Energy that has identified the region’s cheapest routes for carbon-free energy. While specific to Duke Energy’s system, this is: Research on integrating carbon-free resources provides a modeling approach that can be adapted to the carbon-free resource planning of all utilities, using a variety of accessible NREL tools.
Planning Tools for Renewable Energy Systems
NREL’s project with Duke Energy involved two phases. In Phase 1, the researchers conducted a preliminary analysis of adding substantial new solar power to the system, boosting solar power to 30% of annual generation, leading to an 80% carbon-free system when taking into account with the output of wind, nuclear, and hydro – shows how solar limitation increases as more is added to the system in future deployment scenarios. Read the full Phase 1 report learn more.
The recently completed Phase 2 analysis provided a deeper analysis of the potential investments, costs and business impacts as Duke Energy integrates carbon-free energy. At this stage, NREL has deployed a suite of planning tools to evaluate scenarios representing Duke Energy in both the short-term (2030) and long-term (2050) terms. NREL has its . released Phase 2 report this week, the topic of the rest of this news article.
Flowchart illustrates methods and modeling tools used in the NREL Carbon-Free Resource Integration Study.
The NREL researchers started with: high resolution maps of the wind and solar resources of the Carolinas. This resource rating includes hourly resource profiles and removes areas that are not suitable for development. By connecting these cards to NREL .’s open source Possible model for renewable energythe researchers identified developable wind and solar sites in the Carolinas.
NREL then limited Duke’s potential wind and solar sites to sites that meet key system and decarbonization requirements. For this step, NREL used his Regional Energy Implementation System (ReEDS) capacity expansion model to determine the cheapest resource mix and to identify new transmission scenarios that meet the critical requirements of the power system.
For a final validation step, NREL researchers tested the ReEDS resource mix on a complete transmission model of the Carolinas using the commercially available PLEXOS software. NREL simulated the proposed buildouts at hourly resolution and observed how each capability would play out over a year of use.
Simulation results: Gigawatts of new solar energy, wind energy and storage
The figure below shows the generation capacity deployed by ReEDS under a reference case (base) and with the emissions reduction targets of 70% reduction in North Carolina by 2030 and zero-carbon emissions by 2050 (policy). The policy case also includes a “no fossil” scenario in which all fossil units in both Carolinas must be shut down by 2050, including units not in Duke Energy’s service area.
For its 2030 goals, ReEDS estimates that Duke Energy can meet its 70% target by stopping coal and investing in solar, battery storage and wind. Although investments in offshore wind energy and an expansion of existing pumped water storage will come after 2030, ReEDS does not take into account all the logistical constraints for deploying new energy sources, making it important to promote these sources today given the time it takes to generate new generation sources. build and integrate.
In pursuit of North Carolina and Duke Energy’s goals for carbon-free energy, NREL has modeled scenarios of increasing reliance on carbon-free energy. This figure shows installed capacity for 2030 and 2050 scenarios, given business-as-usual expansion, current policy requirements and a zero fossil energy option. (RE-CT = renewable combustion turbines; lfill-Gas = landfill gas; Gas-CT = gas combustion turbine; Gas-CC = gas turbine).
In NREL’s scenarios, some of the retired coal-fired power stations will be replaced by natural gas generation. This replacement reduces CO2 total emissions, but increases methane emissions from pipeline leakage. While pipeline leakage is not calculated in the North Carolina policy target for 2030, NREL measured methane emissions in the scenario analysis, as illustrated in the figure below. In addition, emissions may vary depending on system conditions, with lower emissions associated with the planned coal exit and higher emissions associated with a scenario simulating an extended winter cold spell.
NREL has modeled Duke’s energy system under a base case (2024) and under various 2030 policy scenarios with different weather conditions. NREL’s analysis included emissions from pipeline methane leakage, as well as a scenario capturing a uniquely cold Carolina winter, contributing to carbon emissions.
The difference in emissions based on weather demonstrates the importance of evaluating system operation not only for “typical” weather, but also for more extreme conditions that can strain the system. In the “2036 extended cold snap” scenario, NREL tested the build-up of the 2036 system against weather data from 2018, a year when Duke Energy experienced a prolonged peak load during the winter. This cold spell is especially clear in the figure below, in which fuel consumption rises sharply in the winter months.
“The comprehensive cold snap modeling of 2036 is particularly useful in illustrating the need for technologies that can provide sustainable power during challenging winter periods,” said Mark Oliver, vice president of Integrated System Planning at Duke Energy.
Despite significant amounts of solar PV, wind and batteries with a duration of 4 hours, replace Duke Energy’s coal-fired power plants means finding technologies that can provide energy during a multi-day winter peak when solar energy is less available and recharging batteries can be difficult. Oliver said that “although natural gas is available to meet this need until better alternatives are available, it could be replaced by hydrogen or renewable biofuels as Duke Energy moves towards zero carbon emissions in the future”.
Duke Energy aims for zero carbon energy by 2050
The results for 2050 show a diverse system that is generally solar dominant, smoothed out by storage and supplemented by nuclear and wind. In the absence of fossil fuels, renewable energy combustion turbines (RE-CTs) serve to provide peak power for both the summer and winter peaks. These turbines operate infrequently, but are critical for supplying power during key times of high grid voltage.
“Having generators that can provide energy when called upon during a few critical times of the year, when the system is under pressure, offers a lot of value,” said Brian Sergi, NREL grid analyst and co-author of the study. research. Sergi noted that deploying generation technology that is relatively rare but available at key moments is consistent with other studies examining the challenges of achieving deep decarbonization, including NREL’s recent research. LA100 analysis exploring avenues for a zero-carbon system for the city of Los Angeles. Although modeled as RE-CTs in this study, this niche could be filled by a range of technologies such as seasonal storage and/or operational strategies such as increased import through coordination with neighbors.
A comparison of winter (left) and summer (right) for 2050 scenarios shows that peak hours are needed for winter to overcome cold spell.
The path to achieving the carbon neutral target can influence the optimal mix of resources and the way they are used. For example, the scenario without fossil fuels shows less containment due to a greater use of storage and a greater dependence on net imports to compensate for less natural gas production, albeit at a higher total cost than the policy case itself. Likewise, routes in which neighboring utilities are also pursuing carbon-free goals reduce the opportunities to export otherwise limited power, increasing the value of deploying energy storage in the Carolinas.
The study also shows that there are increasing possibilities for exchange with neighboring grids to balance supply and demand for the increasingly dynamic system with higher levels of sustainable integration. A wide range of sensitivities demonstrate transmission upgrades and builds both within Duke Energy’s service area in the Carolinas and adjacent energy systems, illustrating the robustness of the value of these investments in high renewable outcomes.
An example for others
The analysis performed here identifies a range of routes for integrating carbon-free resources in the Carolinas. The NREL analysis does not replace Duke Energy’s traditional integrated resource planning effort, but provides additional insight into the challenges and opportunities for achieving a zero-carbon system.
The study focused on system enhancements that could meet the emission reduction targets at the least cost, mainly from an operational perspective, and accordingly there are additional questions to be explored on the path to zero emissions. For example, the expected capacity expansions of the ReEDS modeling do not reflect logistical constraints such as the speed of interconnection, supply chains, or other constraints that may limit the true rate of renewable energy integration. Achieving the emission reductions targeted by policymakers and Duke Energy thus requires ongoing research to understand the challenges and opportunities ahead.
Despite being tailor-made for the CarolinasThis study may aid decision-making by utilities, grid operators and policy makers planning for clean energy not just in the Southeast, but across the country.
Follow NREL’s work in energy analysis.
By Connor O’Neil
Article courtesy of National Renewable Energy Laboratory
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