Electricity grids have been moving away from fossil fuel sources and toward more renewable energy sources in order to minimize CO₂ and other greenhouse gas emissions. However, due to the high intermittency, high variability, and low-capacity factor of these renewable energy sources, technical and economic issues have arisen [1], [2]. To maintain supply and demand balance in power networks with significant renewable energy penetration, greater flexibility is required at all times. To accommodate the changes in electricity demand, traditional load following plants such as natural gas power plants have been deployed, which release significant amount of greenhouse gases [3]. These traditional plants must be replaced by alternative carbon-free reliable sources of energy, including as nuclear power plants, in order to truly move toward a carbon-free future [4], [5].

Nuclear power is one of these carbon free alternative energy sources. It is reliable, safe, and does not emit any or greenhouse gases [6]. Nuclear power can be coupled with other sources of renewable energy to generate clean, renewable energy. Studies have shown that these hybrid energy systems can increase the flexibility of the grid, as well as reliability and safety. These hybrid systems can do so by storing excess energy generated during low demand times, and using this stored energy to generate additional electricity during high demand times. Hybrid systems have been shown to reduce cost, maximize revenues, and decrease the grid’s reliance on other fossil-fuel based sources [4].

A nuclear hybrid energy system is proposed by integrating a nuclear power plant with a hydrogen generation plant, a large-scale storage in an underground salt cavern, and a gas turbine cycle [7], as shown in Figure 1. A novel control scheme is developed based on real electricity price percentiles taken from ERCOT. The benefit of the hybrid system over a stand-alone nuclear plant is flexible dispatch, enabling it to store energy when the price is low, and discharging when the price is high, as well as its ability to participate in the ancillary services market. To investigate the potential profits of the proposed hybrid system, an optimized dispatch study is conducted using the developed control scheme. To account for the effect of price volatility on the dispatch control, two locations with different price volatility have been chosen to conduct the study: Houston and West Load Zones. Six control schemes with different aggressive strategies are simulated for each Load Zone to investigate the effect of the control strategy aggressiveness on the economics of the hybrid system. An economic analysis is also conducted based on the optimized dispatch simulation results, comparing the hybrid system to a stand-alone nuclear plant. Policy incentives such as a production tax credit and an upfront tax credit are applied to investigate the impact on the hybrid system economics as compared to a stand-alone plant [8]. A production tax credit (PTC) is a tax credit that is given per kilowatt-hour of electricity generated. An upfront tax credit (UTC) is a tax credit given as a percentage of the total capital investment of the project.

Figure 1. Schematic diagram of the proposed nuclear-hydrogen hybrid system

From the simulation results, it is found that in a more volatile pricing load zone, a more aggressive control strategy maximizes the revenue, while in a less volatile pricing zone, a more moderate control strategy is best utilized. The hybrid system is found to generate 10-40 million USD more annually than a stand-alone power plant. This extra generated revenue is due to the flexible dispatch, as well as the participation of the hybrid system in the ancillary services market. Due to the extra revenue, the hybrid system generates a profit of 8 million USD annually, while the stand-alone plant will lose 22 million USD. A LCOE analysis found that the stand-alone plant has a LCOE of 68.66 USD/MWh, while the hybrid plant has an LCOE of 81.36 USD/MWh. Despite higher LCOE, the hybrid system’s LCOE is comparable to other new forms of electricity generation such as biomass, battery storage, offshore wind... [9]

Payback period and net present value (NPV) are calculated to investigate the economic feasibility of both systems. The results show that both systems are not economically viable, as both have negative NPVs. A production tax credit and an upfront tax credit were applied to both systems as economic incentives. It is found that the hybrid system needs less economic incentives to become economically viable compared to the stand-alone plant. To recover the investment cost within the system’s lifetime, the hybrid system needs a PTC of 9.75 USD/MWh compared to 12.14 USD/MWh of a stand-alone plant. To have a positive NPV, the hybrid system requires a PTC of 17.10 USD/MWh compared to 52.03 $/MWh of the stand-alone plant. As the stand-alone plant loses money, the UTC cannot help the stand-alone plant become economically viable. As for the hybrid system, an UTC of 86.41% can help the plant recuperate its investment money within the plant’s lifetime, while an UTC of 97.56% can make the hybrid system result in a positive NPV.

While the economics of nuclear power plants may appear to be unfavorable at this time, it is vital to remember that the current market includes a generator fleet that is already considered depreciated. When compared to other greenfield investments, the nuclear hybrid energy system is more cost effective. Furthermore, integrating nuclear with large-scale storage provides a cost-effective approach of delivering more carbon-free, yet dispatchable power assets to the grid. This study emphasizes the advantages of hybridization, notably linking nuclear energy with large-scale hydrogen storage, over a stand-alone system.

Bibliography

[1] M. Sheha and K. Powell, "Using Real-Time Electricity Prices to Leverage Electrical Energy Storage and Flexible Loads in a Smart Grid Environment Utilizing Machine Learning Techniques," Processes, vol. 7, 2019.

[2] R. Pinsky, P. Sabharwall, J. Hartvigsen and J. O’Brien, "Comparative review of hydrogen production technologies for nuclear hybrid energy systems," Progress in Nuclear Energy, 2020.

[3] J. S. Kim, K. M. Powell and T. F. Edgar, "Nonlinear Model Predictive Control for a Heavy-Duty as Turbine Power Plant," in American control conference, Washington D.C., 2013.

[4] J. D. Jenkins, Z. Zhou, R. Ponciroli, R. B. Vilim, F. Ganda, F. de Sisternes and A. Botterud, "The benefits of nuclear flexibility in power system operations with renewable energy," Applied Energy, 2018.

[5] F. J. Sisternes, J. D. Jenkins and A. Botterud, "The value of energy storage in decarbonizing the electricity sector," Applied Energy, 2016.

[6] S. Suman, "Hybrid nuclear-renewable energy systems: A review," Journal of Cleaner Production, pp. 166-177, 2018.

[7] A. Ho, K. Mohammadi, M. Memmott, J. Hedengren and K. M. Powell, "Dynamic simulation of a novel nuclear hybrid energy system with large-scale hydrogen storage in an underground salt cavern," International Journal of Hydrogen Energy, vol. 46, no. 61, pp. 31143-31157, 2021.

[8] A. Ho, D. Hill, J. Hedengren and K. Powell, "A nuclear‑hydrogen hybrid energy system with large-scale storage: A study in optimal dispatch and economic performance in a real-world market," Journal of Energy Storage, vol. 51, p. 104510, 2022.

[9] U.S. Energy Information Administration, "Levelized Costs of New Generation Resources in the Annual Energy Outlook 2021," U.S. Energy Information Administration, 2021.