[co-authors: Mary Anne Sullivan, Sachin Desai, Stephanie Fishman]
Many advanced reactor developers are designing their technologies to pair with renewables. A recent report from the North American Electric Reliability Corporation (NERC), the government entity responsible for overseeing America’s bulk power system, underscores the benefits that can be achieved through an advanced nuclear/renewable energy partnership to compensate for the intermittent nature of solar and wind power.
For power grids relying on renewable energy, supply and demand hang in a balance based on the time of day and weather forecast. To maintain equilibrium in grid systems powered by renewable energy, flexible backup sources must remain online at all times. To date, storage resources are not providing the necessary back-up, hindered by both technology and costs, leaving natural gas and hydro plants to take on the role of providing standby capacity services. As the intermittent renewable energy capacity increases in power grids as a proportion of overall capacity, the industry requires more flexible power generation options, providing an opportunity for advanced reactors to support renewables while continuing to decarbonize of the electricity sector. Advanced nuclear power technologies are intended to operate flexibly, either at full capacity (producing large amounts of reliable, carbon free-electricity) or load following paired with renewable energy (producing just enough when needed to meet demand), promoting both decarbonization and reliability of the grid at any time of day.
In May 2021, NERC published its 2021 Summer Reliability Assessment (Reliability Assessment) identifying areas of concern regarding reliability of bulk power systems and the grid for this upcoming summer. Specifically, the Reliability Assessment warns that typically hot-summer states that rely heavily on solar photovoltaic generation (Solar PV), may experience blackouts and energy shortfalls during above-normal peak temperatures.
According to NERC, states like Texas, New Mexico, Arizona, and California, who are predicted to have warmer summer seasons than last year, are at an “elevated risk” of experiencing energy emergencies this summer, specifically, outages during extreme summer peak loads. While Solar PV plants provide energy to support peak demand, the generated output rapidly declines in the afternoon at the time when demand in these states remains high. The regional increase in demand and decline in resources may reduce the quantity of surplus capacity available when California, for example, is in shortfall. The NERC Reliability Assessment puts in starker terms the challenges acknowledged in NERC’s 2020 Long-Term Assessment, issued last December, where NERC explained (with emphasis added): “The addition of variable energy resources, primarily wind and solar, and the retirement of conventional generation is fundamentally changing how the [bulk power system] is planned and operated. Resource planners must consider greater uncertainty across the resource fleet as well as uncertainty in electricity demand that is increasingly being effected by demand-side resources. As a result, reserve margins and capacity-based estimates can give a false sense of comfort and need to be supplemented with energy adequacy assessments.”
As grid infrastructure continues to evolve and weather-dependent resources become critical to maintaining energy reliability, it is important, now more than ever for the electric industry to ensure diversity in its power sources and fuel types. The findings set forth in the Reliability Assessment make this clear, and the advantages of pairing advanced nuclear with renewables, like solar and wind, ensures reliable power generation can continue when the sun is not shining or the wind is not blowing.
The NERC Reliability Assessment also highlighted how abnormal weather conditions can lead to elevated risks to the grid—affecting both generation and demand, as well as causing energy shortages that lead to energy emergencies. The Texas power crisis that occurred in February 2021 serves as an example of why the energy industry must adapt to extreme weather events. As noted in a recent report on this event, when Winter Storm Uri struck Texas this past winter, more than 4.5 million households were left without electricity during an extremely cold snap of weather, with the storm and outages leading to the loss of over 100 lives and causing an economic loss estimated to be about $155 billion. All major fuel sources underperformed during this event, but the nuclear plants in the state were least impacted. Of the four nuclear reactors in Texas, three remained operational and the one that shut down re-opened within a couple days This demonstrates both the dangers that extreme weather events pose to the grid and public health and safety, and also the essential role energy diversity can play in ensuring grid stability during these events.
Advanced reactor companies recognize the significant benefits of hybrid nuclear/renewable energy systems and are developing advanced reactor designs intended to pair with renewable power. For instance, X-energy signed a tri-energy partnership agreement with Energy Northwest and Grant County Public Utility District to site, build, and operate an Xe-100 advanced nuclear power plant. The design will integrate regional electricity systems as both a base and load-following carbon-free power source to optimize grid capacity and stabilize intermittent renewable energy production.
Additionally, TerraPower, alongside GE-Hitachi, developed Natrium, a sodium-cooled fast reactor that leverages technologies used in solar thermal generation systems. Among other qualities, Natrium couples a 345 megawatt electric (MWe) nuclear reactor with a molten salt energy storage system that can flexibly operate in sync with renewable power sources. Its thermal storage has the potential to boost the system’s output to 500MWe of power for more than five and a half hours.
Other companies are developing advanced reactor designs with similar pairing capabilities. NuScale and Oklo developed reactor designs with the ability to generate power to run in tandem with renewable energy from the grid.
And with the deployment of these advanced reactor technologies in the coming years, pairing renewables with advanced reactors can help support a quicker transition to carbon-free power while also ensuring the lights stay on.