In the real electricity system, the question is not so much which technology should prevail, but rather what combination allows reducing emissions, guaranteeing supply and maintaining affordable costs for homes and companies.
It should be noted that, with Rede Eléctrica data in hand, in Spain’s current energy mix, both technologies already coexist, but with very different roles. Nuclear provides continuous, predictable and low-emission generation, regardless of the weather, which makes it a key element for the security of supply and the stability of the network. Faced with this, renewable technologies (especially wind and solar) are essential to advance decarbonization, but their variable nature forces them to be supported with storage, more robust networks and backup mechanisms that compensate for the moments when the wind or the sun is not there.
Alfredo García, nuclear supervisor and disseminator (known as OperadorNuclear on all social networks) assures that “nuclear and renewables do not compete with each other, but rather fulfill different and complementary functions within the electrical mix.” From the scientific-technical field, Ignacio Cruz, director of Scientific-Technical Coordination of CIEMAT (Center for Energy, Environmental and Technological Research), agrees that “in the current electrical mix of Spain, nuclear and renewables fulfill complementary but different functions in the three key dimensions.”
A stable system in transition
The issue of grid stability has become central as wind and solar shares grow. Its greater weight introduces more variability and requires more fine-grained management of electricity flows, which implies reinforced networks, more storage and adjustment services, ideally provided by the renewables themselves.
While these solutions mature, nuclear constantly contributes and provides inertia to the system, helping to maintain operational frequency and robustness. Cruz recalls that “grid forming” technologies are already being tested so that renewable generation associated with converters behaves, in many aspects, like classic plants based on synchronous generators.
For this reason, Alfredo García considers that “the main error is to present the debate as a direct substitution between technologies, ignoring that the electrical system must guarantee supply at all times, not only when conditions are favorable.” In the renewable part, the director of CIEMAT points out another common misunderstanding: “the first mistake is to talk about power, we should talk about energy.” They remember that nuclear has a very high capacity factor, while renewables operate many fewer hours per year, so that, to produce the same energy, the installed renewable power must be “three or four times greater than nuclear.”
2030–2040: what combination is viable
The decisions made in the next decade will mark the appearance of the system between 2030 and 2040.
García defends that the most realistic scenario involves “a sustained expansion of renewables accompanied not only by the maintenance of existing nuclear power as long as it is safe and technically viable, but even by its reinforcement.” In this vision, if a country like Spain chose to expand its nuclear park, even doubling its power through a combination of large reactors and future small modular reactors, the system could be based “on a firm, low-emissions base that would reduce the use of gas to residual levels.” That base would allow renewables to continue growing without each episode of low wind or solar production automatically translating into more combined cycles and greater price volatility.
From the scientific side, the projections are more conservative with nuclear and much more expansive with renewables. Cruz considers that, in the period 2030–2040, “the most realistic combination is renewable solar and wind energy with about 200 GW installed and 30–40 GW of storage (…) producing between 60 and 90 percent of the electrical energy demanded.” The rest should be completed with support that could be based on biomass and biogas with CO₂ capture, green hydrogen or renewable fuels, as long as these technologies manage to complete their learning curve.
The need to extend the use of nuclear power or not, they add, will depend on the evolution of demand and the electrification scenarios that finally materialize.
In any case, both approaches agree that it is not coherent to close firm low-emission generation before having equivalent alternatives. For García, doing so turns gas into “structural support for the system, with the consequent impact on emissions, costs and external dependence.” From the perspective of energy planning, the director of Scientific-Technical Coordination of CIEMAT warns that “energy systems are never designed with a single technology” and that the maturation time factor of projects is critical in any roadmap.
Green, but not renewable: the environmental fine print
That nuclear is considered a green but non-renewable technology summarizes its peculiar fit in the energy transition.
Life cycle studies show that it has very low emissions, comparable to those of wind or hydraulic energy and much lower than those of fossil technologies. Its territorial footprint per unit of energy produced is also small.
However, the great point of friction continues to be the management of radioactive waste, especially long-lived waste. In this area, what is known as OperadorNuclear maintains that the activity generates “small and perfectly controlled volumes, managed under strict regulation and with complete traceability.” Meanwhile, CIEMAT recognizes that nuclear “generates long-lasting dangerous waste compared to renewables with a high volume of waste, but nothing dangerous and mostly recyclable.”
The “B side” of renewables also has nuances that are often left out of public debate. The massive deployment of wind farms and solar plants involves intensive use of materials, land and infrastructure, with environmental and social impacts that must be evaluated and managed.
In the words of Ignacio Cruz, director of Scientific-Technical Coordination at Ciemat, “a renewable system uses more materials, a nuclear one generates less, but more dangerous, material waste.” Renewables require more mineral resources and rare earths, as well as more space, although they require less water resources and their waste is, in general, recyclable. In the nuclear sector, it is insisted that also in renewables “there are debates about critical raw materials, occupation of territory or impact on biodiversity”, and that an honest comparison requires “applying the same level of demand to all technologies, considering the set of impacts and not just direct emissions.”
At this point, both visions agree on the need to explain this less friendly face without turning it into ammunition against renewables or propaganda in favor of other technologies. The director of CIEMAT summarizes it by ensuring that “the key is to compare complete systems, not isolated technologies, and to distinguish well types of impact.” From the nuclear side, it is advocated to “explain it with data and without idealizations”, remembering that the energy transition involves intensive use of materials, land and infrastructure, and that recognizing these effects does not question the usefulness of renewables, but rather helps to better plan their deployment.
A debate about combinations
Behind the nuclear yes/nuclear no slogan or the enthusiasm for renewables, the reality is that energy is a systems problem.
For Álvaro García, “the debate should focus on what combination of technologies allows reducing emissions, guaranteeing supply and maintaining competitive prices.” When a trade-off is forced between nuclear and renewables, they add, “the usual result is greater recourse to gas as a backup technology, with more emissions and greater external dependence.” From the scientific-technical side, a similar warning is issued: “we must try to avoid this binary framework since it distorts real decisions, which are always about combinations and time horizons,” says Cruz.
Ultimately, the meeting point between both visions is that the solution does not involve a single technology, but rather “the best combination that minimizes costs, emissions and risks in addition to guaranteeing energy and technological sovereignty.” The disagreement is in the relative weight that each piece should have, in the speed of renewable deployment and to what extent nuclear should continue to be a pillar of the system or be limited to accompanying the transition towards a model dominated by renewable technologies supported by storage, smart networks and new fuels of renewable origin.