Electricity demand is rising fast. And we need to decarbonize. We have the technologies to generate clean energy—but not the consensus across industry and policymakers on how to assemble them into a coherent grid. Too often we see the energy transition framed by businesses and politicians with the need for ‘baseload’ power—especially when considering the role of nuclear (and natural gas or bioenergy in a future where carbon capture and storage [CCS] become economically viable). But to maximize the benefits of economic, clean, and renewable energy, it’s storage that must take priority—to ‘top-up’ whatever the maximum capacity of clean, cheap, and secure renewables is at any one time.

That top-up can take a number of forms. And nuclear will have a role for decades to come. But that role needs clarifying. Energy storage across different time horizons is one of the most critical innovations needed for the energy transition and global sustainability whether it’s traditional batteries, pumped hydro, or green hydrogen production and storage.

The “nuclear and/or renewables” question is too often framed around the need for baseload power

When wind and solar energy generation drop, the argument goes, baseload power keeps people and businesses going while maintaining the ‘inertia’ that electricity grids need to maintain stability. While true now (with gas and coal in many countries providing that baseload), that doesn’t necessarily represent the best future decarbonized energy system.

A new narrative needs to emerge. Rather than baseload, we need to think about ‘top-up’ and prioritize renewables and storage.

The cost of solar and wind has dropped so dramatically that a viable future exists where these cheap, decarbonized energy sources dominate the grid. Crucially, they should be run at or close to their maximum. With the gap between that maximum solar and wind generation and overall demand met by a highly flexible ‘top-up’. Our World in Data compiles from various sources that solar photovoltaic costs fell by 90% since 2015, onshore wind by 70%, and batteries over 90%.

Top-up is where nuclear falls down

The extreme capital requirements for nuclear energy mean to be economically viable plants must be run at near or maximum capacity. While technically feasible, nuclear is not a flexible top-up option.

Stable nuclear can, of course, provide the inertia to keep grids stable and limit the risk of a trip. But storage in its multiple forms can increasingly provide this stability, with that storage filled by excess renewables.

The jury is still out, say a range of views within the upstream, midstream, and downstream sections of the industry, on whether battery storage will be able to maintain this inertia, so stable baseload is still needed at present.

But other forms of storage exist, and are being rapidly developed, to create a range of stable and flexible options: from pumped hydro (pumping water up to a reservoir when electricity is cheap and clean) to hydrogen (splitting water with renewables then storing across options from tanks to caverns) to industry using plentiful green energy to, for example, pre-grind the feedstock for cement making and storing it in silos.

Batteries are currently most applicable for day-to-day discharge

We do need massive development for longer extreme cases of low solar and wind.

Especially in countries with lower solar potential (think UK, Canada, northern Europe), given wind’s higher variability, battery technology as a full solution is some way off—and so nuclear, especially maintaining and maximizing the longevity of existing and planned plants, has a role—but it should be thought of as the ‘added option’ after the principle of maximizing renewables, batteries, other forms of storage, then going onto nuclear options.

Storage is on the way to outperforming nuclear—and winning the top-up vs baseload competition

We need to develop battery and other forms of energy storage to a point where grids can be run on max renewables, with excess capacity stored when it’s sunny and windy, which can then be used to top-up the missing demand when clouds, night, and low winds come in.

California renewable energy covered 100 percent of its demand for up to 10 hours on 98 of 116 days in a 2024 study in the Renewable Energy journal. The state’s battery capacity is equivalent to over four nuclear plants and is able to absorb a renewables peak of 160% of demand to provide power throughout the nights and other low-renewable periods.

Since 2020, battery storage capacity in CA has more than tripled to 13GW; another 8.6GW is planned by 2027. Battery capacity more broadly in the US rose 63 percent in the first half of 2025, says S&P Global, with Texas playing a leading role.

In 2024, the world added over 200 gigawatt-hours of new grid-scale battery capacity — a 60% jump year-on-year. BloombergNEF projects battery pack prices will fall below $100 per kWh by 2026, the threshold for grid parity with peaking gas.

Given the still-questionable economics of nuclear—and the downsides, however limited they are and continue to improve, while yet-to-be-proven small modular reactors (SMRs) may change the economics in time and the ability of nuclear to provide more flexible and economic contributions to the grid—grids run on renewables and storage would be a much preferable outcome to many experts and the public. No nuclear waste. Lower bills. Minimal risk. Renewables plus storage win public support.

To reiterate, the “top-up” model doesn’t eliminate nuclear—it redefines its role

Stable reactors can anchor grid inertia and supply industrial heat or hydrogen, but they are no longer the only guarantors of reliability. Nuclear and other forms of large one-site generation provide the option to locate generation past grid “bottlenecks” as we wait for grid scale needed for an electrified future. With big network buildouts, renewables become less of a concern. Other generation and storage, like hydro, can also play a role of this kind.

The faster industry and policymakers clear up their roadmaps for nuclear, renewables, and storage, the quicker we’ll reach a stable, affordable, and decarbonized energy system

We have long called for better transition planning—for the energy transition and broader sustainability that works for the environment, for people, and economics. Better transition planning from business and politics.

Renewable energy and storage solutions need higher priority in this top-up energy model, before completing those transition plans with options like nuclear.

It might sound like an insignificant mindset shift. But given the state of the political conversation around energy, and the state of transition plans in industry, we need it soon. If we’re to have any chance of realizing the clean, cheap, and secure future that renewable energy promises.