What generating sources will power future electrical grids?

Looking at nuclear power with environmentalist and proponent Zion Lights

Author of "Energy is Life: Why Environmentalism Went Nuclear"

by Paul Huber

April 2026

Why is nuclear energy important when wind and solar can be increased? Intermittency and capacity factor are the main reasons. Solar energy is more predictable than wind, being based mostly on the Earth’s rotation, but its output is still affected by snow & cloud cover and its average capacity factor is around 25%. That means a 1 megawatt solar farm produces around 250 kilowatts when averaged over time. Wind energy has a higher capacity factor, 30 – 40% depending on geographic location, but its output is less predictable. High pressure weather patterns, for example, can nearly stall turbines over a large area for 1 – 2 weeks. Hydroelectric is another renewable method, but the best sites around the world are already utilized and further expansion would have negative environmental impacts and diminishing returns on power reliability.

If the long-term goal is to electrify more and reduce CO2 emissions, electric grids need to have abundant and reliable power. The systems become destabilized as intermittent sources increase as a percentage of total power, and users will rebel if adequate power isn’t available when they need it. A failure of that is practically and politically unsustainable. Currently, the intermittency dips are mostly compensated for by fast response gas turbine generators. Battery backup is too limited at this time. Theoretically, you could make an all-renewable grid work if you: overbuild the renewable sources to have adequate supply margins, massively expand storage, increase distribution & transmission capacity, and employ smart-grid technologies to orchestrate it all reliably. It sounds easy in the abstract, but real-world engineers know how costly and fragile that would be.

Realistically speaking, baseload and small-scale nuclear energy are essential to decarbonizing and having energy abundance for better standards of living. Its capacity factor is >90%, with most of its downtime being scheduled maintenance and refueling. Zion Lights, a committed environmental advocate, understands this and it has shaped her thinking on a low carbon future. She shares her views and insights in her new book, “Energy is Life”, and answered some of my questions about the topic.

Q1. Were you opposed to nuclear energy when you got started as an environmentalist? If so, why?

Yes, for most of my life I was opposed to nuclear energy. I had been misled by the environmental movement on almost every possible issue relating to it, from waste to safety to pollution. It was a simple fact; if you cared about the environment, you had to be against nuclear energy, and no one questioned this, ever. In fact, everything I believed about nuclear energy was wrong. I also believed that renewable energy alone was sufficient to replace fossil fuels, so it didn't seem important to revisit nuclear energy. Once I started to see the flaws in the 100% renewables argument, I began to consider changing my mind about nuclear.

Q2. What happened to change your thinking about nuclear energy?

The conversation has changed a lot in only the last few years, but a decade ago it was simply impossible to find accurate, fair information about nuclear energy. So my main sources of information were from anti-nuclear activist organisations like Greenpeace. I had begun questioning the idea of 100% renewables, though, and I had a friend who knew a lot about nuclear energy and was able to answer my questions about it. It took several years, but over time I overcame my old objections. I was shocked to learn, for example, that I had been misled by activist "reports" claiming evidence of fish harmed by nuclear radiation and an immense death toll at Fukushima from the power plant meltdown. In fact, no deaths occurred because of the meltdown itself. I felt betrayed, and this led me to question every belief I held, not just about nuclear energy, but also about GMOs and other technologies that the movement was against.

Q3. What do you find to be the most common and strongest public concerns with nuclear energy?

That energy is the same as weapons. Most of us have been told so many stories - or rather, the same repeated story - that nuclear energy is as dangerous as the bomb. It isn't, and statistically it's actually safer than some renewables, eg hydropower. The other convincing story has been about waste, so much so that as soon as one mentions nuclear the immediate response is almost always "what about the waste?" while this same association does not occur with solar, wind, or fossil fuels, which also all produce waste yet that waste is poorly managed - if managed at all - when compared with nuclear waste. In recent years, this has led me to question how much of the anti-nuclear movement was genuinely grassroots, and how much may have been influenced by covert efforts from other countries seeking to exploit parts of it for strategic advantage.

Q4. Accident-tolerant fuels are being developed to prevent the possibility of runaway reactions. What do you know about the time frame for availability and how much of the current fleet of reactors would be able to use this fuel?

Accident-tolerant fuels (ATF) are already being tested in operating light-water reactors, with the first limited commercial deployments expected in the mid-to-late 2020s and broader use likely in the 2030s as they complete licensing and multi-cycle irradiation testing. Most of the current global reactor fleet, particularly pressurised water reactors (PWRs) and boiling water reactors (BWRs), which make up the vast majority in operation today, are expected to be able to use the first generation of ATF designs (such as coated zirconium cladding or doped fuel pellets) as near drop-in replacements during normal refuelling outages, without requiring major reactor redesign, although more advanced ATF concepts will take longer to qualify and confirm compatibility.

Q5. Can you describe the difference between active and passive safety systems, and how these are being retrofitted into existing plants and designed into new ones?

Active safety systems rely on powered equipment, like electric pumps, motor-driven valves, and control systems, to respond to an accident by injecting coolant, removing heat, or shutting down the reactor, which means they depend on external power supplies and operator or automatic actuation. Passive safety systems are instead designed to function without external power or human intervention by using natural forces like gravity, natural circulation, compressed gases, or convection to maintain cooling and containment. In existing plants, improvements have mainly focused on enhancing or diversifying active backup systems (for example, adding additional emergency diesel generators or portable cooling equipment) and incorporating limited passive features such as improved heat removal pathways or passive autocatalytic hydrogen recombiners. In newer reactor designs, particularly Generation III and III+ plants, passive safety is built into the core design, including gravity-fed emergency cooling water tanks, passive residual heat removal systems, and containment cooling that can operate for extended periods without operator action, with the aim of maintaining safe conditions for hours or even days following a loss of power or coolant without the need for active intervention.

Q6. I don’t know of anyone who has a nuclear-only mindset. Ideally, it integrates with renewables as the solution towards net-zero. An argument I often see, however, is that this is difficult because nuclear can’t easily modulate its output (load-follow) for that purpose. Is that a real or perceived problem?

This is a real issue, but it's often overstated, and it depends a lot on what you mean by “can’t load-follow.” Technically, most modern nuclear plants can vary their output to follow demand. Pressurised water reactors (PWRs), for example, are capable of ramping power up or down by several percent per minute and operating stably at reduced output for extended periods. Countries like France have routinely used nuclear plants in load-following modes for decades to accommodate daily demand swings on a grid with a high share of nuclear generation. So from an engineering standpoint, nuclear is not inherently “baseload-only.”

The challenge is primarily economic and operational rather than physical. Nuclear plants are capital-intensive with low marginal fuel costs, so they are most cost-effective when running at high capacity factors. Cycling output up and down can reduce efficiency, increase component wear, complicate fuel management, and ultimately make it harder to recover those high upfront costs in electricity markets that reward flexibility rather than steady generation. By contrast, gas turbines or hydro can ramp quickly with less financial penalty, and renewables like wind and solar are typically dispatched whenever available because their marginal cost is near zero.

In practice, integrating nuclear with renewables is less about whether reactors can load-follow, and more about whether market structures and system design make it worthwhile for them to do so. Some proposed approaches include pairing nuclear with thermal storage, hydrogen production, or district heating so that excess output during periods of low electricity demand can be diverted rather than curtailed. So load-following is a genuine consideration in mixed low-carbon grids, but it’s not a hard technical barrier to combining nuclear with renewables, more a question of economics, system planning, and regulatory incentives.

Q7. Existing “spent” fuel can be recycled and reused. I understand this is already done in some countries. Is the promise of that potential mostly reserved for future reactor designs?

There's no good reason for why spent duel isn't already recycled today - unfortunately ideology has gotten in the way of it being a normal occurrence. In countries like France, spent fuel from light-water reactors is reprocessed and reused in existing reactors. This recovers energy that would otherwise go unused and reduces the volume of high-level waste. The full strategic value of recycling is mostly tied to future reactor designs. These systems could, in principle, use recycled fuel repeatedly and extract far more energy from what is currently treated as waste. However, that requires different reactor physics, fuel fabrication methods, and reprocessing approaches than those used in today’s thermal reactor fleet, so while limited recycling is already commercially practiced, the more transformative benefits are largely associated with next-generation reactor and fuel cycle technologies that are not yet widely deployed.

Q8. Many new designs are being presented, from full-scale 1GW down to 5MW micro-reactors, sharing the benefits of proven standardized design and passive safety. Do you see anything being more advantageous and becoming dominant?

I think the “best” design depends heavily on what problem you’re trying to solve, and there are some clear advantages emerging at different scales. Large, conventional-scale Generation III/III+ reactors (around 1 GW) still offer the strongest economies of scale for bulk, low-carbon electricity where grid infrastructure and financing capacity already exist. If your goal is to decarbonise a large national grid with firm capacity that can run for 60–80 years, they remain hard to beat on lifetime output per site, even if construction risk is higher. Small modular reactors (SMRs), typically in the 50–300 MW range, are attracting the most attention because they trade some of that scale efficiency for standardisation, factory fabrication, and potentially lower upfront capital risk. That makes them better suited to incremental deployment, replacement of retiring fossil plants, and to power data centres. Their passive safety features and modularity are also intended to simplify licensing and construction, which means in theory that they can be built quickly and cheaply. Micro-reactors (≤ 10 MW) address a different niche entirely: remote communities, mining operations, military bases, or off-grid industrial sites where diesel generation is currently dominant and fuel logistics are expensive or insecure. They’re unlikely to play a major role in bulk grid supply but could become important in hard-to-electrify or energy-isolated applications. I'm personally a fan of using all of these technologies: large reactors to provide long-lived backbone generation, SMRs to offer flexible and financeable additions within existing grids and to support expansion of new technologies like data centres, and micro-reactors to serve remote or specialised users. The real differentiator over the next couple of decades may be less about size alone and more about which designs can actually demonstrate repeatable construction, credible costs, and regulatory approval at scale, but I will always be a fan of large reactors because they are so incredibly powerful.

Q9. What is your ideal vision for nuclear energy as a solution for the future?

My ideal vision is one in which nuclear energy is no longer treated as a uniquely menacing technology, but as a proven, evidence-based tool for expanding the sphere of human prosperity while shrinking our environmental footprint. Over the past two centuries, progress has largely meant learning how to do more with less - to decouple human flourishing from land use, air pollution, and resource depletion - and nuclear energy is one of the most concentrated, reliable, and demonstrably safe means we’ve ever devised of producing vast quantities of energy with minimal material throughput. In a rationally governed, decarbonised system, nuclear would supply the bulk of our dependable, carbon-free electricity and heat. It would complement renewables rather than be forced to compete with them, helping to stabilise grids, electrify industry, and ultimately reduce the risks posed by energy insecurity and climate change. I would like to see a future in which nuclear energy helps to end energy poverty everywhere by making abundant, reliable, low-carbon power available not just to wealthy, industrialised nations but to any society seeking to improve living standards without repeating the environmental costs of fossil-fuelled development. Access to consistent electricity is one of the strongest predictors of longer life expectancy, better health outcomes, education, and economic opportunity, and a dense, scalable energy source like nuclear has the potential to provide that foundation irrespective of geography or climate. In this sense, the promise of nuclear energy is not merely decarbonisation, but the moral project of ensuring that the benefits of modern energy - light, heat, mobility, and connectivity - are no longer a privilege of where one happens to be born. □

Zion Lights is an award-winning Science Communicator who is known for her environmental advocacy work and her vision of a high-energy, low-carbon future.
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Out now - her new book, "Energy is Life: Why Environmentalism Went Nuclear". order from Amazon