When most of us think about renewable energy, we usually mean solar panels and wind farms. Although hydro or geothermal power make for great carbon-free renewable power where they exist, for most of the country wind and solar power are the only real options for renewable energy at scale. Those options seem pretty good because wind and sunshine are free and abundant, and the equipment needed to capture their energy is becoming astonishingly cheap.

But, unfortunately, wind and solar have a problem—intermittency. The solar farm in the picture above produces no power at night and little on cloudy days. Similarly, wind generators stop producing when the wind quits. On the other hand, a city, state, or country needs reliable electric power day and night, all year long, regardless of the weather. That means that for wind and solar to be a serious part of the power system, there must be some other form of generation or storage that can step in and seamlessly fill the power gap when the renewables stop producing.

In most installations to date, intermittency has not been much of a problem. Because renewables are still a small part of the energy mix, it has been easy to fill the power gap from the grid.  But using the grid makes for dirty emissions. Most grid power is generated by the only reliable sources available—usually coal or natural gas. So whereas we’d like to believe that building wind and solar farms will allow us to close dirty power plants, it’s not so. Those old fossil-fueled plants have to be kept online to power the grid at night, or whenever clouds cover the sun, or the wind quits.  And because sun and wind outages can last for a week or longer, those old power plants actually need to run most of the time.

Two real-life examples underscore the challenge. Germany has spent some $400 billion on its renewable program, yet carbon emissions have remained stubbornly high. Here at home, California made a heavy investment in renewables to replace coal and nuclear, yet the state’s power-sector emissions have remained essentially flat.  The culprits, of course, are the carbon emissions from the power plants needed to backup the renewables and fill the gap.

Clearly it is time to shift our attention.  While we’ve done a great job improving the technology for capturing energy from the wind and sun, we haven’t done nearly as well addressing the power-gap. As Germany and California show, unless we can deploy carbon-free, gap-filling power, simply adding more renewables will not produce a significant reduction in carbon.

Could the gap be filled with batteries?  Why not charge batteries on sunny and windy days and use them to fill the power gap?  It certainly sounds like a solution—until the problems of scale are examined.

To understand scale and how big batteries would need to be, let’s first take a look at the size of the backup needed to make solar panels reliable 24/7. As every sunbather knows, even on the best days there are only about four hours in the middle of the day when sunshine is strong. Before and after midday, the sun is progressively weaker. Then there is the problem of nights and cloudy days. So perhaps unsurprisingly, even our best solar farms produce significant power only about 25 percent of the time. The rest of the time they produce little or no power. That means a city or economy dependent on solar farms will need to run off its batteries (or other power source) about 75 percent of the time!

Wind is a bit better. Windy Denmark has built so many offshore wind farms that on many days in 2018, the wind supplied more than 100 percent of Denmark’s power. Yet for the full year, wind supplied less than 50 percent. The rest of the time, Denmark filled the gap mostly by buying power from other countries. So an economy dependent on wind farms, even in the windiest locations, will almost surely need to use backup power more than half the time.  For both solar and wind, it takes a lot of backup power.

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he question, then, is just how big a battery (or batteries) would it take to be the backup?

For the answer, consider a specific case for just part of one state. A while ago, well-intentioned activists pushed to close Arizona’s Palo Verde nuclear plant and replace it with solar panels. The plant supplies a third of Arizona’s power and generates about 4 gigawatts (4GW) of 24/7 power. Had the activists been successful and actually replaced Palo Verde with solar panels and batteries, how much battery storage would they have needed? Since even Arizona can have a full week of cloudy days, those batteries would have to hold enough electrons to supply power for a week—some 670 GW hours of battery capacity (4GWx24x7).

Well, 670 GW hours is huge! As a point of comparison, the total battery storage expected to be in place in the United States at the end of 2019—utilities and homes—will be about 3 GW. In other words, just filling the night and cloudy-day power-gap left by substituting solar panels for Palo Verde would require over 200 times more storage than all the batteries in the United States! And what about the largest battery in the world, that giant $66 million Tesla 129 MW battery in Australia? It would take over five thousand of them! But even if all that battery power were somehow possible, it would replace only one power plant that supplies only one third of one state. So although great strides are being made in battery technology and costs, not even a technological miracle could give us the gigantic amount of battery storage necessary to fill the power-gap at scale. Simply put, the laws of physics and scale say that batteries cannot be the answer.

What, then, are the other realistic possibilities for carbon-free backup? One possibility is to continue to use gas or coal plants but capture and dispose of the plant’s carbon. It’s a great idea but, unfortunately, carbon capture (CC) is not yet ready for prime time and may not be for decades. As of this writing, all the present and prospective CC technologies are very energy intensive and expensive. The entire field needs much more research and attention. Similarly, all the other methods of supplying backup, such as various forms of hydrogen, are also very energy intensive and expensive. In fact, every known potential solution to the backup problem requires tremendous additional energy—except one. And that one is nuclear energy.

But wait. Rather than using something as contentious as nuclear, what about accepting some carbon emissions and using natural gas as the backup fuel?  Solar and wind backed up with natural gas can be an improvement over 100 percent coal.  And gas plants can easily deliver the baseload power needed for as long as needed.  As an added benefit, perhaps replacing coal with gas can help the people and communities whose livelihood depends on fossil fuels. While we are changing our economy to mitigate climate change, we must not leave those people behind. Using gas as a “bridge” until we can deploy carbon-free solutions might give us time to include them in the carbon-free economy of the future.

But burning natural gas still emits way too much carbon. And even worse, in addition to its CO2 emissions, natural gas is methane, and methane is 100 times worse for climate change than CO2. It’s almost impossible to avoid leakage and scientists say that if just 2 percent of the gas leaks, the climate effect of using gas is worse than if we just kept burning coal. So even under the best conditions, gas won’t get us anywhere near the greenhouse gas reductions we need. Therefore, gas can’t be a permanent solution—or any solution for long.

Which brings us back to the only possibility left – nuclear. Even if we don’t love it, nuclear is the only carbon-free generating source that can provide reliable backup power at the scale required. It is also the only carbon-free source we know of that can supply—at scale—the massive amounts of additional energy and heat needed for other carbon-mitigating technologies.

However, as we all know, the mere mention of nuclear brings up immediate objections, usually centered on safety, cost, and waste. Let’s very briefly look at each in turn.

Safety. The three notable accidents, Three Mile Island, Chernobyl, and Fukushima were rare exceptions to the safety record of more than a thousand reactors (on ships and land) that have been operating safely for as long as 60 years. No other power or chemical plants come even close to that safety record. Of the three accidents, only one—Chernobyl—resulted in any radiation-caused death or injury. And stories about sterilized land? Again, only around Chernobyl. But Chernobyl was not a typical or “normal” reactor.  The Chernobyl reactor was a freak. It was terribly designed, lacked a containment structure, lacked essential safety features, and was incompetently built and operated by the Soviet Union. It was nothing like a modern Generation II or Gen III water-cooled reactor.

Cost. In recent years, plants built in the West have been astronomically expensive. It was not always so. Almost all of the 98 or so nuclear plants operating in the United States today were built before the mid-1970s when utilities chose them for economic reasons—they actually cost less than equivalent coal or oil plants! But after Three Mile Island, anti-nuclear forces successfully lobbied for massive up-regulation which effectively stopped nuclear by making costs in the United States and the Western world prohibitive. By contrast, the Koreans today build safe, American-designed Gen III nuclear plants for half the cost of a new coal plant—and in less than five years. With more build experience, expertise, and some common sense, America could build safe reactors with build-times and costs just a fraction of what they have recently been.

Waste. Fears of waste have been hugely exaggerated by the media and anti-nuclear lobby.

First of all, there isn’t much of it. All the waste from 60 years of America’s nuclear plant operations would take up less space than one typical Walmart store. Compare that to the much greater space required to store the toxic waste from a single large coal plant. Frankly, compared to other industrial waste problems, the nuclear waste problem is small. And we have all the technology needed to easily, safely, cheaply, and permanently dispose of all our commercial nuclear waste.

In fact, if we updated our regulations, and put some thoughtful planning behind it, we could build enough of the new Gen III or Gen III+ water-cooled reactors to backup all our renewables – and more – with carbon-free energy. And those reactors could all be in place and operating well before 2050. It’s not speculation. France and Sweden converted almost all their fossil plants to nuclear in less than 15 years. We could do the same and have a carbon-free power sector before mid-century.

So far, we’ve been talking about what we could do with water-cooled reactors. They’re good. But as good as Gen III is, Gen IV nuclear promises to be even better. Gen IV technologies are totally different.  They are not water cooled and many have already been thoroughly tested in research labs. Most produce much less waste and some even use existing waste as fuel. Because of their design, they are of little value to terrorists or weapons-makers. Best of all, they are walk-away safe — the physics of Gen IV stops the reaction automatically if the reactor gets too hot.  No operator or mechanical intervention is necessary. For people with concerns about water-cooled reactors, Gen IV could be the answer.

Happily, there are more than 50 entrepreneurial ventures in the United States working on various Gen IV reactor designs. Some are getting close. Oklo is ready to go with a system who’s nuclear heat source doesn’t require maintenance or refueling for 20 years or more and is small enough to fit in a freight container. Thorcon has a design for floating reactors built in shipyards that could be ready to go in less than seven years and shipped anywhere in the world. But there is a problem.  Gen IV companies can’t get permission to build them. It’s our regulatory system. It is set up for water-cooled reactors and not equipped to handle anything else. Before any American Gen IV reactors can be built commercially and brought to market, major changes must be made to the regulatory system.

Finally, to solve the climate problem, the United States cannot do it alone.

The rest of the world must also stop emitting carbon. This is particularly true for the developing world as it searches for ways to satisfy its immense appetite for electricity to power its economy. That appetite will be satisfied with coal unless there is something better and cheaper available. Gen IV could be that something. In addition to saving the planet, Gen IV represents an incredible economic opportunity.

The point is that if we’re going to get serious about mitigating climate change, we’ve got to get moving now. The next few decades will determine just how hot this planet will get. As we’ve seen, simply building more solar and wind farms can’t solve the problem.  We need that carbon-free baseload backup ASAP. We do not have time to wait for some future hope. We can and we must act now with what we have today. Otherwise net zero emissions will have been just a dream that our grandchildren will hate us for not achieving. Especially when it was within reach.