Although both nuclear and renewables are useful to reduce carbon emissions, nuclear is not included in the most ideal power mix due to its waste management, expensive decommissioning and inherent safety risks. While Germany and Japan consider these risks to be greater than the risk of increased carbon emissions, many other countries balance the risks differently.

Aesop wrote a fable called the Oak and the Reed, where the Oak spoke to the Reeds, saying that they are worse off, since any slight breeze will cause them to bend. The Reeds told him not to worry about them, as the wind would cause them to bow, but not to break, while the Oak could not bend to stronger winds. A hurricane came a little while later. The great Oak, while standing proud at the beginning, fell with a great thunder, as the Reeds bent in pity.

A great wind of change is happening in electricity markets, unlike any the utility industry has seen from its beginning. Natural gas has topped out coal in the U.S. for the first time, as EPA regulations and lower natural gas prices hack away at previous price advantages. With falling costs for renewables, more environmentally concerned customers, and governmental promotion policies, renewables are increasing their share of the energy mix and will only continue to do so.

On the demand side, the internet of things (IOT), home batteries and solar power, electric cars, and the opening up of many electricity markets are making customers more flexible, adaptable, and independent. Drives to improve the efficiency of electrical consumption also have the impact of increasing renewable penetration, as less electricity is used in total for the same installed renewable capacity.

With nuclear power’s inability to adjust to power demand, it risks going the way of the great Oak. There are three ways to extend the life of nuclear in the energy mix: either lessen the wind by pricing in nuclear power at a different level, increase the flexibility of nuclear by allowing it to adjust to demand, or build smaller reactors that huddle under the wind, i.e. increase grid flexibility as each incremental reactor is smaller.

Lessening the wind: Pricing in nuclear through policies towards risk and carbon emissions

As the utility grid becomes greener, more flexibility and/or storage is required to allow for the intermittency of wind and solar. The first 5-10 percent can be handled relatively simply, using pricing strategies, flexibility in natural gas plants, and demand management at industrial and commercial facilities. However, once renewable penetration becomes large enough, these strategies cease to suffice.

Once the renewable penetration increases over 60 percent, the challenges related to further decarbonising the grid become exponentially greater, and this is where pricing nuclear makes sense. As Jesse Jenkins, an MIT researcher, points out, “It’s not really a fair comparison to say there’s all this low-hanging efficiency fruit and we should do that instead of nuclear, we should be doing that instead of running coal plants.”

The retirement of Diablo Canyon is one nuclear giant that will be affected by pricing metrics for renewables and intermittency in California’s energy market. Coming in at 2,200MW, Diablo supplies almost 1/10th of California’s power just by itself. While the decision has been highly politicized, PG&E has recently determined that after 2025, California would only need run Diablo Canyon intermittently.

The state hopes to produce 50 percent of its power from renewable sources by 2030.There is no doubt that a full decarbonisation of the electricity grid as quickly as possible should be the goal. Jesse Jenkins notes, “If we want to be 60 percent overall, then that 60th percentage point of renewables is what you should be comparing to Diablo Canyon, not the first cheapest renewable plant you build, in most cases, those marginal plants are quite expensive.”

At these percentages, there are fewer and fewer favourable locations to build renewable generation, more flexibility or storage required in the grid, which all translates into more expensive renewables, despite falling installation costs.

Bending in the wind: demand response in nuclear

As nuclear power plants require large numbers of staff to operate, it often isn’t economically feasible to operate nuclear at 50 or 25 percent power. The portion of fixed costs are simply too high, and economically nuclear makes the most sense at 100 percent power. Related: What Will Happen To Turkey’s Energy Security Following The Failed Coup?

However, many reactors were designed to operate to be load-following. A case in point is the Westinghouse PWR, which was designed to operate on a 12-3-6-3 daily cycle as required: 12 hours at 100 percent power, then a three hour ramp-down to 50 percent power, six hours at 50 percent, and finally a three-hour ramp-up again. Although uranium fuel is not burned as efficiently in this type of operation, it is better suited for the duck-shaped demand curve that California has. New Westinghouse designs such as the AP1000 have greater demand following capabilities than older designs. Nuclear can do the demand response dance, it just hasn’t been asked to the floor.

Huddling under the wind: building small modular reactors

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As older power reactors are retired, smaller reactors can provide greater flexibility in the grid that the larger designs from previous generations. Indeed, if older reactors are giant oaks, SMRs will be reeds. During load following operations plants like the Westinghouse SMR will be capable of “performing ±10 percent load changes at a rate of ±2 percent per minute to support grid frequency response.” Unfortunately, many of the new reactors currently being built will be larger ones, with only Russia, India, China, Pakistan, and Kazakhstan actively building SMRs.

Conclusion

If the goal is to decarbonise the whole electricity grid as quickly as possible, continuing the operation of nuclear reactors makes sense. Further, building new nuclear capacity makes sense at higher total clean power capacity. With today’s technology, a grid completely run on wind and solar would be prohibitively expensive. It is a question of philosophy whether, in the coming decades, the difference is made up by nuclear or natural gas.

Gas meshes better with its ability to ramp up and down as required by the grid. However, it is not carbon-free. Shutting down nuclear plants today will cause challenges down the road, when we seek to completely green the grid. A nuclear plant may not follow demand today. But we do not have enough equivalent storage to compensate for the lost green power. It may make sense to curtail green intermittently now, as we build up the flexibility the grid requires to go completely green.

Japan restarting a considerable part of its nuclear fleet this August after its hiatus due to Fukushima shows how difficult even advanced economies are finding going fully green today without nuclear. Germany chose to delay full decarbonisation over stopping its nuclear fleet. The jury is out on how the rest of the world tackles greening its grid.

The post, Why Renewables Can’t Do It Without Nuclear Power, was first published on OilPrice.com.