Reminder - Primary & Secondary Reserves - What’s That 🧐

The stability of the national electrical grid is essential to ensure electricity remains continuously available in homes, businesses, and public infrastructures. To maintain this stability, it is crucial to precisely manage the balance between electricity production and consumption. This balance is regulated through mechanisms called frequency reserves, which include primary and secondary reserves.

Here’s a brief reminder of these concepts ⤵️

Primary Reserve (FCR)

The primary reserve, also known as Frequency Containment Reserve (FCR), is the first line of defense for the electrical grid against immediate disturbances. Imagine that electricity demand suddenly increases because everyone turns on their heating during a cold snap. The primary reserve intervenes to compensate for this demand surge within seconds to minutes. It works a bit like an airbag in a car: it deploys quickly to protect the system from sudden shocks. Energy sources that can respond very quickly, such as certain power plants or energy storage systems, are used for this task.

Secondary Reserve (FFR)

The secondary reserve, or Frequency Firming Reserve (FFR), comes into play just after the primary reserve. It operates over a slightly longer period, usually from a few minutes to an hour, to further stabilize the grid after the primary reserve’s initial adjustments. You can compare it to adjusting your speed on the highway after avoiding an obstacle: it’s about maintaining stable and safe driving after the initial evasion reflex. This reserve is provided by energy sources that can maintain their production or energy absorption over an extended period, allowing the grid to "firm up" to a new normal.

These reserves are crucial for two main reasons ⤵️

1. First, they ensure that electricity remains constantly available, even in the event of unexpected fluctuations in demand or supply.
2. Second, they help prevent power outages that could occur if these fluctuations are not properly managed. By maintaining the grid’s frequency (the rate at which electricity is produced and consumed) stable, these reserves contribute to the safety and efficiency of the national electrical system.

Can Nuclear Power Plants Perform This Role? 🧐

Nuclear power plants used to have the drawback of being unable to effectively adjust their output to meet the needs of primary and secondary reserves. This statement might have been true in the past, but it is no longer today.

Nuclear plants can largely perform this role within our energy mix. They indeed have considerable primary reserve (PR) capacity and can react instantly. Contrary to what I had mentioned, a nuclear unit, when called upon, can increase its production well beyond the 27 MW of primary reserve usually requested by the grid operator (RTE). In fact, it’s common for this production to reach up to 100 MW within seconds, which is comparatively higher than other energy sources.

Modulation Rate: Nuclear reactors can typically modulate their output between 50% and 100% of their rated capacity. According to the International Atomic Energy Agency (IAEA), modulation can occur at a rate of about 5% of the rated capacity per minute for reactors designed for load-following (including the EPR reactors discussed below), which is comparable to some fossil fuel plants. For example, for a 1300 MW reactor, this means a modulation capacity of up to 65 MW per minute.

Modern nuclear reactors, especially those using advanced technologies like the EPR (European Pressurized Reactor), can modulate their output from 20% to 100% of their nominal capacity. This modulation, as mentioned earlier, can occur at a rate of about 5% of the nominal capacity per minute. However, older reactors and those designed for "base load" operations may have slower modulation rates.

Primary Reserve Response Time: According to the Organisation for Economic Co-operation and Development (OECD) and the Nuclear Energy Agency (NEA), some nuclear reactors can indeed increase their output quickly to contribute to the primary reserve. For example, reactors can be configured to increase their output by 100 MW within a few seconds to minutes, depending on the reactor’s specific requirements and configuration.

So yes, in theory, we have nuclear capabilities to cover a significant part (or even the entirety) of the primary & secondary reserve needs.

"In theory," because nuclear reactors designed for "base load" require costly adaptations that won’t happen overnight. However, it is worth noting that adaptations have been successfully made by EDF. Additionally, with the 10 EPR reactors promised by the government (if they actually come to fruition), will this question still arise at that point?

Let’s take a quick look at the current state of the French nuclear fleet ⤵️

The Current State of the French Nuclear Fleet ☢️

Currently, France has one operational EPR reactor (European Pressurized Reactor) located in Flamanville (Flamanville 3). Regarding reactors designed to operate as base-load, the majority of the French nuclear fleet is intended to operate as base-load power stations. This includes older reactors primarily designed to operate continuously at full power to provide a stable source of electricity. France has a total of 56 nuclear reactors spread across 18 production sites, and apart from the new EPR design, most are older designs, such as the pressurized water reactors (PWR) family, configured for base-load operations.

In France, the ability of nuclear reactors to modulate their output to meet primary and secondary reserve needs varies based on the design and specific technology of each reactor. Historically, nuclear reactors were primarily used for base-load operations, operating at constant output due to their high energy efficiency at full load. However, with the evolution of the electrical grid’s needs and the increasing integration of renewable energy sources, part of the French nuclear fleet has been adapted to allow for operational flexibility.

Adaptation of Reactors for Modulation 🔋

EDF has initiated programs to adapt some of its reactors so that they can modulate their output and thus contribute to frequency reserves:

• N4 Reactors (1,450 MW) and some 1,300 MW reactors: These reactors have been adapted to offer more flexible modulation, allowing them to adjust their output relatively quickly to meet primary and secondary reserve demands. Modulation can include changes in output of around 5% of their nominal capacity per minute, enabling fairly quick adjustments to contribute to frequency reserves.
• 900 MW Series Reactors: There are also efforts to increase the flexibility of these older reactors, although their ability to modulate quickly is generally lower than that of newer, larger units.

A Complex Financial Equation 🪙

Nevertheless, the financial equation is complicated ⤵️

Recently, with the increasing production of renewable energies (RE) such as wind and solar, which have priority access to the grid, modulation has become necessary to avoid overproduction and grid saturation during RE production peaks and low demand. Today, about half of the reactors in France (28 out of 56) participate in this load-following, compared to 20% in 2012.

However, modulation comes with costs. Nuclear reactors are designed to operate optimally at full capacity, as 90% of their costs are fixed. When they are not running at full capacity, the unit production cost increases while revenues decrease. For a reactor modulating at a 75% availability factor instead of 90%, this represents a significant loss in production, which could lead to a considerable shortfall given the current electricity market prices.

A recent example illustrates this issue, we can go back to December 2022:

• On December 12, following a cold snap, the nuclear fleet was used at its maximum available capacity of 41 GW to meet a demand of over 82 GW, but wind power, struggling, only provided 6 GW from a total capacity of 19 GW.
• On December 31, with a very limited demand of 49 GW, wind power benefiting from a winter depression reached 16 GW. As a result, the nuclear fleet, which EDF had increased to 45 GW, became oversized, and beyond modulation, more than ten reactors had to be shut down, and startup times delayed to bring the power down to 27 MW.

What is commonly referred to as the "complementarity between nuclear and non-controllable renewable energies" is actually one-sided due to the priority given to renewable energies on the grid. When they are available, nuclear plants must adjust their output. On the other hand, in the absence of renewable energy, nuclear, sometimes supported by thermal plants, must meet the energy demand on its own.

This issue runs deep, and our leaders will make decisions about this complementarity that is not working in favor of our nuclear fleet ⤵️

Technical Impacts

• Accelerated Wear: Reactors, especially those built between 1978 and 1999, were not designed for frequent modulation. Increased modulation leads to greater mechanical wear, raising random incidents by 25% and potentially causing structural damage such as erosion and chemical imbalances in the reactor cores. This situation accelerates the aging of the primary circuit, especially if the rate of two movements per day is exceeded.
• International Comparison: As noted by the Nuclear Safety Authority (ASN), these reactors undergo higher mechanical stress, limiting their lifespan and safety compared to American reactors, which operate under less variable regimes.

Economic Consequences

• Financial Loss: Modulation reduces the availability factor (Kd) from 90% to 75%, resulting in a loss of production of approximately 1.3 TWh per GW. This represents a lost revenue of 130 to 200 million euros per GW, which, for a fleet of 61 GW, amounts to an annual revenue loss between 7.9 and 12.2 billion euros.
• Increased Costs: The unit production cost also increases, from 50 €/MWh to around 60 €/MWh for a Kd of 75%, resulting in an additional production cost of 66 million euros per GW, or 4 billion euros for the entire fleet.

Is Battery Storage (BESS) a Solution?

To evaluate whether battery storage (Battery Energy Storage Systems, BESS) is a viable solution to compensate for losses caused by the instability of non-controllable renewable energies (RE) in France, we first need to determine the total capacity of the relevant RE and then calculate the associated cost of installing adequate storage capacities.

Installed Renewable Energy Capacity in France

The total installed capacity for non-controllable renewable energies in France by the end of 2022 is as follows:

• Wind: 20.9 gigawatts (GW), including 20.4 GW from onshore wind and 0.5 GW from offshore wind (Statistiques du Développement Durable).
• Photovoltaic Solar: 11.6 GW of installed capacity by 2023 (Lendopolis - Official Blog of Lendopolis).

Total : 20.9 GW+11.6 GW=32.5 GW

Cost of Battery Storage

To calculate the cost of the storage required to stabilize this capacity, we first need to estimate the required storage capacity. Let’s assume that we want to cover about 10% of this capacity for one hour to compensate for short-term fluctuations (which is a conservative baseline assumption for this type of calculation). This requires a storage capacity of:

Required storage capacity=32.5 GW×10%=3.25 GWh

The cost of storage can vary widely depending on the technology and specifications, but taking a realistic price range of 200 to 400 € per installed kWh, the total cost would be:

• Minimum cost : 3.25×106 kWh×200 €/kWh=650 million €

=650 million €

• Maximum cost : 3.25×106 kWh×400 €/kWh=1.3 billion €

=1.3 billion €

Cost Comparison

The financial losses caused by the instability of RE, estimated between 7.9 and 12.2 billion euros, must be compared with the cost of installing batteries:

• Cost of batteries : between 570 million and 1.14 billion euros for a storage capacity of 2.85 GWh.
• Losses due to instability : between 7.9 and 12.2 billion euros.

These calculations suggest that integrating storage solutions could significantly reduce the costs associated with managing the variability of renewable energies, making the grid more stable and predictable, while offering a potentially favorable return on investment considering savings on avoided losses.

Based on a solution that prevents grid instability for 1 hour across the entire capacity of the non-controllable RE fleet, even if we remain in estimations, these calculations demonstrate that it is worthwhile to push further. The cost of storage solutions will continue to decrease as this sector industrializes and demand accelerates.

Conclusion - The Stakes Are Crucial

In conclusion, this is probably why Jean-François Noal explained that the modulation of nuclear plants is a challenge caused by the progress of RE in our energy mix. Yes, nuclear plants can modulate (and do) their output quickly to meet the urgent needs of primary and secondary reserves.

But from a financial standpoint, they shouldn’t be used for this purpose (at least not as frequently). The priority given to RE, which are unstable in their injection into the grid, disrupts the current organization of our energy mix and harms the development of nuclear power. Yet, the government has set an ambitious policy for the expansion of the EDF fleet.

The development of RE in our country, as currently conceived, makes the financial equation unsolvable. We won’t be able to extend the lifespan of our nuclear fleet or find a sustainable financial profitability for EDF. The simultaneous and rapid development of non-controllable renewable energy and nuclear power will inevitably increase the need to modulate energy production. During certain periods, such as summer or weekends, this could even require complete shutdowns of nuclear reactors. Our production is therefore not entirely assured, at least in its continuity.

This conclusion raises many exciting questions about strategic choices in energy policy. Should we remove the priority on the grid currently given to RE? Should it be given to hydropower (pumped storage) and then nuclear? Should we moderate the development of non-controllable RE? Or should we associate new energy storage solutions like in countries without nuclear capacity?