The mastering of large electrical systems - A major challenge at a time of energy transition and the development of renewable energies

REE: The energy transition is reflected, in particular, by a change in the modes of production of electrical energy, with a rapid increase in the share of renewable energy. What are your thoughts on this evolution?

André Merlin: A large electricity system like the one we have been developing in Europe since the end of the First World War is a complex system. The National Academy of Engineering in the United States even went so far as to say that it was the most complex system created and realized by the human mind in the twentieth century. Very quickly, long before the opening of markets, it was realized that in order to master this complexity, decision support tools were needed.

The most complex system created and realized by the human mind in the twentieth century...

This complexity is mainly because electricity is not directly storable. Therefore, there is a constant need to balance supply and demand, which is highly variable throughout the year, week and day. In order for this to be carried out under technically acceptable conditions from the point of view of network equipment and rotating machines, three decisive parameters must be continuously monitored: frequency (with, in Europe, a reference of 50 Hz and an admissible range between 49.5 Hz and 50.5 Hz), voltage, and current. Any deviation from the reference values poses a considerable risk to the grid, i.e. a complete collapse of the electrical system (blackout).

France has experienced two blackouts: on 19 December 1978, the whole country was plunged into darkness for almost a day; in 1987, the ice-jamming of the water intakes of the Cordemais power plant led to the shutdown of its electricity production and the resulting voltage instability led to a widespread blackout throughout western France. In addition, in November 2006, our country nearly experienced another blackout due to an incident in northern Germany that had serious consequences for the entire European network.

For the community, and therefore for the public authorities, such a risk is unacceptable today, given the great dependence of all human activities on electrical energy.

In order to ensure the balance between supply and demand, the transmission operator can carry out two types of power cuts: scheduled as part of predictive load shedding, or immediate and unannounced as part of interruptibility, which is essential to avoid the collapse of the power system. It is thanks to the latter device that we escaped the European blackout during the November 2006 incident.

The electricity market has added degrees of complexity, but community sensitivity to the availability of electricity is increasing.

REE: In relation to this complexity and the risks associated with it, what role have the major changes in the electricity sector over the last twenty years played - or are still playing -?

A.M.: The European electricity market set up from the 1990s onwards has added degrees of complexity to the power system. Firstly, in order to give every customer the possibility of choosing his supplier anywhere in Europe on the principle of third-party access to the grid, it was necessary to translate trade into physical flows and to create an IT infrastructure and power exchanges in Europe. Secondly, the development of intermittent renewable energies means that variations in production have to be compensated for by other controllable means of production. The difficulty stems in particular from the fact that, as degrees of complexity are added, the community's sensitivity to the availability of electricity increases, since electricity is essential to all our activities.

With regard to the permanent maintenance of the supply-demand balance, massive energy storage equipment connected to the grid could - in theory - be a solution to this problem, but we can see the limits of this solution:

• Concerning the so-called gravity storage, limiting the number of sites that can accommodate pumping stations (even if there are still a few);
• Regarding electrochemical storage, there are the problems of cost, unless there is a technological breakthrough, which is currently unpredictable.

The conclusion that is reached fairly quickly is therefore that as these intermittent renewable energies develop, it will be essential to have the means of guaranteeing power, obtained by conventional production systems capable of load monitoring. Today, in France, it is mainly nuclear power that plays this role, thanks to the steering capacity that the French nuclear industry developed; and which was absent from the American industry that originally built these plants. In Spain, these are gas-fired plants; in Germany, they are coal-fired plants, which are gradually being replaced by gas-fired plants.

REE: What you are telling us goes against some of the ideas that have been put forward, according to which the rate of renewable energies in an electricity system could grow without limits.

A.M.: Indeed, these ideas are based on studies that are more than questionable, going as far as envisaging ‘a 100% RE electricity mix’.

They are questionable both technically (system operability) and economically: failure to take into account the economic impact of the intermittent nature of some RE, which requires the provision of other complementary means and makes comparisons, made without precaution, of kWh prices between intermittent energies and energies from controlled power plants irrelevant. It makes little sense to compare the price of a MWh from wind energy with that of a MWh from nuclear energy (including the ‘large fairing’), which are respectively given at 64 and 62 euros per MWh. As wind power is by nature intermittent, the guaranteed production needed to compensate for the absence of wind must be taken into account. Jean-Marc Jancovici has also shown that the lack of controllable means of production leads to an explosion in the price of energy.

REE: However, if we follow the American economist Jeremy Rifkin, the decentralisation of electricity production, which accompanies the development of RE, could lead to savings on the electricity network...

A.M.: That idea is wrong. At the distribution level, it is obvious since the non-guaranteed nature of solar or wind energy production does not allow these theoretical savings to be made and these new means of production must be connected to the grid. However, it is at the level of the large transmission and interconnection network that the development of intermittent means of production must be accompanied by new investments, in particular a strengthening of international interconnections. These interconnections are indispensable, both to strengthen solidarity between countries in the face of supply and demand contingencies, to enable the integration of electricity markets and to integrate renewable energies by taking advantage of a certain aggregation of production on a continental scale.

International interconnections must be developed, but to what extent?

The European Commission is therefore correct to encourage the creation of new interconnections, particularly between France and neighbouring countries: the Iberian Peninsula, Italy, Ireland and the United Kingdom. The problem is that these structures are becoming increasingly expensive because they must be either under water or under ground, due to the difficult acceptability of erecting very high voltage pylons, as we have seen with the France-Spain line project. The question arises as to how far will we go in the development of interconnections. There is a calculation to be made to show that these operations are profitable. It is up to the network managers to highlight these assets in discussions with the Commission.

REE: Will we go as far as intercontinental interconnections?

A.M.: Maybe. There are plans to do so. I will mention two of them.

On the one hand, a high-capacity interconnection between Europe and Africa, which could, depending on the times, operate in either direction: from Africa to Europe to take advantage of the immense solar energy resources in the Saharan and sub-Saharan zones and from Europe to Africa to guarantee the supply of the regions concerned at times when this energy is not present. This is technically feasible, although the impact on the functioning of the systems remains to be explored in greater depth. The political difficulties of such a project are also quite obvious.

The other intercontinental interconnection project was mentioned by our Chinese colleagues from the State Grid Corporation of China at the 2012 CIGRE in Paris. It would link the Beijing region to continental Europe to take advantage of the time difference in activities between these areas. During his presentation in 2012, the President of SGCC went so far as to give a price estimate per MWh delivered in the eastern part of Germany. The use of very high voltage levels (of the order of one million volts) makes it possible to envisage this on a technical level, but the economic profitability of such a project remains to be demonstrated.

Rotating machines (thermal, hydroelectric, or nuclear power stations) are needed to maintain the stability of the system.

REE: Let's come back to the technical problems arising from the development of renewable energies and the limits that electricity network operating constraints can impose on this development. Before focusing on Europe and France, what lessons can we learn from other experiences?

A.M.: Beyond the need to compensate for the intermittent nature of renewable energy production sources, the loss of voltage stability is a major risk, highlighted by many major incidents that have occurred recently. A few recent examples illustrate this:

• In 2016, a series of blackouts in Australia had significant social and political repercussions, following which the South Australian government decided to order new thermal generation capacity;
• in 2017, in Taiwan, following a major blackout, a referendum led to the decision to keep nuclear power;
• in the United Kingdom, a major incident took place in August 2019. The cause of this failure was the loss of thermal production, but also the loss of offshore wind farms. The transmission system operator, National Grid, studied the consequences and has just launched a call for projects, the aim of which is to increase the system’s electromechanical inertia.

Continental Europe may be less sensitive to this risk at present, particularly because "small" countries with high levels of renewables rely on interconnections to maintain voltage stability. The risk is still potentially present, which is why the shutdown of coal-fired power plants must be compensated, at the very least, by the commissioning of gas-fired plants.

REE: In Europe, precisely, and particularly in France, where do we stand in relation to these risks, and what are the limits that should not to be exceeded?

A.M.: It must be understood that electricity production from wind or photovoltaic sources does not naturally bring the inertia provided by thermal or hydraulic power station rotating machines. This inertia is fundamental to ensure the proper functioning of the electrical system, with all of its automated systems.

It is not possible, given the diversity of situations, to draw up a law rigorously establishing the share of production from renewable sources acceptable in a large electrical system. Thus, while wind and photovoltaic energy make a good contribution to energy supply, they do not necessarily contribute to capacity needs. A study by EDF's R&D department suggests a wind and photovoltaic production rate of around 40%, a fairly commonly accepted order of magnitude.

A limit rate of renewables reached around 2030?

In the current situation, there is no major risk, but the French government has ambitious targets for its energy mix. It foresees a much greater production of electricity from renewable energies. For example, one of its objectives is to see wind, solar, hydro, and bioenergy account for 32% of its energy mix by 2030. Given the growth in the share of electricity in the total energy consumed, this figure of 32% of the energy mix could correspond to almost 55% of the electricity mix; if we subtract hydropower production from the total renewables, since hydropower plants contribute to the voltage holding capacity, we see that the share of renewable production in the electricity mix could approach 50%, which shows that it is time to start addressing this issue.

In addition to the crucial technical issue of the system's operational reliability, there is another subject which I feel should be dealt with quickly, in connection with the development of renewable energies: it concerns the operation of the electricity market and the rules governing the use of the various means of production. Situations of negative marginal costs, which are fundamentally shocking, are becoming increasingly frequent; they are linked to the principle of the obligation to purchase production from renewable sources, particularly wind and photovoltaic energy, in clear contradiction with the principles governing the use of the various means of production. This contradiction is manageable as long as renewable energy production is marginal. Here too, it is high time to address this problem and to put in place a solution to ensure a smoother functioning of the system: in the short term, for example, renewable energies could be introduced into the market, with a reasonable bonus.

REE: To push back the limits, particularly in terms of the acceptability of intermittent RE in the power system, various solutions are being discussed: demand management, particularly through ‘predictive load shedding’, increasing storage resources, including the use of electric vehicle batteries, the contribution of intelligent distribution networks, microgrids, better coordination of system control resources at the European level, etc.

What measures do you consider to be the most effective, if not the most urgent?

A.M.: You mention a large number of solutions to push back the system’s. Among them, the possibilities of load shedding are fundamental. This measure must obviously concern major industrials as well as other professionals and domestic consumers. In order to control the management of load shedding among this diffuse customers and to do so in a way that respects people's safety, it is necessary to set up aggregators working in conjunction with the transmission system operator. Intelligent distribution networks, of which the communicating meter (in France, Linky) is the cornerstone, also have their role to play.

Microgrids, whose emergence, particularly in Germany, would be in line with a societal trend towards local energy communities, should also be taken into account; in France, however, they would run the risk of undermining the network access tariff equalization, to which many players are very attached. Among them, in particular, the National Federation of Concessionary and Regulated Local Authorities, as well as the main French distribution network operator, Enedis. Similarly, the development of self-consumption, subsidized by the local authority, would be to the detriment of collective investments, with a risk of undermining the network access tariff equalization.

Some solutions to push the limits a little

The development of network energy storage is the most commonly discussed solution; however, the limitations of this solution under current technologies have already been mentioned above: as far as battery storage is concerned, the constraint is economic, although the cost of stationary storage is falling dramatically and is expected to continue to do so. It may also be environmentally friendly. Gravity storage in pumping stations is more economical, but the sites likely to be equipped are now geographically limited in France.

As for the use of electric vehicle batteries to support the supply-demand balance on the grid, a structure known as Vehicle to Grid, it is an attractive idea. It is worth exploring, even though it is currently at the R&D stage. Here too, the development of aggregators will be necessary.

REE: All these solutions improve system robustness but, at the same time and paradoxically, increase its complexity. Beyond these solutions, can control of the complexity of the European system be further improved by management and system steering means?

A.M.: Yes, there is undoubtedly room for further progress, although the creation of ENTSO-E (European Network of Transmission System Operators for Electricity) has already been a significant step forward. Its value must be extended, which presupposes, in particular, transfers of competences and better coordination of forecasting management. It is not a question of having a single control centre for the European network but of better coordination, both in terms of real time and forecasting management. Experience has shown that serious incidents have been at least partly attributable to misunderstandings between control centres.

There is still room for improvement in system management.

Coordination between transmission system operators is beneficial to the system, while maintaining national control. In Europe, this justified the creation of CORESO, which initially brought together RTE and its Belgian counterpart ELIA at the end of 2008, and which now brings together many other power systems, from Portugal to Ireland via Italy. In the United States, the case of the PJM (Pennsylvania-New Jersey-Maryland) operator is another example, with a coordination area that has spread to many other states since its launch.

To move in this direction, one could imagine, in the case of Germany, moving from four control centres to a single coordination centre, or at most two.

This progress towards enhanced coordination of the European system will certainly take time, but it is necessary.

REE: In the public debate on energy issues, it seems to us that the important issues we have just mentioned are not very present. It is true that they are complex. What can we do to raise awareness, or even convince our fellow citizens?

A.M.: Engineers need to express themselves more than they do today. It is high time to take care of this.

REE: You are now deputy mayor of the town where you were born (Pleaux) and vice-president of the Cantal Departmental Energy Union. In the light of this new experience, how do you see the role of local authorities in the energy transition?

A.M.: Local authorities have a major role to play in energy transition. The experience I have had in recent years in my town and my department shows that their interventions concern, first of all, demand management.

For example, in my town, the renovation of the public lighting system, which made it possible to reduce the subscribed power by a factor of four, the renovation of the municipal swimming pool’s heating system with the installation of a heat pump instead of electric resistance heating, the town hall and post office heating by replacing an oil boiler with a wood pellet boiler, etc.

Local authorities are also involved in other areas, such as the installation of charging stations for electric vehicles and, above all, policies for the installation of generating electricity from renewable energies. In my department, although we are very reluctant to install wind turbines for environmental reasons, we are promoting projects for ground-based solar power plants, one of which is associated with an agricultural-solar project. However, we are faced with a problem of under-equipment in the network (source substation saturated and too far away...), which leads us to take an interest in the renewable energy connection schemes planned by Enedis and RTE. Communities are thus involved in energy planning, but perhaps without mastering all the skills that would be required for this.

REE: By way of conclusion, how do you see the French electricity network, say, in 2050?

A.M.: The transmission network has a bright future ahead of it. Compared to the current network, the 2050 network will be much more underground, including high and very high voltage, right up to the international interconnections. These will have developed further, to an intercontinental scale.

Direct current will have become more important at both ends of the chain (major interconnections and local networks).

Above all, however, unless there are major technological breakthroughs, which are not yet in sight, the network will have to continue to rely on solid power plants to ensure its stability: nuclear power plants, if new ones can be commissioned, or gas-fired plants, despite the drawbacks in terms of greenhouse gases.

But I'm not a clairvoyant...

About André Merlin

André Merlin is the founder and former Chairman of the RTE Executive Board, of which he is now Honorary Chairman. He has been a special advisor to the European Commissioner for Energy and Chairman of CIGRE and Medgrid.