Luc Deroo is the managing director of ISL, a French consulting engineering firm that is active in dam and reservoir work across Europe, Africa, and Asia. He is also involved in the French Committee on Dams and Reservoirs and in the International Commission on Large Dams (ICOLD). His work in ICOLD particularly focuses on emerging challenges for reservoirs linked to demographic change, climate change, and technological advances. In this interview, Mr. Deroo tells Hydro Leader about his work and his outlook on the future of the hydropower industry. 


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Hydro Leader: Tell us about your background and how you came to be in your current position. 

Luc Deroo: I’m the managing director of ISL, a consulting engineering company based in France that is active in the fields of dams, hydropower, water resources, and related activities. We are active in Europe, Africa, and Asia. I’m also involved in international organizations like ICOLD. I am the chair of ICOLD’s technical committee dealing with emerging challenges for reservoirs. I also work on hydropower and dams conferences. I sit on the steering committee of these conferences and chair sessions, which focus mainly on innovation. I have spent some time working in Africa, especially in Algeria, Cameroon, Ethiopia, and Tunisia. 

A diagram for an integrated floating solar–hydro power plant.

Hydro Leader: Would you tell us about ISL as a company? 

Luc Deroo: ISL is not a big company. It has 120 employees, most of them in France and maybe 20–25 in other countries in Europe and Africa. We’re active in Western Europe, Africa, and Asia. We work on hydropower projects— both greenfield projects and the improvement of existing hydropower plants—and dam and reservoir projects. We focus on the latter in countries like Algeria and Tunisia, where they tend to focus on water resources, since they don’t have enough water for hydropower. 

Hydro Leader: You’re also involved in the French Committee on Dams and Reservoirs. Would you tell us about that organization? 

Luc Deroo: It is the French member organization of ICOLD. It is mainly active in the field of dam safety, largely because there are not a lot of new dams being built in France. The people involved in the committee focus on safety issues related to the existing dam and levee portfolio in our country. The committee is also active in sharing experience on projects abroad through technical exchanges. 

Another of the committee’s current activities is the preparation of the next ICOLD congress, which will be held in Marseille, France, in 2021. During this congress, there will be a symposium prepared by the French committee entitled “Sharing Water: Multipurpose Reservoirs and Innovations.” Multipurpose reservoirs are, for instance, reservoirs that are used both for hydropower and for water resources. 

Hydro Leader: You are the chair of the ICOLD Technical Committee on Prospective and New Challenges for Dams and Reservoirs in the 21st Century. What are these prospective and new challenges for the 21st century, and how do they differ from 20th-century challenges? 

Luc Deroo: The pace of the construction of new reservoirs has decreased in many countries in the world, while the need for water and renewable electricity has increased. That means that there is a disconnect between needs and the reality of reservoir construction today. This was the starting point of this committee. The question it addresses is how to make dams and reservoirs a key component of addressing the challenges of the 21st century. 

What are these challenges? One is demography: We have to feed, provide water to, and provide cheap electricity to quite a lot of people, many of whom don’t have access to those resources even now. Climate change is also a game-changer for water resources and renewable energy. Also, we believe that dams and reservoirs, though they have some adverse effects, can also help foster biodiversity. People don’t usually think of dams and reservoirs having that effect, but they should, because freshwater environments contain ecological habitats of high importance for biodiversity. We know that reservoirs have a negative effect on biodiversity because they obstruct rivers, but they also have a positive effect because of their capacity to provide water in dry seasons. Better addressing these challenges may pave the way for new types of reservoirs and new ways of thinking about dams’ effects on biodiversity. 

Hydro Leader: How does climate change affect dams and reservoirs, and how do you see them changing to address that? 

Luc Deroo: Climate change interacts with dams and reservoirs in three areas: mitigation, adaptation, and direct effects on infrastructure. Reservoirs can help mitigate climate change by providing hydropower, which is a renewable resource, and supporting the development of solar and wind power. Solar and wind power are intermittent and unpredictable. They need storage, which can naturally be provided by reservoirs. In terms of adaptation, we know that climate change affects water resources. Extreme events and dry spells are more common today. Dams and reservoirs can provide benefits like water storage and flood mitigation and can protect coastal cities. Eventually, climate change will directly affect infrastructure. Climate change changes the water regimes of many rivers, which affects hydropower production. All these effects are interconnected, and devising

ISL performed the implementation study and monitored the construction of the new Kissir Dam in Algeria, which is located less than a mile from the Mediterranean Sea.

projects that integrate all three of these aspects is the most efficient way to combat climate change. 

Hydro Leader: You mentioned the integration of hydropower with other renewable sources. Do you see facilities in the future being constructed specifically with that integration in mind? 

Luc Deroo: I’m quite sure they will be. This is, in my opinion, a major change that has occurred in recent years. The integration of solar power and hydropower is particularly important. For instance, the World Bank asked ISL to assess the opportunities for solar-hydro integration in Western Africa, including in Burkina Faso, Côte d’Ivoire, and Mali, where electricity is expensive and there are not enough appropriate places for additional hydro projects but there is a lot of sun. Those countries are thinking about solar power, but their grids and networks are not strong enough to integrate a large share of solar energy. Our assessment showed that integrating existing hydropower plants and new solar plants at the same location could be an efficient solution to that problem. With certain projects, we’re at the point where integrated solar-hydro power plants could replace thermal power plants of several hundred megawatts (MW). That’s something that’s been initiated in various places in the world, and in the future, we’ll see specific projects based on this idea of integration. 

Next week, our ICOLD committee will meet, focusing specifically on that topic. It has attracted quite a lot of interest from the dam community and the solar community, specifically the floating solar community. 

Hydro Leader: Is pumped storage also a major part of that conversation? 

Luc Deroo: Yes. Pumped storage is key, because we cannot develop solar and wind generation without storage. There are three options on the table. One is pumped storage— reservoirs storing power in the form of water. A second is having a grid strong enough to withstand these intermittent sources of electricity and to balance them among countries, which is what Europe is trying to do. The third is developing alternative storage methods using batteries, hydrogen, compressed air, and so on. Pumped storage won’t

be the only option, and we have to be aware of that. There is some argument about which methods to use and why. 

We have to devise new ideas and new methods to make pumped storage a bit cheaper and more adapted to the different contexts we have in various countries, including countries where there are no mountains. One way to do this is to associate with solar power plants, making use of existing reservoirs. French engineer François Lempérière showed the immense potential of such combinations, for instance with the twin dams concept. Another idea is to use seawater for pumped storage in projects along the coast. A third idea would be to devise pumped storage power plants that have other purposes as well—plants that could be used not only to store electricity but also to perform flood protection functions or to store water for other uses, including biodiversity support. 

Hydro Leader: Are any large dams or reservoirs being planned in France today, whether for water supply, hydropower generation, or pumped storage? 

ISL was the consultant for the new Ramdane Djamel Dam in Algeria.

Luc Deroo: There are some being planned, but that does not mean that they will be constructed. Today, France relies primarily on nuclear power and is working to enhance its network to integrate solar and wind as well. In addition, electricity prices have decreased a lot across Europe. Europe has an excess of power production capacity, so prices are low, and nobody is really thinking about constructing new hydropower plants. However, like other Western European countries, we have quite a few small power plants under construction, and there are several pumped storage plants that may be started in Europe in 2021 or 2022. 

Hydro Leader: Would you tell us about your work with tidal energy? 

Luc Deroo: The history of tidal energy in France goes back to the 1960s, when a tidal project was built on the Rance river estuary in Brittany. However, it was the only one ever built, because France decided to pursue nuclear energy as its primary energy source. Recently, there has been renewed interest in tidal energy. In the UK, a 300 MW project has been developed near Cardiff called the Swansea Bay Tidal Lagoon. Seeing that this project had the approval of many stakeholders, including the local government, the local population, and nongovernmental organizations like Greenpeace and the World Wildlife Foundation–UK, we thought that we might be able to do something similar in France. A small group led by French energy utility Électricité de France and including various professionals started to prepare a report entitled Energy in France. The group found that there were opportunities at quite competitive prices. However, the Swansea Bay Tidal Lagoon project was postponed, and today in France, there isn’t the need for new electricity production capacity. 

One possibility for the future may be combining tidal energy and coastal protection. That combination may make such projects more attractive. There are currently one or two ongoing projects in France that would combine coastal protection not with tidal, but with wave energy. 

Hydro Leader: What is distinctive about the hydropower industry in France, and how does it differ from the hydropower industry in the United States and in other countries? 

Luc Deroo: In France, the industry is mainly focused on the maintenance and improvement of existing power plants. Utilities want to improve their power plants to make them more efficient; to allow them to generate more kilowatt-hours; and to make them more flexible, especially so that

they can adapt to rapid fluctuations of the network and to changes in the market price of electricity. 

Another issue is achieving hybridization with solar by interconnecting existing hydropower plants with solar power plants so that they can deliver electricity to the grid when it is most needed, namely when the electricity prices are higher. 

The third issue is protecting the environment and preserving biodiversity. That encompasses various operations, such as removing old structures. We carry out far fewer removal operations than in the United States, but we do have some old structures that we need to remove. In some places, we are also changing the use and operation of power plants to mitigate effects downstream, including by reducing rapid variations of discharge, providing additional discharge, and causing artificial floods downstream to benefit biodiversity. 

There is also something that in Europe is called ecological continuity, meaning letting fish migrate upstream and letting sediment go downstream. A lot of the structures on rivers have been modified to allow these things to happen. Another thing that ties into this topic is small hydro. There is a strong trend toward the use of small hydro equipment on existing small dams and weirs. Many existing small dams are being equipped with turbines to capture energy. 

Hydro Leader: What is your outlook on the future of the energy? 

Luc Deroo: In my opinion, one thing that could be a big trigger for changes in the near future would be to change the way we look at hydropower, dam, and reservoir projects. Today, these projects are assessed in terms of monetary cost and profits. However, dams and hydropower plants, especially when there are reservoirs included, have negative effects on biodiversity that cannot be quantified in monetary terms. On the other hand, they also provide big benefits for the population and for the environment that are also not easy to quantify. An advance in our methods that would allow us to take account of these externalities would majorly change the way we see these projects and how they perform. It might also make a big difference in the way we operate existing projects. In Africa and southern Europe today, water is much more valuable as a resource for consumption and agricultural use than it is as an input for hydropower production. If we can communicate that new hydropower projects provide benefits in those areas as well, it can make hydropower projects more competitive against solar or wind, which do not have the same external benefits for societies and environment. 

Luc Deroo is the managing director of ISL. For more about ISL, visit