20 Mar 2023
9 min

Alqueva's floating solar panels combine innovation and sustainability

It was inaugurated in 2022, pioneering how energy will be in future: innovation hand in hand with ecosystems. 

The Alqueva floating solar power plant, initiated following a successful pilot-protect in the Alto Rabagão reservoir, is now Europe's largest solar energy production platform floating on a lake. This project is not only notable for its size – its development required many technical problems to be overcome and it serves as an example for projects on other lakes, where the same concept can be replicated.  

Innovate with what already exists: is this possible? 

Innovations in a project of this type come in several layers - from the initial concept to the reality. A journey through these different stages is worthwhile to better understand the pioneering aspects and their undeniable benefits. 

It is certainly exciting to create something from scratch. But innovation can also involve analysing what already exists and how it can be taken in a new direction. This was the thinking that gave birth to our project: look at existing infrastructure, such as hydroelectric dams, and think about increasing their potential.  

From combining the vast area of water with solar energy came the idea of creating a floating solar power plant. The Alqueva project puts into practice the innovative 


concept tested in the pilot project developed at the Alto Rabagão reservoir. The same hybridisation idea has also been researched in other parts of the world, proving it is both feasible and an excellent solution with numerous advantages: 

  • Combining the two energy sources – hydro and solar – makes it possible to use a single grid connection point (that of the reservoir) more effectively. In fact, this is the first time the hybridisation concept of adding a new technology to the same grid connection point has been implemented in Portugal. The advantage is clear: connection points are rare assets, but are not used at capacity throughout the day, meaning that spare capacity can be used to make them more effective.  
  • Another positive aspect of this project is that no new electrical transmission lines need to be built, since the floating power plant uses the infrastructure already in place for the energy produced at the dam.  
  • Adding a floating photovoltaic power plant is complementary to the dam, given that, in general terms, when it rains (benefiting hydroelectric production) there is less sunlight and vice-versa.  
  • Another notable advantage is constructing the power plant on the surface of the reservoir behind the dam leaves land available for agriculture or recreational activities, for example, while having less impact on the environment and landscape than a land-based solution. 

Hybridisation, combining electrical energy produced by water, sun, wind and storage, is a logical path for growth in which EDP continues to invest, enabling it to produce cheaper energy, optimise resources and reduce environmental impact.Miguel Stilwell d’Andrade,CEO of EDP, during the inauguration ceremony for the Alqueva Floating Photovoltaic Solar Power Plant.

The challenges of hybridisation 

Deciding that a floating photovoltaic platform connected to the same connection point as the hydroelectric power plant would be the ideal solution, presented the project with another technical challenge: building it on a reservoir associated with a dam. Alqueva is the "largest reservoir in Europe", which may seem a title with little impact but, in reality, constructing on such a reservoir is an engineering challenge. It is located in very deep valleys (almost 70 metres deep), with steep banks, and the surface of the lake oscillated by more than 20 metres. 

Given the configuration of the reservoir in the installation area, the depth at which the platform is moored varies, meaning special care was needed because its anchoring systems could not be fixed rigidly. This is so technically complex that other innovative projects are need to gain experience and provide guidance, such as the FRESHER research project, which has tested different anchoring systems, including special elastic cables that allow the platform to follow the rise and fall of the water level. 

As the level of the reservoir varies over the months, the moorings must be sufficiently elastic to allow for the changes in level between the minimum and maximum expected, while also ensuring that the platform does not move from its position, countering the action of the strong winds that blow in this area. This presented a complex engineering exercise that would be simpler in a concrete water reservoir, for example, which already exist in other parts of the world. 

Welcome to the future of energy in Europe 

It was also decided to add another layer of innovation: a battery with nominal power of 1 MW and storage capacity of around 2MWh is an essential element for maintaining grid stability in the case of renewable energy, because production is not linear, but unstable, dictated by the natural elements. When clouds appear or the morning is foggy, the solar energy production curve drops. Having a battery makes it possible to store the energy produced by the floating power plant at time of greater production (sun exposed) and to export this to the grid when solar production falls.  

But energy storage is already commonplace at hydroelectric installations. At Alqueva, energy is stored in the form of water on days when this element is in excess, to generate energy on days of greater demand. This is thanks to a pumping system which runs on energy produced by the floating solar power plant when activated. 

This complex production hybrid has created a type of ecosystem very similar to how Europe will produce energy in the future when it has high penetration of renewables, enabling renewable energy use to be maximised and ensuring the stability of the grid, while having much lower environment impact. 

Reduced impact on the environment 

"Behind the thinking that led to this project is the question: what can we do that has the lowest impact on the environment? We not only want to make a project that is solar, wind or from another renewable source, but one that has the lowest possible impact on the environment and minimises the use of natural resources as much as possible. This is what drives this type of project," says Miguel Patena, responsible for the Alqueva Floating Solar Photovoltaic Power Plant project at the time of its inauguration.  

The Landscape is one of the most significant descriptors in environmental studies for this type of project and the impact may be considered positive by some and negative by others. Environmental concerns were actually part of the genesis of this project, not only through the investment in renewable energy and utilisation of infrastructure, but also in how the engineering was conceived, through innovation, to pioneer reductions in the environmental footprint. 

Traditionally, the panels in a floating solar power plant sit on plastic floats. Looking to the future, and because EDP is committed to sustainability and with promoting the circular economy, EDP challenged Amorim Cork Composites, which markets cork, and Isigenere, which manufactures floats, to produce a float with lower CO2 footprint. Together, the three companies developed an unprecedented float, made with composites of cork and HDPE (recycled plastic), unlike alternatives, which are made entirely from virgin plastic. 

As a result, these floats have a carbon footprint about 30% lower than traditional ones and the two companies plan to continue the partnership to develop carbon neutral floats. Its blue colour is well camouflaged in the water. 

flutuadores Alqueva

What do we have now and what does the future hold? 

When crossing the large structure of the dam, pause for a moment in the middle to admire the future. On one side, the work of the artist João Louro, which celebrates the phrase "On a clear day you can see forever". On the other, a photovoltaic mirror rests on another mirror, the water surface. The set of approximately 12,000 panels – identical to those installed on the roof of a building, for example – float on approximately 25,000 floats, over an area of four hectares. 

They were installed with an inclination of 5 degrees and east-west orientation, which may seem strange, since the panels on land, in Portugal, have an optimal inclination of 30 degrees and are oriented to the south, but this is the best way to resist the wind and take advantage of the entire area, reducing shadows and extending production hours. The result is 7.5 GWh of annual energy that will benefit 1500 families in the region. 

Although these numbers are large, it should be remembered that the area of this platform is 6000 times smaller than the total area of the reservoir – that is, the platform occupies the equivalent of 0.016% of the total area of the reservoir. "If 3% of the Alqueva area were occupied with solar panels, there would still be 97% of the area free for all other activities," explained Prime Minister António Costa, during the inauguration of the project in July 2022. 

It is possible to continue to add to the production facility made here without cannibalising this space of incredible natural beauty and with many other uses for the local economy. For now, EDP plans to add 70 MVA in floating solar energy to that already produced in Alqueva, this being the capacity won in the first auction of floating solar power conducted in Portugal this year. 

These approximately 70 hectares of panels will not be connected to the dam's electrical infrastructure, but directly to the transport network and will be hybridised with wind, another complementary source to solar – in winter there is less sun and more wind, in summer, the opposite. There will be another 70 MVA in solar and 70 MW in wind turbines placed a few kilometres from the reservoir. 

photo of the Alqueva dam, with the floating solar platform and the work of the artist João Louro with the phrase "On a clear day you can see forever"

The path to decarbonisation 

"Alqueva is today an example of innovation and sustainability, which we will soon be reinforcing with the new project won in the first floating solar power auction in Portugal," said Miguel Stilwell d'Andrade, adding that, "EDP is a global pioneer in floating solar panels technology, which is a remarkable leap forward in the expansion of renewables and in accelerating the decarbonisation process". 

The European Union is committed to achieving carbon neutrality by 2050 and, with innovative projects like this, EDP is not only contributing to the common goal, but going further. We have set the target to be 100% green by 2030. Making the transition to achieve this future target has already begun and the investment in solar energy is key.