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What exactly is flexibility? A visit to Portugal's hydropower plants lifts the veil on the future of energy

Understanding flexibility – in generation, storage, and operations – offers key insights into how renewable energy can adapt to our evolving needs. A step behind the scenes at EDP’s historic hydropower plants in Portugal provides a glimpse into the energy systems of the future, writes Greg Tracz.

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PORTO, 2 AUGUST 2023 – Flexibility – it’s the ability to adapt easily to a variety of demands. Take the azulejos, the traditional ceramic tiles of Northern Portugal. These versatile tiles, mostly white, offer more than aesthetic appeal; they also provide a reflective shield against the fierce Iberian sun and a protection against dampness. The infinite visual combinations they offer and their practical qualities explain their long-lasting presence in the region’s urban landscape.

Just as azulejos meet a range of expectations, the energy sector is currently facing pressure to evolve beyond power production – helping to stabilise the power grid and safeguarding the environment. At the heart of this transformation is the concept of flexibility. The more flexible a power plant can become, the more valuable it may be to the energy system.

To find out about the various facets of flexibility, I recently joined a select group of energy professionals on a journey through the verdant landscapes of Northern Portugal and the hidden pathways carved under the mountain.

EDP, Portugal's power utility, provided access to three of their power plants, which are part of the XFLEX HYDRO initiative, a European Union funded 4-year research and innovation programme that seeks to push the operational limits of hydropower.

Operating 49 hydropower plants with a total installed capacity of 5,076 MW, EDP is no small player in the energy sector. Our journey included visits of Caniçada, Alto Lindoso and Frades 2 power plants, all situated within the Cávado-Lima Production Center in Northern Portugal.

Each plant reflects the era in which it was built, showcasing in their own way a facet of flexibility within the hydropower realm: the ability to start and stop at short notice, the ability to balance power generation and environmental protection, and the ability to store energy on demand.

In recent years, the power plants have also embraced a wider definition of flexibility, one that is now entering policy discussions on the future of energy: operational flexibility, or flexibility from improved operations.

Caniçada: from ‘supply side flexibility’ to ‘flexibility from improved operations’

Built in 1954 and refurbished in the early 2000s, Caniçada embodies the spirit of classic hydropower. It's a medium-sized plant with an installed capacity of 62 MW and an average annual generation of 354 GWh. The heart of this powerhouse consists of two Francis turbines of medium head. Francis turbines are the most common water turbine in use today. As it churns out energy, Caniçada also plays a crucial role in maintaining environmental flows, carefully balancing energy production with the ecological needs of the region.

"Eachplant tells its own story," Diogo Cordeiro, Senior Innovation Manager atEDP Produção, explained, as we navigated the recently refurbished infrastructure. "We don't see our hydropower plants as static assets; weconstantly seek to improve their operation and outcomes.”

With XFLEX HYDRO, EDP and its partners set up a methodology to evaluate the benefits of shifting from the current fixed-speed set-up to variable-speed technology. By harnessing the flexibility inherent in variable speed, they discovered that the plant could improve overall efficiency and achieve the same power output with less water. This is particularly relevant considering that extreme, off-design conditions, are likely to increase in the future.  

“We don’tsee this type of exercise as a luxury.” Diogo Cordeiro commented, as he laid out the company’s strategy. “Our ultimate goal is to run 100% on renewables,and hydropower will be a central role in this strategy. We’ve got to make sure we’re making the most of our assets, and exploring ways to increase their flexibility is part of our job.”

What Mr Cordeiro refers to is flexibility from improved operations, one of five types of flexibility defined by the International Renewable Energy Agency (IRENA). The other types include: supply-side flexibility, demand-side flexibility, flexibility from storage, flexibility from grid infrastructure, and flexibility from improved operations.

Hydropower has long provided supply-side flexibility and flexibility from storage. In as little as three minutes, a hydropower plant with water storage capacity can surge to life – far quicker than nuclear or fossil-fuelled power plants. The plant effectively serves as a colossal water battery, with power available on demand. But, as I discovered on this tour, the real buzz is about extending flexibility through improved operations.

At first glance, the concept might appear a bit nebulous. But at its heart, improved operations give a power plant the ability to increase its efficiency and provide stability services to the grid. These improvements might include shorter dispatch intervals, subtle injections of power to maintain the frequency of the grid, and the participation in markets for these very services. To the uninitiated, this language might sound complex, but in essence, it speaks of power plants' role in maintaining a steady power grid despite fluctuating energy generation and consumption.

Crucially, this type of operational flexibility also offers energy companies a chance to increase their bottom line. When a market exists for grid stability – or ancillary – services, this can translate into additional revenues for the power plant.

XFLEX HYDRO experts visit Alto Lindoso hydropower plant

Alto Lindoso: providing services under extreme conditions

Our next stop, Alto Lindoso, provides a striking snapshot of hydropower's evolution. Commissioned in 1992, the year the UN Convention on Climate Change was signed, Alto Lindoso is a multipurpose facility with an installed capacity of 630 MW. Its timing coincided with a heightened global awareness of environmental concerns. Over the years, the project demonstrated the role of multipurpose hydropower in improving the region’s resilience to extreme events.

Situated in a region known for heavy rainfall, the Alto Lindoso dam plays an essential role in flood control. By managing water inflows and outflows, the plant can minimise the impact of floods on downstream areas, thereby demonstrating the value of multipurpose hydropower. The project also played a role in slowing down the effect of a dramatic drought in the region in 2022.

“The Alto Lindoso complex has been part of the region’s landscape for over 30 years now" Carlos Madeira, Executive Board Member at NEW, EDP's R&D Centre for New Energy Technologies explains."Like all the hydropower plants in our portfolio it is an enduring asset. I have witnessed its construction and I still marvel today at its constant reinvention. By adapting to changing demands from the social and regulatory environment, the plant has demonstrated its value time and time again.”

The XFLEX team's goal for this site involved evaluating two low CAPEX opportunities to extend the services offered by the hydropower plant. Tellingly, the team showed that the power plant could continue to provide grid stability services even in times of low water inflow. “Today in the energy sector, flexibility is a much sought-after quality.” Mr Madeira notes.

"Alto Lindoso marks a shift in our thinking," João Gonçalo Maciel, Managing Director at NEW, reflects. “Extending the operating range of Alto Lindoso was made with minimal cost. No new rotors, no new turbine, just the power of computer calculations and simulations.”

Ilídio Francisco, from EDP shows where flexibility is being implemented.

Frades 2: a glimpse into the future

As we journeyed to Frades 2, I was eager to discover how hydropower had adapted to more recent challenges. This project, commissioned in 2017, is a direct response to the rise of intermittent renewable energy sources in the Portuguese energy mix. As a pumped storage hydropower plant, Frades 2 provides back up power during periods of high demand, when wind and solar power may not be sufficient.

For Joanna Freitas, Board Member at EDP Produção, Frades 2 is emblematic of the type of power plant that is needed to incorporate a greater proportion of wind and solar technologies in Europe: “Frades 2 is part of a network of pumped storage plants that we have developed in Portugal” she explains. “These giant water batteries are a key part of the puzzle if we are to increase massively the amount of renewables in the energy mix and maintain the stability of energy provision in Europe.”

Incidentally, Frades 2 is also one of the most advanced power plants in Europe. Its two generation sets are an impressive spectacle – the largest of their kind in Europe, and one of the few variable-speed groups in operation. This technology enables a greater level of control over energy production and delivery.

Even there, astonishingly, more could be done to increase the power plant’s flexibility: “XFLEX is a project that pushes the boundaries of how we can use hydropower plants in a more flexible and responsive way, and Frades 2 was no exception.” Ms. Freitas notes.

The XFLEX HYDRO project uses the site to demonstrate two enhancements to the plant operation: hydraulic short-circuit with variable-speed units and smart controls to optimise grid services, with a particular focus on fast frequency services. These insights serve as a testament to the potential flexibility held by improved operations.

The learnings gathered from this trip were profound. By witnessing first-hand, the innovative work being done at EDP, I was able to better understand the growing importance and multi-faceted nature of flexibility in the energy sector. Clearly, understanding and implementing flexibility is key to ensuring the resilience and sustainability of our energy future.

As the day drew to a close in Porto, I recalled something João Gonçalo Maciel said during our visit: "Most of the time, innovation is incremental. The basic and very sound science of hydropower generation will not change overnight. But every day we are finding new, more efficient way to operate. The next frontier is to use data, digital systems and artificial intelligence to help operators find untapped potential for optimisation."

If we put our ear to the ground, we may be able to pick up the signals of an upcoming revolution in the energy sector, driven by incremental innovation and the push for flexibility. 'Flexibility' is far from just a technical term used by industry insiders. Rather, it’s a tangible, crucial aspect of how we must adapt our energy system to face the challenges of the future.