Renewable: New turbine technology will make hydropower more flexible

Sun and wind provide affordable, clean and renewable energy, but its production is determined by the weather, not by need. That is why we need other energy sources that can create a balance between supply and demand.

In the world of renewable energy, adjustable hydropower is the most suitable option, but even hydropower is not flexible enough in all situations. This may now change.

International research collaboration

The Francis turbine, which is the most common turbine in hydroelectric power plants, is best operated at full load, i.e. with maximum water flow and water pressure. If there is too little water, turbulence and pressure fluctuations can form in the water that can quickly damage the turbine.

"This means that the turbines must either be run at close to design loads or stopped completely, which reduces the flexibility of the power plant," says Erik Jacques Wiborg in Statkraft. He is a turbine expert and the internal project manager for Statkraft in two research projects, AFC₄Hydro and HydroFlex, under the EU framework programme Horizon 2020.

The two projects have slightly different approaches but both are aimed at making hydropower plants more flexible. Industry partners and research institutions from several countries are participating in the projects.

"Increased flexibility will make it easier to use adjustable hydropower even with larger, faster and potentially short-term fluctuations in wind and solar energy production. Today, lithium battery is about the only technology suitable for that job," says Wiborg.

Many hydropower plants must meet minimum water flow requirements in the watercourse downstream from the power plant, which means that they often have to divert water around the turbines.

"Due to the technical limitations of the power plant, we can't always use this water for power generation, at least not without significantly reducing the service life of the turbine. With new or improved turbines we will be able to run hydropower plants at lesser loads and increase the reaction time of the machines," he explains.

Counter-flow technology

The AFC₄Hydro project will develop technical solutions for the gentle operation of turbines under adverse loads. The goal is to increase the service life and flexibility of existing turbines. The project will further develop a technology that Statkraft previously helped develop with Flow Design Bureau and Troms Kraft Energi (see video below).

"This is a system where we inject water to counteract swirling flow and pressure fluctuations that can damage the turbine. Today's system works, but it has the potential for improvement. We are working on a solution where we can adjust the angle of the nozzles that inject the water, which will improve effect and reduce water consumption," explains Wiborg.

"We are also testing a technology using mechanical pistons downstream from the turbine runner. These can create positive or negative pressure that counteracts pressure fluctuations in the water. Time will show what works best under different conditions," he adds.

Newly developed turbine

The second project, HydroFlex, focuses on designing turbines and associated systems that can withstand faster starts and stops several times a day.

"It is the response time that prevents hydropower from offering the same flexibility as batteries," says Wiborg.

The HydroFlex project will further develop turbines, generators and transformers that can respond faster.

"As an important environmental measure, we will develop a system in the same programme that will reduce the effect of frequent changes in water flow downstream from the power plant. Just as with noise-cancelling headphones, counter-waves must be created that neutralise the fluctuations coming out of the plant. This will make the water flow in the river more constant, even if we stop and start production more often," says Erik Jacques Wiborg.