When we cut fossil energy and nuclear power, and switch to a more sustainable energy system, there is a risk of having a power system that is less stable, with a greater risk of outages over large parts of the country and greater price variations.
Here hydropower comes in with two important properties: storage capacity and swing mass.
Swing mass means that hydropower has great forces in swing at all times - literally. A solar panel, for example, has zero swing mass, and it becomes almost like an on/off switch when the sun shines and when it doesn't.
In a hydropower plant, on the other hand, there is a turbine of several hundred tons that rotates, and it takes time to change its speed. That inertia is actually one of the keys to a stable power system, because it keeps the wheels (literally) always turning and becomes a buffer that ensures a steady frequency of 50 Hertz (Hz) in the power system. This frequency regulation is what makes our power system stable, so that we rarely lose power these days, and that service can be provided by hydropower in a renewable energy system.
But when more unregulated power (solar and wind) enters the energy system, hydropower must change production more often and faster. In addition, pumped storage power is now becoming an even more relevant topic. Water is then pumped back into the reservoirs when the electricity price is low, so that the water can be stored and used when the price or demand is high. All this leads to more variation in the operation of the hydropower plants and can lead to more wear and tear and uncertainty, which in turn requires income from system services that make up for it.
Can benefit from offering stability
Through his research, Tor Inge Reigstad has developed a new control system for variable-speed hydropower plants, which will improve the frequency stability of the system and increase the damping of power oscillations. In cases with little rotating mass (few generators connected), then hydropower plants in for example southern Norway can swing towards power plants in Finland. If the oscillations become too large, the power system will, in the worst case, break down. The regulation system he proposes means that hydropower producers who operate the power plants at variable speed can deliver "fast frequency reserves" FFR to the energy system. This means that in less than 2 seconds they can handle imbalances by regulating production and thus the frequency in the system.
By exploiting the flexibility of the frequency converter between the generator and the grid, and the kinetic energy of the rotating mass in the generator and turbine, variable speed hydropower (VSHP) can provide system services such as virtual (synthetic) inertia, damping of oscillations and FFR. Simply put, the power plant can change its output in milliseconds by extracting or supplying energy from the rotating masses. The speed of the turbine and generator will then change but can be regulated back to the speed that gives the best efficiency by controlling the amount of water through the turbine.