A new study by IFISC (CSIC-UIB) scientists, developed in the context of the European Project VPP4ISLANDS and published in IEEE Transactions on Sustainable Energy, proposes a model that emulates how the electricity grid behaves when a large amount of variable renewable generation is introduced into it. The researchers validated the model based on current data from Gran Canaria and analysed the increase in the island's wind farm capacity.
The frequency of an electricity grid constitutes a good indicator of the balance at any time between electricity generation and consumption demand. In the absence of efficient storage methods, the present scenario is one in which generation is adapted to demand in real time. This poses many technological challenges, especially if the percentage of electricity generated from variable renewable sources such as the sun or wind is to be increased. One of the difficulties in increasing the share of renewable generation is that production depends on environmental factors and is not instantly available whenever it is needed. Knowing how the grid, and specifically its frequency, will respond to an increasing variable renewable generation is key to considering a transition to a more sustainable world.
To study how the frequency will behave with these changes, the researchers proposed a model that reproduces the electricity grid in Gran Canaria as a paradigmatic example of an island. In this model, a network is proposed in which each node corresponds to a power plant or substation. The power stations are assumed to have conventional power generation including control capacity. Specifically, in the case of Gran Canaria, they are combined cycle, gas and steam turbines and diesel engines. The model has been validated on the basis of real data on demand, generation and frequency fluctuations.
To test how the introduction of renewables would affect the grid stability, the researchers simulated what would happen in a scenario with increased wind generation, i.e. increasing the installed wind farm capacity. In doing so, they observed that fluctuations in grid frequency would be well above the established limits. These limits, regulated by law, exist to ensure the integrity of the infrastructure, which could be damaged if the grid frequency variations exceed a certain value. In such a case, the supply and generation of some parts of the grid would have to be shut down to avoid collapse.
In order to reduce frequency variations, the researchers increased the secondary control of conventional plants. In this way, it can be estimated what measures should be taken in a future scenario to prevent an increase in the wind farm from affecting the grid infrastructure. These estimates are made for both summer and winter. In addition to checking what controls would need to be implemented, the model allows checking which transmission lines need to be upgraded or reinforced to be prepared for a scenario with increased wind adoption. The model can be generalized and the authors are working in its application to the case of the Balearic Islands in order to move towards more sustainable electricity generation.
M. Martínez-Barbeito, D. Gomila and P. Colet, "Dynamical Model for Power Grid Frequency Fluctuations: Application to Islands with High Penetration of Wind Generation", IEEE Transactions on Sustainable Energy, doi: 10.1109/TSTE.2022.3231975.