Renewable energies related to the sun or wind will be decisive in the transition to a 100% renewable energy system. These energy sources have many advantages in terms of cost, efficiency and sustainability, but they also represent a risk in terms of reliability of grid operation when deployed on a massive scale. This risk stems from their variability over different time scales, having less production in cloudy days, for example. This makes it necessary to implement additional control and storage systems compared to a grid dominated by generation with conventional energy sources.
Researchers at IFISC (CSIC-UIB) have published a study in which they analyze how the risk of blackouts in the electricity grid varies when conventional power plants are progressively replaced by variable renewable energy sources (VRES), up to generation fractions with renewables above 80 percent. In the article, published in IEEE Access, they have used a model of self-organised criticality for power system outages, known as the OPA (ORNL-PSERC-Alaska) model, and have taken the Balearic electricity system with a high penetration of solar energy as a case study. They have also taken into account a small amount of wind energy, but this energy source is too variable in the Balearic Islands for it to be convenient to implement it massively.
In this work, the researchers only take into account day-to-day variations in renewable production and introduce a storage capacity equivalent to three days of generation to ensure a more constant energy supply. They also assume the current consumption pattern without additional savings measures. The results of the simulations show that, starting from the current case where renewables account for 3 %, up to 30-40 percent of the conventional generation capacity can be replaced by solar PV without increasing the risk of blackouts. Furthermore, this risk is slightly reduced by the fact that solar production is more spatially distributed than conventional production (i.e. there are more production points), which reduces the load on the distribution grid. By further increasing the renewable fraction of installed capacity, keeping the total generation capacity equal to 140 percent of consumption, the risk of blackouts increases exponentially due to the lack of supply on days of low renewable production, mainly in winter.
So, to increase the fraction of renewable energy above 40 percent and guarantee supply at all times to maintain the risk of blackouts at the current level, there are two options: either maintain conventional generation capacity while increasing renewable capacity, or install a large renewable overcapacity. The researchers' calculations show that, in the second case, to reach 80 percent renewable production without increasing the risk of blackouts, solar power capacity must be installed that can produce 2.5 times the annual demand during the year. Even so, in order to guarantee supply during periods of low renewable production, this scenario maintains an installed conventional capacity equivalent to 32% of consumption. Scenarios with less conventional generation would require much more long-term storage capacity.
Carreras, BA, Colet, P., Reynolds-Barredo, JM, Gomila, D. Assessing blackout risk with high penetration of variable renewable energies. IEEE Access. Doi: https://doi.org/10.1109/ACCESS.2021.3114121.