10:45 AM - 11:10 AM
[U05-05] Dark Doldrums (Variable Renewable Energy Drought) in Japan and their Future Changes
★Invited Papers
Keywords:Climate change, Variable renewable energy, Dark doldrums, Energy drought, Machine learning
Variable renewable energies (VRE), such as wind and solar power, can contribute significantly to the mitigation of climate change because they do not emit carbon dioxide when generating electric power. On the other hand, so-called “dark doldrums (Dunkelfaute) = energy drought”, in which a period of “sunless and windless” lasts for several days, leads to the risk of long-term energy supply disruptions due to an imbalance between electricity demand and supply when VRE penetration is high. Although the amount of VRE installed in Japan is not large enough to cause problems from dark doldrums, it is necessary to clarify the detailed timing and causes of dark doldrums in order to achieve both carbon neutrality by 2050 and a stable electricity supply. In this study, we use historically reconstructed long-term VRE generation output and electricity demand to clarify the climatological and meteorological characteristics and factors behind the occurrence of dark doldrums and extreme high residual load events (ExRL; electricity demand minus VRE output) in Japan. We also evaluate the impact of climate change on the occurrence of these events in Japan by utilizing the large-scale ensemble climate projection data named d4PDF (database for policy decision making for future climate change).
Dark doldrums are events in which cloudy days and light wind days continue for several days, during which PV and wind power generation are insufficient. The analysis results for the Tohoku region, for example, show that three days of sunless-windless occur several times a year, and tend to occur frequently from early summer to autumn. The factor causing dark doldrums in this region is the stagnation of the rainy season (Baiu) and autumn (Akisame) rainy front. Not only is PV power generation affected by the front, as the wide area of the Tohoku region is covered by clouds, but wind power plants are unevenly located on the Sea of Japan side, which makes it impossible to effectively generate power from the northeasterly air currents blowing toward the front. With regard to future changes, the frequency of dark doldrums events tends to increase under climate change impacts. In addition, annual cumulative and peak electricity demand tends to increase with increasing temperatures, suggesting the possibility of an unprecedented long-term ExRL event. Under the energy conversion to VRE, other power sources will be needed to cover the electricity demand during the no-light and no-wind periods, and considering that this event will last for several days, weekly planning of electricity supply and demand will become more important.
Additionally, the potential impact of changes in VRE installed capacity on the relationship with weather and climate was also investigated using three simplified future target scenarios of VRE installation. The results show that at the current level of VRE installation, ExRL is seen in the winter season, but the difference between winter and summer seasons will narrow with an increase in VRE installation. On the other hand, the variability of ExRL on daily and weekly scales increases. To analyze the winter weather pattern (WP) associated with ExRL, a self-organizing map was applied to historical atmospheric circulation fields derived from atmospheric reanalysis data. Under conditions with low (current) levels of VRE introduction, ExRL is associated with a cold-surge type WPs. However, under future conditions with higher levels of VRE introduction, the results showed a shift in ExRL WPs to a south coastal cyclone type. On the other hand, there are large interannual variations in the frequency of ExRL occurrences, which are currently strongly associated with winter monsoon-related climate variability, but this relationship weakens significantly with increasing levels of VRE installation. This is shown to be due to the WP dependence on the relationship between the amount of VRE generation output and electricity demand. To ensure energy resilience and maintain a stable electricity supply in the future, it is important to understand and take into account the dependence of electricity supply and demand on weather and climate conditions in power system design and VRE installation planning.
References
Ohba, M., Y. Kanno, S. Bando, 2023: Effects of meteorological and climatological factors on extremely high residual load and possible future changes, Renewable and Sustainable Energy Reviews, 175, 113188. doi:10.1016/j.rser.2023.113188.
Ohba, M., Y. Kanno, and D. Nohara, 2022: Climatology of Dark Doldrums in Japan, Renewable and Sustainable Energy Reviews, 155, 111927. doi:10.1016/j.rser.2021.111927.
Dark doldrums are events in which cloudy days and light wind days continue for several days, during which PV and wind power generation are insufficient. The analysis results for the Tohoku region, for example, show that three days of sunless-windless occur several times a year, and tend to occur frequently from early summer to autumn. The factor causing dark doldrums in this region is the stagnation of the rainy season (Baiu) and autumn (Akisame) rainy front. Not only is PV power generation affected by the front, as the wide area of the Tohoku region is covered by clouds, but wind power plants are unevenly located on the Sea of Japan side, which makes it impossible to effectively generate power from the northeasterly air currents blowing toward the front. With regard to future changes, the frequency of dark doldrums events tends to increase under climate change impacts. In addition, annual cumulative and peak electricity demand tends to increase with increasing temperatures, suggesting the possibility of an unprecedented long-term ExRL event. Under the energy conversion to VRE, other power sources will be needed to cover the electricity demand during the no-light and no-wind periods, and considering that this event will last for several days, weekly planning of electricity supply and demand will become more important.
Additionally, the potential impact of changes in VRE installed capacity on the relationship with weather and climate was also investigated using three simplified future target scenarios of VRE installation. The results show that at the current level of VRE installation, ExRL is seen in the winter season, but the difference between winter and summer seasons will narrow with an increase in VRE installation. On the other hand, the variability of ExRL on daily and weekly scales increases. To analyze the winter weather pattern (WP) associated with ExRL, a self-organizing map was applied to historical atmospheric circulation fields derived from atmospheric reanalysis data. Under conditions with low (current) levels of VRE introduction, ExRL is associated with a cold-surge type WPs. However, under future conditions with higher levels of VRE introduction, the results showed a shift in ExRL WPs to a south coastal cyclone type. On the other hand, there are large interannual variations in the frequency of ExRL occurrences, which are currently strongly associated with winter monsoon-related climate variability, but this relationship weakens significantly with increasing levels of VRE installation. This is shown to be due to the WP dependence on the relationship between the amount of VRE generation output and electricity demand. To ensure energy resilience and maintain a stable electricity supply in the future, it is important to understand and take into account the dependence of electricity supply and demand on weather and climate conditions in power system design and VRE installation planning.
References
Ohba, M., Y. Kanno, S. Bando, 2023: Effects of meteorological and climatological factors on extremely high residual load and possible future changes, Renewable and Sustainable Energy Reviews, 175, 113188. doi:10.1016/j.rser.2023.113188.
Ohba, M., Y. Kanno, and D. Nohara, 2022: Climatology of Dark Doldrums in Japan, Renewable and Sustainable Energy Reviews, 155, 111927. doi:10.1016/j.rser.2021.111927.