The COVID-19 pandemic has had a significant negative influence on energy consumption in 2020. On April 7, 2020, in response to the rapid spread of the infection, the Japanese government imposed a state of emergency. This action impacted energy consumption, energy production, and electricity prices. This study compares the impact of a reduction in load demand on renewable energy in the Japan public power grid under a state of emergency declaration (April to May 2020). Using publicly available data, comparisons are made for Kyushu, Tokyo, Kansai, and Hokkaido and assessed in relation to epidemic severity and geographical distribution. The results can be summarized as follows. (1) The consumption profiles and amounts of power consumption reduction are different in different areas. Tokyo shows the largest share of reduced load, followed by Kansai, Kyushu, and Hokkaido. The load reduction was mainly seen during the day, which reflects the differences in people's activities relative to the same period in 2019. (2) Different means of power dispatch, including power generators, energy storage systems, and transmission lines are used and compared in terms of responses to the changes in electricity consumption profile. (3) The overall fall in total load demand and the change in load sequence affected the integration and curtailment of photovoltaic power generation and consequentially caused the electricity price to drop. This paper clarifies the effects of COVID-19 on the public power grids of Japan. Further, it establishes the impact on policymakers in relation to the development of renewable energy.
I. INTRODUCTION
A. Background
According to Refs. 1–4, the outbreak of the novel coronavirus disease (COVID-19) has had a considerable impact on every sector of economic life. To prevent the spread of the disease, the Japanese government called a state of emergency on April 7, 2020, requiring 13 prefectures to shut down some public facilities and requiring that human contact be reduced by more than 70% by implementing telework. As described in Refs. 5 and 6, these restrictions were expanded to the national level on April 16. On May 25, the declaration of emergency, which had lasted nearly 2 months, was lifted. Under the declaration, public facilities were closed, and large industry and other businesses were also affected. The user-side structure of electricity distribution changed, and this affected the overall amount of electricity consumption and load demand distribution as well.
These circumstances can be expected to alter the supply of renewable energy and traditional fossil fuel energy with the load reduction. With declining energy demand due to the spread of COVID-19, it would be economically reasonable to give priority to renewable energy due to its low marginal cost. By contrast with traditional electricity generation methods, renewable energy does not require fuel. During the COVID-19 pandemic, it can be expected that the rate of transition from fossil fuels to renewables would consequently be maintained or strengthened further. However, unlike the conventional technologies of power supply, renewables that have intermittency characteristics may pose challenges to the operational management of grids, such as power sector dispatch,7,8 renewable curtailment,9,10 and real-time spot-market prices.11,12 Therefore, due to the intermittent characteristics of photovoltaic (PV) electricity output and seasonal patterns in relation to electricity demand (particularly in transition periods), this paper analyzes the impact of electricity load changes on PV power integration and its influence on the power grid during the epidemic period (April 7 to May 31). This paper studies 4 of Japan's electrical distribution areas, taking geographical distribution and the severity of the epidemic into account, to assess how power dispatch was affected by the load reduction caused by COVID-19.
B. Literature review
1. Worldwide studies of COVID-19 in the energy sector
The spread of COVID-19 has had a significant influence on economic activities worldwide, in addition to killing many people.13 According to the COVID-19 tracking system developed by Johns Hopkins University (JHU), as of May 31, 2020, there had been more than 5 × 106 cases of COVID-19 recorded around the world.14 Many countries imposed restrictions to slow the spread of the virus, including closing educational institutions, partial or full lockdowns, requiring employees to work from home where possible, and so on.15,16 The energy sector, a pillar of the global economy, suffered a great deal. Because electricity is essential for most economic activities, we could use electricity demand to assess the impact of a change on the economy, as observed in Refs. 17–19. In Japan, hourly data for electricity demand in 10 regions are available on websites maintained by electricity transmission companies. Investigating decreases in electricity demand could provide an important and immediate understanding of how economic activities are affected by a pandemic or other occurrence. On April 7, 2020, the rapid spread of COVID-19 infection prompted the Japanese government to announce a state of emergency. The impact of the state of emergency on electricity demand in Japan has been empirically estimated.20 Because the U.S. is among the most severely affected by COVID-19, a cross-domain approach to analyzing the short-run impact of COVID-19 on U.S. electricity sector is presented. The results indicate a significant reduction in electricity consumption that is strongly correlated with the number of COVID-19 cases, degree of social distancing, and level of commercial activity.21 Because of the significant drift in electricity load consumption due to changes in human activity during the pandemic, it is essential to analyze the impact of COVID-19 on electricity.
The use of renewable energy reduces greenhouse gas emissions and ensures the continued energy supply. The capital cost of renewable energy has significantly dropped in recent years, and it is expected to fall still further. Depending on Refs. 22 and 23, renewable generation therefore may be more attractive on a cost basis than traditional fossil-fuel-based power technology. In Japan, the capacity of PV power generation has grown rapidly in recent years, particularly after the feed-in tariff (FiT) policy was launched by the Japanese government in 2012.24
2. PV integration
Limited by fossil fuel resources and environmental mitigation, the development of renewable energy is urgent.25,26 In Japan, with the launch of the FiT system in 2012, PV power generation started developing nationwide, and the installed capacity of the PV system increased sharply from 100 MW in 2011 to 10 GW in 2019.27,28 However, with integration of massive accounts of PV power into the grid, it resulted in compression of baseload generators.29 When the electricity supply exceeds the demand, Japan's public power grid gives priority to the use of pumped storage and regional connecting lines for electricity dispatchment. Based on the current priority feeding rule, the power curtailment of PV power generation is then carried out to adjust the excess electricity.30 In addition, to increase the penetration of PV, energy storage systems,31 regional transmission lines,7 hydrogen production,32 battery,23 and other flexible systems are used to power peak shaving and valley filling. These citied studies focus on analyzing the impact of variable PV penetration rates on the public grid, or how to increase the penetration rate of PV in the grid. However, this paper mainly analyzes the correlation between load and PV from the perspective of the impact of load characteristics on PV penetration. In addition, it analyzes the direct penetration and suppression of PV power generation considering the power generation composition of the study area. It provides new ideas for the development of PV in each region.
3. Electricity pricing
Electricity markets are becoming increasingly important for the global energy sector.33,34 By adjusting the design of the electricity market, new challenges can be met, and renewable energy can be integrated into the power generation mix. However, the intermittent nature of the limited knowledge of future renewable energy power generation and the randomness of weather conditions have profound impacts on an integrated power system and constitute real challenges to grid operation and management, as well as to the operation management of real-time electricity spot market prices.35,36
Due to the intermittent nature and non-dispatchability of PV and wind power generation, these sources of energy are classified as variable renewable energy (VRE). Aimed at assessing how intermittent renewable production depresses electricity prices, a previous study investigated the effects of intermittent VRE power generation on electricity price formation in Germany. Found that PV power generation reduces the volatility of electricity prices by scaling down the use of peak-load power plants.34 Variable wind power reduced the electricity price,37 but at the same time increases their volatility.38 The impact on prices has decreased over time in line with an increase in VRE electricity production.39 These causes difficulties to managers in the choice of power generation units.
This paper analyzes not only the impact of changes in PV penetration on electricity prices, but also the comprehensive impact of power generation composition on electricity price. It complements previous studies on the influence of single energy and region on electricity prices. Moreover, this paper selects four Japanese public power grids with different power-generation structures and load characteristics. A correlation between generation structure and electricity price is clearly indicated. This result provides a reference value for price makers to find the ideal generation portfolio. The results also help clarify the contribution of different energy sources to the electricity price, and could help inform the integration of renewable energy into the electricity market.
C. Objective
The Japanese government's COVID-19 emergency program significantly altered people's habits and activities at the country level. These changes are reflected in the use of the electric power system, in particular, with regard to electricity consumption curves. The integration of renewable energy changes with different match magnitudes between loads and the generation of power from renewable energy. However, due to the stochastic characteristics of the output of renewable energy, its integration into a power grid is attended with challenges to the management of power grid operation, and this can also affect price fluctuations in the real-time spot market.
Therefore, this manuscript evaluates the impacts of the state of emergency on electricity demand in the Japanese public electrical grid from April to May 2019 in two main aspects. These are the impact of the total load reduction on power generation structures and changes in load demand characteristics on renewable energy penetration. The real-time electricity market is also analyzed due to its strong relationship to renewable energy. The relevant framework for this research is given in Fig. 1.
The epidemic has caused changes in human activities, which affect power consumption and time. This changes the electricity demand curve accordingly. Power generators on the supply side are affected by the load characteristics on the demand side. This is especially true for PV power generation with intermittent characteristics. This paper focuses on the influence of load characteristics on power generation units, with a special focus on PV power generation. In addition, few studies have investigated the impact of different power generation structures on electricity prices. This paper analyzes four Japanese public power grids with different power demand characteristics and power supply ratios.
The remainder of this paper is organized as follows. The data resources examined are described in Sec. II. Section III presents the analytical methodology for load reduction and its impact on electricity prices. The impacts of COVID-19 on total load and the countermeasures taken by public grids in response to the electricity demand reduction are discussed in Sec. IV. In Sec. V, we describe the changes in specific load sequences and their impacts on renewable energy penetration. This section also assesses the influences of integrated renewables on electricity market prices, assessed using publicly available market data. The conclusion and a discussion are given in Sec. VI.
II. DATA SOURCES
Japan reported its first coronavirus case on January 16, 2020. In response to the rapid spread of the infection, the Japanese government announced a state of emergency in seven prefectures in three areas on April 7. The state of emergency was extended to the entire country on April 16, and it was canceled everywhere on May 26.5 During the emergency, the government restricted the use of public facilities, prohibiting restaurants, bars, stores, gyms, and other companies from normal operations as well as restricting people from moving, consequently reducing much economic activity. These changes are reflected in the electric power system, particularly in changes in electricity consumption. Therefore, we compare April and May 2020 to a reference period in 2019.
The Japanese public electric grid is divided into 10 areas.6 Different regions have different power generation compositions, show different load demand profiles, and experienced different levels of severity of the epidemic. Kyushu, Tokyo, Kansai, and Hokkaido were selected as the research objects by comparing the distribution of the severity of the pandemic, as indicated in Fig. 2, as these areas had the highest numbers of cases. According to the COVID-19 system developed by NHK, as of May 31, 2020, there were 21 037 infections nationwide, affecting 28 of 46 prefectures.20
Distribution of infected people and research areas (as of May 31, 2020).
Figure 3 depicts the installed capacity of power generators in the research areas according to Refs. 40–43. Renewable energy includes biomass energy, geothermal energy, PV energy, and wind energy. These data resources are combined with hourly load demand from different sectors downloaded from the websites maintained by Japan electricity power companies.44 Beyond power generation data on both the supply and on the demand sides, the storage capacity and transmission lines between regions also play a significant role in real-time power balancing in different public grids. Load demand in different areas and its influence on the penetration of renewable energy and consequent changes in real-time spot market price are also analyzed. For this purpose, we use hourly market spot trading prices in the research areas from the Japan Electric Power Exchange (JEPX).44
Data from April and May 2020 are compared to data from April and May 2019. Our final data set includes data on hourly load demand distribution, installed capacity of the power supply, and real-time spot market price distributions from Kyushu, Tokyo, Kansai, and Hokkaido, running from April to May for 2019 and 2020.
III. METHODOLOGY
A. Electricity load balance between supply and demand
The objective of this paper is to analyze the impact of changes in load characteristics on power generation, particularly the PV power penetration in different regions during the pandemic period and its further impact on electricity prices. The adaptability of the power grid to PV is closely related to the load shape, which determines the reliable operation of the dynamic balance between regional power generation and power consumption. Because the power grid needs to be balanced between the supply and the demand sides, daily supply and demand can be assessed as follows:
where, Pcons presents the power generation from base-load plants, including nuclear power, hydropower, geothermal power, and coal power; Pflex is defined as flexible generators that can adjust their output to adapt to the situation of the PV and power grid, such as gas power; dis refers to the discharging power system, PVdirect is directly accommodated PV, integrated by power grid; and Loadgrid stands for total electricity demand.
The availability of PV power generation, the capacity of the pumped hydrostorage system (PHS), and the flexibility of the power grid restrict the direct integration of the PV power generation. The load decreased during the epidemic period, but in cases of overproduction, it is difficult to reduce the constant output of nuclear power as a basic part of the load. Therefore, in this case, PV panels were controlled to reduce output. For this reason, excess power is generated by PV. In this study, two parameters are employed to evaluate PV penetration in the power grid. One is the PVdirect which is used to present the ratio of PVdirect in the power grid, as shown in Eq. (2). Then PVcur is given as the ratio of PV production curtailment in Eq. (3).
where Ppv represents total PV power generation, output presents the total electricity generation on the supply side, and trans is the flow of power transferred across regional transmission lines.
B. Impact of power generators on electricity price
Due to the low degree of correlation between PV power generation characteristics and load curve, the load distribution is reshaped to resemble a “duck curve,”45 thereby reducing residual load demand. In the peak load response, the low marginal cost of renewable power generation is generally given priority, which reduces the traditional thermal power generation. Japan's grid managers generally favor PV or wind power generation, fuel oil power generation, and PHS to meet peak load. However, limited by the capacity of pumped storage and constant output power generation, PV curtailment is increased when the penetration rate of PV power generation exceeds the basic load unit.30
Therefore, as the penetration rate of renewable energy with lower marginal costs increases in the power generation structure, the overall price of the electricity market decreases, and grid operators, in response, lower the sale price of electricity. This paper considers the impact of PV on electricity price through a correlation between the distribution characteristics of price fluctuation and PV power generation. The interaction between PV and electricity price is analyzed by comparing the PV penetration-load histogram, price-distribution histogram, and daily price fluctuation trend between the implementation period of emergency state and the same period in 2019.
IV. ELECTRICITY CONSUMPTION CHANGE DURING THE COVID-19 PANDEMIC
A. Total load demand reduction
As seen in Fig. 4, electricity demand was reduced to varying degrees for all objective areas due to the COVID-19 pandemic. The drops in Tokyo and Kansai were more noticeable than those in Kyushu and Hokkaido. The reduction in electricity load caused by the gradual limitation of people's behavior and activities after the imposition of the state of emergency by the Japanese government during the epidemic period. The closure of public facilities and industrial centers had a particularly large effect on electricity consumption. However, differences in demand between research areas were also affected by the voltage composition of power consumption on the user side.
Comparison of demand reduction for the month of April and May 2019 and 2020 for Kyushu, Tokyo, Kansai, and Hokkaido.
Comparison of demand reduction for the month of April and May 2019 and 2020 for Kyushu, Tokyo, Kansai, and Hokkaido.
There are three major types of voltage produced by power utilities: including low voltage, high voltage, and ultra-high voltage (UHV). For UHV, the voltage supplied is more than 7000 V. This is used for large-scale factories and facilities that use electricity on a large scale. High voltages are defined as alternating current voltages ranging from 600 to 7000 V, and low voltages are below 600 V, respectively, for small and medium factory facilities and homes. In 2019, in Tokyo and Kansai, the main consumption came from the primary sector (34.85% and 34.85%, respectively), the secondary (industrial) sector had 31.25% and 29.02% of total load, and the residential sector accounted for 33.90% and 34.20% of total demand. In Kyushu and Hokkaido showed dominant consumption in the residential sector, at 49.74% and 40.79%, respectively. During the state of emergency, people's activities were limited, and they had increased demand for residential electricity as a result. However, the decline in commercial and industrial demand for electricity was far greater than the increase in residential demand. To sum up, the load reduction for Tokyo and Kansai was more noticeable than that for Kyushu and Hokkaido, as indicated by the differences in the composition of electricity consumption.
B. Dispatch on power generation sectors
Due to the differences in infrastructure for regional and power generation, load demand reduction has different impacts on the different regions. The composition of power generation is divided into three parts for our analyses, namely, traditional thermal power generation, nuclear power generation, and renewable energy power generation, as well as and dispatching departments, including PHS and interconnection lines.
Figure 5 shows the energy generation mix and percentage changes for the four areas most affected by COVID-19 pandemic. First, Kyushu Electric's rate of renewable energy power generation increased by 30.31% in April and May of 2019 to 35.38% in the same period of 2020. The total electricity demand for April and May of 2020 fell by 4.52% compared to the reference time of 2019, and for the real-time balance of power demand and supply, the constant output of nuclear plants was significantly reduced, from 43.67% to 36.90%. PV and wind power account for the largest proportion of renewable energy generation. However, the main obstacle to using PV and wind energy is its variability or intermittency, with power outputs fluctuating depending on unpredictable climate conditions. Therefore, increasing the percentage of thermal power generation can balance load demand at night or during periods of no wind or sunlight. In addition, discharged PHS power of can be used in conjunction with flexible thermal power plants to adapt to peak load at night, so PHS and interconnection line utilization therefore increase with increases in power generation percentage of VRE, as shown in Fig. 5.
Breakdown of power generation for April and May 2019 and 2020 for Kyushu, Tokyo, Kansai, and Hokkaido.
Breakdown of power generation for April and May 2019 and 2020 for Kyushu, Tokyo, Kansai, and Hokkaido.
Second, both Kansai and Tokyo Electric Power generated less than demand, with nearly 15% of the load demand coming from the neighboring regions through interconnection lines, unlike the case of Kyushu. In addition, renewable energy accounted for almost 20% of electricity generation in both areas, which is a lower rate than that in Kyushu. To balance between supply and demand on the grid, flexible thermal power generation in the Tokyo area fell to 67.29% from 75.75% in 2019, and that of Kansai Power fell to 48.08% from 54.77%. Due to the reduction in the baseload, the imbalance between supply and demand came at some moments when load demand is relatively high, which led to an increase in the power import capacity to compensate for the reduction in electricity due to partial closure of the thermal power system. Therefore, the proportion of power generation for the interconnection lines of both the Tokyo area and the Kansai area increased by about 5%, as shown in Fig. 5.
Finally, Hokkaido had the least reduction in total load affected by the epidemic. There was little change in renewable energy generation, and the increased thermal power generation resulted in a 4.02% reduction in electricity imports and a 5% increase in electricity exports.
This result indicates that grid operators made trade-offs between stability between power plants and VRE. At the same time, the power balance was also affected by the supply and demand of the power load as well as by the installed capacity of pumped storage and connection lines.
V. CHANGES IN LOAD PROFILES AND THEIR IMPACT ON RENEWABLE ENERGY SOURCES
A. Load-related statistics
Although Fig. 4 presents acceptable results for total load reduction, the performance can be evaluated more accurately through a histogram of electricity load and electricity consumption profiles, as shown in Fig. 6, for all possible 1 h intervals over 122 days of 2019 and 2020 (April to May). Compared to the same period in 2019, the fitted curve for 2020 shows a tendency to move toward the left, which can be attributed to reduction in electricity load due to the limitation of people's activities. The electricity load distributions exhibit short tails (see Fig. 6), which represented a noticeable reduction from peak load; however, this should also be understood in relation to the time distributions of the load. Figure 7 illustrates the load distribution profiles aligned to the load histogram to comprehensively describe changes in load sequence due to COVID-19. The blue line in Fig. 7 represents trends in weekly electricity demand in April and May of 2020, and the red line shows the load for a reference week in 2019. Due to the high level of electricity consumption by large-scale factories during working hours, the peak load mainly occurs during the day, between 9:00 and 18:00, thus a significant peak load reduction was caused by the closure of factories and public facilities. To compare peak load reduction in research areas, Fig. 6 indicates a more noticeable kurtosis in Tokyo and Kansai than that in Kyushu and Hokkaido and decreases significantly for electricity loads higher than 34 000 MW and 17 000 MW, respectively. This is further evidence that peak load reduction is correlated with the composition of the electricity consumption voltage.
Comparison of load histograms for April and May 2019 and 2020 for Kyushu, Tokyo, Kansai.
Comparison of load histograms for April and May 2019 and 2020 for Kyushu, Tokyo, Kansai.
Comparison of weekly load profiles for April and May 2019 and 2020 for Kyushu, Tokyo, Kansai, and Hokkaido.
Comparison of weekly load profiles for April and May 2019 and 2020 for Kyushu, Tokyo, Kansai, and Hokkaido.
Figure 7 presents a closer comparison, at the week level among the regions. It is obvious that electricity demand was reduced during daytime working hours from Tuesday to Saturday. However, the reduction in peak load reduction around 18:00 on Sunday nights showed a small downward trend, indicating that people were more restricted in their activities during working hours than in the reference times in 2019, and normal evening activities continued on Sunday night. In contrast with other weekdays, Monday mornings in 2020 showed a chaotic trend across all four regions. An important factor to consider is that Mondays mark the start of the work week, and in 2020, employees tended to work remotely, with more work being done than on the remaining weekdays. For Hokkaido, as seen in Fig. 6, the daily consumption profile during the pandemic is very similar to the profile of the pre-pandemic reference days in 2019. Therefore, the impact on Hokkaido power was appreciably smaller than that in Kyushu, Tokyo, and Kansai.
B. Impact on PV integration
Due to the mismatch between real-time renewable energy generation and grid load, the changed load sequence affects the integration of PV power generation into the public grid. The descriptive statistics for total PV penetration and curtailment ratio in 2019 and 2020 are shown in Table I. Kyushu had the dominant PV penetration, followed by Hokkaido, Tokyo, and Kansai. In the research areas, total PV penetration in 2020 was slightly higher than that in 2019, and PV curtailment only occurred in Kyushu and increased in 2020 compared to 2019. Figure 8 depicts changes in PV penetration except for values lower than 10%. As can be observed, compared to the reference time, all regions showed the tendency to have a right-hand long tail, indicating an increasing penetration of PV, as seen in the larger values in 2020. Both the increased PV penetration and the curtailment relate to the flexibility of electricity generation and the implantation of dispatch storages. Taking Kyushu and Tokyo as examples, Fig. 9 depicts the daytime power balance schedule in Kyushu and Tokyo when PV accounts for the largest proportion of power generation, respectively. The day with the highest PV penetration is selected to illustrate the impact of increasing the PV integration ratio on different public grids, and the loads are normalized to peak value. However, the flexibility of available resources and the necessity of real-time balancing of the power system limits the integration of VRE penetration in the public grid. For Kyushu, PV penetration reached 69.61% in April and May 2020, and the limited available capacity of PHS and interconnector lines with the neighboring regions could not help releasing balance pressure under the overlarge integrated PV capacities. Thus, due to the operational constraints, approximately half of PV production needed to be reduced. In Tokyo, the maximum PV penetration in 2020 reached 41.92%, as flexible of thermal generators combined with PHS systems and regional interconnector lines absorbed PV production without causing any curtailment during the emergency. In both Kyushu and Tokyo, the results of the analyses indicated that flexible thermal generators and dispatch systems in PHS implantation and interconnector lines played an important role in reducing PV curtailment during the massive PV production periods. The utilization of PHS and interconnection lines were greater in 2020 than for the comparable day in 2019, as shown in Fig. 9.
Descriptive statistics for PV power generation in 2019 and 2020 (April to May).
. | PV penetration (%) . | PV curtailment (%) . | ||
---|---|---|---|---|
Year . | 2019 . | 2020 . | 2019 . | 2020 . |
Kyushu | 17.00% | 20.68% | 9.38% | 10.72% |
Tokyo | 8.50% | 9.29% | 0.00% | 0.00% |
Kansai | 7.45% | 8.07% | 0.00% | 0.00% |
Hokkaido | 9.80% | 11.62% | 0.00% | 0.00% |
. | PV penetration (%) . | PV curtailment (%) . | ||
---|---|---|---|---|
Year . | 2019 . | 2020 . | 2019 . | 2020 . |
Kyushu | 17.00% | 20.68% | 9.38% | 10.72% |
Tokyo | 8.50% | 9.29% | 0.00% | 0.00% |
Kansai | 7.45% | 8.07% | 0.00% | 0.00% |
Hokkaido | 9.80% | 11.62% | 0.00% | 0.00% |
PV penetration histograms for April and May 2019 and 2020 for Kyushu, Tokyo, Kansai, and Hokkaido.
PV penetration histograms for April and May 2019 and 2020 for Kyushu, Tokyo, Kansai, and Hokkaido.
Comparison of daily power balance for April and May 2019 and 2020 in Kyushu and Tokyo.
Comparison of daily power balance for April and May 2019 and 2020 in Kyushu and Tokyo.
C. Impact on electricity price
The increasing integration of renewable energy sources has a profound impact on power systems, as they are challenging for the operation and economy of real-time trading markets in their intermittency. Due to the changing daily pattern of electricity demand, the wholesale price of electricity fluctuates as real-time supply and demand change. To better understand the relation of real-time spot markets to demand, taking Kyushu as an example, Fig. 10 shows the color-scale distribution of real-time electricity trading markets in Kyushu at hourly intervals for April and May 2019 and 2020. First, compared with 2019, the real-time market prices for 2020 dropped significantly, especially in the early morning, noon, and evening. As previously discussed, the peak load reduction mainly occurred in the night and early morning affected by the epidemic limitation. Therefore, the load reduction interval and the electricity market price distribution in Fig. 10 feedback a good correlation between electricity demand and electricity price. In addition to the morning and evening, the data clearly indicate that the electricity price at noon was significantly reduced compared to 2019. This was caused by the increasing penetration of PV power generation. The share of PV power in the grid reshapes the price pattern and reduces the electricity price accordingly. The overall impact of electricity demand and PV integration rate on electricity prices are illustrated in Fig. 10. To accurately compare the impacts of the PV power integration changes on spot trading price within four research areas. Figure 11 presents a histogram of the spot market prices for Kyushu, Tokyo, Kansai, and Hokkaido in April and May 2019 and 2020. The results indicate that in both 2019 or 2020, Kyushu and Kansai had similar spot trading distributions, as did Tokyo and Hokkaido. In addition, Kyushu and Kansai had a relatively leftward tendency, indicating a lower spot trading price than that in Tokyo and Hokkaido. To allow more detailed comparison of results, the statistics of the average real-time spot market price in research areas are presented in Table II.
Market spot trading prices in Kyushu during April and May 2019 (left) and April and May 2020 (right).
Market spot trading prices in Kyushu during April and May 2019 (left) and April and May 2020 (right).
Histogram of spot market prices in Kyushu, Tokyo, Kansai, and Hokkaido during April and May 2019 (left) and April and May 2020 (right).
Histogram of spot market prices in Kyushu, Tokyo, Kansai, and Hokkaido during April and May 2019 (left) and April and May 2020 (right).
Summary statistics of average electricity price in research areas.
Time periods . | Kyushu . | Tokyo . | Kansai . | Hokkaido . |
---|---|---|---|---|
2019 (April to May) | 6.70 | 9.77 | 6.87 | 10.44 |
2020(April to May) | 3.73 | 6.29 | 3.91 | 6.16 |
Time periods . | Kyushu . | Tokyo . | Kansai . | Hokkaido . |
---|---|---|---|---|
2019 (April to May) | 6.70 | 9.77 | 6.87 | 10.44 |
2020(April to May) | 3.73 | 6.29 | 3.91 | 6.16 |
VI. DISCUSSION AND CONCLUSIONS
In this work, the impacts of COVID-19 on the public electrical grids of Kyushu, Tokyo, Kansai, and Hokkaido are analyzed through a comparison of data drawn from the declaration of emergency period and a reference period (April and May 2019 and 2020). The primary findings of this paper are as follows:
COVID-19 caused reductions in load demand of varying magnitudes in 2020, with the reduction in Tokyo being the largest, followed by those in Kansai, Kyushu, and Hokkaido. The closure of large factories and the limitation of people's activity due to the emergency declaration resulted in a large reduction in working time.
Most electricity companies took countermeasures to respond to the load reduction due to the COVID-19 pandemic. These measures contained three main aspects, including the adjustment of the traditional generation of thermal nuclear power, the penetration of renewable energy power, and the utilization ratio of dispatch sectors, such as PHS and transmission lines between neighborhood regions.
First, the supply of renewable energy was not influenced by COVID-19. Because renewable energy has a lower marginal cost than thermal and nuclear power generation, the penetration of renewable power generation in the public grid increased with the decline of total load-demand reduction.
With the increasing penetration of renewable energy and decreased electricity demand, different degrees of compression for thermal power generation and nuclear power generation were obtained in the baseload composition. Pumped storage and transmission lines in Tokyo and Kansai directly consume the impact of the increased amount of renewable energy on the power grid without causing power suppression. Therefore, thermal power generation is mainly used to adjust load fluctuations, which decrease as load demand decreases. Maximum daily PV penetration reached 69.61% in the power grid of Kyushu, and the balance of supply and demand could not be maintained through power dispatch systems such as PHS and interconnectors. Consequently, the frequency and amount of curtailment of PV increase with decreases in demand and increases in supply. This caused the share of nuclear power generation to decrease from 40.12% in 2019 to 36% in 2020. The increasing penetration of PV power generation and the decreasing share of nuclear power generation are due to the intermittent characteristics of VRE, such that thermal power generation is increased to meet imbalances in power generation between the supply side and the demand side during the night or times of weak sunlight that reflect the low amount of PV power generation. Hokkaido exhibited the least impact from COVID-19 on load demand reduction, with an imported electricity amount that slightly decreased with the decreased total load-demand reduction.
In summary, the impact of COVID-19 on the power generation structure of the four research regions was thoroughly analyzed and compared. Once the load is reduced, the power company should immediately adjust the structure of the power generation and regulate the operation of the power grid, meanwhile ensuring the stability and reliability of the power grid. This reflects the importance of having a range of power generation structures to respond to natural disasters in a timely way.
Due to the closure of large-scale factories that consume UHV electricity, as well as the increased electricity consumption in the low-voltage residential areas, the load demand sequence was different during the study period. Therefore, the matching degree of PV power generation and load demand changed accordingly. PV penetration increased with the load demand reduction in the research areas, but PV curtailment ratio only increased in Kyushu due to the limitations of dispatch storage systems and almost 70% (normalized to peak demand) baseload operation demand. Hence, the overall load decline did not cause a decrease in PV power generation, and its penetration rate in the four regions increased, improving the utilization rate of PV.
Electricity spot trading prices decreased with the increased proportion of PV power generation. Because PV power generation reshapes the distribution pattern of the grid load, it can have a significant impact on the electricity trading price, particularly in the case of high PV penetration. It was further found that the trading price in Kyushu and Kansai had a lower value than that in the same period in Tokyo and Hokkaido, which indicates the need to explore the contribution of different power generators on prices more fully.
PV intermittent output has a significant impact on the balance between supply and demand on a power grid, particularly for a high penetration rate of renewable energy. This paper analyzes the interaction between load and renewable energy power generation, the composition of baseload units, and real-time spot market prices through total load demand reduction and changes in load demand characteristics during the pandemic period. A reduction in load demand leads to a partial outage of traditional thermal power generation based on fuel supply. On the other hand, considering economic constraints, it is necessary to maintain PV power generation with lower marginal costs. In this case, due to the increased penetration of PV power generation, technical and operational challenges such as intermittency and stability arose. However, these problems can be solved by adjusting the generation structure. Energy storage capacity and non-schedulable continuous generation units in this generation structure reveal the possibilities and limitations of future PV generation penetration. Moreover, correlations appeared between PV power generation and electricity price across regions of Japan, which shows that increased PV penetration can reduce the electricity market price to further strengthen national energy independence by increasing the PV penetration rate and reducing the electricity price. Overall, this paper presents a comprehensive understanding of the impact of COVID-19 on the public grid of Japan and allows the measures taken by different electricity companies faced with the sudden load change to be compared, to the benefit of the policymakers considering the future development of renewable energy.
AUTHORS' CONTRIBUTIONS
All authors contributed equally to this work.
ACKNOWLEDGMENTS
The authors thank Kyuden Electric Corporation, Tokyo Electric Corporation, Kansai Electric Corporation, and Hokkaido Electric Corporation for graciously providing the power generation and consumption information for Kyushu, Tokyo, Kansai, and Hokkaido, respectively.
DATA AVAILABILITY
The data that support the findings of this study are available from the corresponding author upon reasonable request.