Today, Renewable Energy Institute released a research report entitled "Decarbonizing Grid Systems with Renewables.”
To realize a 100% renewable energy-based power supply and to build a decarbonized society, it is essential to have a system that effectively utilizes the widely distributed renewable energy potentials in Japan, which operates efficiently from the power plant to the point of demand.
What does a power system that supports 100% renewable energy look like? To further explore this, Renewable Energy Institute established a study group of academics and other experts - a Transmission Grid Study Group - to examine the construction of a transmission grid based on the premise of decarbonization by renewable energy in 2050, investment schemes to realize such a grid, flexible demand-side measures, and infrastructures needed to realize such a grid. Renewable Energy Institute compiled this report based on the discussions made by the study group.
We hope this report will contribute to the realization of decarbonization through renewable energy deployment in Japan.
Full Report in Japanese（29.6MB）
<Table of Contents>
Chapter 1: The State of the Debate on Strengthening the Grid to Accelerate the Integration of Renewables
Section 1: Global Trends
Section 2: Transmission Grid Master Plan for Carbon Neutrality in 2050
Chapter 2: Grid System and Flexible Demand for Decarbonization with Renewables
Section 1: Analysis of OCCTO Master Plan Replication Scenarios
Section 2: Analysis of the 100% renewable energy scenario
Section 3: Future vision of grid reinforcement and flexible demand for carbon neutrality
Chapter 3: Examination of Transmission Line Investment Schemes
Section 1: Transmission Line Development Scheme for Offshore Wind Power Development
Section 2: Activities to Combine Offshore Wind Power and Interconnectors
Section 3: Feasibility of Simultaneous Development of Offshore Wind Power and Interregional-connection Lines in Japan
List of References
Appendix 1: Results of Analysis in the "OCCTO Master Plan Replication “Scenario
Appendix 2: Results of Analysis in "100% renewable energy scenario”
Setting the two scenarios and comparison; one is the "OCCTO Reproduction Scenario," which reproduces the "Long-Term Policy for Wide-Area Grid - the Master Plan for Wide-Area Interconnected Grid" published by the Organization for the Promotion of Wide-Area Operations (OCCTO) in March 2023. Another is the “100% renewable energy scenario” based on the results of the joint study "Renewable Pathways to Climate-neutral Japan" published in 2021 by Renewable Energy Institute, the German think tank Agora Energiewende, and Finland's Lappeenranta University of Technology. With the two scenarios, electricity supply and demand simulations were conducted considering the general transmission and distribution utility ("TSO") areas, excluding Okinawa and inter-regional interconnection lines.
・In terms of transmission capacity, the results of the "OCCTO Reproduction Scenario” were almost the same as those of the "Long-Term Policy for Wide-Area Grid - the Master Plan for Wide-Area Interconnected Grid,” which is based on the case where renewable energy accounts for about 50% of the electricity supply in 2050. On the other hand, the results indicate the necessity of further implementation of transmission capacity if the share of renewable electricity supply is to be increased than the "Master Plan.” For example, at least 12 GW of capacity is needed between Hokkaido and the Tokyo TSO area.
・The study also analyzed the effectiveness of "flexible demand" - e.g., EV recharging, heat production, hydrogen production, etc.- and storage batteries when renewable energy generation exceeds demand. Flexible demand and storage batteries were identified to generate additional benefits even when the benefits from strengthening transmission lines are small. However, to utilize "flexible demand" on a large scale, it is necessary to procure and operate these “resources” at low cost, and it is essential to develop ways to provide incentives to consumers and regulations and systems to encourage these actions. As for storage batteries, it was found that the economics of storage batteries are inferior to those of transmission line reinforcement in terms of price and service life in 2050, which can be assumed at present, but the situation may change drastically depending on technological progress.
・In Europe, transmission operators have begun to develop submarine transmission cables to transport power from offshore wind farms to land and high-capacity transmission lines to transport power from land to large demand areas.
Regarding Japan, the report proposes a method of extending inter-regional interconnection lines radially to the main areas of offshore wind power development and a way of using remote islands that are not connected to the grid as hubs, similar to Denmark's energy island concept, as a means to simultaneously develop offshore wind power and transmission cables to transmit power to demand areas, while reducing the total cost of investment to extend transmission system.
Conclusion of the Report
This report was prepared by Renewable Energy Institute, REI, based on the discussions held by the “Grid Study Group” on the infrastructure needed to realize a decarbonized society based on renewable energy in 2050, as well as the investment scheme to realize such a society, and demand-side measures and infrastructure to meet the needs of variable renewable energy sources.
In Japan, discussions on the Basic Energy Plan and the Green Growth Strategy have led to targets for the introduction of solar and wind power generation in 2050, and in particular to discussions on the expansion of power grids to transmit electricity from Hokkaido, Tohoku, Kyushu, and other areas with enormous offshore wind power generation potential to the large demand areas of Tokyo, Chubu, and Kansai. The OCCTO's master plan study indicated that the base scenario would connect the Hokkaido and Tokyo areas with 6 to 8 GW of transmission lines, with a renewable energy share of 48%. Although in addition, "flexible demand" such as EV charging, heat demand from heat pump water heaters, and hydrogen production, as well as the introduction of storage batteries, were discussed in the process of the Master Plan, still the separation of the effects from the transmission line expansion was not evident in some areas.
In light of the situation described in the OCCTO Master Plan above, the Grid Study Group examined how much transmission line capacity would be needed to decarbonize the grid through renewable energy and how effective "flexible demand" would be in increasing the share of renewable energy, based on the "OCCTO Master Plan Replication Scenario," which simulates the base scenario of the OCCTO Master Plan, was used to analyze and discuss the results of the study. The results are shown in Chapter 2. The analysis results confirmed the potential for benefits to outweigh investment by connecting Hokkaido to Tokyo with an 8 GW transmission line and reducing the output control of electricity generated by offshore wind in the Hokkaido and Tohoku areas, thereby reducing fuel costs and CO2 emission costs. In addition, it was found that the benefits of an expansion beyond 8 GW would be diluted in relation to the investment. This provides some support for the results of the OCCTO Master Plan.
Our analysis confirmed that "flexible demand" and storage batteries are effective means of further reducing the amount of curtailment of renewables in a situation where the effect of reducing the amount of output control by increasing transmission lines is becoming less and less likely to be realized. However, to utilize "flexible demand" on a large scale, it is necessary to procure and operate those means at a low cost, and it is essential to establish ways to provide incentives to consumers and regulations and systems to encourage them to do so. As for storage batteries, it was found that the economics of storage batteries are inferior to those of transmission line reinforcement in terms of price and service life in 2050, which can be assumed at present, but the situation may change drastically depending on technological progress. When the effect of transmission line expansion wears off, it will be practical to introduce "flexible demand" and storage batteries based on technological advancement and establish a system.
In addition, a "100% renewable energy scenario" was established separately from the "OCCTO Master Plan Replication Scenario" to provide almost all of the electricity supply through renewable energy, and the same analysis was conducted as described above. The installed capacity of solar and wind power was 1.5 to 2 times larger than the "OCCTO Master Plan Replication Scenario," heat demand at about eight times, and EV charging demand and hydrogen demand at about 2.4 times, all were set at flexibility. In addition, storage batteries were installed with 3.8 times the capacity of the "OCCTO Master Plan Replication Scenario. In this case, the benefits of a 12 GW expansion between Hokkaido and Tokyo exceeded the costs. In other words, to achieve a higher renewable energy ratio than the 50-60% assumed in the OCCTO Master Plan, more regional connection lines between Hokkaido and Tohoku areas and Tokyo area are needed, with 12 GW as a rough estimate. This result indicates that to promote decarbonization through renewable energy, transmission line expansion beyond the OCCTO Master Plan may be necessary.
The analysis of the "100% renewable energy scenario" also showed that even with hydrogen from renewable energy sources, in reducing the cost of power generation, it is essential to rely as little as possible on hydrogen-fired power, for example, using interconnectors. Without interconnectors with neighbouring countries, 19% of the electricity supply would come from green hydrogen-fired power generation. Still, in the case of introducing interconnectors, the ratio of hydrogen-fired power generation could be reduced to 16% at the lowest point, and the overall cost of electricity generation in Japan could be reduced by about 0.5 yen/kWh. In addition, it was found that the international grid line is expected to promote the direct use of renewable energy power and increase Japan's energy self-sufficiency rate. The analysis results showed that electricity self-sufficiency would increase even after considering electricity imports from the interconnectors. This again presented the need to consider interconnectors as a means of adding flexibility and reducing the cost of electricity generation.
Meanwhile, in Europe, due to decarbonization and the energy crisis, there is active discussion on expanding the introduction of renewables and strengthening the power grid in conjunction with it. Solar PV and wind power will be considered the primary power supply means. In particular in Europe, concerning offshore wind power generation, which can be introduced on a large scale, there are cases that transmission operators are taking the initiative to develop both subsea cables to send power generated by offshore wind power to onshore and high-capacity transmission cables from onshore points to large demand areas.
As examples, the Kriegers Flak between Germany and Denmark, the Multi-Purpose Interconnector between the UK and Belgium, and the Energy Islands in Denmark are introduced in the report. And it proposed for Japan the method of extending inter-regional connectors radially to major offshore wind power development areas and the method of using remote islands not connected to the grid as hubs, as in Denmark's Energy Island concept, as a means to simultaneously develop offshore wind power generation and transmission lines and transmit power to demand areas, and proposed a way to develop the power grid that would reduce the total investment cost.
Based on these findings, Renewable Energy Institute will advocate governments, businesses, and society in general that decarbonization through renewables is possible and that the power grid is necessary to achieve this goal. REI intend to deepen practical discussions toward the purpose of a carbon-neutral world in which renewables are decarbonized.