Verification of output curtailment of renewable energy power generation facilities
Output curtailment due to supply-demand balance constraints
To ensure a stable electricity supply, supply and demand always need to match. When the electricity supply exceeds demand in an area even after implementing such measures as output curtailment of such power generation facilities as a thermal power source or pumping operation of pumped-storage hydropower facilities, it requires output curtailment of renewable energy power generation facilities.
When there is a possibility that the electricity supply exceeds demand in an area, the OCCTO arranges the long-cycle cross-regional frequency regulation, which transmits electricity to other areas through cross-regional interconnection lines. With such cross-regional operation of supply and demand, we try to mitigate output curtailment of renewable energy power generation facilities.
When the electricity supply still exceeds demand even after output curtailment of variable renewable energy sources (solar and wind power generation facilities), and a deterioration in the supply-demand situation is recognized, we try to ensure the stable supply by giving an instruction to interchange power in accordance with the Electricity Business Act.
Precedence order of output curtailment based on the rule of priority dispatch (summary)
(i) Power generation and other facilities secured in advance by general power transmission and distribution companies as balancing capacity; pumping operation of pumped-storage hydropower facilities, and charging of storage batteries for improving supply-demand balance
(ii) Power generation and such other facilities as a thermal power source not secured in advance by general power transmission and distribution companies as balancing capacity; pumping operation of pumped-storage hydropower facilities, and charging of storage batteries for improving supply-demand balance
(iii) Long-cycle cross-regional frequency regulation
(iv) Output curtailment of Biomass single-firing power source
(v) Regional resource biomass power source
(vi) Variable renewable energy (solar and wind power)
(vii) Instruction by the OCCTO in accordance with the provisions of Electricity Business Act (instruction at the time of deterioration in the supply-demand situation)
(viii) Long-term fixed power sources
Output curtailment due to congestion in power supply facilities (grid constraints)
To promote the further integration of renewable energy power generation facilities while maximizing the use of existing power transmission and substation facilities, a non-firm connection has been introduced, which connects a new power source to the grids without system reinforcement on the assumption that output control is conducted during grid congestion. As a result, general power transmission and distribution companies and power distribution companies are supposed to conduct output control of power generation or other facilities based on a precedence order for output control as prescribed in the Network Codes if congestion occurs during normal times in power supply facilities other than interconnection lines, distribution transformers, and distribution facilities.
Precedence order of output control
Output control method
(i) Balancing power source *1
Merit order
(ii) Thermal and other power sources among non-firm connected non-balancing power sources *2
Nondiscrimination
(iii) Power storage systems among non-firm connected non-balancing power sources *3 *4
Merit order
(iv) Thermal and other power sources among firm connected non-balancing power sources *5
Nondiscrimination
(v) Power storage systems among firm-connected non-balancing power sources *3 *4
Nondiscrimination
(vi) Biomass power source among non-firm connected non-balancing power sources *6
Nondiscrimination
(vii) Variable renewable energy (solar and wind power) among non-firm connected non-balancing power sources
Nondiscrimination
(viii) Biomass power source and long-period fixed power source among non-firm connected non-balancing power sources *7
Nondiscrimination
(ix) Biomass power source among interim non-firm connected non-balancing power sources *6
Nondiscrimination
(x) Variable renewable energy (solar and wind power) among interim non-firm connected non-balancing power sources
Nondiscrimination
(xi) Biomass power source and long-period fixed power sources among interim non-firm connected non-balancing power sources *7
Nondiscrimination
- *1 Including the pumping operation of pumped storage hydropower generators, charging of energy storage facilities for improving supply-demand balance, and discharge suppression of power storage systems for which a contract for utilization of surplus power is executed
- *2 Including dual-fueled biomass power source and pumped storage hydropower generators
- *3 On-site energy storage facilities that do not charge from grids shall be treated equally with on-site power generation facilities
- *4 Only discharge suppression
- *5 Including dual-fueled biomass power source (except FIT generator) and pumped storage hydropower generators
- *6 Single-fueled, regional resources (except for those for which output control is difficult)
- *7 Regional resources (for which output control is difficult)
Verification and publication of the validity of an instruction of output curtailment of renewable energy power generation facilities
When output curtailment of renewable energy power generation facilities (solar and wind power generation) is conducted because of supply-demand balance constraints or congestion in power supply facilities (grid constraints), we verify the decision and the operation of output curtailment conducted by general power transmission and distribution companies and publish the results of such verification.
As for the output curtailment due to supply-demand balance constraints, we also verify whether the output curtailment was conducted in a fair manner throughout the year and publish the result of verification in the next fiscal year.