Using cross-regional grid interconnection to relieve growing energy storage demand in renewable energy integration: A case study from China

With the rapid growth of wind and solar generation, power systems face increasing balancing and energy storage needs. Cross-regional interconnection provides spatial flexibility through tie-line power exchange, yet the implications of tie-line scheduling flexibility for capacity planning remain insufficiently understood. This paper uses the Gansu–Shandong–Zhejiang interconnected system in China to quantify how tie-line scheduling timescales affect storage requirements for bulk energy shifting and system balancing. Within a common capacity planning and dispatch optimization framework, three stylized tie-line scheduling strategies are compared: Daily Fixed, Monthly Fixed, and Annual Fixed, representing decreasing levels of scheduling flexibility. Results show that greater tie-line scheduling flexibility changes the optimal capacity configuration, particularly the required battery energy storage (BES) capacity. Compared with Annual Fixed, Daily Fixed reduces BES capacity additions by 59.2% and total system cost by 22.8%. Sensitivity analyses further show that this advantage remains robust to variations in storage parameters and tie-line capacity. These findings indicate that the planning value of cross-regional interconnection depends substantially on its operational flexibility.