Integration of DG in MV-grids: Challenges encountered by the grid operator

Due to economical and political trends, in the Netherlands the electricity produced by distributed generation units has increased significantly. From 2004 on in the Stedin area, three large greenhouse areas have been developed. In each greenhouse a CHP-plant is installed and as a DSO Stedin saw the number of new CHP-plant connections in its MV grid increasing. Legal rules oblige Stedin to connect CHP-plants in a much shorter time frame than normal project times for necessary grid extensions. This leads to a major grid planning problem, especially when a grid extension of the transmission grid is involved. To solve this planning issue, Stedin has used three approaches: reducing project times, eliminating the need for HV-substations, and better predictions allowing for longer project times. Each approach is illustrated with a case study: (1) In Tinte in a short time a modular HV-substation was built and connected via a branch off to an overhead line. (2) In Oostland I major MV-grid extensions were used to connect CHP-plants with nearby load centres and eliminating the need for expansion of a TSO-substation. (3) In Oostland II market intelligence and expert knowledge were used to develop long term scenarios for development of the amount of CHP-plants in this area. Based on these scenarios a long term plan for grid development was made. The optimal solution for integrating a large amount of CHP-plants depends strongly on the local grid situation. Standardization and modular design can reduce the project time considerably. However, planning permissions do limit these possibilities and the benefit of project time reduction starts after completing the permit procedure. For areas where a large amount of DG will be developed and extension of the transmission grid and substations is inevitable the scenario based approach offers a possibility to develop the grid in a proactive way. This approach permits an early start of the development of transmission grid extensions and TSO - substation development.