There is a trend in many power systems, across the world, towards utilizing more distributed energy resources (DERs), from rooftop solar photovoltaics, batteries and plug-in electric vehicles to smart appliances, energy efficiency and demand response. DERs can provide services to both Distribution System Operators (DSOs) and Transmission System Operators (TSOs). The conventional fit-and-forget approach that many DSOs follow may need to change to perform more active operation of the system as well as new roles. The roles of TSOs and DSOs will be evolving in kind as more DERs start to change load and generation patterns in distribution grids. With increasing penetration of DERs, the coordination between system operators will expand, in terms of information exchange, monitoring and analytic capabilities, computation of prices of electricity services, forecasting, scheduling and activation of resources, as well as system operator responsibilities. DSOs and TSOs must be able to monitor and engage resources as well as study and share information in a timely manner to enable efficient markets and reliable system operations. This paper explores the current and future relationship between the TSO and DSO with a focus on the European and US liberalized power sectors. The coordination between TSOs and DSOs is of utmost importance for the grid to obtain the full value from services provided by DERs such as, but not limited to, firm capacity, congestion relief, loss reduction, reactive power, voltage control and frequency reserves. Examples and recommendations for future coordination between the TSO and DSO will be examined and presented, as well as new interactions with market parties, such as DERs’ aggregators or directly with DERs’ owners.
Keywords: Distribution system operator, transmission system operator, distributed energy resources, transmission-distribution coordination functions.
Published: February 2016.