Task 1: Perform an overview on energy storage projects worldwide and survey on regulatory frameworks and trends for energy storage. Similarly, study the operational fundamentals of power markets and ancillary services, and the potential role of energy storage for RES integration in a market environment.

Task 2: Assess the system's flexibility requirements, studying the transmission network development options and build network models for the horizon 2020.

Task 3: Develop an optimization algorithm for the selection of the preferred sites and sizing of the energy storage alternatives taking into account the level of flexibility requirements.

Task 4: Build and simulate scenarios for network planning allowing both conventional and energy storage alternatives.

Task 5: Perform multi-attribute and multi-scenario analysis. Build and apply the decision-aid methodology for alternative selection, through the use of trade-offs and risk indices. As final task, perform a regulatory survey on the use of energy storage by multiple electricity system actors.

During the last three years R&D Nester also published several articles as result of the work accomplished, namely:

• "Planning Energy Storage in Power Transmission Networks", IGESC 2014 - IEEE Green Energy and Systems Conference 2014, Nov/2014, California, USA;
• "Siting and Sizing Dispersed Energy Storage in Power Transmission Networks", IGESC 2015 - IEEE Green Energy and Systems Conference 2015, Nov/2015, California, USA.

The work performed during the last 3 years gave a strong contribution for the understanding of the potential multiple roles of energy storage in the electrical system, as well as the technologies involved and their main characteristics. This project also contributed for the development of an in-house methodology and a tool for energy storage planning, which allows the comparison of different technologies and solutions which can be used by Network Operators or other energy actors to plan their infrastructures including energy storage solutions.