The International Renewable Energy Storage conference (IRES) is the world's premier peer reviewed platform for research and development in renewable energy storage policy, technology, networks, management and interactive prosumer models, business applications, smart grid integration and stabilization applications. Over the course of two days more than 60 presenters explored how effective and cost efficient energy storage system can be applied not only to compensate for supply variability in renewable energy but to drive the revolution towards 100% renewable based sector coupling and energy trading systems. In the past 14 years, the IRES conference has gained a reputation for presenting all forms of energy storage technology: batteries, thermal energy storage and power-to-gas were presented just as much as small-scale and large-scale solutions for home storage and industrial heating. Offering insight into the technological development and presenting current framework conditions for the successful and systems integrated use of storage solutions the conference provides a reliable environment for sharing and discussing new distributed renewable energy storage and networking technology.

Energy storage systems, dynamically linked into and active in distributed grid based and island systems are essential in the rapid, urgent local and global moves to fully renewable energy supply. To assist in the essential transition the IRES program was launched by EUROSOLAR and the World Council for Renewable Energy (WCRE) in 2006. Over these past years it has emerged as the central platform for sharing knowledge and exchanging ideas on a key issue of future energy supply. The highly interdisciplinary event is an international gathering of all relevant stakeholders: leaders from the energy storage industries, renewable and conventional energy businesses, grid operators and utilities, from the hybrid and electric vehicle sector, as well as the building trades, science, associations, policy makers, political leaders and the investment and financial community.

Given the Covid-19 restrictions, the planned physical event was transformed into a digital format. Users, investors, industrialists, researchers and stakeholders met online to present and discuss the newest research on energy storage, its (international) potential and outstanding examples of success. More than 60 presentations from international researchers were held over the course of the two conference days. EUROSOLAR thanks all authors who contributed to the outstanding program and the high scientific level of the conference.

This second set of EUROSOLAR IRES Proceedings published by Atlantis Press reliably presents the very best of IRES entries, and a collective, high-resolution picture of a dynamic field of storage disciplines. EUROSOLAR expresses its sincere gratitude to all supporters and contributors, researchers, conference participants and especially our exceptional Scientific Committee: without its input and participation neither the conference nor the publication of this special issue would have been possible.