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Electricity power systems worldwide have traditionally been designed to a vertically connected scheme characterised by centralised generation. Over the last few decades, several factors have dictated a gradual shift from the central-control approach to a more distributed layout where distributed generation (DG) technologies are effectively integrated and not just connected (appended) to the networks; amongst others liberalisation of electricity markets, security and quality of supply and environmental issues. Photovoltaic powered distributed generation (PV-DG), although still having a much lesser impact than other DG technologies, is increasingly being embedded into electricity distribution networks worldwide within the framework of successful regulatory state and marketing programmes. PV-DG has added values (benefits) for the electricity systems that extend from peak power and load reduction (when deployed close to electricity consumption points) to participation in grid-supporting or grid-forming modes of operation. The question arises as to what the present situation of PV technology is for its optimal integration in distribution networks, whether there are still technical barriers to overcome as well as new opportunities for PV in future renewably supplied electricity systems. This paper presents the current state of knowledge concerning these topics from a European perspective with regard to different grid structures. It also discusses existing standards, new opportunities to provide grid services and research and development needs identified to fully exploit the added-value-and still developing-benefits of PV-DG.

An increasing number of energy storages will be installed in buildings with photovoltaic systems. However, batteries with only local operation tasks do not exhaust their technical potential. Using the available battery capacity in terms of power and energy to provide ancillary system services is therefore economically reasonable. Providing primary control reserve power in combination with increasing local self-sufficiency has been identified as a promising option for decentralised PV battery systems. Thereby, part of the battery capacity is used to provide grid services and the remaining part for the management and optimisation of local system operation. Provision of self-sufficiency increase is limited, when the battery's state of charge is within certain limits. In this study, it is shown that the simultaneous use of the battery to locally increase self-sufficiency reduces the need for external power sources to correct the storage level. The operational concept, the technical solutions, and a sensitivity analysis are presented. Furthermore, billing and measuring issues as well as the current regulatory framework conditions in Germany are discussed

Technical regulatory frameworks have a great influence in the operation and prospects for Battery Energy Storage Systems(BESS) as providers of fast frequency response. Following this premise, provision of fast frequency response with BESS in Germany, Great Britain and Sweden is analyzed for the products available in each country. An operation strategy, which dynamically utilizes degrees of freedom (DEGOF) found explicitly or implicitly in regulation, maintains the battery's state of charge (SoC) while also reducing cycling. The extent to which the operation strategy is beneficial for BESS prospects is limited by the adequacy of the technical regulatory framework and the available DEGOF. This strategy provides operational improvements for all products considered, with the largest improvement potentials seen for the products available in Great Britain (FFR and EFR).