Many countries introduced subsidy schemes that were successful in incentivising investments into residential solar PV. The resulting growth of the global PV market was accompanied by cost reductions for PV systems, reductions of PV subsidies and, often, increasing electricity retail prices. Along with decreasing costs for battery storages, these developments made self-consumption and self-sufficiency continuously more attractive. However, the profitability of PV-storage systems depends on many factors, including technological, political and geographical aspects. We present a simulation model to identify the most profitable sizes of PV and storage systems from a household perspective and explore what drives the profitability of self-consumption and self-sufficiency. We compare and contrast Germany and Ireland to account for regulatory and geographical differences. Our results show that PV-storage systems are generally profitable in Germany and that, after minor technology cost reductions, this result holds even in the absence of subsidies. In Ireland, such systems are not yet profitable but this may change soon with expected technology costs reductions. The share of electricity demand that will be required from the grid may be reduced to 25-35%. Implications for the electricity retail business and policy makers are discussed including distributional concerns and system efficiency considerations.

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Germany's energy turnaround is leading towards an increasing integration of photovoltaics throughout its distribution grid. As solar power generation fluctuates greatly, distribution system operators are faced with the challenge of preventing grid component overload and voltage range violations. One solution might be to integrate battery storage systems into private households and reduce active peak power at the grid connection point. Since peak shaving is often impossible with the conventional operating strategy of the storage system, solar plants must sometimes be throttled back. In this study, a fuzzy control system is introduced that reduces peak feed-in and thus also energy losses due to throttling back solar power. The system uses solar surplus and battery charge level as input parameters, and standardises them to ensure easy adjustment to different combinations of plant size and storage capacity. Load flows for a complete year were modelled using real-world measurement data, which showed that even small electrical storage capacities (<5 kWh) reduce energy losses considerably and produce only small losses in self-consumption. Thus, there is an economic benefit for plant operators which switch from a conventional to a grid-optimised operating strategy.

Purpose The aim of this paper is to introduce a newly developed multi-criteria analysis for the comparison of two grid expansion alternatives, conventional and voltage-regulated distribution transformer. The case study comprises environmental, economic, technical and social aspects. Design/methodology/approach The newly developed method decision condition Preference Ranking Organization METHod for Enrichment Evaluation (DC-PROMETHEE) combines scenario planning with the multi-attribute decision-making method PROMETHEE. DC-PROMETHEE supports the decision-maker to evaluate the total potential of an alternative considering a large number of decision conditions. The calculated performance indicator supports the decision-maker to select the best alternative. Findings The voltage-regulated distribution transformer shows a high overall potential in the present case study. This leads to the recommendation to the investigated distribution system operator to include the voltage-regulated distribution transformers as a grid expansion measure. Practical implications The DC-PROMETHEE can be applied to other distribution system operators by considering their individual grid topology and preferences. Other fields of application are infrastructure investments in the service area, in which expansion alternatives are evaluated in a large number of decision conditions. Examples include telecommunication, gas supply, water supply, sewage and rail networks. Originality/value This paper develops the DC-PROMETHEE approach. The DC-PROMETHEE enables the multi-criteria evaluation of a few alternatives in a large number of decision conditions.