Towards Energy Prosumers: A National-Scale Residential Modelling for Solar Performance Assessment in Italy ^†

The fast growth of Renewable Energy Communities (RECs) in Europe makes the development of robust analytic frameworks for the simultaneous technical and economic performance evaluation a necessary activity. In Italy, characterized by having transposed the European RED II Directive with a dedicated law on collective self-consumption and RECs, assessing design options becomes crucial for policymakers, local authorities, and future community members. Common annual average-based evaluation methods tend to overestimate self-consumption and self-sufficiency because they do not take into account the temporal mismatch between photovoltaic generation and household demand. In our analysis, hourly data modeling is carried out using a combination of publicly available datasets provided by Italian energy authorities and online simulation tools, which results in synthetic but representative time series of generation and demand. Three performance indicators-the Self-Consumption Index (SCI, Self-Sufficiency Index (SSI), and Overproduction Index (OPI)-were calculated for one, two, and three aggregated households under photovoltaic capacities of 3 kW, 4.5 kW, and 6 kW. The results also document that SCI falls and OPI rises with an increasing PV size and aggregation that improves the generation-consumption simultaneity and thereby diminishes inefficiencies. This triggers a financial analysis in which we investigate three producer profiles: (i) an investor that sells all the electricity, (ii) a single prosumer who self-consumes then sells the excess and (iii) a prosumer sharing in a REC. In all cases we then calculated Net Present Value (NPV) and the payback period. Toys on this show that aggregation and energy sharing metrics improve the economics of the system but oversized systems generate losses and longer payback times. In conclusion, through this work, we show the necessity of uniting hourly energy strategies and financial analysis for designing sustainable and economically optimal RECs within the Italian legislative context.