Characteristics of the Use of a Photovoltaic Micro-Installation for a Residential Unit in a Multi-Family Building: A Case Study from North-Eastern Poland

This study assessed the operational performance of a 3.6 kWp prosumer photovoltaic (PV) micro-installation located in Durąg (province of Warmia and Mazury, Poland). The analysis was carried out from 1 January 2023 to 31 December 2025, covering electricity generation, self-consumption levels, energy imports and exports to the electricity grid, household electricity demand coverage, and selected technical and economic indicators. Average annual electricity generation was 3155 kWh, with the highest value (3230 kWh) in 2024. The average annual energy yield was 876.4 kWh kWp−1. The highest average monthly electricity production (502.7 kWh) was observed in June, while the lowest (24.3 kWh) was recorded in December. A very strong positive correlation was observed between electricity generation and solar irradiation (r = 0.99). The theoretical coverage of annual household electricity demand by PV generation was 84.4%, whereas the actual overall electricity demand coverage under the net-billing scheme was 48.2%. The highest level of self-consumption (1217 kWh) was noted in 2024. The highest electricity consumption from the grid was recorded during the winter months, particularly in January and December, whereas the largest energy surpluses were exported to the grid in May and June. An economic analysis showed that increasing self-consumption was a crucial factor in improving the profitability of PV micro-installations operating under the net-billing scheme. Reducing the amount of electricity exported to the grid lowers electricity costs, enhancing user economic benefits. The average annual savings amounted to 383.1 EUR. The results obtained confirmed that a PV micro-installation used by a residential unit in a multi-family building could effectively enhance a household’s energy and economic security. However, its operational efficiency is primarily determined by solar irradiation, seasonal climate variations, and the users’ electricity consumption profile.