Evaluating net-zero energy buildings and their grid interaction: A comprehensive framework for operational phase and a Nordic case study

This paper presents a synthesized evaluation framework for assessing Net-Zero Energy Buildings (NZEBs) during their operational phase, with a specific focus on grid interaction under real market conditions. The framework integrates four established Key Performance Indicators (KPIs): Load/Generation Balance, Self-Consumption Rate, Emission Reduction Rate and Cost Reduction Rate – using high-resolution operational data, hourly grid emission factors, and spot prices. Demonstrated through a case study of a large Finnish residential NZEB equipped with a ground-source heat pump and off-site solar PV, the analysis reveals both the potential and limitations of PV-based solutions in cold climates. While the system achieved an 89% annual load/generation balance, hourly analysis showed a 31% self-consumption rate, with most PV production exported during periods of low prices and low emissions. Operational emissions and electricity costs were reduced by 56% and 41%, respectively, compared to a baseline without PV. However, sensitivity analysis indicates that economic outcomes are highly dependent on prevailing market conditions, highlighting the importance of multi-year evaluation. The framework's parallel KPIs, when used collectively, enable stakeholders to assess trade-offs and guide practical decisions regarding demand-side management, energy storage, and operational strategies. The economic analysis focuses on market exposure, including O&M costs for PV, but excluding investment costs. The framework is flexible and can be applied to NZEBs with various configurations, supporting robust, data-driven decision-making for improved cost-effectiveness and decarbonization.