## 4 Results and Discussion
### Discussion  
The results of this study underscore the significant environmental and economic advantages of the kindergarten's energy upgrade, providing critical insights into its performance under both constrained and stable operational conditions. The analysis highlights the impact of pandemic-induced operational disruptions on energy performance, emphasizing that energy efficiency measures must be evaluated across different usage patterns to fully assess their long-term viability. For the environmental KPIs, it is essential to recognize that RES alone is insufficient to achieve meaningful sustainability improvements, especially if a country's energy mix already incorporates a high share of renewables. The real change must come from enhancing the building's energy efficiency, which reduces overall energy demand and ensures that RES integration maximizes environmental benefits. Without such improvements in a building's energy performance, even extensive RES installations may fail to deliver optimal sustainability gains, as the excess energy consumption will offset potential environmental benefits. This reinforces the need for a holistic approach, combining renewable energy solutions with efficiency upgrades to achieve substantial reductions in PED and GWP [5,57,64].  
In Austria, where energy policy favors net billing over net metering [65], the economic outcomes of PV systems are influenced by reconciliation periods, system size, and usage conditions. Yearly reconciliation delivers the most favorable results, minimizing LCC and payback periods by effectively utilizing surplus energy credits. Conversely, shorter reconciliation periods (e.g., monthly or daily) increase costs and extend payback periods due to reduced energy balancing efficiency. PV system size also plays a critical role; smaller systems achieve higher Return on Investment (ROI) and shorter payback periods by optimizing energy production and minimizing grid reliance. Larger systems, however, lead to up to 49% higher WLC, emphasizing the need for appropriately sizing PV installations to align production with demand. These findings highlight the variability in economic benefits across consumption patterns and scenario parameters, such as electricity prices and subsidies. The complexity increases when comparing energy upgrades across countries, illustrating the challenge of establishing consistent EU-wide policy measures.  
By integrating LCA and LCC with scenario-based evaluations, this study provides a robust framework for assessing the long-term impacts of renewable energy systems and retrofitting measures. Future research could build on this by exploring additional scenarios (e.g., incorporating additional operational conditions, such as seasonal demand fluctuations or hybrid usage models), incorporating real-time grid emissions and electricity price data  
Figure 8: ROI in Different Usage Cases and Schemes.  
to improve the accuracy of economic and environmental assessments under dynamic market conditions, and applying findings to larger building portfolios with different energy efficiency solutions to generalize findings across diverse contexts.