Wastewater treatment plants are among the most energy-intensive municipal facilities in Germany and are therefore highly relevant to climate mitigation. This paper investigates the technical and economic potential of integrating renewable energy technologies into wastewater treatment plants in Germany, explicitly considering operational flexibility as an additional optimization strategy.

The work uses open-source tools to build a sector-coupled model plant representing the electricity, heat, and gas system of a wastewater treatment plant. The analysis is based on plant operational data, weather data, and energy price data, which are combined in an original techno-economic and scenario-based modelling approach. The study aims to assess how the inherent flexibility of biological wastewater treatment processes can facilitate the integration of variable renewable energy sources.

To answer the research question, four scenarios are evaluated: (i) a baseline without renewable energy integration, (ii) a system with photovoltaic (PV) and wind power, (iii) an extended system including PV, wind, and operational flexibility measures, and (iv) a system comprising PV, wind, and battery energy storage systems. The model is accordingly expanded to incorporate renewable generation and storage technologies, enabling the assessment of different system configurations and operational strategies.

The scenarios are evaluated with respect to grid electricity demand, on-site energy consumption, degree of energy autonomy, peak load reduction, operational costs, and revenues from electricity export. In addition, sensitivity analyses and dynamic economic assessments are conducted to compare the profitability of the investigated configurations. As part of ongoing work, dynamic electricity pricing on the demand side is being integrated to further refine the economic evaluation.

Preliminary results indicate that renewable generation reduces energy-related costs in all scenarios considered. The combination of wind power, ground-mounted photovoltaics, and operational flexibility provides the most favourable economic outcome, mainly by reducing grid electricity purchases and enabling additional feed-in revenues. The addition of battery storage proves particularly effective if the main objective is to maximize on-site consumption and increase energy autonomy, as it temporally decouples generation and demand while also contributing to peak-load reduction. The analysis further indicates that renewable generation alone is less effective in limiting peak loads than system designs that combine generation with flexibility and storage. At the same time, none of the investigated configurations achieves full net energy autonomy.

Overall, the findings demonstrate that renewable energy integration can significantly enhance both the energetic and economic performance of wastewater treatment plants. They highlight the importance of sector coupling and flexibility-oriented system design for the decarbonization of municipal wastewater infrastructure. The results further underline that detailed simulation is essential to identify and evaluate practical transition pathways toward more sustainable and economically efficient plant operation.