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This paper proposes an extension for feasibility assessment of residential energy (heat and electricity) supply solutions in an operational environment undergoing major changes. In order to improve the life cycle economy of the energy supply, the design has to accommodate technological, economic, and regulatory changes in operational environment over the long time. New elements must be included in feasibility assessments of energy supply to ensure consideration of future economic opportunities and risks. The extended feasibility assessment brings up the profitability of “future proofed” more sustainable solutions with lower risks related to utilization costs and with improved resale value preservation. The findings of systematic literature study were structured and clarified into a decision support matrix to guide the assessment process. The procedure was verified by identifying the optimal energy supply solution for a net-zero energy single-family house in Southern Finland. The verification demonstrated that the procedure provides new insights on the economy and the climate implications of the energy solutions.

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Organic Rankine cycles have been identified as a suitable technological option for converting low-grade heat into electricity with relatively high efficiency, and the organic Rankine cycle technology has been successfully implemented in different power production systems and in recovering heat in industrial processes. This paper studies the greenhouse gas emission reduction potential by using organic Rankine cycles for recovering exhaust gas heat of biogas engines. The study concentrates especially on the biogas engine power plants in Europe. Life cycle assessment methods are used and various waste heat utilization scenarios are compared. According to the results, greenhouse gas emissions can be reduced significantly if the thermal energy of the exhaust gases, otherwise lost in the process as waste heat, is utilized for additional electricity production by means of organic Rankine cycle. However, there may already be use for the exhaust gas heat in biogas plants in the form of heat power. In these cases, the use of organic Rankine cycle does not necessarily lead to greenhouse gas emission reductions. The results also indicate, that the working fluid leakages and production as well as the organic Rankine cycle construction materials and production have only marginal effects on the results from greenhouse gas perspective.