Many different approaches have been developed to quantify and evaluate sustainability. Here a review is performed on sustainability assessment based on Life Cycle Thinking, which mostly means Life Cycle Sustainability Assessment (LCSA). Until the end of 2018, 258 publications can be found, from which 146 include a case study. The highest number of publications appeared between 2016 and 2018 and, compared to the years before 2016, the number of authors has increased. However, in recent years the focus has been more on case studies than on methodological aspects of LCSA. The presented holistic approaches for LCSA are either too broad or too narrow for scientific guidance. Therefore, many questions concerning LCSA are still open, e.g., regarding definition of sustainability dimensions and the desire or need for multi-criteria decision-analysis. An underlying problem is the lack of discussion about sustainability concepts. The momentum in the community to perform case studies for LCSA should be used to also develop more guiding principles.

Background: The levelized cost of electricity (LCOE), expressing the price per unit that a technology must receive over its lifetime to break even, is a useful indicator, but insufficient for a comprehensive investment appraisal of PV-battery (PV-BES) projects. For household PV-BES systems, aimed at prosumers in the German context, our paper seeks to look at the revenue side in addition to the costs side of the investment decision. We extend the LROE (levelized revenue of electricity) to consider the impact of different fiscal options available to households seeking to install PV-BES systems. From this, we calculate the levelized profit of electricity (LPOE), linking the cost-focused and revenue-focused perspectives of prosumers facing investment options. We calculate the LPOE for six different fiscal options available to prosumers, four household types with different socio-economic characteristics and for different sizes of PV-BES systems. Results: In terms of preliminary results, we identify the most advantageous fiscal option and the drivers of LPOE in relation to PV-BES systems in Germany. We find that the switching from the standard to small business tax setup is the optimal fiscal option for all households and all technology combinations, but the optimal income tax decision depends on the present value of revenues compared to tax deductibles. The LPOE is particularly sensitive to changes in CAPEX and retail electricity prices, with the FiT rate, VAT rate and Income Tax rate being somewhat influential. From an LPOE perspective, self-consumption is incentivized through lower FiT rates and higher electricity prices, whereas the abolition of the EEG contribution and low FiT rate adversely affect the LPOE of different options. Stand-alone PV remains the most attractive option, with bundles with storage showing weaker profitability performance. Conclusions: LPOE complements the LCOE and LROE indicators and offers a comprehensive investment analysis, integrating fiscal considerations. Moreover, it offers greater guidance as to the relative attractiveness of different technology configurations and technology sizing. Mechanisms could be implemented to enhance the profitability of residential PV-BES systems in line with energy policy objectives.