Solution of issues in emergy theory caused by pathway tracking: Taking China's power generation system as an example

Emergy theory is effective to evaluate sustainabilities by tracking all the resources of a product formation process and converting them to solar emergy baseline. Emergy transformity (Tr) is essential to obtain the emergy value of a product. However, a secondary product coming from different production pathways will have various Trs, making it difficult to select a representative Tr when it is used as an input of other systems. Different methods for representative Tr are used in previous studies without considering the characters of different pathways. A method to obtain representative Tr is proposed in this study by classifying the pathways for a secondary product into the technological-impacted-systems and environmental-impacted-systems with the advanced and average values adopted as the representative Trs, respectively. Based on the market share and representative Tr of each pathway, the weighted average value could be obtained as the representative Tr of the product. The on-grid power generation system of China is taken as a case study. The nuclear and coal-fired power generation systems belong to technological-impacted-systems, while the renewable power generation systems belong to environmental-impacted-systems. According to the proposed method, the representative Tr of electricity generated in China is 1.13 × 10⁵ sej/J.