Performance indexes and output allocation for multi-fuel energy systems

In this paper we take into account the concept of conversion efficiency by exploring Multi-Fuel (MF) energy systems. A MF system can be defined as a system with various fuel energy input and useful product output. The difficult task in defining a performance index for MF systems consists in quantifying the contribution of each input fuel to the total output energy. This paper intends to make few proposals and start a discussion that would be helpful to assess the MF system performance. The conventional first law efficiency, normally used to assess performance of Single-Fuel (SF) system, can be applied but it provides incomplete information for a MF system. The electric equivalent efficiency, the relative and overall MF synergy index concepts are introduced as most significant performance indexes; these new performance indexes are presented with the aim to evaluate the MF performance compared to reference SF scenarios. Proposed performance indexes are analyzed, discussed and compared from a general point of view, identifying aspects of relation and main differences. The introduced conversion efficiency indexes are applied and discussed to a specific co-combustion power plant case. The influence of the reference scenarios, as it is highlighted in the paper, results of key importance. The evaluation of the proposed indexes is of relevant interest with the goal of formulating a specific and unified theory about MF power energy systems.