Energy Systems Analysis for a Solar Economy

Mallapragada, Dharik S. Ph.D., Purdue University, December 2013. Energy Systems Analysis for a Solar Economy. Major Professor: Rakesh Agrawal. The use of solar energy for human needs faces challenges owing to its relatively low energy intensity and intermittent availability, coupled with the constrained availability of renewable carbon and land resources. This study uses systems analysis tools to identify carbon and energy efficient transformations of solar energy for different purposes, including transportation fuels and grid-scale energy storage. These efforts have been complemented with a feasibility analysis of existing fossil-energy and other hybrid pathways. In an era of limited fossil resources, liquid fuels from sustainably available (SA) biomass could meet the energy needs of the transportation sector. We present a method for synthesizing augmented biofuel processes, which improve biomass carbon conversion to liquid fuel (ηcarbon) compared to standalone biofuel processes by using supplemental solar energy in the form of H2, heat, and electricity. For any target ηcarbon, our method identifies a process, which is guaranteed to consume the least amount of solar energy among all competing designs, thereby minimizing the land area requirement for biofuel production. A non-convex mixed integer nonlinear programming (MINLP) model allowing for simultaneous mass, heat, and power integration, is built over a process superstructure and solved using global optimization tools. As a case study, we consider biomass thermochemical routes of gasification/FischerTropsch (FT) synthesis and fast-hydropyrolysis/hydrodeoxygenation. For ηcarbon =7095%, the synergistic gain of the optimal integrated process is evidenced from the ∼28-156% lower solar energy consumption compared to augmented gasification/FT