Diminishing petroleum reserves and oscillations of the global petroleum market, together with the influence on the environment in terms of greenhouse gas emissions have accelerated the needs to explore renewable feedstocks and to seek novel sustainable production systems. Process synthesis, the core of process systems engineering, can be predicted to be the powerful tool to construct an environmental-friendly, cost-effective sustainable energy system. Following the brief descriptions of the main methodologies for process synthesis, the present article reviews current activities on the optimal synthesis of biorenewables conversion processes, polygeneration processes, as well as carbon capture processes. Set in the context of exist achievements and future energy and environment requirements, we further elucidate the potential research vistas on optimal synthesis of novel energy systems, specifically, (a) novel biorenewable conversion process; (b) innovative materials-based carbon capture process; (c) solar/wind driven energy conversion system; (d) integrated biorenewable conversion process for the production of chemicals. Finally, challenges about the above aspects are concisely discussed. (c) 2012 American Institute of Chemical Engineers AIChE J, 2012