Distributed renewable fuel and power: challenges and
Andrew Allman and Prodromos Daoutidis
Recent research in the development of novel energy systems has been moving towards a more decentralized, renewable based infrastructure. In particular, distributed microgrids and biorefineries have been identified as systems that can increase the resiliency of the energy infrastructure, reduce the carbon emissions associated with the production of power and fuels, and mitigate the losses, emissions, and risks inherent in long distance transport of power and fuels. Extensive research exists on the design and operation of microgrids and biorefineries, and previous studies suggest that synergies between the two systems may make a combined system more efficient than the sum of its parts , . For example, including an electrolyzer with a renewable microgrid allows for carbon-neutral hydrogen generation which can be used for shifting syngas, generating ammonia, or reacting platform chemicals to fuels in a biorefinery. Additionally, heat, power, and produced fuel can be passed between the two systems.
Motivated by these considerations, this work considers combined power and fuel polygeneration systems. A reference architecture is proposed combining a microgrid with wind turbines, solar panels, microturbines, and hydrogen storage with a biorefinery containing both gasification-based and thermochemical fuel producing pathways. Such an architecture inherently contains multiple time scales: power and heat demands must be met instantaneously, but fuel demands can be met over daily or weekly requirements. The combined model contains a large number of variables from the microgrid (required due to its shorter time scale) and nonlinearities from the biorefinery (required for accuracy in capturing chemical transformations). As such, optimizing the combined system design is more difficult than optimizing each system individually. We address the optimal design of such a "system of systems" by decomposing and reformulating the problem in a way that isolates different time scales and nonlinearities. We also discuss and provide insights on a number of research challenges and opportunitites that emerge in the design, operation, and control of such polygeneration systems. On the enterprise level, fuel and power supply chains must be considered to determine locations where distributed polygeneration is economically viable. On a system-wide level, unit scheduling programs that are proactive and robust to uncertainties in supply and demand are needed. On a local level, novel control architectures must be developed that take into account the complex interconnections between subsystems, the multiple time scales present in the system, and the different operating states of the microgrid.
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 B. Subhadra and M. Edwards, "An integrated renewable energy park approach for algal biofuel production in United States", Energy Policy, vol. 38, pp. 4897-4902, 2010.
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