Quantification of benefits of the campus grid operations as a microgrid
The US grid's weak ability to withstand severe weather incidents, particularly with the growing number of events due to climate change, the slow pace of expansion of transmission grids and the increased push to integrate deeper penetrations of renewable resources in recent years, has raised many questions about the reliability and resilience of the electricity supply as well as about the design and operational paradigm of the distribution grid. The increased implementation of microgrids in distribution networks (DNs) indicates that microgrids provide promising alternative approaches to address many of these issues. The growing interest in microgrid implementations provides evidence that many projects are, in effect, able to realize such benefits. However, the lack of a general methodology that can comprehensively quantify the benefits of applying the microgrid concept to any power system limits the much broader implementation of microgrids as the investments made in the microgrid area are not justified. In light of this situation, we developed a quantification methodology and carried out the quantification and comparative analysis of the benefits of the operation of the University of Illinois at Champaign-Urbana (UIUC) campus utility system (CUS) as a microgrid versus its current operations. The UIUC campus is a microcosm of a city with diverse facilities including the academic buildings and laboratories, student housing facilities, theatres, health center, sports stadiums, libraries, veterinary hospital and an airport. The UIUC campus is critically dependent on the CUS for its chilled water, steam and electricity demands year round. The UIUC CUS has all the required characteristics of a microgrid including distributed energy resources (DERs), critical and non–critical loads and a defined electrical grid boundary. Thus, we may view the CUS as a microgrid. Consequently, consideration of the UIUC CUS via microgrid optics allows us to carry out a comparative quantification of the benefits of the UIUC CUS operated as a microgrid versus under the current operational paradigm. For the quantification methodology, we use a stochastic simulation approach that provides the capability to quantify the impacts of CUS operations in terms of economic, reliability and emissions metrics of the CUS operations under a specified operational paradigm. The approach is based on the explicit representation of the various sources of uncertainty together with the time-varying nature in the demand–side and supply–side resources in the CUS. The simulation approach models the uncertainty in the demands, available capacity of conventional generation resources and the time–varying, intermittent renewable resources in terms of discrete–time random processes (r.p.s). Such a representation explicitly takes into account the time correlations in each input variable. A key exponent of the simulation approach is the formulation of the so–called energy scheduling optimization problem (ESOP). The ESOP solution is an essential building block in our approach and is used to determine the CUS resource scheduling decisions with the explicit consideration of the uncertainty effects. Under the current operational paradigm, the schedule of the energy resources is based on heuristic techniques and does not involve the deployment of formal optimization techniques. The ESOP solution replaces the current heuristics–based approach to determine the optimal schedule and loading levels of the CUS energy resources so as to minimize the CUS operational costs. We use this optimal scheduling as a proxy for the current operational paradigm. In this way we can carry out on a consistent basis a comparative analysis of the UIUC CUS operational performance as a microgrid – the so–called microgrid operational paradigm – and those under the optimal operations of the current paradigm. A modified ESOP and its solution is also adopted in the simulation methodology for the quantification of the CUS operational performance under the microgrid operational paradigm. A salient feature of the ESOP mathematical formulation is its ability to capture the inter–dependencies in the electricity and steam services that the UIUC CUS provides under each operational paradigm. The simulation approach makes use of the Monte Carlo simulation (MCS) techniques to represent the impacts of sources of uncertainty on the CUS operations under each operational paradigm. As such, we systematically sample the r.p.s to generate the realizations, or sample paths, that we use to emulate the scheduling of the CUS for a given operational paradigm via the ESOP. The ESOP solution maps the sample paths of the loads and supply resources into the sample paths of the r.p.s we use to measure the performance of CUS operations. The evaluation of the metrics of interest is based on these resulting s.p.s. We demonstrate the capabilities of the simulation approach by carrying out various case studies on the UIUC CUS. We discuss a set of representative studies to gain important insights about the current UIUC CUS operations and under the application of the microgrid concept to the UIUC CUS. The studies provide clear understanding of the interactions between the electric and steam utility in the UIUC CUS and the limitations on electric system operations imposed by the requirement to meet the steam loads. A key observation made from these case studies is that the extent of the benefits of the microgrid concept application to a power system attained would depend on the characteristics of the system as well as the location of the system in the geographical footprint of the distribution system. There is a broad range of applications of this methodology, including resource planning studies, reliability, economic and environmental assessments and operational studies. A particularly attractive feature is its ability to provide answers to various “what if” questions of any nature. The methodology described in this thesis is general in a sense that it can easily be adapted to demonstrate the extent to which the benefits of the microgrid concept application can be realized in any particular power system when it is operated as a microgrid versus when it is operated under its current paradigm.
Microgrid, Quantification, Monte Carlo simulation
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign