Modeling and optimal scheduling of integrated thermal and electrical energy microgrid

Microgrids have become attractive electricity supply and management options that support local power generation, increased reliability, sustainability, and cost reductions. Microgrid sources often include solar PV, wind, and a thermal generation. Thermal generation alone has low conversion efficiency. On the other hand, a combined heat and power (CHP) generator provides additional benefits by taking advantage of the exhaust heat from the generator to fulfill the thermal demand of a building. Thus an integrated microgrid that includes renewable energy and a CHP unit to serve electrical and thermal loads of buildings can achieve higher overall efficiency. In this paper, we model a thermal and electrical energy microgrid, which accounts for the nonlinear efficiency of a Capstone CHP unit and the thermal dynamics of a building. We present the steady-state model as well as the optimization scheduling formulation to minimize the integrated operating cost of the microgrids. The model is simulated under three electricity pricing structures to gain insight into the impacts of pricing on the daily operation of the microgrid.

I. Introduction

Distributed energy resources (DERs) such as solar PV, wind and combined heat and power (CHP), provide an alternative solution that can offer reduction of emissions, increased reliability, and cost savings if operated optimally. Solar PV and wind power virtually have a zero-cost source of fuel, but are variable and less predictable. Without storage capabilities available, these resources are limited and cannot serve as the only source of power. Fossil fuel generators and connection to the grid provide a controllable source of power to balance renewable generation and demand at all times. These resources form an integrated thermal and electrical microgrid that can be operated locally, with a point of common coupling with the larger electricity grid. By scheduling these resources optimally, the cost of energy to the customer can be reduced, and the net load seen by the electricity providers can decrease as well.