Abstract
Congestion caused in the electrical network due to renewable generation can be effectively managed by integrating electric and thermal infrastructures, the latter being represented by large scale District Heating (DH) networks, often fed by large combined heat and power (CHP) plants. The CHP plants could further improve the profit margin of district heating multi-utilities by selling electricity in the power market by adjusting the ratio between generated heat and power. The latter is possible only for certain CHP plants, which allow decoupling the two commodities generation, namely the ones provided by two independent variables (degrees-of-freedom) or by integrating them with thermal energy storage and Power-to-Heat (P2H) units. CHP units can, therefore, help in the congestion management of the electricity network. A detailed mixed-integer linear programming (MILP) optimization model is introduced for solving the network-constrained unit commitment of integrated electric and thermal infrastructures. The developed model contains a detailed characterization of the useful effects of CHP units, i.e., heat and power, as a function of one and two independent variables. A lossless DC flow approximation models the electricity transmission network. The district heating model includes the use of gas boilers, electric boilers, and thermal energy storage. The conducted studies on IEEE 24 bus system highlight the importance of a comprehensive analysis of multi-energy systems to harness the flexibility derived from the joint operation of electric and heat sectors and managing congestion in the electrical network.
Highlights
The massive deployment of renewable energy sources (RES) vastly reduces greenhouse emissions and operating costs
Given that our model is based on the use of renewable generation in a lossless transmission system, the use of the renewable integration (RI) index is proposed that compares the share of renewable energy employed in the constrained and unconstrained cases: RI
Due to its low coefficient of performance (COP) of 0.99, the electric boiler is only used in Case 4 to prevent the wind spillage and not to replace the heat generated from the combined heat and power (CHP) actively
Summary
The massive deployment of renewable energy sources (RES) vastly reduces greenhouse emissions and operating costs. Additional works have focused on developing convex models based on multi-energy virtual power plants, i.e., distributed energy generation operated as one larger plant; and integration of RES [7] These models aimed to analyze the energy flow between the systems and economics, neglecting the effect of the network constraints on the flexible operation of the units. The main contribution of this paper is the formulation of a model that allows the assessment of the flexibility impact derived from the integration of electric and thermal infrastructures via large scale CHP plants, thermal storage, and P2H For this purpose, a mixedinteger linear programming (MILP) model for unit commitment is presented that characterizes in a detailed manner the non-convex performance curves of electric generators, gas boilers, cogeneration units with one and two degrees-of-freedom, thermal energy storage, and power-to-heat units. The largescale thermal energy storage follows practices employed in modern DH systems [11]
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