Increasing the Flexibility of Combined Heat and Power Plants With Heat Pumps and Thermal Energy Storage

Abstract

Combined heat and power (CHP) plants are efficient regarding fuel, costs, and emissions compared to the separate generation of heat and electricity. Sinking revenues from sales of electricity due to sinking market prices endanger the economically viable operation of the plants. The integration of heat pumps (HP) and thermal energy storages (TESs) represents an option to increase the flexibility of CHP plants so that electricity can be produced only when the market conditions are favorable. The investigated district heating system is located in Germany, where the electricity market is influenced by a high share of renewable energies. The price-based unit-commitment and dispatch problem is modeled as a mixed integer linear program (MILP) with a temporal resolution of 1 h and a planning horizon of 1 yr. This paper presents the optimal operation of a TES unit and a HP in combination with CHP plants as well as synergies or competitions between them. Coal and gas-fired CHP plants with back pressure or extraction condensing steam turbines (STs) are considered, and their results are compared to each other.

A comprehensive thermodynamic analysis of load‐flexible CHP plants using district heating network

“…where i represents HDHN and substation, respectively, and Q i,abs , Q i,rel , and η i represent the heat released from the exothermic side (kW), heat absorbed by endothermic side (kW), and heat efficiency of related heat-exchange process, respectively. In the substation, heat transfer fluids of both the exothermic and the endothermic sides are liquid water, and thus, heat release in the exothermic side (Q sub,rel ) and heat absorption in the endothermic side (Q sub,abs ) can be quantified by Q sub;rel=abs ¼ m sub;rel=abs c p Δt sub;rel=abs (11) where m sub,rel/abs and Δt sub,rel/abs are the mass flow (kg/s) and temperature variation (°C) of water in the related sides, respectively. As for the HDHN, the HSSE is condensed to heat PCW in the exothermic side, and the released heat can be quantified as…”

“…1,2 In the countries treating coal as the main energy source, such as China [3][4][5] and Germany, 6 coal-based CHP plants have been highly developed along with the sharp increase of heat and power demand. 7,8 In recent years, with the rapid development of renewable energy sources, CHP plants are encouraged to enhance operational flexibility to reduce the renewables curtailment, including extending the load range [9][10][11] and reducing the start-up time. 12 Moreover, the better quick-response ability is also required to follow the changing electric power demand continuously, 13,14 because the rapid expansion of intermittent renewable energy 15 makes the balance between electricity production and consumption in the grid hard to keep.…”

Optimal operation of the combined heat and power system equipped with power‐to‐heat devices for the improvement of wind energy utilization

“…At present, the combined operation of the heating system and electric power system (well known as combined heat and power system, CHPS) has been recognized as a promising approach to breaking through the limited flexibility of the independent electric power system. 4,5 By utilizing the energy storage of the heating system 6 or auxiliary heating devices, such as the heat storage (HS) 7 and power-to-heat (P2H) devices, 8,9 the joint production of electric and heat power of the CHP units can be decoupled, contributing to the ability enhancement of the electric power system for better wind power integration.…”

“…4,5 By utilizing the energy storage of the heating system 6 or auxiliary heating devices, such as the heat storage (HS) 7 and power-to-heat (P2H) devices, 8,9 the joint production of electric and heat power of the CHP units can be decoupled, contributing to the ability enhancement of the electric power system for better wind power integration. 4,5 By utilizing the energy storage of the heating system 6 or auxiliary heating devices, such as the heat storage (HS) 7 and power-to-heat (P2H) devices, 8,9 the joint production of electric and heat power of the CHP units can be decoupled, contributing to the ability enhancement of the electric power system for better wind power integration.…”

Multi-Objective Optimal Capacity Planning for 100% Renewable Energy-Based Microgrid Incorporating Cost of Demand-Side Flexibility Management

“…Several African countries have also taken significant steps and shown visible commitment towards massive green energy uptakes mainly by wind and solar energy. Countries such as Kenya [5], Ghana [6], Mauritius [7], Nigeria [8], Egypt, and South Africa [9] are currently making efforts in the integration of renewable energy technologies on both small and large scale. However, the incorporation of variable renewable energy resources (VREs) such as wind and solar energy increases the flexibility needs of a power system.…”