Flexible Heat and Power Generation: Market Opportunities for Combined Cycle Gas Turbines and Heat Pumps Coupling

Climate pledges, besides the need for a secure, reliable, and affordable supply of energy, are posing the challenging target of an energy sector’s carbon footprint reduction that does not jeopardize the access to energy itself, ensuring the demand satisfaction, consequently economic growth, the right to development of all countries, and the energy poverty reduction. From the policy point of view, the United Nations 2030 Sustainable Development Agenda is often considered as a reference, it states 17 general goals adopted by all the UN member states, the 7th and the 13th concern specifically the right to access clean and affordable energy and the climate action. Then, each country has implemented locally or regionally, specific policy instruments to support the shift from a fossil fuel-based economy to a climate-neutral one, a process commonly defined as energy transition. Even if the implemented policy tools may differ from each other, the effects are somehow similar worldwide: massive renewable energy power generation capacity has been installed in the last decade, and even a larger amount is foreseen to be installed in the next years. Nevertheless, the stochasticity of the sources and the non-programmability, that characterized many renewable generators, pose serious challenges in the electricity grid management with an increased demand for efficiency and flexibility from traditional programmable power plants. Such power plants have shifted their traditional role from constant baseload generators to fluctuating backup capacity and service providers. Consequently, the operating hours have been reduced and the costs have increased because of the frequent start-ups, the lower efficiency in off-design, and the increased need for maintenance that flexible operation requires. Thus, despite the fact they turn out to be essential to grid management, dispatchable generators often face economic issues and their viability is no longer certain. Besides the electricity sector, on which the attention is often focused, the transition toward a decarbonized economy is needed also in the other sectors. Among these, heating is one of the most relevant. Heating still largely relies on fossil sources, even if district heating networks, waste heat recovery, heat pumps, and other forms of coupling with less carbon-intense sectors are available technologies that can reduce the sector impact in the future. This thesis aims to explore solutions coupling Combined Cycle Gas Turbine (CCGTs) power plants with Heat Pumps (HPs) in other to enhance the flexibility of power plants, pursuing the threefold target of an increased ability in providing services to the grid, reduced uncertainty about economic viability, and the supply of a reduced carbon intensity heating. The Introduction and the first chapter describe in detail the motivations for this thesis, the context in which the investigated technologies are supposed to operate and review the existing literature. Chapter 2 focuses on the Combined Cycle Gas power plants, investigating the effects of flexible operations on emissions and quantifying the benefits of inlet air conditioning as a measure for flexibility enhancement. Chapter 3 concerns heat pumps, a model developed for techno-economic analysis is presented alongside some results comparing different fluids and heat sources for different supply temperatures. Chapter 4 combines what is presented in the previous two chapters investigating solutions for CCGTs and HPs coupling. Different coupling concepts have been explored for two main purposes, a flexibility increment, by inlet air conditioning, of those plants devoted only to power generation, and the coupling of the heat pump to a combined heat and power CCGTs. The power-oriented concept is based on an inlet air conditioning unit consisting of a heat pump, cold storage, and some heat exchangers. The unit operates heating, to increase the off-design efficiency, or cooling, to boost the net power output, and the gas turbine inlet air according to different operational modes. The combined heat and power concept uses a high-temperature heat pump that, integrated with the CCGT, harvests privileged heat sources (different options are investigated) increasing the maximum thermal output and the global efficiency. Warm storage is also included allowing flexible management of the coupled HP and CCGT. Finally, Chapter 5 describes the market context in which power plants operate today. It focuses on the importance of recognizing the economic value of flexibility in the ancillary services market. A novel model of optimal dispatch for power generators and storage is presented, it schedules the power plant, or storage, operations optimizing not only the profits in traditional energy-only markets but the overall expected profits considering also the services markets and keeping into account the uncertainty of offers/bids acceptance.