Session: 03-03 Pumped Thermal Energy Storage

Paper Number: 107001

107001 - Thermodynamic Performance Investigation of Environmentally Friendly Working Fluids in a Geothermal Integrated Pumped Thermal Energy Storage System 

The over reliance on fossil fuels to meet our energy needs is one of the reasons for accelerated global warming and climate change. To avoid the catastrophic consequences of climate change, there is an urgent need to significantly reduce the emission of greenhouse gases into the atmosphere. As such, several nations have committed to significantly cut their greenhouse gas emissions, with some committing to reaching net zero by 2050. This requires an immediate transition to renewable and clean energy systems. Among the available renewable energy technologies, solar energy and wind energy have the potential to meet a significant portion of the global energy demand. However, solar energy and wind energy are intermittent, available when there is less demand for energy, and not available when there is significant demand for energy. As such, there is a need to develop technically and economically feasible energy storage technologies to match the demand and supply of energy. Recent advances in the development of energy storage technology have led to reduced costs and increased deployment. For large-scale energy storage, pumped hydropower is the most technically and economically developed technology, accounting for the largest share of the installed capacity. However, pumped hydro has geographical limitations requiring the presence of a water body and sufficient elevation for the storage reservoir. A recently introduced technology for large-scale energy storage with no geographical limitations is the pumped thermal energy storage technology. It consists of a high-temperature heat pump cycle connected to a thermal energy storage medium and an organic Rankine cycle for discharging the stored energy when needed. The system uses excess and low-cost electrical energy when available to drive the high-temperature heat pump to charge a thermal energy storage system, typically a latent thermal energy storage tank. During peak hours, the stored energy is used to run a power cycle to meet the peak energy demand. Although the PTES technology has shown potential, it is still in the development stages requiring significant improvements before commercial adoption and widespread use. To achieve high round-trip efficiencies, PTES systems require a low-cost high-temperature source for the heat pump cycle. In this paper, a PTES system coupled to a borehole heat exchanger installed in an abandoned oil well is considered. The mathematical model of the PTES system and the borehole heat exchanger is developed using the first and second laws of thermodynamics. With the developed model, the thermal and thermodynamic performance of the PTES system for different working fluids, including Butene, R1233zd(E), R1234ze(Z), R1224yd(E), R32, RE245cb2, and R152a was investigated. For borehole heat exchanger outlet temperatures between 60 and 120^oC and heat exchanger temperature drops between 20 and 60^oC, the net power ratio i.e. the ratio of electrical energy discharged to the electrical energy stored was found to be between 0.5 and 1.4. This shows that the system has the potential to give back more than 100% of the energy used to charge the thermal energy storage system. High net power ratios are obtained at high source temperatures. Moreover, each of the considered working fluids showed an optimal heat exchanger temperature difference for maximum exergetic efficiency.

Presenting Author: Aggrey Mwesigye University of Calgary

Presenting Author Biography: Dr. Aggrey Mwesigye is an Assistant Professor of Renewable Energy in the Department of Mechanical and Manufacturing Engineering in the Schulich School of Engineering. He leads the Sustainable Thermal Energy Research Group. His research focuses on the development, modeling, and optimization of sustainable thermal energy systems for different applications, including space heating and cooling, refrigeration, power generation, and cold chain among others. His research has been published in leading journals in energy, including, Applied Energy, Energy Conservation and Management, Renewable Energy, Energy, Solar Energy, and Applied Thermal Engineering among others. Dr. Mwesigye’s research is currently looking at optimal system configurations of alternative and sustainable energy technologies for providing space heating and cooling in extremely cold climates with potential applications in Canada’s northernmost communities and especially, rural areas where there is over-reliance on diesel to meet their energy needs. The other research focuses on the performance improvement of concentrating solar thermal technologies and their applications for simultaneous generation of electricity and heat, geothermal energy systems and high heat flux electronics cooling. Dr. Mwesigye is a registered Professional Engineer with Professional Engineers Ontario and the Association of Professional Engineers and Geoscientists of Alberta. He is a Member of the American Society of Mechanical Engineers (ASME) and an Associate Member the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE).