UC Irvine

Buildings account for 39% of global carbon emissions through their reliance on conventional central power plants for their needs. As part of the efforts to meet the climate goals, policies are proposed and adopted to achieve zero net energy buildings. Renewable distributed energy resources (DER) such as microgrids/nanogrids can meet the buildings’ energy demand locally. Although solar and wind are fast-growing renewable energy resources, their intermittent nature creates a mismatch between demand and supply. Hence, these sources must be complemented with other energy systems to maximize their utilization and reliability. High temperature solid oxide cell (SOC) systems are efficient electrochemical energy conversion technologies that could be used for this purpose. SOC systems can operate reversibly to store and regenerate electricity; in the solid oxide electrolysis cell (SOEC) mode it converts electricity into H2, and in the solid oxide fuel cell (SOFC) mode it generates electricity by oxidizing fuels. While their high operating temperature renders benefits such as fuel flexibility and high-grade heat, thermal management remains a challenge, especially in dynamic conditions.

The goal of this work is to conceptualize and design integrated SOC systems with solar PV, wind, and batteries to supply the energy demand of different types of buildings. The dynamic operation, control, and thermal management of these hybrid SOC-based systems is studied in Simulink/MATLAB. Spatially and temporally resolved physical models of SOFC, SOEC, and balance of plant components are developed and integrated in Simulink. In one part of this study, the models are used to develop a self-sustaining energy system for islanded residential/industrial buildings equipped with PV/wind, where SOEC/SOFC are coupled with these systems store/restore energy (power-to-gas). Meanwhile, SOFC and SOEC are thermally integrated to minimize the reliance on external energy sources. Several control methods are implemented for power and thermal management of the system during dynamic conditions. In another part of this work, the effect of SOFC is evaluated in achieving Zero-Net-Energy (ZNE) residential buildings. The ZNE study is based on the time-dependent-valuation (TDV) of energy established by the California Energy Commission. First, PV is sized to achieve ZNE in 16 California climate zones (CZ) already equipped with a battery (LG Chem RESU10H) and a SOFC (BlueGEN) with certain capacities. Next, the economic feasibility of having SOFC for ZNE homes is studied. An open-source tool called Distributed Energy Resource Optimization (DERopt) is used to find the optimal dispatch operation of each technology to achieve ZNE home with minimum cost. The model uses Mixed Integer Linear Program to find the optimal configuration of PV, battery, and SOFC for buildings connected to electric and gas grids in 2025, 2035, and 2045. The results show that SOFC was adopted by DERopt in 2045 for ZNE homes at the current cost projections of SOFC. SOFC is an economical option for homes only when the ZNE constraint is imposed. Without the ZNE constraint, the SOFC levelized cost of energy must be reduced to a much lower value to compete with other technologies such as PV. Moreover, the fuel delivered to the SOFC must be fully decarbonized in order for the SOFC to be an optimal choice for ZNE homes; because the gas consumption by SOFC must be offset by renewable electricity export to the grid if it is not decarbonized. In the optimized ZNE configuration in 2045, SOFC played a significant role in reducing the building energy demands by supplying 50% of electric load and 60% of domestic hot water demand. The resulting configuration for ZNE homes shows that even with SOFC that building is connected to both gas and electricity grid, the total energy cost is the lowest for buildings electrified with efficient heat pumps.