Comparative analysis of a solar-geothermal system with energy retrofit based on innovative Indexes

Integrating multiple renewable energy sources into buildings is essential for achieving a net-zero carbon future, especially within the building sector. This study incorporates a photovoltaic-thermal (PVT) array in a conventional ground source heat pump (GSHP) system and presents four distinct designs that change based on system layouts and energy recovery mechanisms. Two innovative indicators, COPTLR and SCOPTLR, are proposed to effectively measure the efficiency of hybrid energy systems which include GSHPs, as well as to examine the overall utilization ratio of shallow geothermal energy. By applying numerical investigation, long-term systematic analysis is presented along with economic metrics and proposed innovative performance indicators. The findings indicate that the proposed cooling and heating retrofit mechanism, along with the implementation of a schedule control, can reduce the GSHP power consumption by 63.2%. Meanwhile, investment tax credit (ITC) and favorable retail tariffs can lower the long-term levelized cost of energy (LCOE) to 0.077 $/kWh. The minimum values of COPTLR and SCOPTLR in the proposed system are 0.492 and 0.483, respectively. This investigation fully demonstrates the advantages of the designed solar-geothermal system and highlights the effectiveness of the proposed performance indicators.