The photovoltaic/thermal (PV/T) system offers the potential for highly efficient cogeneration and presents significant opportunity for practical applications as compared to pure PV system. However

there is less research concentrating on comprehensive comparison between these two systems. In this study

mathematical models for both conventional PV system and water-cooled PV/T system are first established; then

annual effective energy gains of these two systems can be determined. In particular

five representative cities in various climatic zones of China including Harbin

Beijing

Shanghai

Kunming

and Guangzhou are involved. Furthermore

a comprehensive comparison between the two systems

considering levelized cost of electricity (LCOE)

energy payback time (EPBT)

energy return on invested (EROI)

and carbon emission reductions (CER)

is conducted based on energy gains. The results show that the annual electricity gain of PV system is 9.3–23.5 % more than that of PV/T system because of the low operation temperature. But the comprehensive efficiency of PV/T system can be improved by 19.1–33.3 % because of the extra heat gain. It's noteworthy that the performance of PV/T system is notably influenced by the interplay between ambient temperature and solar irradiation

the highest energy gain is observed in mild climate regions devoid of extreme cold conditions. Despite the PV/T system incurring an initial investment and operational and maintenance costs 1.7 times higher than that of the PV system

along with approximately three times the energy consumption during production

it demonstrates a favourable annual energy return. Upon computation

the LCOE is estimated to decrease by approximately 47.2 % to 59.8 %

the EPBT can be shortened by 0 % to 25.0 %

the EROI is projected to increase by 0 % to 47.3 %

and the CER is enhanced by three times when compared to pure PV system.