Comprehensive evaluation of low-grade solar trigeneration system by photovoltaic-thermal collectors

Solar trigeneration systems based on photovoltaic-thermal collectors can play a positive role in promoting renewable energy integration in buildings. Usually, low-grade solar heat produced by photovoltaic-thermal collectors does not meet the temperature requirement for driving absorption chillers, leading to unsatisfactory system performance. In this study, the solar absorption-subcooled compression hybrid cooling system, which is capable of utilizing heat at temperatures as low as 60 degrees C, is coupled with photovoltaic-thermal collectors to be a low-grade solar trigeneration system. In spite of heat recovery for heating and cooling, the electrical output of collectors decreases, due to the losses caused by the additional glass cover and elevated operating temperature. Therefore, through quasi-steady simulations based on annual meteorological data of three subtropical cities, this system is assessed from energy, economic and environmental viewpoints. The results show that in Guangzhou, the specific annual electricity saving of this system is up to 170.6 kWh/m(2), which is 17.3% higher than that of a comparable photovoltaic system. The parametric analysis suggests that increasing the solar filed area gives rise to a shorter payback period. With the maximum available solar filed area of 600 m(2), the minimum payback period and the maximum electricity saving can be achieved by the absorption subsystem capacities of around 40 kW and 180 kW, respectively. The most economically viable system is obtained in Zhuhai where annual solar irradiation is close to 1400 kWh/m(2) and electricity prices are relatively high. This study is useful for the development of solar trigeneration systems based on photovoltaic-thermal collectors and energy saving in modern cities.