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SUMMARY In this paper, an experimental work is carried out to investigate the characteristics of solar thermal collection using supercritical CO2. This solar thermal conversion is based on supercritical CO2 natural convection, which is much easily induced because a small change in temperature can result in large change in density close to the critical point. In addition, its critical temperature is 31.1°C and low enough to be easily reached in the low-temperature solar thermal conversion system. The obtained results show that the supercritical CO2 flow rate is smooth curve and not affected by the sudden variation of the solar radiation. The solar thermal conversion operation process can be divided into three periods: starting-up, transition, and stable period. When the system reaches the stable period, the CO2 flow rate will keep at a high value even if the solar radiation stays at a low level. It is also found that the smaller local solar radiation variation is, the better ability of keeping the flow rate near the peak level the supercritical CO2 fluid owns. It is also found that a small pressure difference can drive a supercritical CO2 flow with high flow rate. Furthermore, high solar thermal conversion efficiency is found at a high mass flow rate and under operation pressure near the critical point. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Using carbon dioxide as working fluid receives increasing interest since the Kyoto Protocol. In this paper, thermodynamic analysis was conducted for proposed CO2-based Rankine cycle powered by solar energy. It can be used to provide power output, refrigeration and hot water. Carbon dioxide is used as working fluid with supercritical state in solar collector. Theoretical analysis was carried out to investigate performances of the CO2-based Rankine cycle. The interest was focused on comparison of the performance with that of solar cell and those when using other fluids as working fluids. In addition, the performance and characteristics of the thermodynamic cycle are studied for different seasons. The obtained results show that using CO2 as working fluid in the Rankine cycle owns maximal thermal efficiency when the working temperature is lower than 250.0°C. The power generation efficiency is about 8%, which is comparable with that of solar cells. But in addition to power generation, the CO2-based solar utilization system can also supply thermal energy. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, the performance of solar energy powered transcritical cycle using supercritical carbon dioxide for a combined electricity and heat generation, is studied experimentally. The experimental set-up consists of evacuated solar collectors, pressure relief valve, heat exchangers and CO2 feed pump. The pressure relief valve is used to simulate operation of a turbine and to complete the thermodynamic cycle. A complete effort was carried out to investigate the cycle performances not only in summer, but also in winter conditions. The results show that a reasonable thermodynamic efficiency can be obtained and COP for the overall outputs from the cycle is measured at 0.548 and 0.406, respectively, on a typical summer and winter day. The study shows the potential of the application of the solar energy powered cycle as a green power/heat generation system. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, a solar water heater using supercritical carbon dioxide as working fluid is proposed and experimentally studied. For supercritical carbon dioxide, a small change in temperature or pressure can result in large change in density, especially in the state close to the critical point. Thus, natural convective flow of the supercritical carbon dioxide can be easily induced by solar heating or water cooling. Such convective flow absorbs and transports heat to water in solar collector tubes. Motivated by the above idea, an experimental setup was designed, and a solar water heater was tested. The obtained results show that natural convective flow is well induced, and a flow of 1900 Reynolds number can be achieved even in winter, when the lowest level of solar radiation condition occurs. Furthermore, the measured collector and heat recovery efficiencies are 66.0% and 65.0%, respectively. More details of its mechanism are to be studied, and a complete performance analysis is needed. [ABSTRACT FROM AUTHOR]