An experimental study on temperature control of a solar receiver under transient solar load

© 2019 International Solar Energy Society Solar thermochemical process technology has great potential to store solar energy as chemical fuels, however, there remain several challenges that have hindered its industrial commercialization. One of the main challenges is the transient nature of solar energy which causes instability and reduces the efficiency of the process. A promising solution to cope with this problem is to use a variable aperture mechanism to regulate the light entry into solar receiver. A robust control algorithm is required to automatically adjust the aperture size and keep the temperature semi-constant under various transient conditions including short or long cloud coverage and natural variation of solar radiation from sunrise to sunset. In our previous work, an adaptive predictive controller was developed for aperture size adjustment and its performance was evaluated by computer simulations. The present work takes our previous study to the next level by experimental evaluation of the proposed controller on a solar receiver radiated by a 7 kW solar simulator. Two different variable aperture mechanisms, namely as iris mechanism and rotary aperture, are used for adjustment of the light entry into the receiver. Experimental results indicate that both of the mechanisms have reasonable performance in response to changes to a setpoint and disturbance in incoming solar radiation. However, the iris mechanism exhibits superior performance due to its capability of continuously changing the aperture size. For an elaborated evaluation of the iris mechanism, a real day of solar irradiation was simulated in the lab by changing the power level of the solar simulator based on a normal irradiance profile of a sunny day. According to the experimental results, the required temperature control was achieved with a maximum error in the temperature setpoint less than 1.95 °C.status: Published onlin