Pull down characteristics of a bottle cooler with DC compressor operated under sunlight and artificial solar simulator

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

This work envisages on the development of an indoor solar simulator setup for operating PV panels and PV powered refrigeration appliances with a DC compressor. The use of DC powered devices helps in the elimination of inverters which aid reduction of cost and power loses. The solar simulator focuses on providing a test facility for a bottle cooler with a DC compressor solely powered from a PV panel of 125W capacity. Halogen lamps are used in the simulator as they are inexpensive, readily available and their light intensity can be fully controlled by regulators. The lights in the solar simulator are arranged in a zig-zag pattern to obtain uniform illumination throughout the panel with minimum overlapping of light radiation. In order to perform various test conditions with respect to the light intensity, the distance between the simulator and the panel can be varied. The solar simulator is kept ON for a minimum of 30 minutes prior to the testing to obtain a steady state and uniform levels of irradiation. The compressor used in the bottle cooler is a DC powered Danfoss BD35K compressor which has an inbuilt control unit for smooth operation of the compressor during fluctuating solar irradiation and it works for a wide range of voltage of 10 to 45 V. The refrigerant used in the bottle cooler is iso-butane due to its low GWP and ODP values. An experimental comparison in the pull down characteristics of the DC powered bottle cooler and I-V characteristics of the PV panel used was performed using sun light and artificial solar simulator. In both cases, the bottle cooler unit is kept in the same environmental condition except for the PV panel that is kept in both conditions separately. The I-V characteristic experimentation was performed by applying load through a rheostat. Based on the I-V characteristics, the panel efficiency was found to be 9.27% under sunlight and 6.93% under the solar simulator setup. It is to be noted that the panel temperature was higher at outdoor conditions compared to that at indoor testing as fan cooling was provided during the test under the simulator. The average light intensity on the panel was lower at outdoor compared to indoor testing conditions. The pull down temperature was obtained by placing RTDs at various locations in the cabin and the average value was taken. The pull down time for the bottle cooler under the sunlight was 32.78 minutes while it was 29.5 minutes when tested under the solar simulator. Although the panel efficiency and the pull down time with the solar simulator is lower than the values observed from the open sun light, due to its consistency the simulator can be used as a test facility for PV powered DC appliances.