Researchers in China have built a PV-powered air conditioning system that can store electricity through ice storage. The performance of the system was evaluated taking into account operational efficiency and stability, and the scientists found that a device based on a variable speed compressor and MPPT controller showed very good ice making ability.
June 28, 2021
From the PV magazine Global
Scientists in China have developed a direct-drive photovoltaic air conditioning system that can store solar energy through ice storage. The latter is a common heat storage technology based on standard cooling equipment and an energy storage tank that is able to store cold while shifting energy consumption to the night, off-peak hours.
“The novelty of this work is that it proposes a solar cooling system powered directly by distributed PV and completely replacing the rechargeable battery with inexpensive ice,” said Guoliang Li, author of the research collaboration PV magazine. “Solar air conditioning systems with PV panels of different sizes, with and without MPPT controllers and various types of compressors were built and tested in the open air in order to experimentally investigate the operating characteristics of the air conditioning system with different levels of solar radiation.”
According to the research group, PV-powered air conditioning systems are often equipped with batteries for energy storage, which creates challenges in terms of low power, high initial investments and complex configurations for practical applications. “The ice storage system for the PV-powered air conditioning system with reduced batteries was examined in our previous work,” he explained. “It proved the feasibility of the ice bank, in which the batteries were only used as a buffer and the average energy efficiency of the system could reach 7.65%.”
The proposed new system consists of: a PV system with 12-16 monocrystalline modules with an output of 190 W, mounted at an angle of inclination of 30 degrees; a control system based on an inverter and an MPPT controller; an ice making system having a variable speed compressor with a frequency range of 360 Hz; a capacitor; a liquid storage device; a capillary; an evaporator; an ice storage tank; a gas-liquid separator; a variable speed pump; and a heat exchanger.
The performance of the system was evaluated taking into account the operational efficiency and stability. “The optimal matching relationships have been found and experimental results of the system with a speed-controlled compressor and an MPPT controller have shown very good ice making ability and reliable operation as well as a great improvement in the available photovoltaic power,” said Li of the average PV-to-compressor power efficiency ( PPE) and the coefficient of performance (COP) of the systems were improved by reducing the duty ratio, which in turn decreased the operating stability ratio (OSR) of the compressor.
Through their analysis, the scientists found that using an MPPT controller improved the system's PPE by 81.7% compared to that of the system without MPPT, and that the variable speed compressor was more adaptable for PV-powered cooling.
The proposed system is presented in the paper “Study on Matching Characteristics of Photovoltaic Fault and Refrigeration Compressor in Solar Photovoltaic Direct Drive Air Conditioning Systems” published in Renewable Energy. The research group includes scientists from Yunnan Normal University and Jiaxing University.
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