For any solar thermal system involving solar collectors, the efficiency of solar collectors will always be needed to observe its performance. Instantaneous efficiency of the collectors is defined as the ratio of useful energy absorbed by the working fluid to the amount of solar radiation falling on the collector.

The Coefficient of Performance (COP) is used to describe the performance of a heat pump system. It is defined as the ratio of energy released in the condenser coil and water tank to energy used to run the compressor.

where Xpp is defined as:

3. Results and Discussion

The meteorological condition for the day during the experiment conducted in December is shown in Figure 2. It can be seen that the ambient temperature is relatively constant with a value close to 30 °C. The maximum solar radiation value reaches around 1000 W/m2, and it varies during the period of measurements with the lowest value around 400 W/m2

The efficiency of the liquid solar collector is shown in Figure 4. The collector, at 2 m2, has an efficiency in the range of 50 to 60 percent. As shown in Figure 5, the coefficient of performance (COP) tends to have a relatively stable value. It varies between 8 and 9.

From Figure 6, it can be seen that the maximum water production rate is close to 0.9 kg/hr. The performance ratio is a function of water production rate, thus the change of production rate will affect the performance ratio. From Figure 6, the performance ratio is shown to be close to 1.3.

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