Model Validation

Every model developed in this work has been individually tested and validated with data from the real system, but only the full hybrid model will be presented here to save space. Two experiments of 400 and 150 min are presented. The latter ex­periment is so short because it has been prepared to force changes in the operation modes of the plant.

The first validation test uses real data collected on 28/08/08. Figures 7.32(a) and 7.32(b) show the environment conditions for the validation test and the system vol­umetric flows, respectively. Figures 7.32(c) and 7.32(d) show the real system and simulated output temperature and the operation mode, respectively.

The experiment started when the system output temperature was close to the operating point. For the first 190 min, the irradiance increases from 480 W/m2 to 600 W/m2 and the ambient temperature stays high (solid and dashed lines in Fig. 7.32(a), respectively). Valve V1 stays open at 50%, setting a stable vol­umetric flow. During this first half, the system configuration mode is set to s1 (see Fig. 7.32(d)), where the solar collectors are fixed in the system configura­tion.

first 190 min approximately, the radiation starts to decrease and the tanks with water stored with a temperature of around 52°C are connected into the system configuration. This water is pulled out to the pipes, cooling down the water temperature in the primary circuit, as can be observed in Fig. 7.32(c), where the solid line is the real temperature output and the dashed line the simulated one. In this second half, the system configuration mode changes between modes s2 and s4 (see Fig. 7.32(d)), where tanks are fixed and the solar collectors are included and excluded from the system configuration.

As can be seen in Fig. 7.32(c), the real and simulated temperatures are similar and the most discording point is found in the mode change, where the model response is faster than the real system one, causing a faster temperature decrease in the model temperature output.

The second test uses real data collected on 07/09/08 during the afternoon. Fig­ure 7.33 shows how the system is forced to change among modes more frequently than usual. Figures 7.33(a) and 7.33(b) show the environment conditions for the validation test and the system volumetric flows, respectively. Figures 7.33(c) and 7.33(d) show the real system and simulated output temperature and the operation mode, respectively.

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Time (min)

Fig. 7.33 Hybrid model results. Date 07/09/08 (courtesy of M. Pasamontes et al., [284])

Modes s1, s4, s5 and s7 define the system behavior. The gas heater was frequently turned on during the experiment, causing increases in the system output tempera­ture. The changes in the operation mode are shown in Fig. 7.33(d).

At the start of the experiment, the system output temperature is around 50°C and only the solar collectors are connected (mode s1). From minute 15 to minute 42, the system configuration mode swaps from s1 to s5 and back again, producing a low, but continuous, increase in the system output temperature. After 42 min, the system configuration includes solar collectors, tanks and gas heater for 6 min. The temperature of the tank is 88°C, so a fast increase in the system output temperature is produced when it is included in the system.

Next, the system operation mode is changed to s4, turning off the gas heater for 7 min and then the operation mode changes from s4 to s1, excluding the tanks from the system and causing a temperature decrease for the next 23 min.

Finally, the system configuration mode swaps between s1 and s5, where solar collectors are fixed and the gas heater is included and excluded from the system configuration. The effect on the gas heater on the output temperature can be ob­served in Fig. 7.33(c).

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Fig. 7.35 Inlet and output temperatures of the generator (courtesy of D. Zambrano et al., [411])

Time (h:min)