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3.0 CSP Rig Development

The development of the scalable CSP rig is presented in three subsections, with design iterations from Semester 01, as well as tests and analyses for each subsection, detailed on the respective pages below.

3.5 Integrated Test Results

This section evaluates the performance on integration of the light, thermal transmission and TES subsections.

The iterations below show how can the thermal performance of an integrated small-scale CSP-TES system be improved by reducing heat loss and optimizing circulation conditions.

3.5.1 Initial integration

The pipe is routed from the receiver through the central frame and connected to the TES and pump. A longer pipe length was used initially to allow flexibility in positioning TES, and is reduced later. Control plastic drum with minimal insulation with equal amount of water volume is used in comparison with insulated TES.

Pipe is not insulated initially. Later insulation was partially applied along the full pipe length due to flexibility limitations of PUR/PIR and restrictions on insulating certain sections of pipe to avoid damage on removal. In the end, pipes are fully insulated.

Sensor used: DS18B20, RDXL6SD-US-B-CAL-3, SP-420, DHT11(for rain detection)

3.5.2 Iterations and Results

3.5.2.1 Iteration 1: Effect of Pipe Insulation

Iteration 1 assesses the impact of insulation on the integrated system. The details on iteration 1 is below.

Discussion: The insulated system achieved a higher TES water temperature and a larger TES–control temperature difference than the uninsulated system. This is because pipe insulation reduces heat loss from the fluid during circulation, allowing more thermal energy collected from the receiver to be retained and transferred into the TES. As a result, the maximum energy stored in the TES increases, leading to a higher peak temperature. In addition, the rate of temperature rise in the TES is steeper in the insulated case, indicating faster heat accumulation. The insulated system also showed longer temperature retention near its peak temperature. This trend is consistent with the expected reduction in heat loss along the piping network (see Appendix B0 for theoretical computation).

Result: The maximum temperature difference between TES water and control water increased from 5.19°C in the uninsulated system to 8 °C in the insulated system, corresponding to an improvement of 54%. The average heating slope of the TES water also increased from 2.03°C/h to 2.33 °C/h, and the duration near the maximum temperature was extended in the insulated system. Therefore, the results support the hypothesis. At the 80% confidence level, the two-tailed test gave p ≈ 0.148 for maximum temperature difference and p ≈ 0.200 for heating slope, indicating weak statistical significance.

Limitation: Solar irradiance varied from day to day, so the two cases were not tested under perfectly identical weather conditions. The analysis assumes that the irradiance conditions were broadly comparable based on similar peak and average values, although 15/3 was a rainy day and may not be suitable for direct comparison in hypothesis testing. Other uncontrolled factors, such as ambient temperature and transient cloud cover, may also affect the observed temperature profiles.

3.5.2.2 Iteration 2: Effect of TES Water Volume and Pump Mode

Iteration 2 was conducted to assess effect of TEs water volume and pump mode on the integrated system. The details on iteration 2 is below.

Discussion: The 10 L relay-controlled system achieved a higher peak TES temperature, a larger TES–control temperature difference, and a longer temperature retention period than the 20 L system without relay. This can be explained by two main factors. First, reducing the TES water volume increases the temperature rise for the same amount of stored heat because the thermal mass of the water is smaller. Second, switching off the pump after 17:00 reduces night-time heat loss through the receiver loop, allowing more thermal energy to remain inside the TES. As a result, the TES temperature remained above the control temperature overnight and cooled more slowly. The relay-controlled system also remained above 40°C for a longer duration, which is beneficial for hot-water applications requiring sustained useful temperature.

It is also notable that turning the pump on causes a sudden temperature rise, which should be minimized to maximize heat transfer to the TES. In addition, the pump is turned off before the TES reaches its peak temperature, leading to avoidable heat loss during cooling.

Result: The maximum temperature difference between TES water and control water increased from 8.25°C in the 20 L partially insulated system without relay to 11.56°C in the 10 L partially insulated system with relay-controlled pump mode, corresponding to an improvement of 40.1%. The retention time above 40°C also increased from about 4.5 h in the earlier 20 L configuration to 8.67 h in the 10 L relay-controlled configuration, corresponding to an improvement of about 92.7%. Moreover, the cooling duration before the TES temperature approached the lower threshold increased from about 11 h to 17.5 h, an extension of about 59.1%. Therefore, the results support the hypothesis that reducing TES water volume and isolating the TES from the receiver during non-heating hours improve thermal retention and extend the duration of useful hot water.

Limitation: Solar irradiance varied from day to day, so the two cases were not tested under identical weather conditions. The relay-controlled setup used a fixed switching schedule rather than a temperature-responsive valve, so the TES was not fully isolated under all operating conditions. The selected pump on/off times were based on expected irradiance patterns and may not have matched the exact solar conditions each day. In addition, more than one variable was changed simultaneously, namely water volume and pump mode, so the individual contribution of each factor cannot be isolated from this iteration alone. The retention times and temperature differences were also estimated from the graph and may contain small reading errors.

3.5.2.3 Iteration 3: Effect of Pipe Shortening and Improved Insulation

Adjustment:

The TES was repositioned to shorten the pipe, reducing the total surface area exposed to the surroundings and therefore reducing heat loss along the pipe. Insulation coverage was also improved by adding air-conditioning insulation in areas that could not be fully covered by PUR/PIR insulation.

During removal of the previous pipe configuration, it was observed that some sections of the aluminium pipe lacked PUR/PIR insulation along the longer pipe sections because the spray insulation could not reach deeper regions of the pipe. In addition, support structures intended to keep the hose centered could not be inserted into the longer pipe sections, causing the hose to rest against the side of the aluminium pipe. These issues likely increased heat loss and reduced the effectiveness of the previous system.

Iteration 3 focusses on shortening the insulation and refining the timing for the pump mode in the integrated system. The details of iteration 3 are below.

Discussion:

The updated system achieved a higher TES peak temperature and a larger TES–control temperature difference than the previous partially insulated system. Shortening the pipe reduced the length over which heat could be lost to the environment, while improved insulation coverage reduced exposed sections that previously acted as heat-loss points. The additional use of flexible air-conditioning insulation also helped insulate bends and regions that PUR/PIR insulation alone could not cover effectively. As a result, the TES retained more useful thermal energy, and the water remained above 40°C for a longer period.

After the second iteration, the relay timing was shifted 1 hour earlier. However, the pump start and stop times still did not align with the actual heating onset and peak temperature, as these depend on daily weather conditions.

Result:

The maximum temperature difference between TES water and control water increased from 11.56°C in the 10 L partially insulated system with relay-controlled pump mode to 18.88°C in the 10 L fully insulated system with shortened pipe and improved insulation, corresponding to an improvement of 63.3%. The duration for which TES water remained above 40°C also increased from about 7 hours 55 minutes to about 9 hours 4 minutes on one day, and from about 8 hours 40 minutes to about 9 hours 1 minute on the other day. Therefore, the results support the hypothesis that shortening the pipe and improving insulation reduce heat loss and improve useful hot-water retention.

Limitation:

Solar irradiance and ambient conditions varied from day to day, so the two cases were not tested under identical weather conditions. In addition, the relay timing was changed from 10:00–17:00 to 09:00–16:00, so the observed improvement cannot be attributed solely to pipe shortening and insulation enhancement. The durations and temperature differences were estimated from the graph and may contain small reading errors. Further testing under the same relay schedule and weather conditions would provide a more direct comparison.

3.5.3 Conclusion and Future Work

Overall, the system performance improved across the three iterations. Pipe insulation, reduced TES water volume, relay-controlled pumping, and shorter pipes all contributed to higher water temperature and longer useful hot-water retention.

Future work may include:

  1. Replacing the relay with an insulated valve to improve TES isolation from the receiver loop, and
  2. Developing an integrated control system that uses irradiance and humidity data to optimize isolation timing under varying weather conditions, particularly during rain.
Next: 04. Final System