A dual-mode novel Parabolic Trough Collector for process heating applications in small scale industries-Thermo-hydraulic and performance investigation

Only a few industries worldwide use solar heat for industrial processes, despite the fact that it is a proven and cleaner solution. More over, Small-scale industries need hot water and low-enthalpy steam, but such systems receive scant attention due to the active nature of Parabolic Trough Collectors as well as the use of less efficient flat plate technology in this temperature range. This delineate the opportunity for research focus in efficient passive technologies especially in low temperature range. In this regard a novel dual mode Parabolic Trough Collector based on an Open Natural Circulation Loop (PTC-ONCL) is proposed here. Focus of this work is to assess the proposed system's suitability for process heating applications requiring hot water/low enthalpy steam, especially in rural areas. Experiments are conducted on an in-house prototype. A novel methodology for correlating actual solar data to the input heat load for the in-house test facility is developed. Five representative solar days are considered for individual tests. Startup, transient, and efficiency parameters are evaluated. Productivity, industrial viability, and environmental impact are also accessed. Throughout the test, the loop maintained a stable flow, where the start-up oscillations, thermal oscillations and type-I instabilities are observed. The system operates at an unprecedented efficiency of 72 +/- 4% in hot water mode and 70 +/- 5% in Steam generation over a 7 h period. The economic analysis shows an ambitious Levelized Cost of Heat of 2.8 cents/kWh, with a payback period of 3.21 years. Moreover environmental study shows its huge potential in reducing the CO2 emissions. A dimensionless index is proposed to represent the solar day and is correlated to predict the average water temperature and steam generated with RMSE values of 0.98 degrees C and 0.125 kg respectively. The solar day index comprehends the total irradiation, wind velocity and the ambient temperature. The proposed PTC-ONCL system is capable of producing an annual average of 8.67 kgday(-1) and/or 150 L of hot water at an average temperature of 89.07 degrees C. The results, and the system's low cost and near-maintenance-free nature demonstrates its capability in the desired application, both technologically and economically.

Automated summary

Solar energy for industrial processes is not widely used, but this study proposes a new dual-mode Parabolic Trough Collector based on an Open Natural Circulation Loop. The system is evaluated for its suitability in providing hot water/low enthalpy steam for process heating applications, especially in rural areas. Experimental assessments, economic analysis, and environmental impact are conducted, showing the system's potential in efficiency, cost-effectiveness, and emission reduction.