Performance and economic analyses of linear and spot Fresnel lens solar collectors used for greenhouse heating in South Korea

This paper compares the thermal performance characteristics of LFL and SFL (linear and spot Fresnel lens, respectively) solar collectors for heating identical greenhouses in Chuncheon, South Korea. LFL and SFL collectors with similar storage capacities and Fresnel lens surface areas were tested under the same weather and operating conditions. Both systems were equipped with a dual-axis solar tracker for tracking the sun position and a circulating pump for forced convective heat transfer. Economic analyses of the solar collectors were performed by considering the current interest rate, inflation rate, and electricity prices in South Korea. The available energy per unit area and thermal efficiency were higher for the SFL than for the LFL collector. The discounted payback period decreased and electricity savings increased when the storage capacity was increased with either collector. All results indicate that SFL collector performance was about 7-12% higher than that of LFL collector. It is also noticed that changing the inlet flow rate of the greenhouse heat exchanger may be a good solution for obtaining the seed germination temperatures needed for different crops.