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The second law of thermodynamics is used to analyze the potential for exergy conservation in solar collector systems. It is shown that the amount of useful energy (exergy) delivered by solar collector systems is affected by heat transfer irreversibilities occurring between the sun and the collector, between the collector and the ambient air, and inside the collector. Using as working examples an isothermal collector, a nonisothermal collector, and the design of the collector-user heat exchanger, the optimum operating conditions for minimum heat transfer irreversibility (maximum exergy delivery) are derived.
Bejan et al. (Sun,) studied this question.