1. Explain why the average rate per square meter at which solar energy reaches Earth is one-fourth of the solar constant. 2. Explain why we can't concentrate sunlight to temperatures hotter than the 5,800-K solar surface. Hint. Think about the second law of thermodynamics. 3. Why does stratification in a solar hot-water tank help increase the efficiency of solar energy collection? 4. At what time of year would you expect maximum midday insolation on (a) a solar collector tilted at latitude and (b) at horizontal collector? 5. How is a parabolic trough concentrator simpler than a parabolic dish? 6. In what way is the electrical output of a PV module not compatible with the electric power grid? 7. Some people claim that passive solar houses made of stone or concrete, because of their large thermal mass, don't need insulation. Discuss this claim