Final answer:
The question focuses on the physics of solar irradiance on a vertical surface facing due south at solar noon. It touches on the factors that influence the efficiency of solar panels, including their orientation towards the sun and ground reflectivity. Therefore, the correct option is 1.
Step-by-step explanation:
The question deals with the concept of sunlight incidence and the behavior of solar panels based on the position of the sun in the sky. It pertains to the field of physics, specifically the isotropic diffuse model for solar irradiance and the Earth's rotation relative to the sun. The solar noon is when the Sun is at its highest point in the sky, and typically, for a fixed solar panel facing due south, this would be the optimal time for solar irradiance, assuming the sky is clear. This is because, especially in the northern hemisphere, the sun tends to be in the southern part of the sky during midday. The 90° slope described in the question refers to a vertical orientation, which is quite unusual for solar panels, as they are typically tilted at an angle equal to the latitude of the site. Furthermore, ground reflectivity influences the amount of diffuse light received by the panel. Considering the example of a flat panel facing south and its annual average yields, the question suggests the use of solar panels and the way they are affected by various environmental factors, such as their orientation and the time of day, which are central concepts in the design and efficiency of solar energy systems.