Why is the maximum temperature only reached in the afternoon when the weather is sunny?
The daily course of the temperature is not only determined by the solar radiation, but also the heat emission from the ground plays a decisive role. The energy that reaches the earth from the sun on a cloudless day depends on the position of the sun, which is highest at true noon. Then the path through the atmosphere is shortest, and thus the light attenuation is lowest. In addition, the incident sunlight is distributed over a significantly larger area in the morning and evening hours than at noon.
To illustrate the temperature development on an almost cloudless sunny day, you can imagine a bathtub whose water level should correspond to the current temperature. As the sun rises, the tap is turned on a little and water begins to trickle into the tub. Now the faucet is slowly opened more and more until it is fully open at true midday. Then you slowly start to close it again and after sunset no more water runs into the bathtub.
Without a drain, the water level, i.e. the temperature, would continue to rise, so the tub would eventually overflow. Luckily, the ground radiates energy upwards. The amount of energy released also increases with increasing temperature. This corresponds to a bathtub drain that opens wider and wider as the water level rises.
Shortly before sunrise, currently between 4:57 a.m. in Berlin and 5:30 a.m. in Cologne, the temperature or the water level is low, so little water runs off. As the sun rises, the tap is turned on. At first it only dribbles, but just a few minutes later the inflowing water is exactly the same as the outflowing water and the lowest temperature is reached. After that, the water level, i.e. the temperature, begins to rise because more water flows in than flows out. As the water level rises, more and more flows out, but the inflow during the midday hours is greater than the outflow and the water level, like the temperature, continues to rise in the afternoon.
In summer, between 4:00 p.m. and 6:00 p.m., the point at which inflow and outflow balance out again is reached. Now the water level is highest, so it is warmest. From then on, the outflow predominates and the temperature drops again.