12 p.m.
1. The height of the sun is the highest: When the height of the sun is the highest, the radiation energy received at the ground is the largest and the photothermal energy absorbed by the system also increases accordingly. Therefore, the photothermal energy production period will be more complete around midday than other times.
2. The temperature difference changes significantly: around noon, the air temperature is relatively high, and the change in the height of the sun and the increase in ground temperature form a larger temperature difference. , the power generation loss will be relatively high and more efficient in power generation.