Why is the noon solar intensity greater in the summer solstice than on the winter solstice?

The reason is the angle of the sun during the summer solstice. The earth is tilted toward the sun rather than away from it. Summer solstice means the day is the longest of the year and winter solstice means the sun is its greatest distance in the celestial equator. June 21 and December 21 is the start of the solstice and this happens twice in the year.