What's the difference between the summer calendar and the lunar calendar?

They are the same thing, there is no difference.

Summer calendar = lunar calendar, which is a combination of yin and yang. It is unscientific to call it the lunar calendar instead of the lunar calendar. Lunar calendar and solar calendar are calendar types, while summer calendar and lunar calendar are calendar names.

Origin:

It is said that our ancestors used this calendar in all lunar calendars as early as the Xia Dynasty. So people also call it the summer calendar. After liberation, it was still called the summer calendar. After 1970, it was renamed as the "Lunar Calendar" in China. As for the origin of the name "lunar calendar", it is probably because the country has been founded on agriculture since ancient times, so the calendar must serve agriculture.

Divination and astrology prevailed in ancient China, and astronomical observation occupied a great position in imperial power. The calendar changed in every dynasty to meet the needs of imperial power, and the summer calendar was born under such circumstances. For thousands of years, with the change of dynasties, the integration of calendars has become our current lunar calendar.