It's difficult to pinpoint the very first kingdom to use a solar calendar with certainty. Early civilizations often had complex systems for tracking time and seasons, and the development of calendars was a gradual process.

Here's what we know:

* Ancient Egypt: They are often credited with developing the first solar calendar, around 3000 BC. This calendar was based on the solar year (365 days) and had 12 months of 30 days each, with 5 extra days added at the end.

* Other early civilizations: While the Egyptians are often cited as the first, other civilizations like the ancient Babylonians and Chinese also had sophisticated calendars that incorporated solar observations.

Important note: It's worth remembering that "first" can be tricky when discussing ancient history. It's likely there were other societies with calendars based on the sun, though their records may have been lost or are yet to be discovered.