A while back I wrote this handy function for Arduino called rolling average. This is a good function to have when working with sensors from a weather station.
It could easily be adapted to have an array with 24 objects in it to average something like light levels or sunshine over a day. To do this I would change int sensorReadings; to int sensorReadings; and long interval = 2000; to long interval = 3600000;. This way it updates once an hour for 24 hours.
I find using a light sensor is an easy to test that it works correctly.
I set it up like this – https://learn.adafruit.com/photocells/using-a-photocell