Can someone complete the blank in the sentence below?

The reason for _________________________________ is because earth is tilted 23 1/2 from a line perpendicular to its orbit, the length of daylight varies and because of the angle at which the sun’s energy strikes a given location through the year.

How does the solar battery charged using solar panels?What is the mechanism that converts solar energy in to electrical energy? How can a car be run on solar energy?what could be its maximum speed?

Hi I would like to work on building science like install panel solars,wind and you know building science also I want to star a business sell products of renewable energy like solar panels,wind,hydro,etc.

So which career can fit in those jobs? thanks