solar energy is a renewable / inexhaustible resource & the supply of an inexhaustible resource does not change over a long period of time ->  the supply of solar energy will not change over a long period of time  to a human, a time period of 10 years or more years is considered very long & billions of years is a longer period of time than 10 years ->  to a human, a time period of billions of years is considered a very long time  the supply of solar energy will not change over a long period of time & to a human, a time period of billions of years is considered a very long time -> the supply of solar energy will not change over billions of years