energy delivered by the sun to the Earth is approximately a million trillion (1018) kilowatt-hours a year, compared with our “measly” needs (on this scale) of 150 trillion (1.5 × 1014) kilowatt-hours we collectively use each year. So on the scale of what the Earth receives from the sun, our energy use represents only about 0.015 percent of what is in principle actually available to us. To put it another way: more energy is delivered by the sun in just one hour than is used by the entire world in a single year. Indeed, the scale of solar energy is so vast that in one year it is about twice as
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