Sentence:  Energy has seldom been found where we need it when we <WSD>want</WSD> it. Ancient nomads, wishing to ward off the evening chill and enjoy a meal around a campfire, had to collect wood and then spend time and effort coaxing the heat of friction out from between sticks to kindle a flame. With more settled people, animals were harnessed to capstans or caged in treadmills to turn grist into meal. 
Meaning of the word marked with <WSD> tags:  To wish for or desire (something); to feel a need or desire for; to crave or demand. (from 18th c.)