Energy consumption – an important indicator of level. In those days, when the person got a, collecting forest fruits and hunting on animals, he needed per day about 8 MDZh of energy. After an fire this size increased to 16 MDZh: in agricultural society it is a of 50 MDZh, and in more developed – 100 MDZh.
The sun shone and warmed the person always: and nevertheless once people tamed fire, started burning down wood. Then wood gave way to coal. Reserves of wood seemed boundless, but steam-engines demanded more high-calorie "forage".
The story about energy can be infinite, alternative forms of its use are incalculable provided that we have to develop for this purpose effective and economic methods. Not so important, what your opinion on needs of power, on power sources, its quality, and prime cost. To us, apparently. it is only necessary to agree that the scientific wise man which name remained to unknown told: "There are no simple decisions, there is only a reasonable choice".