Water Power at www.japanese-home-gardens.com

WATER POWER, the utilization of water as natural liquid to produce energy, or power, controlled amounts. The power of water in the natural process of nature is enormous and often awesome. Gre waterfalls and storm-tossed waters sending to mendous waves crashing on the beaches are v: ible evidence of the mighty power of water, f though the potential for water power is grei practical limitations relating to the gathering ai control of the power of water permit only an i finitesimal percentage to be developed. For e ample, the power of water resulting from the a tion of the ocean waves throughout the wor represents an enormous amount of energy; ho ever, no practical method of utilizing this pote tial has yet been devised. The most common for of using the power of water is in the exploitatk of the difference in head, or the drop of wat through a height, by developments on streams ai rivers.

Neglecting losses, the theoretical power available from a steady stream of water dropping from a surface elevation h feet above a lower elevation may be determined by the expression 62.4 XQXh = horsepower (theoretical) ~~where Q is the rate of flow in cubic feet per second. The overall efficiency of a water power plant is the power output (mechanical or electrical) divided by the theoretical power available, the result generally being expressed in percentages. Efficiencies of greater than 80 percent are achieved in modern large installations.

The area oabc on this curve represents the total amount of power available during a year. The area odbc is proportional to the annual primary or firm power. For a proposed water power plant having an installed capacity three times (300 percent) the firm power capacity, the area defb is proportional to the annual secondary or surplus power. The power of area eaf is wasted. By construction of a storage reservoir it is possible to store some water during flood periods and release it during periods of low flow, thus increasing the primary power to the area ojhc and changing the flow-duration curve at the power site to the curve in the figure marked with storage. The economics of proposed installations can be investigated with the aid of this curve to ascertain the significance of changes in selected power capacity and reservoir capacity.