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· Solar Energy

Barrington, New Jersey,

Solar Houses and Solar House Models, 2d ed.
Edmunds Scientific Company, 1972-73.

Compiled through
June 1974

J. SELECTED GLOSSARIES

1. Excerpt from a book by J. Richard Williams, Ph. D., "Solar Energy-Tech-

nologies and Applications,” Ann Arbor, Mich., Ann Arbor Publishers, Inc.,
1974

SOLAR ENERGY
Technology

and
Applications

by
J. Richard Williams, Ph.D.
Associate Professor of Mechanical Engineering
Georgia Institute of Technology

Atlanta, Georgia

Copy

Copyright © 1974 by ANN ARBOR SCIENCE Publishers, Inc.
P.O. Box 1425, Ann Arbor, Michigan 48106
Library of Congress Catalog Card Number 74–78807
ISBN 0-250-40064-2
Manufactured in the United States of America
All Rights Reserved

56-516 0 - 75 - Pt. 1C - 74

GLOSSARY

Absorption cooling. Refrigeration or air conditioning achieved by an

absorption-desorption process that can utilize solar heat to produce

a cooling effect. Absorptivity. The ratio of the incident radiant energy absorbed by a sur- ·

face to the total radiant energy falling on the surface. Albedo. The ratio of the light reflected by a surface to the light falling

on it. Ambient temperature. Prevailing temperature outside a building. Anaerobic fermentation. Fermentation process caused by bacteria in the

absence of oxygen. Bio-conversion. Use of sunlight to grow plants with subsequent use of

the plants to provide energy. Brayton cycle. Power plant using a gas turbine to drive a compressor and

produce power. A gas is compressed, then heated, then expanded through a turbine, then cooled. The turbine produces more power

than is needed to drive the compressor. British Thermal Unit (BTU). A unit of energy which is equal to the amount

of heat required to raise the temperature of a pound of water one

degree Fahrenheit. Capital cost. The cost of construction, including design costs, land costs,

and other costs necessary to build a facility. Does not include operat

ing costs. Capture efficiency of plants. The ratio of the energy absorbed and con

verted into tissue by plants to the total solar energy falling on the plants. This energy, usually about 3% or less of the total incident

solar energy, can be released when the plants are burned. Collector efficiency. The ratio of the energy collected by a solar collector

to the radiant energy incident on the collector. Concentration ratio (concentration factor). Ratio of radiant energy inten

sity at the hot spot of a focusing collector to the intensity of unconcentrated direct sunshine at the collector site.

116

Glossary

Convective heat transfer. Transfer of heat by the circulation of a liquid

or gas. Degree day (DD). One day with the average ambient temperature one

degree colder than 65°F. For example, if the average temperature is

55°F for 3 days, the number of degree days is (65-55) times 3, or 30. Diffuse insolation. Sunlight scattered by atmospheric particulates that

arrives from a direction other than the direction of direct sunlight.

The blue color of the sky is an example of diffuse solar radiation. Direct conversion. Conversion of sunlight directly into electric power,

instead of collecting sunlight as heat and using the heat to produce

power. Solar cells are direct conversion devices. Direct insolation. Sunlight arriving at a location that has not been scat

tered, also referred to as direct beam radiation. Dynamic conversion. The collection of sunlight to heat a fluid that oper

ates an engine to produce power. An example is the use of concentrated sunlight to boil water and operate a steam engine to produce

power. Electrolysis. The use of an electric current to produce hydrogen and

oxygen from water. Equilibrium temperature. The temperature of a device or fluid under

steady operating conditions. Faceted concentrator. A focusing collector using many flat reflecting ele

ments to concentrate sunlight at a point or along a line. Fossil fuel. Coal, oil or natural gas. Fuel cell. A device, somewhat like a battery, that uses a chemical reaction

to produce electricity directly, such as the reaction of hydrogen and

oxygen to produce electric power with water as a product. Geosynchronous satellite (synchronous satellite). An artificial satellite in

a synchronous orbit 22,300 miles from the earth that can remain continuously above the same spot on the earth, since the period of the

orbit is 24 hours. Heat of fusion. The heat released when a liquid becomes a solid (freezes),

equal to the heat absorbed when a solid melts-often tabulated in

units of BTU/pound. Heat transfer fluid. A liquid or gas that transfers heat from a solar col

lector to its point of use. Heliostat. An electro-optical-mechanical device that orients a mirror so

that sunlight is reflected from the mirror in a fixed specific direction,

regardless of the sun's position in the sky. Hot spot. The location on a focusing collector at which the concentrated

sunlight is focused and the highest temperatures are produced. If the heat is to be collected, a heat exchanger is located at the hot spot

and a heat transfer fluid flowing through the heat exchanger is heated. Incidence angle. The angle between the direction of the sun and the per

pendicular to the surface on which sunlight is falling.

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