Energy storage
Energy storage mediums are matter that
store some form of energy that can be drawn
upon at a later time to perform some useful
operation. A device that stores energy is
sometimes called an accumulator. All forms
of energy are either potential energy (eg.
chemical, gravitational or electrical energy)
or kinetic energy (eg. thermal energy). A
wind up clock stores potential energy (in this
case mechanical, in the spring tension), a
battery stores readily convertible chemical
energy to keep a clock chip in a computer
running (electrically) even when the com-
puter is turned off, and a hydroelectric dam
stores power in a reservoir as gravitational
potential energy. Ice storage tanks store ice
(thermal energy)at night to meet peak de-
mand for cooling . Even food is a form of en-
ergy storage, chemical in this case.
History
Energy storage as a natural process is as old
as the universe itself - the energy present at
the initial creation of the Universe has been
stored in stars such as the Sun, and is now
being used by humans directly (e.g. through
solar heating), or indirectly (e.g. by growing
crops or conversion into electricity in solar
cells). Storing energy allows humans to bal-
ance the supply and demand of energy. En-
ergy storage systems in commercial use
today can be broadly categorized as mechan-
ical, electrical, chemical, biological, thermal
and nuclear.
As a purposeful activity, energy storage
has existed since pre-history, though it was
often not explicitly recognized as such. An ex-
ample of deliberate mechanical energy stor-
age is the use of logs or boulders as defens-
ive measures in ancient forts - the logs or
boulders were collected at the top of a hill or
wall, and the energy thus stored used to at-
tack invaders who came within range.
A more recent application is the control of
waterways to drive water mills for processing
grain or powering machinery. Complex sys-
tems of reservoirs and dams were construc-
ted to store and release water (and the po-
tential energy it contained) when r