Renewable Energy Resources for Irrigation - Practices of Irrigation and On-farm Water Management - page 481

Cars, planes, trolleys, boats, and machinery also transform energy into work. Work
means moving or lifting something, warming or lighting something.
There are many sources of energy that help to run the various machines invented
by man. The discovery of fire by man led to the possibility of burning wood for
cooking and heating thereby using energy. For several thousand years human energy
demands were met only by renewable energy sources - sun, biomass (wood, leaves,
straw), hydel (water), and wind power. As early as 4,000-3,500 BC, the first sail-
ing ships and windmills were developed harnessing wind energy. With the use of
hydropower through water mills, things began to move faster. Solar energy is being
used for drying, heating, and generating electricity.
13.1.2 Concept and Definition of Renewable Energy
Renewable energy effectively uses natural resources such as sunlight, wind, rain,
tides, and geothermal heat, which may be naturally replenished. Renewable energy
technologies include solar power, wind power, hydroelectricity, biomass, and biofu-
els for transportation. According to the International Energy Agency, “Renewable
energy is derived from natural processes that are replenished constantly.” In its var-
ious forms, it derives directly from the sun, or from heat generated deep within the
earth. Included in the definition is electricity and heat generated from solar, wind,
ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen
derived from renewable resources.
Most renewable energy comes either directly or indirectly from the sun. Sunlight,
or solar energy, can be used directly for heating and lighting homes and other build-
ings, for generating electricity, and for hot water heating, solar cooling, and a variety
of commercial and industrial uses.
The sun's heat also drives the winds, whose energy is captured with wind tur-
bines. Then, the winds and the sun's heat cause water to evaporate. When this water
vapor turns into rain or snow and flows downhill into rivers or streams, its energy
can be captured using hydropower.
Along with the rain and snow, sunlight causes plants to grow. The organic matter
that makes up those plants is known as biomass. Biomass can be used to produce
electricity, transportation fuels, or chemicals. The use of biomass for any of these
purposes is called biomass energy.
Hydrogen also can be found in many organic compounds, as well as water. It's
the most abundant element on the earth. But it doesn't occur naturally as a gas. It
is always combined with other elements, such as with oxygen to make water. Once
separated from another element, hydrogen can be burned as a fuel or converted into
electricity.
Not all renewable energy resources come from the sun. Geothermal energy taps
the earth's internal heat for a variety of uses, including electric power production,
and the heating and cooling of buildings. The energy of the ocean's tides comes
from the gravitational pull of the moon and the sun upon the earth.
The ocean can produce thermal energy from the sun's heat and mechanical
energy from the tides and waves. Flowing water creates energy that can be captured
and turned into electricity. This is called hydroelectric power or hydropower.