Renewable Energy Resources for Irrigation - Practices of Irrigation and On-farm Water Management - page 509

through a turbine. In binary plants, the hot water flows through heat exchangers,
boiling an organic fluid that spins the turbine. The condensed steam and remaining
geothermal fluid from all three types of plants are injected back into the hot rock to
pick up more heat.
The geothermal energy from the core of the Earth is closer to the surface in
some areas than in others. Where hot underground steam or water can be tapped
and brought to the surface it may be used to generate electricity. Such geother-
mal power sources exist in certain geologically unstable parts of the world such
as Chile, Iceland, New Zealand, United States, the Philippines, and Italy. The two
most prominent areas for this in the United States are in the Yellowstone basin and
in northern California. Iceland produced 170 MW geothermal power and heated
86% of all houses in the year 2000 through geothermal energy. Some 8,000 MW of
capacity is operational in total.
There is also the potential to generate geothermal energy from hot dry rocks.
Holes at least 3 km deep are drilled into the earth. Some of these holes pump water
into the earth, while other holes pump hot water out. The heat resource consists
of hot underground radiogenic granite rocks, which heat up when there is enough
sediment between the rock and the earth's surface. Several companies in Australia
are exploring this technology.

13.9 Modeling the Energy Requirement

Model can be used to design, simulate, and predict the performance of an irriga-
tion system powered by a renewable energy source. The model predicts the energy
demand based on the water demand for the irrigation system.
Different approaches may be used in predicting water demand. The water
demand may be predicted using metrological data, and a statistical distribution may
be used to predict the expected upper limits of water demand. The lower limits of
available energy are predicted using the metrological data and also by stochastic
methods. The amount of energy to be required is calculated based on the minimum
irrigation interval demanded, and then the renewable energy system is designed to
assure the desired reliability.

13.10 Factors Affecting Potential Use of Renewable Energy
in Irrigation

The use of renewable energy-based pumps in irrigation depends on several factors:

• availability of the renewable energy

• cost of the system (pump and the energy harnessing system)

• groundwater requirement for irrigation and its availability

• alternate energy availability and its cost

• reliability of the renewable energy