Renewable Energy Resources for Irrigation - Practices of Irrigation and On-farm Water Management - page 484

Fig. 13.1 Solar photovoltaic cells using for generating electricity

13.4.2 Assessment of Potential Solar Energy Resource

There is no shortage of solar-derived energy on Earth. Indeed the storages and flows
of energy on the planet are very large relative to human needs. The amount of solar
energy intercepted by the Earth every minute is greater than the amount of energy
the world uses in fossil fuels each year. Tropical oceans absorb 560 trillion giga-
joules (GJ) of solar energy each year, equivalent to 1,600 times the world's annual
energy use. Annual photosynthesis by the vegetation in the United States is about
50 billion GJ, equivalent to nearly 60% of the nation's annual fossil fuel use.
There are many different ways to assess potentials:

13.4.2.1 Theoretical Potential
The theoretical potential indicates the amount of energy theoretically available for
energy purposes, such as, in the case of solar energy, the amount of incoming
radiation at the earth's surface.

13.4.2.2 Technical Potential

The technical potential is a more practical estimate of how much could be put to
human use by considering conversion efficiencies of the available technology and
available land area.
The technical potentials generally do not include economic or other environ-
mental constraints, and the potentials that could be realized at an economically
competitive level under current conditions and in a short time-frame is still

lower.
Ideally, detailed solar data for each location should be used in evaluating
the potential of using a solar photovoltaic (SPV) pump. However, to make an
initial macro-level assessment, broad (nation or state wise) solar radiation avail-
ability characteristics are readily available in the literature. It is recommended
by UNESCAP that for installing SPV pump, the average daily solar radiation in