Page 12 - A Comprehensive Guide to Solar Energy Systems

4 A CoMPREHENSIVE GUIdE To SoLAR ENERGy SySTEMS

In January 2017, it was reported that Chinese companies plan to spend US$1 billion
building a giant solar farm (of 1 GW) on 2500 ha in the Ukraine, on the exclusion zone
south of the land contaminated by the 1986 nuclear explosion.
The amount of solar energy shining on the earth (with wavelengths ranging from 0.38
to 250 µm) is vast. It heats our atmosphere and everything on the Earth and provides
the energy for our climate and ecosystem. At night, much of this heat energy is radiated
back into space but at different wavelengths, which are in the infrared range from 5 to
50 µm [1]. This energy heats the greenhouse gas molecules (such as carbon dioxide and
methane) and water molecules in the atmosphere. The explanation is as follows. Us-
ing Co 2 and H 2 o as examples, this heating process takes place because the radiated IR
frequency is in sync (resonates) with the natural frequency of the carbon─oxygen bond
of Co 2 and the oxygen─hydrogen bond of H 2 o. The increased vibration of the bonds ef-
fectively heats the Co 2 and H 2 o molecules. These heated molecules then pass the heat to
the other molecules in the atmosphere (N 2 , o 2 ) and this keeps the Earth at an equitable
temperature. The vibrating frequencies of the o─o bond in oxygen and the N─N bond
in nitrogen molecules are very different from these radiation frequencies and so are rela-
tively unaffected. As there are many more water molecules than Co 2 or CH 4 molecules
in the atmosphere, the overall contribution of the H 2 o molecules to the greenhouse ef-
fect is larger than the contribution by Co 2 or CH 4 or the other minor greenhouse gases
(GHGs), such as chlorinated hydrocarbons. However, as the Co 2 concentration has in-
creased from 280 ppm (280 parts per million or 280 molecules per million molecules)
before the industrial revolution, to 410 ppm (observed at Mauna Loa observatory on
April 21, 2017), and as the H 2 o concentration in the atmosphere remains relatively con-
stant, it is the Co 2 (together with other GHGs) that is largely responsible for present-day
global warming.
Sunlight can be harnessed in a number of ever-evolving and ingenious ways, which
include solar heating (usually water, Chapter 6), photovoltaics (for electricity production
and the main focus of this volume), concentrated solar thermal energy (Chapter 7) and
also solar ponds [2], space heating [3], molten salt power plants [4], and even artificial
photosynthesis. Some of these technologies have been developed only in the past 30 years
as ways of mitigating climate change and the build-up of atmospheric carbon dioxide
from the burning of fossil fuel. The strength of solar energy lies in its inexhaustibility and
also in the wide variety of ways that it can be harnessed ranging from small scale to large-
scale applications.
In 2016, renewable energy supplied less than a quarter of electricity in the world. The
renewable energy total of 23.7% is made up of: pumped hydroelectricity being the most
prevalent, with 16.6%; wind 4%; and solar only 1.5% (Section 1.7). In spite of the rela-
tively low values for wind and solar energy, their rate of implementation is amazingly
rapid and the predictions for the future are promising. As an indication of things to
come, we note that on May 15, 2017 Germany received almost all of its electricity from
renewable and for 4 days (May 7–10, 2017) Portugal ran on renewable energy (wind,
solar, and hydro) alone [5].