Environmental Engineering Reference
In-Depth Information
Fig. 8
SSB model: key to a sustainable civilisation
the desert by extracting the extra value from the
sand through the cooperative research with
Saharan countries. We have been working for
proving the feasibility and superiority of SSB-PV
to provide an absolute solution of sustainable
development for the future world (Koinuma and
Boudghene Stambouli 2013 ). The fi rst key tech-
nological task is the development of solar-grade
Si from desert sand.
cially of semiconductor grade (SEG-) by four to
fi ve orders of magnitude. The over-specifi ed
quality (>10 nines) of SEG-Si had been the main
reason of the high cost of Si solar cell. Despite
the recent temporal low price of Si by the over-
production in China, the development of new
SOG-Si (~6 nines purity) process with minimum
energy consumption is presumed to be the fi rst
priority for realising clean sustainable energy for
the future. It must be noted that SOG-Si PV is
more promising and not only fashionable, i.e. so-
called innovative and next-generation PV, but
also conventional power stations (Koinuma et al.
2013 ). Si renaissance strategy is derived from a
pioneering but forgotten research in the 1980s on
SOG-Si from silica sands (Koinuma et al. 2013 )
to make it smarter by the 'Beyond Siemens pro-
cess' shown in Figs. 9 and 10 . Among various PV
systems, only Si PV (4 % of desert areas) could
cover all the energy needs in the world.
5.1
General Scheme
of Silicon Process
Silicon dioxide (SiO 2 ) is the most abundant natu-
ral resource on Earth. If we could develop an effi -
cient process for reducing SiO 2 to solar-cell-grade
silicon (purity level >99.9999 %) and use this to
make polycrystalline (polysilicon) solar cells,
solar energy could be converted into electricity
with about 15 % effi ciency. This effi ciency
appears to be lower than conventional power gen-
eration systems (about 40 % effi cient), but it is
substantially higher in view of the fact that sun-
light is fuel free.
Process fl ow of silicon is depicted in Fig. 8 .
Silicon is the second most abundant element in
the Earth's crust, much more than iron (Fe), but
Si production scale is far lower than Fe, espe-
5.2
Purifi cation of Silica Sands
The collaborative industry (Taiheiyo Cement Co.
Ltd., in Japan) developed a process for purifying
amorphous silica sand in Japan by the original
wet process of dissolution in aqueous NaOH
solution followed by the neutralisation to
Search WWH ::




Custom Search