Civil Engineering Reference
In-Depth Information
nanotubes. The method that is currently used most is arc discharge (Iijima,
1991; Ebbesen and Ajayan, 1992) which basically consists of a high current
being placed between two graphite electrodes in a helium atmosphere
producing a nanotube that has a maximum length of 50 micrometres
(Collins and Avouris, 2000) with a product yield of 30%.
The second is laser ablation, which is used for single- and multi-walled
nanotubes (Guo
et al.
, 1995a, 1995b) but mostly SWNTs. In the basic process,
the laser changes a graphite piece into vapour in a reactor, while at the same
time gas is drawn into the chamber and the nanotube forms on the cold
surfaces in the reactor. Although this yields 70%, which is more than arc
discharge, it is also the most expensive method (Collins and Avouris, 2000).
The fi nal method, which was also mentioned in the quantum dot section, is
CVD (chemical vapour deposition) (Bunch
et al.
, 2005). It is expected that
CVD will probably be the most commonly used method in the commercial
production of carbon nanotubes in the future and it is expected that it could
reach industrial scale during this century.
In the future, with improved production, or by varying nanotubes, effi ci-
ency will improve (Landi
et al.
, 2005; Cataldo
et al.
, 2012), costs will reduce,
the expected effi ciency of 71% will be closer to reality (Anon., 2006) and
properties such as lifetime can be realistically considered.
12.6 Future trends
The future development of PVs is principally split into three areas -
countries' governments, the scientists/researchers, and consumers, with each
of them having a varied amount of responsibility. Governments are respon-
sible for encouraging and supporting the research, development and inte-
gration of its progression into each country and they could introduce
subsidies and incentives as encouragement for consumers and companies.
In developing countries specifi cally there are many options for the use of
solar power in remote locations that could enable up to two billion more
people to have electricity; for example, the kerosene lamps that are cur-
rently used in villages could be replaced by a 5 W system with a battery
backup for approximately $500 per village.
In developed nations energy demands are high so solar energy is an
additional power resource to support the traditional sources. In many large
developed countries, power accessibility is not the problem, and rather the
issue is the installation of distribution lines, which can cost up to $30,000
per km. Therefore, for remote locations, a PV array would be a more sui-
table and cheaper alternative.
Governments worldwide are defi nitely making plans for solar power to
be part of future energy strategies, and this is supported by the fact that
in the last fi ve years the cost of this technology has reduced by about
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