Environmental Engineering Reference
In-Depth Information
in mind. Using correct local quotes for the average costs of the construction and oper-
ation of a solar pond is very important; this will help to make a sound economic
judgement.
Irrespective of the location of the proposed solar pond the economics of a solar
pond will depend on the costs associated with land purchase or lease, operating and
maintenance costs, and capital equipment, the lifetime of the pond and the associated
depreciation rate, and the real discount rate or return on investment sought.
In addition to the land the other major expensive components of a solar pond are
its liners (installed), solid salt or brine, excavation of earthen dam walls, monitoring
system, heat exchangers. There are good economic benefits of scale, for example, in
excavation and setting up nearby evaporation ponds for salt recycling, so that larger
solar ponds are more economically favourable where the land is available. However,
the maintenance of pond stability and heat extraction may become more difficult as
the area increases.
Although solar ponds from hundreds of square meters to thousands of square
kilometers are feasible, the sizes likely to find greatest application are in the range of
1 to 10 hectares. Larger facilities than this would probably use unit sizes of 10-20
hectares rather than one extremely large pond, for reasons of operational safety and
reliability.
Solar ponds can be economically viable for industrial process heating, including
manufacturing processes requiring low-temperature heat and aquaculture and drying
applications, at sites where land and water (brackish or sea water) are available, and
solar radiation is high. In the right situation solar ponds for heating can readily be
economical in areas where natural gas is not available and the only alternative fuels
are LPG or oil, and may even compete against natural gas where the price of the latter
is high. Of course, a key benefit of a solar pond is a zero greenhouse emissions source
of heat.
Solution mining uses low temperature heat for extracting minerals from the mines.
The by-product of such mining operations is plenty of high salinity or brackish water.
One of the major requirements for constructing a solar pond is a large and continuous
supply of saline water and in return the solar pond can continuously supply a large
amount of low temperature heat. So the economics would be more favourable when
a solar pond is integrated with a solution mining site.
The use of solar ponds as the source of heat for thermal desalination processes
such as multiple effect evaporation or multistage flash processes is also potentially
one of the most economic zero-emission options for providing fresh water from saline
ground water or sea water. With the world running desperately short of fresh water,
solar ponds for desalination is a potentially important area of application.
Life cycle analysis, covering embodied energy and emissions in the materials used
and in construction, indicate that solar ponds have one of the lowest greenhouse gas
emissions per unit of thermal energy produced over their lifetime of any of the renew-
able energy options. This is if a solar pond is constructed and operated using locally
available resources.
The use of local labour in the construction and operation of a solar pond can
create employment opportunities in regional areas. Hence on a 'triple bottom line'
evaluation, solar ponds in a well-chosen application can rate very well on economic,
environmental and social criteria (Esquivel et al., 1993; Akbarzadeh et al., 2005).
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