22-05-2012, 01:41 PM
solar thermal collection technology for electricity generation
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Introduction
Since independence in 1947, India has increased its electrical
generation capacity from 1.4 to 148 GW, but has largely neglected
its solar resource [1]. The current grid connected fuel mix is 63%
fossil-thermal, 3% nuclear, 25% hydroelectric and 9% from other
renewable resources; whereas grid connected solar generation
capacity is a mere 2MW [2]. Recently, however, the Indian
Government has announced a new policy direction through its
National Action Plan on Climate Change, one of whose eight
national missions, namely the National Solar Mission, proposes
substantial investment in R&D and infrastructure to increase the
share of solar energy within the total energy mix [3].
India benefits from a sunny climate, in particular in its northwest
region, which receives some 5.5 kWh/m2 of solar energy daily.
To take advantage of this resource, one option that is currently of
much interest is Concentrating Solar thermal power (CSP). This
technology has been successfully implemented in California, and is
being vigorously promoted for schemes to provide Europe with
power from the Sahara. Detailed feasibility studies for such
schemes have been prepared [4,5]. In India, the uptake of solar
thermal electricity has so far been limited to demonstrations,
Comparative literature review
The purpose of this review is to identify the main technology
alternatives relating to solar collectors, to define the criteria
(technical, economic and environmental), and to research factual
data for use in the AHP study. Some new or little-investigated
technologies are deliberately neglected due to the paucity of relevant
information. For reviews of more general scope the reader is
referred elsewhere [18].
Linear compound parabolic collector (CPC) and fresnel lenses
The 2-dimensional linear compound parabolic collector (CPC) is
considered in this review. The CPC is a non-imaging concentrator.
Compared to imaging concentrators such as the parabolic trough or
dish, it accepts radiation over a wider range of approaching angles
for a given concentration ratio. A typical configuration has a lower
circular portion and an upper parabolic section to form a trough
with an absorber pipe located at the bottom [48]. However, this
type of design tends to be large, hence truncated CPCs are often
used instead; only a slight reduction in concentration results from
a one-third decrease in height [49e51].
Parabolic dish reflectors (PDR)
The Parabolic Dish Reflector (PDR) or Dish Engine is a concave
mirror that focuses sunlight onto a single point receiver. Mirrors
can be facetted-segmented surfaces or a single parabolically shaped
surface made in some forming process. The mounting structure will
then depend upon the type of mirrors used. The system requires
continuous two-axis tracking as the concentrated solar rays are
focused onto a receiver at the single focal point. Stirling engines are
the most common receiver used; however, PV modules, heat pipes,
microturbine and other engines have been considered [21].