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Design of
Solar energy collectors
with the object of capturing in a fluid, the thermal energy component of
solar energy, such that the fluid serves as a transport-carrier
of the energy for use in application-specific purposes can be
particularly significant in that it can be readily deployed in
numerous applications. In particular, the design of a collector
based on known and off-the-shelf items therefore should have
immediate impact and should be a viable task.
In this context then a
synopsized specification for a Solar Thermal Energy Collector at
a minimum should consist of a solar thermal energy absorber made
of borosilicate glass tubes design-integrated into a monolith
device within a
Solar energy concentrator
and should include the use of air, water or glycol as the heat
absorber or carrier, which flows through the integrated absorber
tubes. The fluid flows through the tubes at
some predefined rate set in a controller that pumps it as the
temperature is attained. The selection of the borosilicate tubes
stems from the properties of this type of glass: The emissivity
of the material is very low and therefore the heat absorbed will
not be re-irradiated away, The thermal stability of the glass is
very high and as such it does not suffer thermal shock due to
high temperatures, The linear expansion of the glass is also
very low hence accommodation of thermal expansion is not quite
critical.
The Solar Thermal
Energy Absorber essentially defines the overall configuration
dimensions of the collector even if iteratively and starts off
the design: First, the length of the absorber tubes is
evaluated, and then specified, by heat transfer analysis that
determines the exit temperature of the fluid as a function of
the length together with the other flow characteristics, based
on the insolation of the geographical region of the
intended-deployment of the collector. This evaluation must
accommodate for the quantity of heat absorbed by the
complementary Solar Energy Concentrator, as perfect thermal
reflectivity may not be attainable under practical operating
conditions. Moreover, because the overall efficiency of heat
transfer into the fluid may be impacted by the absorber
configuration, the length may be subjected to some adjustments
based on judicious engineering judgment call. Of significant
note however, is that the performance of the tube with respect to the
amount of the radiant thermal energy that gets transmitted
through the wall into the fluid depends on the material from
which the tube is
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manufactured, hence
the glass of which properties were used in the calculation must be
used in the design. Based the length the rest
of the absorber design then takes off: The
absorber tube manufactured as a double-walled tube with vacuumed
annular in-between glass space, and sealed at both ends. The annular
space vacuum is further maintained with getters of such quantity
determined to operate the solar collector for a design-specified
length of time. The vacuum ensures that the radiant thermal energy passes through the
double-wall of the tubes but the
heat that obtains from the absorption of the radiant thermal
energy is neither convected or conducted out of the
absorber. In particular the borosilicate tubes are
bundle-designed into a form a circular row embedded into a
structure that allows for the fluids to flow into the tubes
from the bottom through and out at the top. Further, the
configuration is such that the absorber is provided with a mount
enabled with a flange, and of a length that allows the positioning
of the absorber tubes within the concentrator it would be assembled
intoThe Solar
Thermal Energy Concentrator for this collector-design consideration,
is of the hemispherical
concentrator-design that concentrates the energy over an axial
linear region. In particular, the length of the linear region is of
the same length of the absorber tubes available for thermal energy
absorption. Moreover, the solar energy reflector should also be a
thermal mirror, such that solar thermal energy component is
reflected primarily. In effect, the efficiency of the mirror is
based on its reflectivity of the thermal energy component instead of
the optical energy component because the thermal mirror is used with
very little regard for the optical component: Whether the choice is
made to absorb the optical component, as well by the absorber,
or not is entire optional. Based on the reflectivity of the mirror,
the support base is designed to enable the removal of heat absorbed
by the mirror, such that the performance of the mirror is restricted
to a very narrow range of temperature variation, in order to support
precision of performance. The heat removal design, however, if
required may be designed to use as coolant the same fluid as
intended for use in the absorber, both for efficiency and for the
simplification of operation needs. Further, the depth of the
concentrator is by design evaluated as to prevent any form of
interference from occurring as the incidence radiation travel path
intersect reflected radiation travel path. Affixed to the support
base of the mirror layer is a mount-contraption for mounting the
absorber.
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Design integration of
Concentrator and Absorber entails several tasks. The first of the
tasks is to have the bundled integrated absorber affixed along
the axis of the hemispherical axial-linear concentrator. The base
flanges are affixed to the absorber support mount of the
concentrator support base structure. Of course, the support mount is
constructed such that the absorber evacuated tube sections of the
absorber situates within the range of the linear focus of the
concentrator such that the solar thermal energy as concentrated
falls right on the integrated absorber tubes. The fluid inlet of the
absorber is interfaced and connected to the outlets of the
concentrator cooling fluids in the case of the operation in which
the same type and form of fluid is being used for both the mirror
cooling and the thermal heat absorption in the absorber. In the case
where different fluids are to be used then the outlets of the
concentrator coolants are connected to the recirculation lines for
conditioning and recirculation, while the absorber inlet line is
connected to the corresponding recirculation line. In both
cases the absorber fluid outlet is connected to the corresponding
feed line of the recirculation line. Under proper connection,
the fluid should flow into the absorber through the inlet and out
through the outlet, and be available for the
application-specification use and then be fed into the absorber in
continuous circulating flow.
The modularity of the design
supports scalability, allowing for the integration
of several collector modules to provide scaled heat supply needs, as
in industries.
Further, although
use-specific form of the absorber has been used in this
concept-driven design, use of evacuated thermal tubes with heat-pipes
can be just as effective, though the specifics of the configuration
of the integrated-bundling of the heat-pipe absorber will depend on
the particular type of heat pipe used in the absorber module.
An application of this
technology of note is the use of the technology for application at homes.
Solar Energy is noted as a good source of energy for priming the
portable
bioenergy technologies for homes. The use of pure water or
glycol enables the adoption of the technology in just about
every house backyard with too much intrusion. Hence, the
collector is effective for the use in homes by home owners
towards different objectives.
Obvious the collector of
the configuration as proffered based on readily available
off-the-shelf products can be effective in addressing
energy adoption issues of interest. |
