COLLECTEUR SOLAIRE

SOLAR COLLECTOR

Description

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SOLAR COLLECTOR


BACKGROUND:
There are a number of solar concentration systems as follows:
1) Solar trough in which sunlight is focused in a linear line in which a solar
receiver tube extends
the length of the solar trough reflector. These reflectors can be joined
together end to end
forming long troughs. An adaptation on this is what is called Linear Fresnel
lens. This
technology is unable to generate high temperatures limiting the operating
temperature resulting
in the steam tubing operating at significantly lower efficiencies. This is
particularly the case in
which energy storage is applied since there is a significant drop in
temperature through thermal
energy storage technologies as it gives up its heat to the steam boiler.
2) Point focus systems are able to generate very high temperatures lending
itself well to high
temperature thermal storage and higher temperature steam turbines, typical of
what would be
used in a coal filed power plant. This has the advantage of much higher
efficiency operation as
well as lower cost since these types of turbines are common compared to
specialized lower
temperature turbines used in lower temperature solar power generation systems.
SHEC Energy
Corporation has developed special solar receiver technology to harness the
solar beam in these
types of systems with very low emissivity loss.
3) Heliostat with central tower. These types systems use large flat mirrors
that focus its energy
to the top of a solar tower. These types of systems have to be large scale in
order to have the
necessary number of heliostats in order to obtain the concentration ratio
necessary to generate
high temperatures. There are a number of issues when building central tower
designs which
include:
a) Emissivity loss; A 40 foot dish for example needs to have a very large
solar target of
at least 40 feet across resulting in a large exposed surface area and
resulting very large
emissivity loss (radiant energy loss).

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b) Dispersion loss; The sun in not a single source point of light and has a
diameter of 1.4
million km (865,000 miles) and is (93 million miles) from the Earth. This
results in a
reflected beam that will spread at a ratio of 1/110. A mirror the size of a
point will cause
a reflected spot size of 1 meter at a distance of 110 meters from the
reflector. The spot
size would be 5 meters at 550 meters distance. This is known as dispersion.
This will
required an even larger target size to collect the light resulting in even
more emissivity
loss.
c) Modulation loss. The further a heliostat is from the solar tower, the more
easily it can
sway on and off target in even mild winds, resulting in substantially reduced
power
output.
DESCRIPTION OF THE INVENTION
The present invention is able to deploy a matrix of much fewer heliostats
around much smaller
towers. For example, only 100 heliostats of conventional design would only
provide a concern
triton ratio of 100 suns. SHEC Energy is able to adapt the geometry of the
various heliostat
segments to bring the reflected beam from each segment to overlap in the space
of one segment,
effectively creating a focused beam the size of one mirror segment. For
illustration purposes, lets
assume a heliostat of 9 mirror segments arranged in 3 rows of 3 coulombs as
illustrated in Fig 1.
100 Heliostats with 9 mirror segments each would have an effective
concentration ratio of 900
suns. 25 mirrors each, 2,500 suns and so on.
Since Heliostats redirect the solar beam to a tower, the articulating segments
adjust to keep the
beam in focus. This happens dynamically as the sun tracks across the sky. The
entire heliostat
moving all the mirror segments adjusts in real time to redirect the sunlight
to the top of the solar
tower. The centre mirror is fixed to the heliostat but the surrounding mirrors
can micro adjust as
the sun tracks across the sky. If the segments did not adjust, the focus would
become elongated
from morning to afternoon.

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Figure 2 shows ne row of mirrors in a top down view. As can be seen in this
exaggerated view,
the geometry of the mirror segments adjust as the entire heliostat is
generally steered to redirect
the suns solar energy to the solar.
Benefits:
Much small towers can be used, resulting in fewer heliostats per tower to
obtain the necessary
concentration ratios to generate high temperatures. This will result in less
dispersion since the
heliostats can be placed closer to the towers. The target size can be
dramatically reduced
resulting in much less emissivity loss. Modulation losses are minimized do the
heliostats being
closer the towers. Large scale stations could employ multiple mini towers.
This could add
another dimension of station performance as the control system could redirect
the reflected solar
beam from one tower to the next during certain times of the day to maximize
power output. For
example, the cross section reflected area becomes smaller at high reflection
angles, also referred
to as cosine loss, the control system can direct a heliostat to focus on
another adjacent tower to
minimize this type of loss.
The benefit of this over point focus solar concentration systems is that there
is no piping
requirement to each solar concentrator, reducing system cost for large scale
deployments.