""<center><h1>Redressable parabolic trough solar collector</h1></center>

<A HREF="http://www.parabolictrough.org/">Back to home</A>

<p>It is a small-size concentrating solar collector, with a reflective
mirror surface under the form of a parabolic cylinder which concentrats the
sunlight to a receiver tube located at the focus line. It is sold as a
disassembled flat kit at very low prices. The kit can be assembled and
installed by the user, much in the same way as most pieces of modern
furniture. <a href=equipments-en.html>How to buy</a>.

<p><center><img src=http://wims.unice.fr/xiao/solar/pic/caisson1.jpg width=500></center>

<p>Once assembled, the collector is a closed box formed by a transparent
cover, a curved back and two flat endplates. It will be water-tight,
protecting the internal surfaces against rain, snow, dust, humidity and
atmospheric pollutants. This guarantees a very long service life of the box.

<p><center><img src=http://wims.unice.fr/xiao/solar/pic/caisson4.jpg width=500></center>

<p>The assembled collectors can now be mounted on a chassis, which in turn
is fixed on the ground, ontop of a roof, on a vertical wall, etc.

<p><center><img src=http://wims.unice.fr/xiao/solar/pic/chassis2.jpg width=500></center>

<p>The reflective surface of the collector is formed using the natural
elasticity of the back plate. This is not exactly the surface we want;
therefore the surface is redressed to correct the errors, with redressing
mechanisms behind the back of the box. Note that we are not using pre-formed
ribs.

<p><center><img src=http://wims.unice.fr/xiao/solar/pic/caisson8.jpg width=500></center>

<p>These redressing mechanisms allow users to readjust the collector should
any deformation occur after a few years of service. This is in general not
necessary, and the collectors will come pre-adjusted in factory. For those
who are interested in doing so, the <a href=diy-en.pdf>DIY document</a>

contains a detailed account of the adjustment method.

<p>The collector accepts 3 types of interchangeable receiver tubes.

<ol>

<li><p>Non-insulated low-temperature receiver. This is a simple metal tube,
painted black or covered by a selective absorption layer. For
low-temperature applications such as water heating, space heating, pool
heating or absorption air conditionning, It offers the best global
efficiency of up to 80%. It is also the most economic receiver.

<p>Quality standard: absorptivity >93%, emissivity <25%, total thermal
loss <35W/m² at ΔT = 50°C.

<li><p>Photovoltaic receiver. This is a metal tube covered at the outside by
a layer of photovoltaic cells. When put under the focus, the photovoltaic
cells receive concentrated light and generate electricity with a much higher
output rate than non-cencentrated cells. The concentrated light also creates
much heat within the cells, which is transmitted through the wall of the
tube to water circulating within the tube. The heated water is then
collected and used for water heating, space heating or pool heating.

<p>This is therefore a combined heat and power generation mode. Besides the
extra heat, the concentrated operating mode also divides the cost of the
photovoltaic cells by a factor of 10 or more, for the same output power.

<p>Quality standard: to be determined


<li><p>Evacuated receiver. As shown above in the pictures, the metal tube is
put within a transparent glass tube of much larger diameter. The annular
space between the tubes is half-evacuated and filled with a low-pressure
low-conductivity inert gas <a href=collector.pdf>(see this)</a>. This
receiver offers a reasonably low heat loss when operating at a high
temperature up to 350°C. The overall efficiency of the collector will be
lowered to 55-70%.

<p>Quality standard: absorptivity >90%, emissivity <15%, total thermal
loss <100W/m² (Argon-filling) or <60W/m²
(xenon-filling) at 350°C; <65W/m² (argon-filling) at
250°C.


</ol>

<a name=quality>Some basic quality standards of the collector are as follows.

<p><center><table border=2>
<tr><td>Concentration ratio<td>40-100
<tr><td>Life expectancy<td>18 years
<tr><td>Overal efficiency<td>55%-80%
<tr><td>Operating temperature<td>Up to 350°C
<tr><td>Resistance to wind<td>>150km/h
<tr><td>Resistance to hail<td>Data missing (very high)

<tr><td>Resistance to snow<td>75kg/m² (0.5m thick at 15% density)
<tr><td>Photodetector working range<td>62° in each direction
<tr><td>Maximal solar angle with<br> respect to cover normal dir.<td>65°
<tr><td>Environment temperature<td>-10°C to 50°C

</table></center>

<p>The optical efficiency and thermal loss depends on the receiver used. In general,
the closed box is <a href=efficiency.html>40% more efficient</a> than the classical
big parabolic trough.

<p>The concentration ratio of the collector is the ratio between the width of
the reflective surface and the diameter of the receiver tube. Although the
collector can support a very high concentration ratio if well-adjusted, this
ratio is better optimised according to the application. We give the
following recommendations.

<p><center><table border=2>
<tr><th>Application<th>Optimal ratio
<tr><td>Residential use up to 100°C<td align=center>50
<tr><td>Photovoltaics<td align=center>40-60
<tr><td>Residential use, 200-280°C<td align=center>60

<tr><td>Regional power plant, 350°C<td align=center>70-80
<tr><td>Desert power plant, 350°C<td align=center>100

</table></center>

<p>You can find discussions about the product in the <a target=_extern
href=http://www.green-life-innovators.org/tiki-view_forum.php?forumId=25>project
forum</a>.

<p><hr>
<p><table width=100% border=0>
<tr><td><A HREF="http://www.parabolictrough.org/">Back to home</A>
<td align=right><a href=http://wims.unice.fr/xiao/index.html>Gang Xiao</a>

</table>""
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