Posted by altsolarthermal on February 9, 2007, 10:09 am
Hello
I was wondering if anyone could advise on the current best
concentration onto double sided collectors from east-west compound
parabolic troughs.
I understand that the limit of best concentration onto a one sided
surface is governed by the sine law. With a half angle of 23.5 º
(ignoring the 0.25 º of the solar radius) this gives a best
concentration of 2.5078 or onto a surface 39.875% of the aperture
size.
For double sided PV cells this gives a theoretical limit of half this,
a surface 19.937% of the aperture size or a concentration of just over
5.01 suns.
Can anyone advise whether this theoretical concentration has been
achieved. Alternately would anyone have any idea of the current best
known?
I cannot identify a better result than a size of 22.75% of aperture
size or a concentration 4.396 suns. To obtain this result a deep
trough using 285% reflective material compared to the aperture size is
needed. This can be truncated to 186.22% reflective material to
provide a concentrator size of 25% of the aperture size or a
concentration of 4.0 suns.
Double sided solar cells seem to be coming available for much the same
price of single sided cells. Given a price of PV cells of $4.00 per
watt, reflectivity of 85% and reflective material cost of only 5% of
PV cell cost this results in a price of $1.60 - $1.70 per watt, which
I believe makes it more than viable without subsidies.
For any who can model CPC's the specifications of the 4.0 sun CPC are:
Parabolic Formula: y = (x / Cos(parabAngle)) ^ 2 - Tan(parabAngle) *
x where parabAngle = -12.1250 º
Parabolic Section Used: (0, 0) - (-0.70696, 0.37098)
Optic axis: 62.23 º running from origin
Height of Optic Axis/Aperture intersection: 0.5819
The CPC can be formed from 1.2 mm aluminium sheet pulled into shape
with threaded rods or wire pulling from the trough rim to the trough's
base. 105 mm PV cells would be used with a trough aperture of 420
mm. This trough can be formed from sheet material 812 mm wide (782.1
mm for trough material + 2*15 mm lips). The 15 mm lips are bent
outwards to provide rigidity and a surface for the threaded rods to
pull against. The trough base is formed with a bend of 123.0 º (this
angle will spread 1.5 º to 124.5 º when the trough is stressed to the
parabolic shape).
A schematic is available at www.thorpies.com/4suns.htm
Thanks for your time
Posted by R.H. Allen on February 9, 2007, 10:47 am
altsolarthermal@thorpies.com wrote:
> Hello
> I was wondering if anyone could advise on the current best
> concentration onto double sided collectors from east-west compound
> parabolic troughs.
> I understand that the limit of best concentration onto a one sided
> surface is governed by the sine law. With a half angle of 23.5 º
> (ignoring the 0.25 º of the solar radius) this gives a best
> concentration of 2.5078 or onto a surface 39.875% of the aperture
> size.
> For double sided PV cells this gives a theoretical limit of half this,
> a surface 19.937% of the aperture size or a concentration of just over
> 5.01 suns.
Why do you need a bifacial solar cell? Do you plant to shine
concentrated light onto both sides of it? If so, how do you plan to keep
it cool? Power conversion efficiency of light shined on the back side of
a bifacial cell is much lower than for light shined on the front, so
between that and the cooling issue you'd probably be better off using
standard monofacial concentrator cells. Or perhaps I'm just not
following you.
> Can anyone advise whether this theoretical concentration has been
> achieved. Alternately would anyone have any idea of the current best
> known?
Yeah, I'm pretty sure I'm not following you. Concentrations much higher
than 5 suns have been achieved with parabolic troughs. Just a few
references that I find with a quick google search:
http://dspace.anu.edu.au/handle/1885/40837
http://www.eia.doe.gov/kids/energyfacts/sources/renewable/solar.html
http://spiedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PSISDG002255000001000557000001&idtype=cvips&gifs=yes
http://solar.anu.edu.au/level_1/research/linearconc.php
Posted by altsolarthermal on February 9, 2007, 4:00 pm
> altsolarther...@thorpies.com wrote:
> > Hello
> > I was wondering if anyone could advise on the current best
> > concentration onto double sided collectors from east-west compound
> > parabolic troughs.
> > I understand that the limit of best concentration onto a one sided
> > surface is governed by the sine law. With a half angle of 23.5 º
> > (ignoring the 0.25 º of the solar radius) this gives a best
> > concentration of 2.5078 or onto a surface 39.875% of the aperture
> > size.
> > For double sided PV cells this gives a theoretical limit of half this,
> > a surface 19.937% of the aperture size or a concentration of just over
> > 5.01 suns.
> Why do you need a bifacial solar cell? Do you plant to shine
> concentrated light onto both sides of it? If so, how do you plan to keep
> it cool? Power conversion efficiency of light shined on the back side of
> a bifacial cell is much lower than for light shined on the front, so
> between that and the cooling issue you'd probably be better off using
> standard monofacial concentrator cells. Or perhaps I'm just not
> following you.
> > Can anyone advise whether this theoretical concentration has been
> > achieved. Alternately would anyone have any idea of the current best
> > known?
> Yeah, I'm pretty sure I'm not following you. Concentrations much higher
> than 5 suns have been achieved with parabolic troughs. Just a few
> references that I find with a quick google search:
> http://dspace.anu.edu.au/handle/1885/40837http://www.eia.doe.gov/kids/energyfacts/sources/renewable/solar.htmlhttp://spiedl.aip.org/getabs/servlet/G=
etabsServlet?prog=normal&id=PSI...http://solar.anu.edu.au/level_1/resea=
rch/linearconc.php
Non-tracking, i don't thing so. All that you point to require
tracking, the weak link.
Yes, cooling is a problem, at the moment, but I think this will be
overcome.
Thanks for the advice on the lower power conversion efficiency of the
reverse side, any idea of what sort of reduction would be appreciated.
Posted by altsolarthermal on February 9, 2007, 9:44 pm
Quick google research indicates that the efficiency of the second side
is only marginally lower, of the order 21% prime side compared to
19.5% on second side for some high efficiency cells.
I would think that this 7% reduction in second side efficiency really
isn't enough to worry too much about.
Posted by [SPICEISLE.COM] Brian Steele on February 10, 2007, 9:04 am
>Yes, cooling is a problem, at the moment, but I think this will be
>overcome.
You could consider a hybrid sollar PV / solar water heating system, where
water acts as the coolant for the cells.
Regards,
Brian Steele
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> I was wondering if anyone could advise on the current best
> concentration onto double sided collectors from east-west compound
> parabolic troughs.
> I understand that the limit of best concentration onto a one sided
> surface is governed by the sine law. With a half angle of 23.5 º
> (ignoring the 0.25 º of the solar radius) this gives a best
> concentration of 2.5078 or onto a surface 39.875% of the aperture
> size.
> For double sided PV cells this gives a theoretical limit of half this,
> a surface 19.937% of the aperture size or a concentration of just over
> 5.01 suns.