[Greenbuilding] Fresnel lenses box solar cooker

Topher topher at greenfret.com
Mon Jun 3 16:12:46 CDT 2013


On 6/3/2013 3:23 PM, RT wrote:
> On Mon, 03 Jun 2013 12:51:27 -0400, Topher <topher at greenfret.com> wrote:
>
>>> Also, I'm pretty sure that I remember my neighbour saying that CPV
>>> systems are typically designed as tracking systems,
>
>> tracking is /already/ more expensive than just
>> adding more panels.
>
> Is this true ?
>
> You may recall that about a year ago I posted some messages to this 
> list about the output from one of my neighbours' 10 kW single-axis 
> tracking array.
>
> He  was regularly getting up to 40% higher production than an 
> identically-sized fixed array in the same neighbourhood. (I had posted 
> a link to a site that provided real-time monitoring data for the fixed 
> array).
Details always matter in this business.  So, perhaps it works out better 
for him, but not around here.  Also, panels have halved in price over 
the last 1.5 years or so.  What was true then may no longer be.  No 
installers around here even consider tracking anymore.

Here is a solar tracker for $1893 USD holds 64ft^2 of panels.
http://www.altestore.com/store/Solar-Panel-Mounts-Trackers/Passive-Solar-Panel-Trackers/Zomeworks-UTRF-072-Universal-Solar-Tracker/p10390/?source=shopzilla
The same store will sell me 5 panels to go on it for $275 each (250W)
http://www.altestore.com/store/Solar-Panels/SolarWorld-Sunmodule-SW250-Poly-250W-20V-Solar-Panel-V25-Frame/p10149/
Total cost: $3268.

Or I could just buy panels with that amount and get about 12 of them.  
For 230% better performance.

Note: I just picked the first one that came up in Google, to remain 
impartial.  YMWV.
>> The problem is not just the cost of the lenses.  In order to get the
>> same output as a 20 meter^2 PV panel array, you need 20 meter^2 of
>> Fresnel lenses; and some means of holding it very steady in the wind, a
>> precise distance away from the collector; plus be able to move the whole
>> unit (including the cooling system), very precisely throughout the day,
>> every day.
>
> I suspect that the above is not much of a challenge for the PV 
> cowboys/gals these days judging by the number of 10 KW tracking arrays 
> one sees mounted atop a single mast when out for a morning bike ride 
> around this neighbourhood.

Perhaps I should back up and get a description of what the 1 square inch 
solar cell you are talking about is going to produce.  If we are talking 
about replacing an average sized home PV array, then we need roughly the 
same sized Fresnel lens, and that needs to be focused on a 1" collector, 
with an appropriate focal distance (presumably many feet).  That is a 
very tough problem.  If we are only talking about the 300x concentrators 
(like the ones Sanjay pointed out), than a 1" cell needs a Fresnel lens 
17" on a side. Much more feasible,  but that is only about 186 Watts 
(/total/ before efficiency losses),  nothing like a whole house system.

Some pertinent quotes for Sanjay's link:
* "Despite having been researched since the 1970s, it has only now 
entered the solar electricity sector as a viable alternative."
* "*Active Cooling:* Typically, liquid metal is used as a cooling fluid, 
capable of cooling from 1,700°C to 100°C."
[required for high concentration systems i.e. > 100x]
*"Thus, it is less dependant on the immature silicon supply chain. 
Moreover, optics are less expensive than cells."

This last I think is debatable at this point.  Silicon supply is pretty 
mature at this point.  Optics are/very/ mature.  Anyone into expensive 
cameras will tell you that cameras keep getting better and cheaper, and 
lenses get better only by getting more expensive.  Cameras are a good 
analogy to solar PV systems because they both do NOT take advantage of 
Moore's law when it comes to the Silicon.  Bigger is better.
In forty years that concentrator technology has been known, it has not 
taken off, in the mean time, prices for solar cells have dropped by 
250x.  If it could have taken off, 1970's was the time for it to do so.

Moving the other direction, I could get thin film flexible panels and 
just glue them to my standing seam roof.  Drastically reduced 
infrastructure.  No racks, no module frames, No aluminum at all. 
Probably worth the 50% drop in efficiency, once the sales volume drops 
the price commensurate with typical panels.


Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.GreenFret.com/
topher at greenfret.com

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