Posted by *Jeff B.* on July 27, 2008, 12:53 pm

Hi there,

Looking to a proposal made to us for a 2 kW PV generator (16.000 ), I

was wondering whether we could design a cheap 1 kW PV generator using

Fresnel lenses in combination with high efficiency multijunction PV

cells.

What if we put 4 triangular multijunction PV cells (or TASC, assembled

into a 3.1cm x 3.18 cm square) close to the focal point of a Fresnel

lens ?

Could a PV generator comprising 25 Fresnel lenses in a 5 x 5 square

(2m x 2m square) with their PV cells approx. 30 cm behind them, the

whole thing being mounted onto a passive solar tracker, do it ?

From the Spectrolab spec: 27 mW/cm (for 1 sun) are produced by the

TASC. The Fresnel lens focuses approx 155 times the solar irradiance

reaching the 4 TASC cells (3.1cm x 3.18cm) thus producing

27x155x(3.1x3.18)=41,25 W. If we consider 25 units of this kind

(Fresnel lens+4 TASC), this would produce approx. 1 kW for approx.

2250 $ or 1450 (plus framing structure to add). Either there is an

error in my rough calculation or this would be a cheap way to produce

electricity. Do you think it is feasible ?

Jeff

25 large Fresnel lenses from 3dLens or BhLens (http://www.3dlens.com/

shop/largefresnellens.php)=25 x 22.68 $

1 spectrolab box of 100 triangular PV cells (http://www.spectrolab.com/

DataSheets/PV/PV_NM_TASC_ITJ.pdf)=250 $

1 Zomeworks UTRK40 passive solar tracker (http://zomeworks.com/files/

pv-trackers/Track%20Rack%20Matrix%202008.pdf) = 1450 $

Posted by *Roderick* on July 28, 2008, 7:25 am

*> Hi there,*

*> Looking to a proposal made to us for a 2 kW PV generator (16.000 ), I*

*> was wondering whether we could design a cheap 1 kW PV generator using*

*> Fresnel lenses in combination with high efficiency multijunction PV*

*> cells.*

*> What if we put 4 triangular multijunction PV cells (or TASC, assembled*

*> into a 3.1cm x 3.18 cm square) close to the focal point of a Fresnel*

*> lens ?*

*> Could a PV generator comprising 25 Fresnel lenses in a 5 x 5 square*

*> (2m x 2m square) with their PV cells approx. 30 cm behind them, the*

*> whole thing being mounted onto a passive solar tracker, do it ?*

*> From the Spectrolab spec: 27 mW/cm (for 1 sun) are produced by the*

*> TASC. The Fresnel lens focuses approx 155 times the solar irradiance*

*> reaching the 4 TASC cells (3.1cm x 3.18cm) thus producing*

*> 27x155x(3.1x3.18)=41,25 W. If we consider 25 units of this kind*

*> (Fresnel lens+4 TASC), this would produce approx. 1 kW for approx.*

*> 2250 $ or 1450 (plus framing structure to add). Either there is an*

*> error in my rough calculation or this would be a cheap way to produce*

*> electricity. Do you think it is feasible ?*

*> Jeff*

*> 25 large Fresnel lenses from 3dLens or BhLens (http://www.3dlens.com/ *

*> shop/largefresnellens.php)=25 x 22.68 $*

*> 1 spectrolab box of 100 triangular PV cells (http://www.spectrolab.com/ *

*> DataSheets/PV/PV_NM_TASC_ITJ.pdf)=250 $*

*> 1 Zomeworks UTRK40 passive solar tracker (http://zomeworks.com/files/ *

*> pv-trackers/Track%20Rack%20Matrix%202008.pdf) = 1450 $*

I would be concerned with how you will be cooling the cells to

operating temperature at this concentration. I have read about

experimental concentrators at 100x, but they seem to have massively

sophisticated cooling systems on them.

Also, that's an excellent price on the cells. Are you certain it

isn't $50 for each cell ($5,000 for the box)?

Posted by *jp838* on July 28, 2008, 1:49 pm

Jeff B. wrote:

*> Hi there,*

*> Looking to a proposal made to us for a 2 kW PV generator (16.000 ), I*

*> was wondering whether we could design a cheap 1 kW PV generator using*

*> Fresnel lenses in combination with high efficiency multijunction PV*

*> cells.*

*> What if we put 4 triangular multijunction PV cells (or TASC, assembled*

*> into a 3.1cm x 3.18 cm square) close to the focal point of a Fresnel*

*> lens ?*

*> Could a PV generator comprising 25 Fresnel lenses in a 5 x 5 square*

*> (2m x 2m square) with their PV cells approx. 30 cm behind them, the*

*> whole thing being mounted onto a passive solar tracker, do it ?*

*> From the Spectrolab spec: 27 mW/cm (for 1 sun) are produced by the*

*> TASC. The Fresnel lens focuses approx 155 times the solar irradiance*

*> reaching the 4 TASC cells (3.1cm x 3.18cm) thus producing*

*> 27x155x(3.1x3.18)=41,25 W. If we consider 25 units of this kind*

*> (Fresnel lens+4 TASC), this would produce approx. 1 kW for approx.*

*> 2250 $ or 1450 (plus framing structure to add). Either there is an*

*> error in my rough calculation or this would be a cheap way to produce*

*> electricity. Do you think it is feasible ?*

*> Jeff*

*> 25 large Fresnel lenses from 3dLens or BhLens (http://www.3dlens.com/ *

*> shop/largefresnellens.php)=25 x 22.68 $*

*> 1 spectrolab box of 100 triangular PV cells (http://www.spectrolab.com/ *

*> DataSheets/PV/PV_NM_TASC_ITJ.pdf)=250 $*

*> 1 Zomeworks UTRK40 passive solar tracker (http://zomeworks.com/files/ *

*> pv-trackers/Track%20Rack%20Matrix%202008.pdf) = 1450 $*

You only need one cell and one lens to test it, ???$0 (you could even

sell a kit, many world wide would like to try that :)

- I doubt it's that simple, some must have already tried. I read about

that kind of cells used with concentrators

- a problem must be that the light spot power distribution is not

homogeneous (*)

- the time life of the cell maybe reduced ?? (*)

- the cell must saturate at ?some light flux ?? (*)

- dissipating the energy is not a problem. With a 100 sun

concentrator, it would give at worse: 1 kW/m2 >> 0.1W/cm2 >> * 100 =

10W/cm2. A 4C/W heat sink used in electronic can easily be fit under

the cell ($.5) and will work without a fan. With this,

you keep your cell below 70C. With that much power to dissipate, a

smart design, profiting of convection, would probably deeply boost

your heat sink efficiency.

Choose your heat sink at: http://www.mouser.com/catalog/634/1876.pdf

Usually they are in aluminium.

If you use circulating water heated at max +20C, you'll need 0.43 L

of water per cm2 of cell per hour, 10 liters per cm2 of cell per day,

~1m3/day for 1 square meter of panel. Not a good idea if water is not

recycled :)

If these cells could work at 100C one could grab the heat use it for

heating ...

(*) I'd like to have your views about these points ???

Sholl

Posted by *jp838* on July 29, 2008, 12:34 am

*> Jeff B. wrote:*

*> > Hi there,*

*> > Looking to a proposal made to us for a 2 kW PV generator (16.000 ), I*

*> > was wondering whether we could design a cheap 1 kW PV generator using*

*> > Fresnel lenses in combination with high efficiency multijunction PV*

*> > cells.*

*> > What if we put 4 triangular multijunction PV cells (or TASC, assembled*

*> > into a 3.1cm x 3.18 cm square) close to the focal point of a Fresnel*

*> > lens ?*

*> > Could a PV generator comprising 25 Fresnel lenses in a 5 x 5 square*

*> > (2m x 2m square) with their PV cells approx. 30 cm behind them, the*

*> > whole thing being mounted onto a passive solar tracker, do it ?*

*> > From the Spectrolab spec: 27 mW/cm (for 1 sun) are produced by the*

*> > TASC. The Fresnel lens focuses approx 155 times the solar irradiance*

*> > reaching the 4 TASC cells (3.1cm x 3.18cm) thus producing*

*> > 27x155x(3.1x3.18)=41,25 W. If we consider 25 units of this kind*

*> > (Fresnel lens+4 TASC), this would produce approx. 1 kW for approx.*

*> > 2250 $ or 1450 (plus framing structure to add). Either there is an*

*> > error in my rough calculation or this would be a cheap way to produce*

*> > electricity. Do you think it is feasible ?*

*> > Jeff*

*> > 25 large Fresnel lenses from 3dLens or BhLens (http://www.3dlens.com/ *

*> > shop/largefresnellens.php)=25 x 22.68 $*

*> > 1 spectrolab box of 100 triangular PV cells (http://www.spectrolab.com/ *

*> > DataSheets/PV/PV_NM_TASC_ITJ.pdf)=250 $*

*> > 1 Zomeworks UTRK40 passive solar tracker (http://zomeworks.com/files/ *

*> > pv-trackers/Track%20Rack%20Matrix%202008.pdf) = 1450 $*

*> You only need one cell and one lens to test it, ???$0 (you could even*

*> sell a kit, many world wide would like to try that :)*

*> - I doubt it's that simple, some must have already tried. I read about*

*> that kind of cells used with concentrators*

*> - a problem must be that the light spot power distribution is not*

*> homogeneous (*)*

*> - the time life of the cell maybe reduced ?? (*)*

*> - the cell must saturate at ?some light flux ?? (*)*

*> - dissipating the energy is not a problem. With a 100 sun*

*> concentrator, it would give at worse: 1 kW/m2 >> 0.1W/cm2 >> * 100 =*

*> 10W/cm2. A 4C/W heat sink used in electronic can easily be fit under*

*> the cell ($.5) and will work without a fan. With this,*

*> you keep your cell below 70C. With that much power to dissipate, a*

*> smart design, profiting of convection, would probably deeply boost*

*> your heat sink efficiency.*

*> Choose your heat sink at: http://www.mouser.com/catalog/634/1876.pdf *

*> Usually they are in aluminium.*

*> If you use circulating water heated at max +20C, you'll need 0.43 L*

*> of water per cm2 of cell per hour, 10 liters per cm2 of cell per day,*

*> ~1m3/day for 1 square meter of panel. Not a good idea if water is not*

*> recycled :)*

*> If these cells could work at 100C one could grab the heat use it for*

*> heating ...*

*> (*) I'd like to have your views about these points ???*

*> Sholl*

Soliloquizing:

for (*) http://www.spectrolab.com/prd/terres/FAQ_terrestrial.htm#section1

a very interesting FAQ written by a cell producer.

BTW, Spectrolab have real products you can buy, not like many others !

Posted by *Jeff B.* on July 31, 2008, 2:09 pm

*> Jeff B. wrote:*

*> > Hi there,*

*> > Looking to a proposal made to us for a 2 kW PV generator (16.000 ), I*

*> > was wondering whether we could design a cheap 1 kW PV generator using*

*> > Fresnel lenses in combination with high efficiency multijunction PV*

*> > cells.*

*> > What if we put 4 triangular multijunction PV cells (or TASC, assembled*

*> > into a 3.1cm x 3.18 cm square) close to the focal point of a Fresnel*

*> > lens ?*

*> > Could a PV generator comprising 25 Fresnel lenses in a 5 x 5 square*

*> > (2m x 2m square) with their PV cells approx. 30 cm behind them, the*

*> > whole thing being mounted onto a passive solar tracker, do it ?*

*> > From the Spectrolab spec: 27 mW/cm (for 1 sun) are produced by the*

*> > TASC. The Fresnel lens focuses approx 155 times the solar irradiance*

*> > reaching the 4 TASC cells (3.1cm x 3.18cm) thus producing*

*> > 27x155x(3.1x3.18)=41,25 W. If we consider 25 units of this kind*

*> > (Fresnel lens+4 TASC), this would produce approx. 1 kW for approx.*

*> > 2250 $ or 1450 (plus framing structure to add). Either there is an*

*> > error in my rough calculation or this would be a cheap way to produce*

*> > electricity. Do you think it is feasible ?*

*> > Jeff*

*> > 25 large Fresnel lenses from 3dLens or BhLens (http://www.3dlens.com/ *

*> > shop/largefresnellens.php)=25 x 22.68 $*

*> > 1 spectrolab box of 100 triangular PV cells (http://www.spectrolab.com/ *

*> > DataSheets/PV/PV_NM_TASC_ITJ.pdf)=250 $*

*> > 1 Zomeworks UTRK40 passive solar tracker (http://zomeworks.com/files/ *

*> > pv-trackers/Track%20Rack%20Matrix%202008.pdf) = 1450 $*

*> You only need one cell and one lens to test it, ???$0 (you could even*

*> sell a kit, many world wide would like to try that :)*

*> - I doubt it's that simple, some must have already tried. I read about*

*> that kind of cells used with concentrators*

*> - a problem must be that the light spot power distribution is not*

*> homogeneous (*)*

*> - the time life of the cell maybe reduced ?? (*)*

*> - the cell must saturate at ?some light flux ?? (*)*

*> - dissipating the energy is not a problem. With a 100 sun*

*> concentrator, it would give at worse: 1 kW/m2 >> 0.1W/cm2 >> * 100 =*

*> 10W/cm2. A 4C/W heat sink used in electronic can easily be fit under*

*> the cell ($.5) and will work without a fan. With this,*

*> you keep your cell below 70C. With that much power to dissipate, a*

*> smart design, profiting of convection, would probably deeply boost*

*> your heat sink efficiency.*

*> Choose your heat sink at: http://www.mouser.com/catalog/634/1876.pdf *

*> Usually they are in aluminium.*

*> If you use circulating water heated at max +20C, you'll need 0.43 L*

*> of water per cm2 of cell per hour, 10 liters per cm2 of cell per day,*

*> ~1m3/day for 1 square meter of panel. Not a good idea if water is not*

*> recycled :)*

*> If these cells could work at 100C one could grab the heat use it for*

*> heating ...*

*> (*) I'd like to have your views about these points ???*

*> Sholl- Masquer le texte des messages prcdents -*

*> - Afficher le texte des messages prcdents -*

There are two difficult points, the more concentrated:

- the more accurate your tracking system must be

- the more calories you have to dissipate

for the first point, I was in search of cheap/simple passive trackers.

liquid mass transfer (with shadowing apparatus) is attractive by its

simplicity but I have doubt about their accuracy and their reliability

with variable weather conditions. It may require a lot of

experimentations to get worked.

you have to collimate a centimeter radius focused light circle on a cm

square of multijunction PV cells a few centimeters before the focal

point (say at 30 cm from the Fresnel lens (sub degree tracking).

I can't see any Shape Metal Alloy (for solar tracking purposes)

commercially available ?

The simplest tracking system I can see is first to use a square based

pyramid of basic PV cells to ensure a rought differential tracking

(~degree accuracy), orientation of the optical frame by two linear

motors. This is to bring the sunlight closer to the axis of the

Fresnel lens & multijunction cells (this couple form a pyramid, with

mirrors covering the lateral inside faces).

The high quality PV cells are the Spectrolab ones designed to cope

with high concentrations.

There are 9 of them in a 3 x 3 square.

The first tracking system is to ensure that the focussed light spot

intercepts this square (the target is then logged on).

Knowing the amount of light reaching each of the nine cells, you can

finally track in a very accurate manner and ensure maximum electricity

generation.

There are simple circuitry available on the web. The first and second

tracking phases could form a vernier. This system could compensate

analog biases (components in the tracking circuit) increasing with

time.

For the heat dissipation, I am also looking in the direction of high

performance cooling systems available for processors (IBM has its own

concentrator).

There is a liquid metal system (with a magnetic pump) from danamics

that seems very reliable/efficient and with reasonnable appetite (1W),

I don't know its price but you are right, heat dissipation is very

important for the best performance and life time of the cells. If you

expect to get 500 suns foccused on 10 cm and given that your cells

are ~0.3-0.4 efficient, this is a lot of heat of a small solar furnace

to evacuate.

Jeff

PS) it appears that spectrolab do not sell small quantities of

multijunction cells. no order under $000 (120 cells, enought to make

a 3 kW generator). no possibility to build a small 170W PV generator

(suitable for our roofs). looking to Emcore.

> Hi there,> Looking to a proposal made to us for a 2 kW PV generator (16.000 ), I> was wondering whether we could design a cheap 1 kW PV generator using> Fresnel lenses in combination with high efficiency multijunction PV> cells.> What if we put 4 triangular multijunction PV cells (or TASC, assembled> into a 3.1cm x 3.18 cm square) close to the focal point of a Fresnel> lens ?> Could a PV generator comprising 25 Fresnel lenses in a 5 x 5 square> (2m x 2m square) with their PV cells approx. 30 cm behind them, the> whole thing being mounted onto a passive solar tracker, do it ?> From the Spectrolab spec: 27 mW/cm (for 1 sun) are produced by the> TASC. The Fresnel lens focuses approx 155 times the solar irradiance> reaching the 4 TASC cells (3.1cm x 3.18cm) thus producing> 27x155x(3.1x3.18)=41,25 W. If we consider 25 units of this kind> (Fresnel lens+4 TASC), this would produce approx. 1 kW for approx.> 2250 $ or 1450 (plus framing structure to add). Either there is an> error in my rough calculation or this would be a cheap way to produce> electricity. Do you think it is feasible ?> Jeff> 25 large Fresnel lenses from 3dLens or BhLens (http://www.3dlens.com/> shop/largefresnellens.php)=25 x 22.68 $> 1 spectrolab box of 100 triangular PV cells (http://www.spectrolab.com/> DataSheets/PV/PV_NM_TASC_ITJ.pdf)=250 $> 1 Zomeworks UTRK40 passive solar tracker (http://zomeworks.com/files/> pv-trackers/Track%20Rack%20Matrix%202008.pdf) = 1450 $