lense solar power

[northkorea]

have u ever took your glasses as a child and burned things focusing the suns heat with the

lense depending on the thickness of the lense it can burn things fairly fast my ?'s are

could we use lenses to focus on a solar panel to get more power out?

and if that works could we use the same idea as a power tower except using lenses

by using mirrors to reflect the light through a lense to solar panels on the tower

and also for solar heating panels the water in the panels would heat far more faster

then with out the lense

is any of this possible?

[veewee77]

The answer is. . . yes you can, but it will severely decrease the life of the solar cells.

There is a guy doing it with a thing he calls SunBall.

Uses fresnel lenses to concentrate the sunlight on smaller cells producing higher output from each one.

http://www.greenandgoldenergy.com.au

This does not reflect that I endorse this product or site, but if for your perusal.

Doug

[stop4stuff]

bing!

remembered this discussion from last year

http://www.fieldlines.com/story/2005/5/3/205028/6819 - How to make your own silicon solar cell

site google search really works

try it out...

click 'Google search the board' and enter transistor magnifying glass

also read of a report of a design using holograms to concentrate sunlight onto pv cells - http://www.technologyreview.com/read_article.aspx?id=16736&ch=energy

paul

[Ungrounded Lightning Rod]

"concentrators" have been experimented with but it usually ends up being better just to buy more cells.

Early panels had problems with the glue holding the cells to the front glass discoloring and permanently absorbing much of the light, quickly bringing the panel below a bare-panel's output, and shortening the panel life as they continued to discolor.

Modern panels don't have THAT problem.  But when cells get hot their output voltage drops, and most of the light hitting the cells becomes heat.  So (in addition to the damage to the cell from the excess heat) a cell under a concentrator requires more cooling than just circulating air to realize the the gain from a concentrator.

Then there's the probelm that some concentrator designs require sun tracking to work correctly.

So while there's potential gain to be had in power output per unit of cell area, there doesn't seem to be any to be had in power output per dollar of installed stuff.

[Heliotrack]

**and also for solar heating panels the water in the panels would heat far more faster then with out the lens**

Concentrated solar power (CSP) will heat faster but first we have to understand that for a given area there is a constant amount of available solar energy. For a bright sunny day you can figure approximately 1000 Watts per square meter. Now if we took a lens with an aperture of one square meter and focused the sun to a 1 cm diameter focal point there is still only 1000 Watts of energy available but it is concentrated on a smaller area. Actually there will be less energy because some energy will be lost in the lens due to impurities, surface reflection, scattering, and other factors.

This 1 cm hot spot would boil and evaporate a thimble of water very quickly but, generally speaking, it would not heat a gallon of water any faster than would a simple solar water heating panel with a 1 square meter aperture. When we concentrate the sun we are trading low energy over a large area for high energy over a small area, we are not gaining energy.

One advantage to using a lens is that we could circulate our water through a 1 square-cm collector instead of a 1 square-meter collector. Smaller collector means less material to build, but remember that the lens would have to track the sun in order to keep the focus on the collector adding complexity to the system.

Here are some advantages of heating with concentrated solar power...

1. Smaller collector (less material and insulation)
   
2. Smaller re-radiation area meaning less energy loss from the system (this is a double edged sword though because re-radiation losses increase the higher the temperature is over ambient)
   
3. Higher working temperatures can be achieved. (Crucial for steam generation or solar distilling of ethanol or water)
   
   

Here are some disadvantages...

1. Must use solar tracking system
   
2. Risk of fire (Collectors must be made to withstand very high temperatures when they run dry...)
   
   

We have burned up many collectors and broken a lot of glass in our concentrated solar power experiments.

This just barely touches the subject, I could go on for days... but I won't.

I have more information on my website about solar tracking and concentrated solar power. If you have time, check it out.

www.heliotrack.com

Justin

[jacquesm]

I've experimented a bit with concentrating sunlight on solar cells,

see this

photo series.

The short version is: it works, but it makes things hotter and live shorter.

In the long run I've found that it isn't worth the trouble unless you go for

an industrial style solution where the additional heat is used as well.

The main problem seems to be that you'll be generating a lot of excess heat on a relatively small surface and things can get so hot that they catch fire or melt.

You can engineer around all of that (I've gone so far as to water cool boosted solar cells and silver solder connections and such) but it really isn't worth the time or the effort.

As for the 'suncube' listed on this page:

at a maximum of 1KW of incident sunlight per square meter the suncube

has a 810W solar input. Discounting for the bars that hold down the

lenses that's another 5% or so. So say 750 W of usable input power, an overall efficiency of 25% per cell so about 185 Watts output from .9 square meters

of array. That's totally in line with the expected output of an array of that size. Now for the catch: the lenses are plastic and will degrade strongly over time, the cells are heated up far beyond what they're made to withstand and will degrade at a much higher rate than normal, and thermal effects will cause a lot of loss in the cells (solar cells like to be cold, otherwise they perform much less efficient).

It's a neat idea, the gear shown in the picture is clearly experimental, not a product (and if that's the product... well) at $1200 or so I think I can do a lot better with stationary panels especially once you start figuring in the life expectancy of this rig.

just my 2c, your mileage may vary and so on...

[jacquesm]

bad form to reply to your own comment...

I've been reading a bit more on the suncube site, apparently they use 37% efficient 1cm^2 cells that they concentrate 500:1 on.

That's about 30 watts of heat per cell to be dissipated passively via some kind of cooling arrangement at the back, that sounds plausible I've used RF transistors at much higher power levels with relatively small heatsinks.

The guy that came up with this - and the 'sunball' is named Greg Watson.

It would be interesting to know if they've actually shipped product and what the experience of the buyer was with the device...

I did a bit of sleuthing around their site and

http://www.greenandgoldenergy.com.au/Documents/

contains lots of goodies,

GGEPRMTSC20051018a.pdf

is a pdf of a press release that says they're going to install a whole bunch of them, anybody have a way of finding out if it went through ?

PassiveCooling.pdf

shows where they got a bunch of their ideas.

[disaray1]

 The last time I looked around on greenandgold, they were in production for empirical testing, and once completed they would begin delivery to customers.

    The cells are coming from Spectrolab (Boeing) and can be bought...$5000 US for 20 cells, and they are classed as prototypes, which I would interperate as "No Warantee". Interesting product though.

     Sometimes Greg Watson lurks around here....Greg, are you there?

 disaray1

[jacquesm]

interesting, the site claims for the cell prices are much lower than that, about $10.