Improving Efficiency Using a Lens

[Moneer81]

Hello,

I am doing a project for school and was wondering if someone could help me understand the anatomy of solar panels. I am trying to improve the output of a solar panel by focusing and magnifying the sun's solar energy. I am thinking of using some kind of lens, possibly a Frensel lens. The question is, where on the solar panel should I plan to focus the light? Let's take an amorphous type solar panel for example, something I have access to. Or a monocrystalline panel. It sounds like a dumb question but I am thinking that the whole surface of the panel is semi-conducting so anywhere would work, right? Or are there certain spots on the surface of the panel that are designed to be the absorbers of light? Any help would be appreciated. Thanks.

 

[Nigel Goodwin]

The entire panel is sensitive, don't focus to a sharp point, just focus on the entire panel.

I take it you are aware that such a scheme will require accurately tracking the sun, as a slight misalignment will mean it's not focused on the panel any more.

 

[mneary]

A solar panel is most efficient when it's illuminated uniformly. All you'll do with a big lens is melt it.

 

[Moneer81]

The entire panel is sensitive, don't focus to a sharp point, just focus on the entire panel.

I take it you are aware that such a scheme will require accurately tracking the sun, as a slight misalignment will mean it's not focused on the panel any more.

Yes. That would be a problem. It could be solved by mechanically moving the lens to face the sun and provide focus on the panel. Since the sun's path is predictable, a simple set-up could slowly move the lens throughout the day to provide maximum efficiency.

 

[3v0]

A setup more along the line of a solar oven which uses reflectors may work better. You should be able to intensify the light without focusing on a single spot. There still is the possibility of cooking the solar cell if you collect too much light. The materials are cheap, cardboard or plywood and aluminum foil.

Since solar tracking is required to make it work you might set it up to point a bit off the sun when it is too bright. Dead on with clouds.

 

[Moneer81]

A solar panel is most efficient when it's illuminated uniformly. All you'll do with a big lens is melt it.

What if the lens isn't powerful enough to melt the panel? What about a think layer of water sealed between two sheets of acrylic? Focus the light on the panel has to somehow improve the efficiency.

 

[ericgibbs]

What if the lens isn't powerful enough to melt the panel? What about a think layer of water sealed between two sheets of acrylic? Focus the light on the panel has to somehow improve the efficiency.

If you look at some commercial solar sites you will see they use reflectors.

If you stick a focussing lens between the panel and the Sun, the total illumination of the panel stays the same.!!!
Unless the panel area is smaller than the lens area.

All you will do is burn a spot on the panel.

 

[Moneer81]

A setup more along the line of a solar oven which uses reflectors may work better. You should be able to intensify the light without focusing on a single spot. There still is the possibility of cooking the solar cell if you collect too much light. The materials are cheap, cardboard or plywood and aluminum foil.

Since solar tracking is required to make it work you might set it up to point a bit off the sun when it is too bright. Dead on with clouds.

Interesting idea...do you think the backside of the reflectors would block the sun's light when the sun is not directly above the panel, and thus reducing the total daily output?

 

[3v0]

Interesting idea...do you think the backside of the reflectors would block the sun's light when the sun is not directly above the panel, and thus reducing the total daily output?

If they can use them to boil water you should be able to build one to increase the light level.

There are numerous designs for solar collectors and ovens. What I was thinking about was to place the photo cell facing down and reflect light up to it with panels off to the sides. Much like a reflector telescope but you do not need near the precision. Maybe several reflectors curved in just one dimension.

If you design the unit to collect enough light when it is cloudy you will have too much when there are no clouds. If you add a tracker to follow the sun you can move the collector to keep it from cooking the cell/panel.

 

[Speakerguy]

Sort of like a parabolic mic?

 

[3v0]

Sort of like a parabolic mic?

Same principal but focus should be less sharp to cover entire solar cell.

 

[rjvh]

i think that a lens doesn't work to improve efficiency

as you consentrate more solar energy it is manly in the form of heat and one of the things that Photovoltiac cells make less efficient is heat


for heating up water in solar colectors it does work and i made one proto type in small dimentions to messure the differance with if you don't colect more sun (enlarging the sqr meter catchment area)

i only used mirrors no lenses

Robert-Jan

 

[3v0]

Aluminum is used to coat the mirrors on telescopes. I think it should work well for your purpose. My SO has done more work with this sort of think suggest heavy duty Renyolds Wrap over a smooth surface. The smoother you keep the foil the more efficent it will be. But this is not a big deal since you do not want a sharp focus and can always make the collector a bit bigger to overcome inefficency.

It would be interesting if you posted updates on your progress.

 

[bryan1]

Moneer,
As you say this is a school project so why bother with lens or mirrors and go and make a simple tracker for the PV panel. It will get upto 30% more power by tracking the sun. All you need is 2 green led's and a simple circuit to sense the sun and a reasonable delay to stop the hunting. As this is your school project I'm giving you another angle to try and I won't give you the whole fruit an biscuits but I will assist you if you choose this option.

Cheers Bryan

 

[Thunderchild]

mirrors + solar tracking if your not on the equator chances are it won't burn up panels are rated as if they work on the equator (to con us into thinking they are more powerful than they really can be) so con back and get the extra light

 

[Moneer81]

Hello,

Thanks for the great replies and the feedback I received. Sorry for disappearing for a while and not responding right away. I decided to agree with what some of you mentioned and try to do build a sun tracker, and measure the improved efficiency. I think that could result in a nice written report and interesting presentation, given that my audience and colleagues are not likely to be familiary with sun trackers. I have a couple large size solar panels, about 12" by 55" or something like that. I am gonna start on building the frame for it and the circuit that will drive the motor. My question is what would the best choice for a motor be? And can anyone suggest where I can find one or how I can cannibalize one maybe? The solar panel is not huge but my guess it weighs about 20 lbs or so. Thanks.

 

[bryan1]

Hello Moneer,
Weight really isnt an issue on a pv tracker if you have everything balanced and well built. There are 2 ways to do tracking,
1. is to use use 2 green led's to sense the strongest light and redrock.com has some good schematics for this.
2. Is hammer a long nail say 4" into a square board say 6" square, then point it at the sun and use an angle guage to find the azmuith. Once you know that build a simple frame with a centre mount rod and put 2 dead stops an each end of the frame. Then put a very low speed motor via gearing say bike sprockets to get the required reduction, so from the morning until night it will make 1 path between the stops. For example as we just had the winter soltice so I checked the angle for our place and it was 65 degrees. I need to do the same thing in summer and the azmuith can be simply adjusted for each season.

See it aint that hard to make a tracker which will give upto 30% more output from a roof mounted static panel.

Now if you choose to go this route draw up what you think and I can give you some advise on WHAT you show.

As this IS your school project I'll help where I can but only from the advise point of veiw.

Regards Bryan

 

[3v0]

Welcome back.

 

[Moneer81]

Hello Moneer,
Weight really isnt an issue on a pv tracker if you have everything balanced and well built. There are 2 ways to do tracking,
1. is to use use 2 green led's to sense the strongest light and redrock.com has some good schematics for this.
2. Is hammer a long nail say 4" into a square board say 6" square, then point it at the sun and use an angle guage to find the azmuith. Once you know that build a simple frame with a centre mount rod and put 2 dead stops an each end of the frame. Then put a very low speed motor via gearing say bike sprockets to get the required reduction, so from the morning until night it will make 1 path between the stops. For example as we just had the winter soltice so I checked the angle for our place and it was 65 degrees. I need to do the same thing in summer and the azmuith can be simply adjusted for each season.

See it aint that hard to make a tracker which will give upto 30% more output from a roof mounted static panel.

Now if you choose to go this route draw up what you think and I can give you some advise on WHAT you show.

As this IS your school project I'll help where I can but only from the advise point of veiw.

Regards Bryan

Bryan,

Thanks for the help. I think I will be okay with the circuit part. What do you recommend I used for a motor? I just haven't really used anything bigger than toy motors and servos, and I need something with a lot more torque than that to be able to turn the panel. I will run my plan by you soon. I appreciate the help.

 

[Sceadwian]

If you want a dirt cheap high torque DC motor go to a local bargain or thrift store and pick up a couple of the cheapest battery powered drills you can find, they contain decent sized brushed motors and all the gearing required to produce heavy torque. You'll need to figure out how to detect position though, if you're just using a couple of rotating gimbals for the panel it could be as simple as mounting a potentiometer to the drive axis. Using a H-bridge rated to drive the motors and two ADC pins on a micro controller you'll get two axis rotation control. Then the hard part is to calibrate it and program the sun following routines.

Also, you'll want to find as detailed a data sheet on your solar panel as you can, the brightness of direct sunlight can be easily calculated and you can determine how many reflectors you can safely use for your panel. Even just two mirrors should greatly increase your power output without excessive heating.