Things You Can Do With A Giant Fresnel Lens

Ant writes "Here is a link where this guy always wanted Edmund Scientific's Giant Fresnel Lens. 'Melts asphalt in seconds!' the ad said. When he went to graduate school he met several other people with the same enthusiasm for aimless destruction through bizarre means, and just enough combined cash to make it happen. Thus the reign of terror began."

Comments

Nice picture of a giant fresnel lens in action

[PissingInTheWind]

Right here: Cooking with Light.

I have one of these.

[Qender]

I found one of these at my school last year. The first thing I did was take it to the parking lot to set paper on fire. The asphalt under the paper burned. I also melted pennies with it, and it can make holes in soda cans. Is there anything else anyone thinks I should burn with it? it's in my garage.

Laser Communications

[Rob Carr]

Besides destorying things, these fresnel lenses cand be used for all sorts of constructive fun.

A perfect example is a laser communication system. A laser beam can be modulated and used to transmit audio. The receiver needs to collect as many photons as possible from the laser transmitter - hence the use of the fresnel lense. Signals can be bounced off clouds - I've heard of transmissions going over 60 miles!

The Amatuer Radio Laser Communications Page has a good primer that has a link to a lot of the basics. And no, you don't need a ham license - although it helps!

$99 for the cheap fresnel...

[NoMoreNicksLeft]

Could you do something serious with this? Put the damn thing in a rig that follows the sun, and a small steam turbine under it, just how much juice could it provide?

I wish I knew the math to this, but damn, if it could provide even a small fraction of the power I use during the daytime... (by this, I mean 5-10%)

Anyone want to impress me with their math/physics skills?

Re:$99 for the cheap fresnel...

[nelsonal]

If you follow the sun perfectly you could figure on about 1 kW of light (cheesy rule of thumb) hitting your turbine. Assume 30% efficiency and you have 300W of electric power generated for an average of 12 hrs per sunny day. Three light bulbs (or 6-8 florescents) or one fully loaded computer (300 W power supply, no electric heat, iron, or oven. Oh and you'll need a capacitor bank to handle your inductive load when motors start. Go grab your power bill and see how many kW/hrs you use in a month and then figure out how many fresnel lens/turbine array's you would need to achive that power. Storage would be a mofo, although you might be able to sell it into the grid in your area.

Re:Ideas

[uberdave]

From one of the articles: "Cylindrical Fresnel lenses provide a 7:1 concentration, allowing a single multijunction GaInP2/GaAs/Ge cell to collect solar energy equivalent to that gathered by seven cells."

In other words, a fresnel lens does not help in terms of energy gathering. On a cost or mass per area, it does.

Re:It's being done!

[jamesshuang]

They're building a huge pane of glass on the Australian desert. This pane of glass is supended a few feet off the ground, which is painted black. The air between the glass and the ground is heated, and since hot air rises, it travels toward a chimney at the center of this contraption. As it moves through the chimney, a large turbine generates the necessary power. This odd design works extremely well, but requires very bright, sunny locations that don't mind a glass pane a square mile wide!