Building a solar cooker for school

[Berkan]

(Sorry for my bad English, I'm from Germany) Hello! I need to build a solar cooker as a school project. Our build needs to be able to heat 1 liter of water in 80 minutes. My idea was, to heat the water by using a fresnellens. I've bought a 15.6 x 15.6 inches fresnellens for that. I thought about the construction and builded it. Now I have one big question. How am I supposted to heat the water at the focus of the lens? I thought about using a translucent jar with a piece of copper inside of it. The copper is suppost to absorb the sun ray and warm the water inside of the jar. Would this even work?

The attempt at a solution
Using of copper?

 

[Noctisdark]

Very hard but possible, first you need big lens, maybe yours will do, copper is good at absorbing heat, but use black objects, they're better at absorbing radiant energy, and the water which is colder with steal the heat from the black body and so on
So, i advice you to do :
Small expirement to measure the heat of the black body while sun is hitting him through your lens and predict by that how much time will it need to reach 100°C and check if your lens work .
I encourage you :)

 

[Berkan]

Okay, thank you!
I thought about copper, because it has a pretty good thermoconductivity

 

[Rippetherocker]

Any metal will do. Just make sure that it has an adequate surface area. Color the outside black and the inside shiny or white. 80°C is a lot

 

[Berkan]

I'll do that, thank you!