This is a professionally made product ~ we made a REFLECTIVE version which is mathematically the same ~ but this device in this video is smaller than the one we made ~ http://bclee.net/lens.html There are a good number of videos on u-tube that’ll teach you all about this type of lens. One of the advantages to a reflective fresnel lense is you have a fixed focal length so you could set a hunk of meat at the focal point and cook it while the Sun moved ~ our experience demonstrated you have plenty of time to cook before needing to realign the lens.
Cool, thanks for the link.