Last updated: 14 June 2017
A Fresnel lens eliminates the bulk of a convex concentrating lens with the use of a series of angled steps in the front surface of an otherwise flat sheet of glass or plastic. The steps are angled in such a way as to concentrate sunlight at the cook pot as it passes through the lens.
A larger scale version of this concept is created with a series of reflective concentric rings used to redirect the sunlight onto the cook pot. Essentially, the individual ring angles are similar if one were to cut a parabolic reflector into horizontal sections and stack them concentrically. However, this would cause shading, so the diameters of the rings each need to increase slightly to allow the light to reach the cook pot.
- August 2017: Heliac is a Danish company that produces polymer foil solar concentrators for medium size utility installations and solar cookers. They have developed a process to create a clear film with a profile that mimics the shape of a traditional fresnel lens for a fraction of the cost. A prototype has been built that is capable of boiling a litre of water in 10 - 15 minutes. Having a simple framework, the company wishes others to build their own frames and use their material for the lens, encouraging the development of local economies. They offer their design of the framework shown in photos as open source.
- September 2015: Fresnel array for evacuated tube cookers - Bernhard Müller has produced concept images for a Fresnel array that will work to provide more concentrated light on to an evacuated tube (Rand) style solar cooker. The purpose is, to heat any black glass tubes and stacked pots, but not too hot and not too rapidly in order to avoid any damages. This array will boosts the sun by the factor one to 3.11, according to Bernie. If the array assembly is produced inexpensively, this combination of evacuated tube and Fresnel array could provide a low-cost alternative for a solar cooker able to perform in less that ideal sunny conditions.
- December 2012: Bernhard Müller has published findings based on his experimentation with a twin Fresnel lens reflector solar cooker. This cooker was never meant to be a production prototype, and his company, Mueller Solartechnik, no longer manufactures solar cookers. As an engineering exercise, he has shown that incorporating the Fresnel lens produces quite high temperatures(278.6°C/534°F). However, the usable cooking area is small. Read more: Twin Fresnel Cooker
- August 2011: Students at MIT are working on a case study for a new type of solar powered outdoor grill. Based on the technology from MIT professor David Wilson, this grill would collect thermal energy from the sun and store it to allow cooking times for up to twenty five hours at temperatures above 230°C (450°F). Wilson’s technology uses a Fresnel solar reflector to harness the sun’s energy to melt down a container of Lithium Nitrate. The Lithium Nitrate serves as a solar battery. Due to its phase change reaction, the thermal energy is able to be stored for longer periods of time and at higher temperatures, by means of latent heat storage. Heat is then redistributed through convection, which allows for outdoor cooking. A Solar Grill Prototype for a Greener Tomorrow, August, 2011 - BarbequeLovers.com
- April 2010: Patricia McArdle met a group of Navajo high school students who have used designs they found on the internet to make several solar cookers including the Cookit, box cookers and a Fresnel lens solar fryer for making traditional Navajo fry bread. Their Fresnel cooker won second prize two weeks ago at the nationwide Spirit of Innovation contest--beating out some elite science high schools. They and their science teacher, Paul McCarl, working with very limited resources, are now trying to make a large fresnel solar cooker that can be used by Navajo families to make fry bread.
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- Designing a fresnel lens and mirror solar cooker - rimstar.org