The one resource we will hopefully always have on Earth is the Sun. The suns rays are responsible for most life on earth providing plants and humans alike with photons, vitamin D and heat.

There are millions of people across the world without access to safe, reliable fuel for cooking in poorer parts of the world that can lead to severe health problems. In the richer parts of the world solar cooking is overlooked in favour of gas, electric or wood-fired cooking methods due to their abundance, relatively low price and convenience.

Project Vision

I hope to develop an inexpensive low -tech cooking method that can be adapted into the modern lifestyle.

My current knowledge of solar cookers

My only experience with solar cookers coming into this project is a small solar cooker I visited at commune in Portugal and the Parabolic Satellite Dish I have seen used to boil water. Perhaps there is a reason we don’t have more practical ones?

Reasons why I think it might work

I saw somone on Instagram melting rocks with a solar ray he made from an old TV screen

https://www.instagram.com/joemyheck/reel/Cxb1QHwJ6k1/

Global understanding of laser technology is constantly improving, the same for material science, thermo-dynamics and optics.

Initial concept idea

My initial vision for the cooker is:

• a hyperbolic funnel with reflective wall that is aimed at the sun;

• The suns rays are reflected onto a reflective lens:

• Light is reflected into a spherical insulated oven whose walls are made up of tiny mirrors, like a disco ball reflecting the light around the oven.

• There will be a metal mesh suspended in the middle of the oven where the user can place their food, or cooking stone.

• There will be a pizza oven type entrance for accessing the oven.

USE CASE

Pizza and Bread Oven = 250-450oC

Cook 20-100 pizzas between 12:00 and 14:00

Cook 20-100 loaves of bread 13:30 - 16:30

What I need to study and design

Collecting and Concentrating Light

Options:

• Stationary : Compound Parabolic Concentrator uses Edge Ray Principle to optimise the amount of light captured without having to move the concentrator.

History of CPCs

Roland Winston and Henry Hinterberger originally described CPCs in 1966 for the efficient collection of diffuse Cherenkov radiation (radiation generated when a particle moves faster than the phase velocity of light through a medium) during high-energy physics experiments. CPCs were subsequently more widely adopted to concentrate light for solar power production.

• Motional : Sun seeking solar ray capture

Constraints: cost, size of the lens/collector, keeping the reflective parts clean, complexity

Reflectors :

NREL solar furnace is used to test materials and can achieve some ultra high solar fluxes

Oven shape, material

To optimise efficiency I would like to make the oven as light as possible with the best insulation available.

• Thin metal walls (aluminium, lightweight steel)

• Ceramic rings that build a spherical or dome shape

• Wool, cork, percolate, …

• Reflective mirrors to reflect light inside the over and Veta Black/Soot painted walls

• Oven door placement and design

• Thermal Inactive material to weave a cage to hold the food and cooking stone

Control Command

Power and Temperature control - oven and food readiness

• Shutter control

• Sun seeking

• Humidity - introduce steam

• Ventilation

• Auto-cleaning

Revised Concept

CPC’s collect both direct and diffused light and concentrate it at a focal point. My plan is use this property to heat up an insulated oven to a temperature suitable for cooking pizzas (upto 500oC) and bread (upto 300oC).

“If the reflector is geometrically smooth, its redistribution of the radiation amounts to a topological distortion of this region. Applying the basic theorems of topology, we can state that if all the rays on
the surface of this region are transferred to the rim of the desired target region, then the designer can be certain that all other rays will end up inside the target region as well.”
[7]

The use of CPC’s at the National Ignition Facility’s (NIF) Advanced Radiographic Capability (ARC) laser has increased the intensity of the laser by a factor of 10 that it was designed and built for, albeit using gold coated diamond turned plastic CPC targets [3]

“Initially, the CPC targets were produced by coating a diamond-turned mandrel with gold and dissolving away the mandrel, a process that can be expensive and time-consuming. Researchers have since tested CPCs made by additive manufacturing, which have performed almost as well while reducing manufacturing time and costs, potentially opening the door for their use by other laser researchers.”

“Anybody who has a laser with a less than ideal focal spot or pointing stability could use targets like this to reach conditions corresponding to higher effective intensities,” MacPhee said.

Adapting this for solar cooking

CPC production

The researchers at the laser lab moved onto additive manufacturing but their budget is high. For solar cooking application I don’t think I need anywhere near the same efficiency. Truncated CPC’s further reduce costs without losing too much efficiency [5].

In an ideal world I could 3D print the parabolic conic shape and plate it with a reflective material, however I’m unsure which 3D printed plastics can withstand >200oC.

Another option is to print the shape in resin or PLA and cast them in aluminium then polish them.

CPC designers use Monte Carlo ray-tracing software to simulate the light irradiance and behaviour. Some have tried to improve upon the revolved parabola design to reduce the loss of efficiency due to skew ray rejection [8], or to facilitate the manufacturing process [9].

My intial CPC design will incorporate a 3D printed revolved parabola design which I will use with a reflective coating. I intend to place different sizes on the roof of the building in direct sunlight with a temperature sensor underneath the outlet, as close to focus as possible and measure the temperature change throughout the day between the different sizes and without the CPC.

Oven shape, materials and cooking method

I imagine an array of CPCs that concentrate the light similar to how using straws can turn turbulent flow into laminar flow. There can be two cooking methods that I can envisage :

Both types of cooking methods envisage using a dome oven with an inner wall, an outer wall and insulation, possibly using ceramic, aluminium and wool/cork. Both ovens could have a thick plated bottom to store more heat for longer.

Direct irradiation

An abundant amount of light can be directed onto a cooking surface or irradiate the food directly.

In order to cook the something in the oven, it needs to retain it’s heat through insulation. Insulated Solar Electric Cookers [4], powered by 100W solar panels are able to retain heat for extended periods of time, with one adaptation heating up a thick chunk of aluminium for over 250oC allowing the user to boil water in under 60s.

The lighter the oven the faster it will be to heat up and cool down so the method of cooking requires consideration. This project concentrates on cooking pizza for lunch between 12-3pm and then bread 2-5pm in summer where there is often heat and sunlight. Taking Barcelona as an example, from April onwards, the oven may capture light from as early as 8am, typical temperatures being 15oC.

The conic shape of the CPC’s leave space for insulative material on the side of the wall capturing the light which could maximise both heat and light capture.

The question is what material to use ?

• Wool/cork, Mixture of clay with wool/cork, Aluminium inner wall painted black burnt in soot : thickness ?

• Will the cpc performance drop if they get covered in soot from cooking ? Can they just be cleaned after each cook, is ventilation enough to prevent dirt accumulation ?

• Ceramic rings stacked on top of each other ? An aluminium inner wall, wool/cork/insulation stuffed inbetween.

• Use a naturally dark stone that heats up, will it have enough residual heat to cook from underneath or do I have to use a metal cooking tray ?

Conduction

Taking into account the focal length it might be more effective to use a CPC shield that focuses the light onto a metal dome at a distance close to the focal point. This will then heat the oven through conductivity and what’s inside through radiation.

Concerns with this method:

• Too much power may set the aluminium on fire?

• How to insulate the irradiated part of the oven wall ?

Temperature control

An electronic feedback system will have to control the temperature and power through ventilation and shutter speed/open/close.

Abiding to low tech principles and inherent safety, the systems are to be as passive as possible.

RESOURCES:

Nonimaging Optics. (Roland Winston, Juan C. Minano etc.) [1]

Design and development of a novel and cost effective modified Compound
parabolic trough collector, Durgesh Kumar, Punit V. Gharat [2]

https://www.sciencedirect.com/science/article/pii/S0196890424002267/pdfft?md5=0a1650ff946912021f67434b748222fa&pid=1-s2.0-S0196890424002267-main.pdf

Expanded the experimental capabilities of the National Ignition Facility’s (NIF) Advanced Radiographic Capability (ARC) laser. compound parabolic concentrators (CPC), give ARC — NIF’s “laser within a laser” — the ability to produce effects associated with laser intensities more than 10 times greater than it was designed to deliver.https://www.llnl.gov/article/46096/focusing-target-gives-powerful-boost-nifs-arc [3]

Insulated Solar Electric Cooker https://wiki.lowtechlab.org/wiki/Insulated_Solar_Electric_Cooker_(ISEC) [4]

A New Approach for Design Optimization and Parametric Analysis of Symmetric Compound Parabolic Concentrator for Photovoltaic Applications by Faisal Masood 1,2,*,Perumal Nallagownden 1,Irraivan Elamvazuthi 1,Javed Akhter 3 andMohammad Azad Alam 4

https://www.mdpi.com/2071-1050/13/9/4606 [5]

Effect of Surface Radiation on Natural Convection in Parabolic Enclosures by Gerardo Diaz

https://www.tandfonline.com/doi/abs/10.1080/10407780701789518 [6]

New Methods of Reflector Design by Harald Ries, Julius Muschawek and Andreas Timinger

DOI:10.1364/OPN.12.8.000046 Optics and Photonics News 12(8): 46-49 [7]

Toward a best-form CPC-like nonimaging optical concentrator by Isaac Metcalf, Gang Chen, and Thomas A. Cooper . Optics Express • Vol. 30, • Issue 25, • pp. 44556-44568 • (2022) https://doi.org/10.1364/OE.476189 [8]

Performance of compound parabolic concentrators with polygonal apertures by

Thomas Cooper, Fabian Dähler, Gianluca Ambrosetti, Andrea Pedretti, Aldo Steinfeld. Solar Energy Volume 95, September 2013, Pages 308-318 https://doi.org/10.1016/j.solener.2013.06.023 [9]