Description
This tutorial outlines the steps for building a solar electric oven, commonly known as a ‘solar cooker’ or ‘cooker of the future’. Installed in the low-tech apartment of the Urban Biosphere experiment, this well-insulated pressure oven-style cooking system made it possible to steam food with low energy consumption. During the experiment, the cooker was powered by 12V solar panels.
Introduction
The BIOSPHERE EXPERIENCE association experiments with sustainable and desirable futures in which humans live in symbiosis with other living species. In 2024, Caroline Pultz & Corentin De Chatelperron spent four months experimenting with what a low-tech lifestyle in an urban environment might look like: a lifestyle without waste, reducing water consumption tenfold, meeting the UN's 2050 targets for greenhouse gas emissions, while remaining desirable and accessible to all. Armed with experts, volunteers and interns, they imagined and designed a forward-looking ecosystem apartment called Biosphère Urbaine, located in the Paris region in Boulogne-Billancourt. To complete the ecosystem, their colleague Emma Bousquet-Pasturel has set up a vast citizen support network around the flat. At the same time, Emma has been tasked with coordinating a participatory science programme bringing together hundreds of citizens from France and elsewhere to test a simplified version of some of the low-tech systems in the laboratory flat in their own homes.
This tutorial is for a low-tech module in the apartment-laboratory, designed as part of the experiment conducted by Caroline and Corentin in Boulogne-Billancourt.
"Food and energy"
In France, average energy consumption for food varies according to various factors such as eating habits, production and distribution methods, and food storage practices. However, it is generally estimated that average energy consumption for food accounts for approximately 6% to 30% of the total energy consumption of a French household. These figures may fluctuate depending on many factors, including the type of diet (vegetarian, omnivorous, etc.), the frequency of home-cooked meals versus meals eaten outside the home, and the distance travelled by food from its place of production to its place of consumption.
The main challenges of sustainable cooking in a dense urban environment include limited availability of renewable energy, space constraints for installing cooking equipment, and diverse dietary habits that require versatile and adaptable solutions. Greenhouse gas emissions from cooking vary depending on the cooking methods used: “”'traditional gas or electric ovens are among the main contributors to CO2 emissions in urban households'“”. Therefore, implementing innovative solutions for sustainable, low-energy cooking is crucial to achieving the greenhouse gas emission and energy consumption reduction targets set by international agreements, such as the Paris Climate Agreement and the United Nations Sustainable Development Goals.
| First and foremost, Caroline and Corentin set themselves the goal of experimenting with a healthy, organic, local and seasonal diet that would cost less than 6 euros per day per person. On the advice of their nutritionist Anthony Berthou, they opted for a diet consisting mainly of steamed food to preserve as many vitamins as possible from the fresh, organic ingredients sourced from the Ferme Des Loges farm, a few kilometres from their low-tech flat. |
The biosphere diet is based on three types of food:
● A cereal/legume base: These products require long cooking times in water or steam. On cloudy days, these bases are not cooked in the flat but purchased from caterers.
● Seeds, crickets, mushrooms and seasonal vegetables: These foods, such as broccoli, carrots and spinach, are stir-fried in hot oil for just 1 to 2 minutes using a gas cooker fuelled by biogas generated by a biodigester installed at the bottom of the building.
● Fresh vegetables: These include parsley, coriander, young sprouts and germinated seeds that do not require cooking.
After studying their lifestyle in detail to figure out how to use the flat in the best way possible (what time they eat, cook, leave the flat, etc.), Caroline and Corentin were able to work out the overall energy consumption of their flat. The low-tech flat, disconnected from the city's electricity grid, was powered by direct current (12V) thanks to 4m² of photovoltaic solar panels installed on the roof of the building. The laboratory flat therefore consumed between 10 and 20 times less than a conventional flat! This flat maximised the use of direct solar energy, with limited electricity storage capacity (lead solar battery, 80Ah, 12V or 960Wh) to reduce the volume of batteries required. Consequently, it is crucial to design an energy-efficient food cooking system.
The electric solar cooker
This tutorial outlines the steps for building a solar electric cooker, commonly known as a ‘solar cooker’ or ‘cooker of the future’. Installed in the low-tech apartment of the Urban Biosphere experiment, this well-insulated cooker-type system enabled food to be steamed at low energy consumption. During the experiment, the cooker was powered by 12V solar panels.
A brief history of the machine featured in this tutorial:
A preliminary study was carried out in collaboration with students from ICAM Nantes.
Comparison of cooking process for 100g of rice with 200ml of water:
- saucepan: 44 min, 70W/h
- pressure cooker: 40 min, 30 W/h
- rice cooker: 18 min, 80W/h
Based on the results obtained, we chose to start with a pressure cooker because of its significant advantages, such as more uniform cooking of food thanks to the pressure, a larger volume that would allow us to cook portions for several days, and the fact that it does not require a chimney to vent steam, thus reducing losses.
This prototype costs around 60 euros with new components, but it is possible to considerably reduce the cost by using recycled components.
Improvements to be made: Do not attach the heating system to the container, but rather to the insulated box so that it can be removed and washed more easily.
User feedback: As simple as using an oven, it didn't take us long to change our cooking habits. The advantage of this system is having a hot meal ready to eat when you get home from work!Youtube
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Materials
Here is a comprehensive list of the materials you will need. If you already have some of these items, we recommend adjusting the diameters and dimensions of what you have as you follow the tutorial. For items you do not have, we recommend using second-hand materials.
- A pressure cooker – the dimensions of the cooker will determine the size of the entire system – during the experiment, a 4L cooker with a diameter of 22 cm was used.
- A kettle base with plug
- Base part of the kettle "under kettle"
- 3 heating patches/sheets of 50W, 12V (60 mm x 60 mm patches were used)
-1 thermostat - here recuperated from a rice cooker
- Connection lugs (option 1) or tin soldering (option 2)
- An insulator approximately 10 cm thick – here we used leftover Biofib hemp wool to insulate the pressure cooker and lid.
- 1 piece of heat-resistant fabric – here we used black coloured linen
- 2 stainless steel bowls
- 1 with a diameter of 36 cm for the upper part
- 1 with a diameter of 28 cm for the inner part
- Heat-resistant adhesive tape
To connect
- 12 V solar panels or 220 V -12V converter
Tools
This is a comprehensive list of tools to adapt according to what you already have.
- Screwdriver / Drill / Electric screwdriver
- Scissors
- Soldering iron (for option 2)
- Hand saw or jigsaw
- Tape measure
Step 1 - General description
The solar cooker system consists of three parts (1st diagram):
- Cooker
- Insulation (Norwegian cooker built into the worktop with insulated lid)
- Electrical circuit
Here are the manufacturing steps (2nd diagram):
1: receptacle
2: cooker and electrical connections
3: lid
Step 2 - Receptacle
Depending on the size of the casserole dish, adjust the size of your container. For this, you can refer to the Norwegian pot tutorial.
On our side, we built a round box built into the kitchen worktop to save space. We then insulated this container with hemp wool over the entire surface, then covered it with a piece of dark-coloured linen fabric.
Don't forget to plan a place to plug in the kettle base.
Step 3 - Electrical circuit
You will now create the electrical circuit located under the cooker—in the part that touches your stovetop in the classic version.
You can now assemble the electrical connection by referring to the diagrams below.
You can connect the wires using connection terminals or solder them with tin.
When assembly is complete, secure the electrical components (the thermostat, the three heating patches) under the pressure cooker using heat-resistant adhesive tape.
To complete the assembly, place the base (or “under-kettle”) as a lid to cover the entire electrical assembly. Be sure to wrap this base securely with heat-resistant tape to ensure proper insulation and optimal safety.
Step 4 - Lid
Drill holes in both lids (the small one and the large one), ensuring that the holes are properly aligned.
Secure them together using a screw and nut, leaving a gap of approximately 15 cm between the two covers. Ensure that the gap remains even all the way around.
Insulate this space between the two lids by filling it with hemp wool. Then cover the wool with fabric, as you did previously to insulate the Norwegian pot.
Step 5 - Montage final
Your pot is now ready to use! Start by placing the kettle base in the receptacle provided for this purpose. Then plug in the base and connect your pot to the integrated electrical circuit. All that's left to do is cook your food!
Step 6 - Using the cooker
In the Urban Biosphere laboratory apartment, cooking routines have evolved. In the morning, Caroline and Corentin prepare vegetables, grains and legumes, which they place in the cooker before leaving for work. They manually programme the cooking time and heating time, usually set for midday when the sun is at its highest. The cooker then starts to heat up automatically (see Arduino microcontroller tutorial, the brain of the flat) using solar energy for the programmed duration, allowing the food to continue cooking gently inside the cooker for the next few hours. When Caroline and Corentin return from work around 6pm, the meal is ready and still nice and warm!
To replace the Arduino microcontroller (see simplified tutorial), it is also possible to use a mechanical switch timer.
Steam cooking
In addition to preserving nutrients, it also limits the addition of fat while retaining the natural flavours of the ingredients. It is an ideal method for balanced and tasty meals! Here is a list of foods that can be easily cooked in a solar cooker:
- Vegetables: Broccoli, cauliflower, green beans, carrots, asparagus, spinach: vegetables retain their crunch and vitamins when steamed. Courgettes, peppers, mushrooms: for a more tender texture.
- Ravioli and dim sum: Asian ravioli, such as stuffed ravioli and bao buns, are often steamed for a soft texture.
- Vegetable soups and broths
- Steamed cakes
- Steamed white of egg white accompanied by egg yolk mayonnaise
- Steamed scrambled or soft-boiled eggs are an option for gentle, even cooking.
Notes and references
A project conceived by Corentin De Chatelperron, prototype produced by S.M.A.T. as part of the Urban Biosphere experiment.
Thank you to the ICAM students for their valuable contribution: Théo DOUAUD, Simon LUTUN, Loup GUEGUEN, and Jean-François LARGEAU, lecturer and researcher at ICAM Nantes. (ICAM report – solar electric cooker – Théo DOUAUD, Simon LUTUN, Loup GUEGUEN)
Tutorial written by Bertille Maria, with the help of Enzo Audion and Caroline Pultz.
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