Large Solar Cooker for School in Uganda

Problem Statement

According to the World Health Organization, approximately three billion people cook on stoves using biomass fuels and coal. The most common stove used is the three stone indoor stove which causes respiratory disease, deforestation, and climate change. An astonishing 4 million deaths per year are due to the inhalation of emissions from these stoves, which exceeds the amount of deaths caused by AIDS, malaria, and tuberculosis combined. In addition to these fatalities, smoke from indoor cooking stoves can cause extreme eye irritation and risks of burning. Aside from the massive health detriments, cooking using biomass fuels, such as wood, requires large amounts of time to be spent collecting wood. Reliance on inefficient wood- burning stoves creates deforestation and releases carbon emissions, contributing to climate change.

The Beacon of Hope, a boarding school in Uganda, has the task of feeding 700 students two meals per day. The school currently cooks on stoves which use biomass fuel and come with all the aforementioned side effects and inefficiencies. The school makes 6 trips per month to collect wood for cooking. Each trip costs about 300,000 schillings, or 100 USD, and this includes transportation and processing. This is already 600 USD a month for just fuel! Students at the school are prepared 2 meals a day; lunch and dinner. Roughly 230kg of posho (flour) and 60kg of beans are prepared to last the entire day. Using traditional cooking techniques, it takes 1 hour to boil water and 3 hours to cook the beans. They currently cook with 2 large saucepans and each pan requires 250L per meal. Lunch is served from 1pm-2pm and dinner is 6pm-7pm. Our main concern would be the amount of time and money is spent on the wood for biomass fuel, so we hope to find a way to lessen this cost for the good of the school, financially and physically.

Our Goal

We seek to better understand the cooking methods and needs of The Beacon of Hope and design a stove which could help them save time and money, improve their heath, and have minimal environmental impact.

Our plan is to design an electric solar cook stove for a boarding school in Uganda similar in design to the family-sized stoves that have already been built. Additionally, we aim to decrease the emission of harmful smoke particles produced from open fire cooking. Our challenge is constructing a cost-efficient design to keep food cooking after the traditional stoves bring the temperature up initially. Using solar power and insulation, we plan to design a cooker using materials that can be acquired and constructed in Uganda. It is important to make the insulated solar cooker affordable and user friendly.

We will make a prototype that will represent a smaller version of what would be necessary for The Beacon of Hope. This smaller version could also be utilized by individual Ugandan families. In the Physics of Energy class there is also a group working on this project PHYS 310. They will be doing the theoretical calculations for the large scale solar cooker.

Target Community

Beacon of Hope Secondary School :
The community we are designing this cook stove for resides in Soroti, Uganda. In an area where only about 20% of students go beyond 7th grade, Beacon of Hope used to house child soldiers from the civil war, and continues to focus on children living in poverty with no access to education. Offering scholarships and working hard to create a gender-balanced student body, Beacon of Hope strives to give the children a worth-while education with hands-on STEM programs and counseling support. Currently, over 700 students attend the school and there are many partners throughout the world. Beacon of Hope is not only providing an education, but changing the lives of those who need it the most.

Uganda Demographic

Compared to the United States with a 100% primary completion rate and an average intake of 3748 calories, Uganda has a 54% primary school completion rate with an average intake of 2211 calories. With 22.4% of rural people living below the national rural poverty line, Uganda is mainly an agrarian society. The average Ugandan woman has little time to spend on supplement income, spending nine hours a day on domestic tasks.

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The graphic above illustrates where different countries rank in terms of primary school completion rate and food supply. Some countries have a primary completion rate over 100 percent due to the way the ratio is calculated. The completion rate in a given year is calculated as the number of new students entering the final year of primary school, regardless of their age, divided by the number of children in the population who are at the entrance age for the final year of primary school. This allows for the possibility of primary completion rates exceeding 100 percent in some countries, as can be seen from the graphic above.

Soroti District Demographic

  • Population: 315,900
  • Density: 224 people/km^2; In comparison, San Luis Obispo has density of 1347 people/km^2
  • 83% of the population live in rural areas, while only 17% live in urban areas
  • As of 2009, the poverty density was 53%, making it one of the most impoverished areas in east Uganda
  • Legal marriage age in Uganda is 18, but 5 out of 10 women are forced into marriage at a young age
  • 80% of children drop out of school before seventh grade

Soroti is centered around the equator, making it ideal for solar energy use.

Uganda Solar Radiation Map: kWh/m^2

– please convert the 2400 kWh/m2 per year into per day, and do a calculation as to how much you will need to keep your pot warm. Please put scale of miles or meters in the images below.

Satellite Imagery, Google Earth (2017). Soroti, Uganda (left); Beacon of Hope Secondary School (right).

Preliminary Research and Current Technology

Principally, this project will continue research and development conduct by PSC 320, Winter 2017 Uganda School Solar Cooking project. However, it deemed appropriate that we explore current methods of solar cooking that can accommodate the needs of large groups numbering in the hundreds.

1. The Panel Solar Cooker (see below) is constructed from cardboard and foil lining and configured in shape that concentrates sunlight and focuses it onto a small pot, reaching temperatures upward 100 degrees Fahrenheit.1

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Refugee camp in Eastern Chad; Sudanese women prepare food for hundreds (2).

2. The Go Sun Stove is a solar cooking product that can bake, boil, and fry even in cloudy weather,3 to an extent by “[heat] due to diffused radiation available in the atmosphere.”4 It utilizes an evacuated vacuum tube, the same type of tubing used in solar water heaters, that absorbs light and acts as an insulator, reaching temperatures upward 400 degrees Fahrenheit.3 In collaboration with Global Alliance for Clean Cookstoves, the company has developed private and public partners in Peru, Bolivia, Nigeria, Ghana, and India. Large scale government supported pilots are scheduled in 2017.5

(Left) Commercial solar cooking in China (6).

3. The Scheffler Reflector is a large parabolic reflecting dish that concentrates sunlight onto a focal point that can reach temperatures upward 2000 degrees Fahrenheit by a 40 square feet dish, making the technology appropriate for small-scaled industrial use.7 The application to cooking is that the focal point can be fixed onto a hot plate that serves as a medium for effective heat transfer.

Pictured above, the automated Scheffler system (middle) was built and installed for about $4000 to service a bakery in Hidago, Mexico (8). Two state run hostels for girls in Jaipur, India, have installed Scheffler Community Kitchen solar cooking systems (right) to meet the cooking needs for 600 students (9).

The mechanics of the aforementioned technologies is based on solar “thermal” cooking, and they were indicated for practicality rather than best practices. This project seeks to advance research and development in the more advanced solar electric cooking technology which utilizes photovoltaic (PV) solar panels that is researched ongoing by the scientific community and continuingly decreasing in cost for implementation. The district of Soroti has recently inaugurated PV technology, having launched operations for East Africa’s largest solar power plant in December 2016 (see below).

The 10-megawatt facility consists of 32,680 photovoltaic panels, having carrying capacity to provide electricity to 40,000 homes in the surrounding area (10).

Insulated solar electric cooking (ISEC) is principled on the concept of heat retention by means of an insulated layer that encapsulates a cooking utensil, to obstruct heat transmission to the external environment thereby reducing power demand.11 One of the earliest records of heat retention cooking originates from the “Norwegian Cook Box.”12 First exhibited at the 1867 Paris Exhibition, the Norwegian Cook Box relied on heat conservation contributed by felt lining enclosed within a wooden box. In 1906, experiments were conducted at the University of Wisconsin to study the practicability of heat retention cooking adapted to household use.12 The investigations concluded that the most important property of heat retention is the determination of the best material to use as insulation; for, one experiment found that the material of which the outside retainer was made had no appreciable effect on the conservation of heat. Accordingly, another experiment recorded the temperature change over time employing different packing materials. The apparatus used were: 3,500 cc tin pail for the outside retainer, 1,250 cc tin cans for the inside retainer, and the various insulating materials. The findings of the study are presented below.

(left) Table 1: Temperature Against Time; (right) Corresponding Curve Graph

The experiment results indicated mineral wool to be the best material for heat conservation. Mineral wool is made from “molten glass, stone, or slag (industrial waste) that is spun into a fibre-like structure,” and is widely used as insulation in buildings.13 Nepheline syenites, widely distributed in Uganda,14 is one type of rock used to make mineral wool thermal insulation. However, assuming the absence of facilities to produce materials, readily available rice hulls are deemed more appropriate.

Design Matrix for Solar Cooker

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-Amount of sun solar panel receives
-Environmental impact


To begin some calculations we first needed to find out just how much heat would be needed to boil our pot of water. Using our small scale cooker with roughly 4 L of water inside and the equation Q=mc(Tf-Ti), where Q is the heat, c is the specific heat of the water, m is the mass, and Tf-Ti is the change in temperature, we found that we needed 1240 kJ of heat to boil the water. We now needed to find the amount of power that our cooker was taking from the solar panel. We measured the resistance of our heater to be roughly 10 ohms and we used about half of the max voltage of the solar panel at 40 Volts to find the power using the equation P=(V^2)/R, where P is power, R is resistance, and V is voltage. Plugging in the numbers gives us a power of 160 Watts. With this we could find the time needed to boil our water by using P=Q/t, where t is time. It would take roughly 2.5 hours to boil the water in our small scale solar cooker using that solar panel. This is not a very reasonable time to wait, especially for boiling water.

Our other priority was finding the size of a solar panel that would work for our large scale cooker to boil 250 L of water in 1 hour like they do at the Beacon of Hope. From our solar radiation map of Uganda we can see that Soroti gets about 2200 kWh/(m^2) per year. Converting kWh/year into Joules/second (Watts), we get and intensity of 258 W/(m^2). Performing similar calculations to our small scale cooker, we found a that it took 96000 kJ of heat and about 27000 W to boil the water. Using the equation I=P/A, where I is the intensity and A is the surface are, we calculated that we would need a 104 m^2 solar panel to boil water in our large scale cooker.

Project Update

Preliminary Design Ideas
– Use 25-30 small pots so that food will cook faster, but we are not sure how much space is available for this method
– Creating a separate solar cooker with insulation and then transferring 250 L of hot food and water to these cookers to keep the food cooking, but this method is difficult and inefficient

Because contact with Beacon of Hope has been difficult, the project has been slightly modified with the same goal in mind. Instead of designing a solar cooker for a mass amount of people, we are going to design a smaller scale cooker where the school will boil water using wood and then add the water to the solar cooker. The food will be cooked and kept warm inside the insulated solar cooker. The insulated solar cooker can be given to the students at the school for educational purposes.

Material Costs

5/17″ Stainless Steel Hollow Pipe: $17
Caulking: $2
J. B. Weld: $3
4 Feet Insulated Copper Wire: $1
Nichrome Wire: free, otherwise 25 ft for $6.30
Pot and Lid: $6
Magnesium Oxide: $11
Ice Chest: Free, otherwise ~$10
Rice Hulls: Free

Shop Work

We connected nichrome wire to uninsulated copper wire using J.B. Weld and after caulking one side of the pipe, we used magnesium oxide to center the nichrome wire in the pipe. After allowing the magnesium oxide to dry, we used a pipe bender to bend the pipe into a 6 inch diameter circle. The uninsulated copper wire at both ends connect to the solar panel and are kept in place with electrical tape.



When we did our first attempt at connecting the solar panel, we found that the current was not traveling all the way through the wire. The nichrome wire was probably not held in place by the magnesium oxide powder and was touching the pipe instead. This could be due to the over-bending of the pipe when we first started to round it out. Only the straight part of the pipe was heating up. During our trials, we could not get a current even though it was around 11am- 12pm.
Keeping in touch with Beacon School of Hope was difficult as the school was on vacation. If they are responding in the early weeks, ask as many questions as you can while you still can!


Future Recommendations
Starting with the design of the pipe, stringing glass beads around the nichrome wire can help keep the nichrome wire from touching the sides of the pipe. DO NOT over-bend the pipe by allowing more curvature. The pipe does not need to be sticking straight up and test the resistance after bending. Also test the resistance before using J.B. Weld to hold the copper wires in place because different alignment will provide different resistances.
Rice hulls in an ice chest may not provide the best insulation but in our case, it fit the pot perfectly- try looking into a bag or something with structure. Sleeping bags and a thick towel sound good, but they’re difficult to hold up a rigid structure to contain the rice hulls.

Team Members

Nick Wagner: 3rd year Economics
Kyle Lemmerman: 3rd year Physics
Tiffany Seto: 3rd year Environmental Engineering


1. Cooking with the Sun. (2015). Teaching Science: The Journal of the Australian Science Teachers Association, 61(1), 8-11.
2. McArdle, P. (2010). Solar cooking in Africa-A remarkable technology transfer. [Video file]. Retrieved from:
3. GoSun Stove. (2017). Gosun grill. Retrieved from:
4. Ministry of New and Renewable Energy, Government of India. (2017). Frequently asked questions: solar water heater. Retrieved from:
5. GoSun Stove. (2017). Our dual business model. Retrieved from:
6. Stevens, H. (2012). Commercial solar kitchen using evacuated tubes. [Video file]. Retrieved from:
7. Geo-Mexico. (2012). Appropriate technology project supplies solar powered stoves. (2012). Retrieved from:
8. The earth project: tortilla sunshine. (2012). [Video file]. Retrieved from:
9. Energy Next. (2013). Girls hostel and RIPA in Jaipur get solar cooking system. Retrieved from:
10. Access. (2016). East Africa’s largest solar power plant starts operations. Retrieved from:
11. T., Watkins, T., Arroyo, P., Perry, R., Wang, R., Arriaga, O., Fleming, M., O’Day, C., Stone, I., Sekerak, J., Mast, D., Hayes, N., Keller, P., & Schwartz, P. (2017). Insulated solar electric cooking – Tomorrow’s healthy affordable stoves? Development Engineering 2 (2017) 47-52. Retrieved from:
12. Huntington, E. (1908). The fireless cooker. p. 5-11
13. European Insulation Manufacturers Association. (2011). About mineral wool. Retrieved from:
14. The Mineral, Metals, & Materials Society. (2017). Light metals 2017. p. 10. Retrieved from:


Please be quantitative. We have these numbers. I think you can broaden this statement. You want to learn how they cook and see how you can help them save money.Please state what has been done with this technology already.

Reasonably good start. Please keep developing the website. Learn more about the people, but start outlining possible technology options.

Please describe how they presently cook, and what the problems are. What are the options? What are the costs? Please describe the different technologies. Starting May 8, next week, I’d like to see you making heaters and building a small prototype… possibly collaborating with magic basket people.

– good point. So you will need to design a stove that keeps the pot in place, and you can add the hot water, and then remove the food. Yes, it would be much better if we could have pictures of how they do it now, but you can do your best to design something for now.

-which solar technology are you referring to? Which wood technology are you referring to, and what is 2 pots versus 4 pots? I think you need to better describe the scenarios you are comparing. Please work with the PHYS-310 class and find a lifetime cost for the different technologies. Please talk to me if you don’t understand what to do. On some level there may be little reason to compare solar versus wood because there is already wood being used, and the question is whether we should introduce a competing technology, and if so, which? I think you need to describe the different technologies better.

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