Solar Cooker Project Page

Solar Electric Cooker in Uganda

Problem Statement
People cook using resources that harm the environment, such as coal, wood and others, contribute to millions of deaths from environmental issues. The World Health Organization estimates that three billion people cook with biomass and coal causing 4 million deaths per year from breathing the associated emissions (WHO, 2016). Therefore, changing the way people cook could dramatically increase quality of life for millions of people in this world.

Solar cooking uses the energy that is essential to everyday life: sunlight, and turn that into electrical power and use it to cook. Using sunlight as the power source eliminates the carbon emission from coal or other biomass materials. The chart below shows the amount of carbon dioxide each kWh of fuel produces.

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Figure 1: Amount of carbon dioxide emission for different types of fuel each kilowatt-hour.

Also the need for wood to as fuel leads to deforestation and the reduction of the planet’s natural ability to absorb carbon dioxide. Plants uses carbon dioxide as an energy source and produces oxygen; therefore, we need trees to maintain the environment. Forests are the largest terrestrial store for carbon, also provides livelihood for animals species, which forms the livelihood of human beings. (WWF Global)

The use of renewable energy is also increasing along with the technology, as silicon based solar panels gets cheaper through the years. Graph below shows the trend where photovoltaic modules are going due to Swanson Effect. We could use this effect to estimate the data because solar devices are currently using silicon technology, which is similar to the silicon technology used in computer chips.
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In recent years, the prices are dropping dramatically and it will continue to do so for next few years. Currently, the price of solar is below 50 cents per watt.

Uganda is a developing country in East Africa that lies on the Equator. It is home to roughly 38 million people, with a total GDP of about 92 billion. This works out to be about 2500 dollars per person, which is much less compared to more developed countries. It is also a very fast growing country, with the population growing 10.6 million from 2002 to 2012, or about 3-3.3% per year. To put this in perspective, from 2010-2015, 1.6 million people were born and 370,000 died. The population is one of the fastest growing in Africa yet the average life expectancy being around 58 years. This number is not where is needs to be but has increased drastically over time as more efforts to develop the country have been mounted. Almost 50% of the population are ages 0-14, with close to another 50% being ages 15-64. The figures below shows the life expectancy as a function of time, with the blue trace showing Uganda’s progress, as well as amount of people in poverty. An astonishing 77% of the population is under 30 years old.

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The specific group that we are hoping to work with is the Beacon of Hope School
in the Soroti region of Uganda, as shown right. The school started in 2006, and now serves over 700 rural youths, providing an education that would otherwise be unattainable. Currently, there are around 50,000 people living in Soroti, with a population density of 53% (meaning 53% of the region is populated). This makes Soroti one of the highest concentration of people living under the poverty line in east Uganda.

Climate in Uganda
Much of the border of Uganda is lakeshore, with no direct access to the sea anywhere in the country. Featuring a tropical climate, Uganda is generally rainy with two dry seasons. The land is 200,523 square kilometers and water comprises 41,028 square kilometers.

Current environmental concerns include: draining of wetlands for agricultural use, deforestation, overgrazing, soil erosion, water infestation in Lake Victoria, and widespread poaching. Also, Uganda is one of the countries most likely to be hit the hardest by climate change and should brace itself for further and more serious food security.

As is clear from the population growth and economic situation, Uganda is still a developing nation. A graph of the fecundity of women per time (babies born per women as a function of time) shows that the population, while still growing, is slowing down.
Although the situation is clearly improving, they still face many challenges.

Uganda Energy Use
In 2012, Uganda imported 1.1 million TOE of different petroleum products. This equates out to about 39 Watts per person per year. Compared to the United States, at about 1400 Watts per person per year, Uganda’s energy use is very small. Its main source of energy is biomass. The actual total electrical capacity is 550 MW and the country’s peak demand is about 489 MW, however according to the NDP (Net Domestic Product, or the annual measure of the economic output of the nation that is adjusted for depreciation) the peak power is rising about 22.7% per annum. This is due to the rapid population growth (a woman in Uganda on average gives birth to roughly 5 children.

Since the population and development is the country is quickly expanding, biomass as a main source of energy is beginning to present problems across the country. Wood fuels are largely used for cooking in rural areas and charcoal most provides for the cooking needs of the urban population. High demand for wood fuels has resulted in overuse and depletion of forests, which is why Uganda is a main target of climate change in the upcoming years. In addition to this, households use biomass in very inefficient ways, resulting in higher energy costs and greater fossil fuel emission.

The level of solar energy utilization is still very low while the potential for beneficial use is very high. The average solar radiation is 5.1 kWh/m^2/day. The existing data indicates that the solar energy resource in Uganda is high throughout the year with a variation of only about 20%. This is due to the location near the equator. Soroti, being in the east of Uganda, has some of the highest insolation in the country, as depicted below in the graph, which shows the distribution of solar radiation hitting the country.

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Solar cooking challenges
The school we are building this cooker for is located in Uganda. Over 700 students need to be fed 2 times a day. The school already uses large amounts of time and money gathering wood to feed the stoves. The school makes 6 trips for wood a month, and a single term at the school is 3 months. Each trip costs 100,000 shillings ($100), and this includes the purchasing, transporting, and preparing of the wood. This means that the school is paying roughly $600 per month just for fuel to feed the massive amount of students.

Currently, the school already has a method of cooking. They use 2 large saucepans to cook 230 kg of posho (flour for porridge) and 60 kg of beans to feed the students. Each saucepan requires about 250 kg of water. Using their traditional wood fire cooking methods, it takes 1 hour to boil the water alone but 3 hours to boil the beans. There are 2 meals, lunch and dinner. Lunch is from 1pm-2pm and dinner is from 6pm-7pm.

The weather is roughly 32-35 degrees C during the day. That is almost 90 degrees F; similar to a typical summer day in California. This means that there is plenty of sunlight throughout the day for solar power generation. These solar cookers would help greatly, but the materials to build the panels Uganda would be difficult. The solar panels themselves would have to be imported, but the rest of the design could easily be built from materials at hand such as wood. We would also need to educate the school on the stoves, and work collaboratively with them to figure out how best to implement our solution, and if any changes need to be made. This is an important part of the process, as it allows them to take part in the development process and have a sense of attachment to the product, making them more likely to use it as would most benefit them.

Our Potential Solution
It is clear that cutting back on the amount of wood the school uses would save both money and the overall health of people working in the kitchen, or exposed to the smoke of the cooking process. Although we could not cut out the need for a wood burning stove completely, the introduction of clean solar would go a long way. The primary purpose of the solar cooker would to be keep water at a boil, or to keep food warm. To achieve this purpose, a solar panel is used to drive current through a heating coil. The coil can then be put directly into the pot of food or water, without touching the bottom of the pot. The pot itself can then be placed inside a insulation chamber. The image below shows a simple diagram of the setup.

Wood will still need to be used to get the water to a boil, but the school can use a “hot and fast” fire to get the water boiling. Burning wood quickly and at higher temperatures increases the efficiency, which decreases the total amount of smoke given off, thus creating an environment that is less detrimental to the health of those in the immediate proximity.

The insulation has to be something easily available and cheap. Rice hulls can be used for insulation, as they are essentially free. They have a thermal conductivity of .06 W/m-K. The pots that the school use are 250 L (or .25 meters cubed). Assuming that the pots height are about twice their diameter, we get a height of 1.1 meters. The average temperature during the day in the region is about 33 degrees Celsius. So, if we want to keep the water at its boiling point, this gives a temperature difference of 67 degrees Celsius. We can then choose the insulation chamber to be half a meter thick.

Plugging all this into the conductive heat loss equation:


will give us the amount of conductive heat loss that our heating coil has to make up for. We get a conductive heat loss of about 15 Watts.
To be conservative, we want the heating coil to provide about 20 Watts of power to the water.

It is important that we acknowledge our failures from this project and learn from them. A major failure for us was that we lost communication with the Beacon of Hope school due to them being on vacation. This cut our vital tie to the school as we were unable to get critical information for our project, like spatial dimensions of the kitchen or equipment. This left us having to make educated guesses about what we think their cooking situation is like. This did not leave us in a good place for the project, but it taught us the value of communication in the real world. You will not always get the answers you need right away, and you must learn to adapt.

How we would like this project to be continued in the future would be for groups to use our website to help them further the solar cooker. Not only would we like groups to do more in depth calculations and even build something like this, we want a club to be started at the Beacon of Hope school to allow the students an opportunity to work with us. This will give them ownership in the cooker and that is the most thing about this type of technology. We can’t just build something and give it to people because it is shown that they value it far less than if they had a part in its creation. So to future solar cooker groups, be sure to communicate with Uganda and we can all help each other learn through this project.

Group Photo, from left to right:

  • Adam Patrella: 4th year General Engineering major
  • Brad Shaw: 4th year Physics major
  • Kyle Lemmerman: 3rd Year Physics major
  • Edward Liu: 5th year Electrical Engineering major